1. travel
2. transports
3. air travel
4. helicopters

MASTER'S THESIS
Energy Distribution Improvement for the
Next Generation of Dehumidifiers
Emil Torlen
2015
Master of Science in Engineering Technology
Mechanical Engineering
Luleå University of Technology
Department of Engineering Sciences and Mathematics
Acknowledgments
This project has been done on behalf of Munters R&D department as a final course of the Mechanical Engineering program at Luleå University of Technology. I want to express my warm and sincere thanks to all the
Munters R&D employees for giving me all the information and help needed about their industrial dehumidifiers. A special thanks to my supervisor Jan Pettersson for his patience and kindness during this master thesis
as well as his experience and who have been invaluable for me. Anna-Lena Ljung who supported me under the
project and helped me with the report. The lessons learned from visiting the production in Tobo where Robert
Arnell was a great source of information regarding the rotor. Janne Simsons and Urban Gunnarsson helped a
lot by discussing and giving detailed information about the dehumidifiers from their laboratory tests as well as
experimental data to validate my simulations and calculations against.
Abstract
The project aims to develop a heat shield to lower temperatures on the casing of a desiccant dehumidifier
and to investigate the temperature distribution over the rotor of Munters M X 2 30 dehumidifier. The heat
shield lowers the temperature of a problematic hot surface and increases the energy transferred to the rotor
which increases the efficiency of the desiccant dehumidifier. Concepts are evaluated and developed through
a product development process inspired by Ulrich & Eppinger to ensure that the best concepts are used.
The final concept is produced and will be further investigated at the laboratory at Munters. Simulations of
each concepts are being developed in Solidworks to see the positive and the negative effects of the different
concepts to ensure that the best ideas goes further in the product development process.
Contents
1 Introduction
10
2 Background
11
2.1
Economical aspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
2.2
Heating surfaces due to radiation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
2.3
Temperature distribution over rotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
3 Approach
13
3.1
Situation Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
3.2
Concept development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
3.3
Concept selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
3.4
Detailed design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
4 Situation Analysis
4.1
14
Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
4.1.1
Mechanical dehumidifaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
4.1.2
Sorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
4.1.3
Desiccant dehumidification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
Regeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
4.2.1
Energy Recovery Purge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
4.2.2
Energy Efficiency Purge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
4.2.3
Bypass purge principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
Rotor material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
4.3.1
Glass fiber (base material) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
4.3.2
Carbon fiber–reinforced thermoplastic . . . . . . . . . . . . . . . . . . . . . . . . . .
17
4.3.3
Adsorbents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
4.4
Experimental data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
4.5
Computational Fluid dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
4.6
Thermal Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22
4.7
Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23
4.8
Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23
4.8.1
Perfect heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
4.8.2
Heating and radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
4.9.1
Wall material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
4.9.2
Initial condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
26
4.2
4.3
4.9
4
4.9.3
Boundary conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
26
4.9.4
Radiation and air temperature effects . . . . . . . . . . . . . . . . . . . . . . . . . .
27
4.9.5
Original design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
4.9.6
Simulation conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
5 Concept Development
32
5.1
Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
5.2
Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
5.2.1
Single plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
5.2.2
Double plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
35
5.2.3
Large single plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
5.2.4
Large single plate with fin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
39
5.2.5
Large plate with bottom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
42
6 Concept selection
6.1
6.2
45
Concept development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45
6.1.1
Large single plate (modified) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45
Final concept selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
48
7 Detailed level design
50
8 Discussion and conclusions
51
Appendices
55
A Concept selection matrix
55
B Drawing
55
C Gantt chart
57
5
List of Figures
1
Illustration of radiation from a body to a surface . . . . . . . . . . . . . . . . . . . . . . . . .
11
2
Sketch of a mechanical dehumidification process . . . . . . . . . . . . . . . . . . . . . . . .
14
3
Desiccant dehumidifier model (Mun, 2013) . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
4
Energy Recovery Purge (Mun, 2013) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
5
A bypass flow model (Mun, 2013) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
6
Porous material categorization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
7
Thermometer measure points on the rotor. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
8
Rotor colored after temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
9
View of fan from the same side as shown in Figure 8 . . . . . . . . . . . . . . . . . . . . . .
21
10
A overview of the original design, with declaration of the surfaces . . . . . . . . . . . . . . .
25
11
Temperature differences with and without radiation . . . . . . . . . . . . . . . . . . . . . . .
27
12
Temperature distribution over rotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
13
Flow overview (Mun, 2013) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
14
Result of backside wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
15
Flow trajectories colored after velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
30
16
Result of temperature over rotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
30
17
Location of Single plate concept. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
33
18
Temperature distribution from two angles, front and back side. . . . . . . . . . . . . . . . . .
33
19
Flow trajectories colored after velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
20
Temperature distribution over rotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
21
Location of the upper and lower plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
35
22
Temperature distribution from two angles, front and back side. . . . . . . . . . . . . . . . . .
36
23
Flow trajectories colored after velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
36
24
Temperature plot over rotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
25
Location of Large single plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
26
Temperature distribution from two angles, front and back side. . . . . . . . . . . . . . . . . .
38
27
Temperature distribution over the rotor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
38
28
Temperature of fluid over the large plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
39
29
Location of Large single plate with fin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
40
30
Fins improvement on the plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
40
31
Temperature distribution from two angles, front and back side. . . . . . . . . . . . . . . . . .
41
32
Temperature distribution over the rotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
41
33
Location of the Large plate with bottom . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
42
34
Temperature distribution from two angles, front and back side. . . . . . . . . . . . . . . . . .
43
6
35
Rotor temperature distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
43
36
Location of Large single plate (modified) . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45
37
Temperature distribution from two angles, front and back side. . . . . . . . . . . . . . . . . .
46
38
Radiation distribution with the fluid temperature colored over the flat plate. . . . . . . . . . .
46
39
Velocity plot seen from the side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47
40
Rotor temperatures for the Large single plate. . . . . . . . . . . . . . . . . . . . . . . . . . .
47
41
Location of configuration holes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
50
42
Sequence diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
56
43
Planning of master thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
57
7
List of Tables
1
Temperatures of the thermometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
2
Mesh result and mesh size of the original design . . . . . . . . . . . . . . . . . . . . . . . . .
23
3
Material properties setup in Solidworks . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
26
4
Initial conditions in Solidworks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
26
5
Boundary conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27
6
Base configuration M X 2 30 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
7
Temperature extreme points of original back wall . . . . . . . . . . . . . . . . . . . . . . . .
29
8
Temperature extreme points of original rotor . . . . . . . . . . . . . . . . . . . . . . . . . . .
30
9
List of specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
10
Temperature extreme points of single plate concept over back wall . . . . . . . . . . . . . . .
33
11
Temperature extreme points of single plate concept over rotor . . . . . . . . . . . . . . . . . .
34
12
Temperature extreme points of double plate concept over back wall . . . . . . . . . . . . . . .
36
13
Temperature extreme points of double plate concept over rotor . . . . . . . . . . . . . . . . .
37
14
Temperature extreme points of back wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
38
15
Temperature extreme points of double plate concept over rotor . . . . . . . . . . . . . . . . .
39
16
Temperature extreme points of large plate with bottom on back wall . . . . . . . . . . . . . .
41
17
Temperature extreme points of Large single plate with fin concept over rotor . . . . . . . . . .
42
18
Temperature extreme points of large plate with bottom on back wall . . . . . . . . . . . . . .
43
19
Temperature extreme points of large plate with bottom . . . . . . . . . . . . . . . . . . . . .
44
20
Temperature extreme points of large plate when modified . . . . . . . . . . . . . . . . . . . .
46
21
Temperature extreme points of large plate when modified . . . . . . . . . . . . . . . . . . . .
47
22
Concept weight matrix, full matrix is found in appendix A . . . . . . . . . . . . . . . . . . .
48
23
Point matrix of concept and specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
49
8
Nomenclature
T
Temperature increase C
Q˙
Watt J/s
V˙
Volume flow m3 /s
⇢a ir
Density of air kg/m3
C
Temperature in Celsius
Cpair Specific heat of air kJ/kg K
Re
Reinolds number
CAD Computer aided design
CFD
Computational Fluid Dynamics
COP
Coefficient of performance
EEP
Energy Efficiency Purge
ERP
Energy Recovery Purge
MOFs Metal–organic frameworks
MRF Moisture removal factor
9
1 Introduction
Munters
Munters was founded by Carl Munters, Marcus Wallenberg, Carl Gustaf Wicander and Erling Berner at 1955,
today owned by Nordic Capital. Munters is a global leader in energy efficient air treatment solutions, they
possess a wide range of products where the biggest customers are part of the food, pharmaceutical and data
center sectors.
Background of the problem
Dehumidification systems are today very common in industries, shopping malls, event areas, animal plants
and hospitals. The process is to take away water from the air to prevent mold, increase comfort and meet the
required air moisture ratio for various reasons. The process is energy consuming, most of the energy goes to the
regeneration process to recover the applications moisture uptake. This is usually done with heat from different
sources such as waste energy, electricity, steam, gas or warm water. This thesis will focus on Munters industrial
M X 2 30 dehumidifier which have a power of 30 kW and a flow of 2700 m3 /h. Today there are many methods
used to increase the efficiency and to decrease the energy consumption of the dehumidifiers. Increasing the
energy efficiency with a fraction can result in a high cost saving due to the high power used.
Objective
The objective of this thesis is to present a design concept of energy efficient regenerating technology which
can be used in future dehumidifiers for Munters. This should be done by analyzing their current products and
by practice the science of the company and scientific articles. The project has as a goal to reduce local energy
wasteful temperature spots and increase the temperature at the rotor.
Thesis scope
Due to the time limitation not all parts of the dehumidifier will be discussed and evaluated. The main scope is
to produce concepts that solves the problem with the thermal radiation coming from a electrical heater.
10
2 Background
Dehumidification processes are today a widely used phenomena to increase the comfort for humans and to
keep the climate at required levels in buildings. Controlling the humidity in the air is important to prevent
mold, condensation and to increase the comfort indoors. The temperature is a crucial factor for the air quality,
a colder temperature will demand less moisture in the air for condensation to occur since the dew point will
decrease with the dry bulb temperature. At the dew point temperature the air will be saturated with water and
condensation will occur, which can be a problem for many reasons as explained earlier. The energy required will
increase for a dehumidifier when the dew point temperature decrease which leads to a more energy consuming
application at low temperatures.
2.1
Economical aspect
The operation of dehumidification processes makes the energy consumption area worth to investigate. The
coefficient of performance (COP) is a very important factor calculated as a fraction between the energy going
to work and the total energy consumption. The COP for the whole dehumidification process is crucial, a saving
in a fraction of percentage will reduce the total life cycle cost. The cost could also be reduced if part of the
energy is waste energy from another process or application.
2.2
Heating surfaces due to radiation
It has been reported from Munters laboratory tests that it exists surfaces that reaches temperatures around 80 C.
The surfaces is isolated but high temperature on the surface is energy waste and should be lowered if possible to
reduce the energy loss. All bodies above absolute zero emit thermal radiation, the thermal radiation increases
with the temperature and are emitted to surrounding bodies. The energy absorbed do solely depend on the
emissivity of the material. A black body absorb all the energy hitting the surface. In practice no such surface
exists and therefore some energy is reflected by the surface. Figure 1 shows a body which emit thermal radiation
to a surface.
Figure 1: Illustration of radiation from a body to a surface
11
2.3
Temperature distribution over rotor
Tests have shown that the temperature distribution over the rotor is not homogeneous, the temperature does
have local high temperature spots which could reduce the life time of the rotor. Since the rotor is the most
complex and most expensive part of the desiccant dehumidifier it is of great importance to reduce those local
temperature spots and try to get a more homogeneous temperature distribution over the rotor.
12
3 Approach
In the development for the next generation of dehumidifiers a method brought by Ulrich & Eppinger is used as
a structured way of finding the real core to the problem (Ulrich and Eppinger, 2008). In this master thesis Solidworks is used to simulate and to construct the parts needed for the solution. Solidworks is a CAD (Computer
aided design) program where sketches and calculations can be made for the product.
3.1
Situation Analysis
A wide situation analysis is made to see where and what is the real problem for the current application as well as
how the application is used today. Simulations will be done on the existing parts to see how the flow is moving
through the dehumidifier and boundary conditions are estimated from experimental results done by Munters
combined with approximated properties.
3.2
Concept development
A specification of the parts in the new concept is done to meet the required desires and demands on materials,
temperatures and flows. The specification will then be used to evaluate the different concepts and to estimate
the best concept.
3.3
Concept selection
In the concept selection CAD- models will be used and verified to fit and essential problems with manufacturing
will be viewed. Concepts are being further developed to ensure that the knowledge and all positive aspects of
the concepts are being used. Matrixes of concepts and specification are made to ensure that the concepts fulfill
the demands and desires.
3.4
Detailed design
In the detailed design the product should be as detailed as possible and should be ready for production. Desires
from the construction engineers, production line and manufacturers will be evaluated and payed attention to,
this is crucial to optimize the product. At last construction drawings will be made for manufacturing. In this
process it important to identify problems with the components and it is important to ensure safety and quality.
13
4 Situation Analysis
4.1
4.1.1
Theory
Mechanical dehumidifaction
The most common dehumidification process, mechanical dehumidification, occurs naturally and depends on
the temperature change of the medium. Mechanical dehumidification can be forced by dragging the moist air
over a refrigerated coil where the temperature decrease will allow some air condensing and remove moist from
the air. When condensation occurs the moisture in the air decreases and the heat increases, this is due to the
energy release of the water going from an evaporated state to a liquid state. Figure 2 is a sketch of a mechanical
dehumidification process, the refrigerant is flowing in a loop where it changes pressure, this will allow the
condenser side to be cold and condense water from the air.
Figure 2: Sketch of a mechanical dehumidification process
4.1.2
Sorption
Sorption is the phenomena of adsorption and desorption. It is a environment friendly alternative to the mechanical dehumidification which use gases that often are not environment friendly. It consists of a desiccant material
which have small pores with the ability to hold mediums. When the desiccants pores are filled with a medium
it adsorbs and when the desiccants pore are emptied it is called desorption. Different desiccants can be used to
achieve various of properties.
14
4.1.3
Desiccant dehumidification
The desiccant dehumidification have at least two sectors, a process sector which is the largest and takes up
the moist from the air and a recovery sector which recovers the humidity uptake performance of the desiccant.
When the air is entering at the process side, it takes process air from the room of which it needs to reduce the
moisture in. The air is then passed through the process side of the desiccant wheel into micro channels. Since
water is dipolar it will create bonds on to the surface in the channel, it bounds with van der waal bonds. This
is called adsorption which means that the water is still in the evaporated state and not in a liquid state. As
the wheel is rotating there will be some heat carried from the recovery sector to the process side and this heat
will along with the heat from the adsorption process produce a heat increase at the process outlet which will
supply air to the room. The amount of heat carried over from the recovery sector will increase with wheel
rotation speed and the temperature of the regeneration sector. The regeneration temperature is dependent on
the material used in the rotor along with the depth of the rotor. The temperature of the material should be as
close to the process air as possible to increase efficiency of the rotor and reduce the transportation of heat from
the regeneration side. The transportation can be decreased by using purging which decreases the temperature
in the material before it enters the process sector(Mun, 2013). An illustration of a desiccant wheel is displayed
in Figure 3
Figure 3: Desiccant dehumidifier model (Mun, 2013)
4.2
Regeneration
The main goal of the regeneration process is to dry out the rotor as energy efficient as possible, today this is
done by heating the air and there is a number of different ways to heat the air. The chosen regeneration process
is often selected with respect to the dehumidifiers environment. Today it is common to use steam, gas, hot water
and the most frequently used is electric power. Since the function of the applications should be to increase the
15
temperature of the regeneration air to a certain
T it is very effective and common to use the resources in the
environment to pre-heat the air. These are though not always as effective as it needs to be, therefore multiple
energy sources are combined. Preheating with hot water as far
T as possible and heat the remaining degrees
with electricity, steam or gas is very common to save energy.
4.2.1
Energy Recovery Purge
The Energy Recovery Purge (ERP) system takes reactivation air before it is heated by the heater and bypass
a small flow into the other end of the rotor. The air is then injected into the warm end of regeneration sector
to decrease the temperature of the desiccant material and increase the temperature of the air, this will increase
the desiccant water adsorption capability. The air will then return to the cold side of the rotor and mix with
the reactivation air. This will save energy since the air is preheated by the purge and the desiccant material is
cooled down. Desiccant materials do not have a very good moisture uptake at high temperatures and not using
a purge will cause the first degrees in the process side to be inefficient (S.J Slayzak, 2000). Figure 4 illustrates
the ERP system (Mun, 2013).
Figure 4: Energy Recovery Purge (Mun, 2013)
4.2.2
Energy Efficiency Purge
Energy efficiency purge (EEP) has the design of ERP but instead of decreasing the power usage as in ERP it
uses a higher power and heats up the air faster, leading to that the regeneration section will increase to
T
faster. This increases the capacity of the rotor and a more efficient recovery process. EEP systems consume
higher power than ERP but is usable and favorable when designing low dew point applications.
4.2.3
Bypass purge principle
The bypass function allows a fixed airflow to be used when process airflow exceeds the maximum rotor flow
capacity. When the airflow is larger than the capacity of the rotor the air is directed through the purge. An
overview of a bypass purge principle can be seen in Figure 5.
16
Figure 5: A bypass flow model (Mun, 2013)
4.3
Rotor material
The material of the rotor should possess properties that give enough mechanical strength so that the rotor does
not collapse due to it’s own weight. It should be able to withstand heat of the regeneration area (⇠ 140 C)
and have a desiccant layer which is a good adsorbent. The rotor is the heart of the desiccant dehumidifier and
therefore the adsorbent used is crucial for the moisture removal (Narayanan, 2011). Today silica gel is used as
a desiccant material, there are also a variation of additives that can be added to give further properties such as
purification of the air.
4.3.1
Glass fiber (base material)
Glass fiber consists of a material that have many thin fibers in it. The fibers are made of glass and can be put in
different directions to enhance strength in that specific direction. Therefore the strength of the material will vary
with direction, the fibers can be put in random order to archive a homogeneous strength through the material.
Fiber glass have a wide range of use and is thereby used in many applications. The fibers are commonly used
with a polymer that will help the material to be rigid. There are different types of fiber glass, the mechanical
properties among them vary due to the composition of the glass fiber. E-glass is the most commonly used glass
fiber due to its price and weight which makes it a favorable for big production volumes (Mutnuri, 2006). Fiber
glass is an insulating material and have a low thermal conduction (⇠ 0.04W/mK). Fiber glass do not have any
melting point instead it becomes softer and starts to degrade.
4.3.2
Carbon fiber–reinforced thermoplastic
Carbon fiber is similar to glass fiber, instead of fibers of glass it consists of fibers of carbon. The strength to
weight ratio is high, higher than glass fiber which makes it advantageous for applications that require strength
and light weight such as in aerospace, automobile and sport goods. Carbon fiber is as glass fiber, direction
dependent. In the direction of the fiber the strength is good and thermal conductivity is much better in the
parallel direction than the transverse. Carbon fiber as well as glass fiber is often weaved to archive the required
17
properties of the material, the weave pattern is decided from the use in the application such as design geometry
or strength requirements.
4.3.3
Adsorbents
Adsorbing should not be confused with absorbing. Absorbing is due to the imbuing of a permeate and is rather
a form of material’s intrinsic permeability then the chemical polarity attraction. Adsorbents uses adhesion
to create a surface layer with the adsorbate on the adsorbent. The bond made is Van der waal bonds which
are rather weak bond and is the sum of the intermolecular attractive forces (van der waal forces). Physical
adsorbents usually have the properties of a porous material with different pore size and physical adsorbents can
maintain their properties if it is heated up so it can desorb the adsorbed permeate and therefore go back to the
original state, this makes it very usable in applications like dehumidifiers and this section will bring up some
usual physical adsorbents used for dehumidifiers.
The porous materials can be categorized within these four groups showed in Figure 6
Figure 6: Porous material categorization
Silica Gel
Silica gel is a mesoporous material (SiO2 ) and Silicon dioxide is a common material used for desiccant dehumidifier wheels, due to the low production cost and high surface area. Silica gel is an amorphous material of
mainly silica particles, the surface area depends on how the material is packed and the pore size affects the volume (Aristov, 2011). Silica gel is favorable in desiccant wheels due to the low regeneration temperature which
is about 50 - 90 C. This generation temperature is strictly dependent of the recovery of the materials property
as well as the time the material is exposed to this temperature (Aristov et al., 2001). The exposed regeneration
time is related to pore size, It can adsorb water up to 35-45% of its dry weight and it is environmental friendly
as well (Ng et al., 2001).
Silica gel composites / hygroscopic salts
Silica gel can be combined with salts, this can give properties with much higher water uptake (almost doubled),
which means that the difference
w will be much higher and therefore more favorable in applications with
demands on lower RH-value (Aristov et al., 2001). The characteristics can be modified by changing the salt
18
type and the weight percent of the salt type (San, 2006; Freni et al., 2010). By using hygroscopic salts the
desportion temperature can be lower than 90 C (Freni et al., 2010).
Activated Carbons
Activated Carbon (AC) is produced from natural products such as wood, coal nutshells etc. It is a porous
material belonging to microporous group of materials and is very common in applications such as gas and
water purification. It has a higher porosity than silica gel and the adsorption heat is lower. It is used in kitchen
fans and dehumidification processes. In a kitchen fan it adsorbs the os from the air and in dehumidification it
has the ability to remove smells. It’s also a favorable ingredient in desiccant wheels for shopping malls due to
the purification of the air. The properties of AC makes it useful and it has a high surface area ranging between
500-1500 m3 /g. It’s considered to be a microporous group of material. AC with lower porosity leads to higher
thermal conductivity and is easier to manufacture than AC with higher porosity (Wang et al., 2011).
Zeolite
Zeolite is a crystalline microporous alumina silicate mineral, which occurs naturally but can be industrially produced on a large scale as well another benefit is that it is possible to manufacture the zeolites in a specific pour
size (Nóbrega, 2014). Since zeolites have this crystalline structure it has a high heat desorption temperature.
250-300 C, due to the high temperature it doesn’t make it a future material for the desiccant wheel since the
regeneration temperature is low for dehumidifiers.
Metal–organic frameworks
Metal–organic frameworks (MOFs) consists of metal ions coordinated in one, two or three dimensions. MOFs
can be porous and have a very high adsorption capability due to the high surface area which can be between
4300 m2 /g - 5950 m2 /g (Saha and Deng, 2010). MOFs compared with silica gel and zeolite is less hydrophilic
which means that it can release more water molecules in the same time and partial pressure.
4.4
Experimental data
The temperature distribution over the rotor today is measured in Munters laboratory. The temperature distribution of the air is not homogeneous and is measured with nine thermometers, see Figure 7. The measurements
are done when the application has reached balance.
Table 1 shows the average temperature of the rotor (
C). This temperature is one of the verification’s
used later in simulations. The temperature can be colored for each thermometer to get a better view of how the
temperature is distributed over the rotor, see Figure 8.
19
Table 1: Temperatures of the
thermometers
Figure 7: Thermometer measure points on the rotor.
Number
0
1
2
3
4
5
6
7
8
Mean
Max
Min
Temperature C
Figure 8 shows that there is a hot spot on the outer part of the rotor ( at thermometer 7). This hot spot have
a temperature of
C. Investigating the model of the dehumidifier reveals why the temperature distribution
looks like this.
Figure 8: Rotor colored after temperature
The fan location confirm the temperature distribution over the rotor, this shows that the location of the fan
is the driving parameter of how the distribution over the rotor looks like. The location of the fan can be seen in
Figure 9.
20
Figure 9: View of fan from the same side as shown in Figure 8
4.5
Computational Fluid dynamics
Fluid dynamics is the natural science of liquid and gases in motion. It has various of subdisciplines such as
aerodynamics and hydrodynamics. The fundamental theory of hydrodynamics comes from the motion equations for a fluid with no inner friction (viscosity) which are formulated by Leonhard Euler. The Euler equations
can therefore only be approximated if the inner friction is small. The equations are complemented by Luis
Navier and George Stoke to the Navier-Stoke equation(Bark, 2015).
Solidworks Flow Simulation solves the Navier-Stokes equations which are formulations of mass, momentum and energy conservation laws for fluid flows. Non-Newtonian fluids are considered by introducing a
relationship with either the density, temperature or viscosity depending on the fluid characteristics. A problem
formulation is specified depending on geometry, initial and boundary conditions (SolidWorks, 2012). Conservation of mass in the Cartesian coordinate can be expressed with the following equations.
@⇢
@
+
(⇢ui ) = 0
@t
@xi
(1)
Conservation of angular momentum
@⇢ui
@
@p
+
(⇢ui uj ) +
@t
@xj
@xi
@
(⌧ij + ⌧ijR ) + Si = 0, i = 1, 2, 3
@xj
(2)
Conservation of energy
@⇢H
@t
+
@⇢ui H
@
@p
=
uj (⌧ij + ⌧i j R ) + qi +
@xi
@xi
t
21
⌧ijR
@ui
+ ⇢✏ + Si ui + QH
@xj
(3)
H = h+
u2
2
where u is the velocity of the fluid, ⇢ is the density of the fluid, Si is a mass-distributed external force per
unit mass due to a porous media resistance, h is the thermal enthalpy of the fluid, Q is a heat source and qi is a
diffusive heat flux. ⌧ is the shear stress tensor of the viscous fluid.
Turbulent and laminar flow The state of the flow is categorized after the Reynolds number (Re) which
is the ratio of the inertial forces to the viscous forces
Re =
Inertialf orces
⇢vL
=
.
V iscousf orces
µ
(4)
The size of Re indicates whether the flow is turbulent or laminar. If the Re-number is greater than a specific
number the flow is seen and handled as a turbulent flow. Turbulent flow is distinguished by re-circulation and
creates a chaos in the flow. From equation 4 it is seen that the kinematic viscosity, velocity and the geometry
are the driving parameters for the Reynolds-number. One of the most common Computational Fluid Dynamics
(CFD) models is k
k
✏ model, which is used to simulate flow characteristics for turbulent flow conditions. The
✏ model is a two equation model, where the first transported variable is the turbulent kinetic energy, k and
with the second transported variable ✏ which is the turbulent dissipation. The flow model gives good results
with a mean pressure gradient that is small which is the case for a dehumidifier.
Steady and unsteady flow
A steady flow is considered to be independent of time, this means that every
point in the flow is the same at all times. In other words the time derivative is zero at all times
@
@t
= 0. A
unsteady flow is the opposite of a steady flow. This means that the flow is not the same at different times,
therefore a unsteady flow requires one more dimension to be calculated.
Boundary layer
A boundary layer is a transitional layer between two bodies with different properties.
The boundary layer is used to describe the flow in near-wall regions (SolidWorks, 2012). In the boundary layer
the shear stress of the fluid becomes important since the force from the viscous shear stress tends to drag the
body in the flow direction. Boundary layer flows are categorized in laminar and turbulent flow, often the flow
is both or shifting between them and therefore it is called a transitional layer.
4.6
Thermal Radiation
All bodies above absolute zero emit thermal radiation. Thermal radiation can be emitted, absorbed and reflected
by surfaces. A black body do only absorb thermal radiation, a white body reflect all thermal radiation and the
grey body both absorb and reflect. The energy leaving a radiating surface can be expressed with
qT = ✏ T 4 + ⇢t · qT,i
22
(5)
where ✏ is the surface emissivity,
is Stefan-Boltzmann’s constant and T is the temperature of the surface.
✏ T 4 is the energy leaving the surface according to Stefan-Boltzmann’s law. ⇢t is the surface reflectivity. qT,i
is the incident thermal radiation hitting the surface. In Solidworks the emissivity and energy parameters are
known and the surfaces are treated as grey-bodies of where the emissivity is set for each material(SolidWorks,
2012).
4.7
Mesh
Solidworks mesh the model in a Cartesian network, the mesh is rectangular everywhere in the computational
domain. At the intersection between the solid and fluid the mesh is finer and split up uniformly in smaller cells
to capture the interface. In each cell the maximum angle is measured to the normal of the face, if that angle is
above a specific value the cell divides until the threshold is met.
The mesh size will affect the time and iterations it will take for the solver to converge to the correct answer.
A good mesh will reach convergence with lesser computer power than a bad mesh. A comparison of mesh
quality and mesh size of the original design is displayed in table 2. The mesh quality is measured from 1 to 8
and number 8 is the finest. The cell amount is increased with mesh quality but the result of the temperatures at
the rotor and back wall is pretty much the same with mesh quality 5 and 8. Mesh quality 5 requires less time
to converge therefore this mesh quality is used in simulations. Solid cells are the cells that contains only solid
material, Fluid cells are the ones where the air will move and partial cells are the cells which contains both a
fluid region and a solid region.
Table 2: Mesh result and mesh size of the original design
Mesh Quality
ROTOR
ROTOR
ROTOR
Back wall
Back wall
Back wall
Solid Cells
Fluid Cells
Partial Cells
Total Cells
4.8
Min
Avg
Max
Min
Avg
Max
Unit
[C]
[C]
[C]
[C]
[C]
[C]
3
Value
5
Value
8
Value
488
2392
2304
5184
3621
23696
10119
37436
9549
61870
19816
91235
Calculations
In order to give estimates of the current situation calculations are made on the radiation and heating of the air
to give a better understanding of where the energy in the dehumidifier is going.
23
4.8.1
Perfect heating
A perfect heating is here referred to heating of the medium without losses and radiation. The heater have a
energy consumption of 30kW and is heating the air to a temperature of which is used for the regeneration
process. By applying the law of advection
˙ T =
Q˙ = Cpair m
(6)
Q˙ = Cpair V˙ ⇢air T
(7)
Type
Energy source
Specific heat
Volume flow
Density
Temperature difference
Variable
Q
Cpair
V
⇢air
T
Value
30
1.005(20 C)
0.25(20 C)
1.2(20 C)
Dimension
kW
kJ/kgK
m3 /s
kg/m3
C
Rewriting equation 7
4.8.2
T
=
Q˙
Cpair V˙ ⇢air
(8)
T
=
30kJ/s
= 99.5 C
1.005kJ/kgK · 0.25m3 /s · 1.2kg/m3
(9)
Heating and radiation
Results from Munters lab shows that the temperature of the air from the heater is close to the temperature in
section 4.8.1, but there is some energy going to thermal radiation since all bodies that have a higher temperature
than absolute zero will emit thermal radiation. It is estimated that the air is heated to 94.1 C and other losses
are estimated to be 2% of the heaters power, which leaves the radiation energy to
Q˙ total = Q˙ convective + Q˙ radiation + Q˙ losses
Q˙ radiation = Q˙ total
Q˙ radiation = Qtot
Q˙ radiation = 30kW
Q˙ convective
Q˙ losses
Cpair V˙ ⇢air T
0.02 ⇤ Qtot
1.005kJ/KgK · 0.25m3 /s · 1.2kg/m3 · 94.1 K
0.02 ⇤ 30kW = 1028.85
(10)
(11)
(12)
(13)
(14)
(15)
24
The thermal radiation is estimated to 3.5 % of the total energy from the heater. This is a small portion of the
total energy consumption of the heater.
4.9
Simulation
Simulations are done in Solidworks and approximations are made from Munters laboratory tests and the estimations above. The simulation includes a scenario setup from the results that have been evaluated by Munters
laboratory, parameters have been set after the tests to receive as good simulation setup as possible. The simulation includes flow, radiation and heat transfer. The model is then evaluated and compared to the real laboratory
setups to achieve as realistic model as possible. In Figure 10 an overview of the simulation volume is shown,
this is the inside of the dehumidifier M X 2 30. The heater is located where the air is entering, the air heats up
and flows against the back wall. The back wall is the surface that receives heat from the heater and is today
classed as a hot surface. The air is flows to the rotor and passes an area that is used for configurations for the
flows. The rotor is the outlet for the flow, and the air is flowing through thin channels and it is estimated that the
flow is homogeneous. The simulation will converge when it reaches the goals setup in the simulation. There are
goals at the surfaces to find the rotor temperature, back wall temperature and goals related to the flow. When
the calculations reaches a point where those are not changing that much it will stop, no upper limit in iterations
are set.
Figure 10: A overview of the original design, with declaration of the surfaces
4.9.1
Wall material
The material of the wall is today a Aluzink - Aluminum Zink coated sheet. This material is used for most of the
base components for the dehumidifier, a thickness of 1 mm is used for the simulations. This material is used to
simulate the temperature of the wall. The material properties are displayed in table 3.
25
Table 3: Material properties setup in Solidworks
Aluzink
Density
Specific heat
Conductivity type
Thermal conductivity
4.9.2
7880.00 kg/m3
15.1 J/(kg*K)
Isotropic
15.00 W/(m*K)
Initial condition
Initial conditions are set as close to the test environment in Munters laboratory as possible. In table 4 the
initial conditions are showed. An environmental pressure of 1 atmosphere is used, the velocity of the air flow
surrounding the dehumidifier is 0, this is because the dehumidifier is inside a room. The initial solid temperature
of the solid material is 20 C as the temperature of the room. The turbulence model is k
✏ with the intensity
of 2 % and the length of 0.004 m, this is the default options in Solidworks. Investigating these parameters do
not seem to give effect on the temperatures, but the temperature distribution is affected. Therefore it seems
valid to use the default parameters since no information about the flow is given from experiments. The flow is
considered to be steady, and therefore it will look the same at all times (see section 4.5).
Table 4: Initial conditions in Solidworks
Thermodynamic parameters
Static Pressure
Temperature
Velocity parameters
Velocity vector
Velocity in X direction
Velocity in Y direction
Velocity in Z direction
Solid parameters
Default material
Initial solid temperature
Radiation Transparency
Turbulence parameters
Intensity
Length
4.9.3
101325.00 Pa
20 C
0 m/s
0 m/s
0 m/s
Aluzink
20 C
Opaque
2.00 %
0.004 m
Boundary conditions
The boundary conditions are set to mimic the test environment. A flow of 0.25 m3 /s is used, which is corresponds to 900 m3 /h. The flow outlet is set at the rotor and since there is a suction fan the boundary condition
on the rotor is set as an outflow while the inlet is set to environmental pressure. The flow is estimated to be
turbulent, this is due to the fact that the air is mixing in the channels and the geometry of the inlet do have many
obstacles in the flow path. Boundary conditions can be seen in table 5
26
Table 5: Boundary conditions
Boundary Conditions
Thermodynamic parameters
Environment pressure
Temperature
Turbulence intensity and length
Intensity
Length
Boundary layer parameters
Boundary layer type
Flow vectors direction
Volume flow rate
4.9.4
101325.00 Pa
C
2.00 %
0.004 m
Turbulent
Normal to face
0.25 m3 /s
Radiation and air temperature effects
In order to verify that the radiation have any effects on the air temperature and the temperature of the back wall
a simulation model is setup with the corresponding effect on the radiation in section 4.8.2. The result is then
compared with a simulation without any radiation. In Figure 11 the both simulation results on the back wall is
shown. Comparing Figure 11a and Figure 11b it is clear that radiation have effects on the back wall since the
radiation creates a hot spot on the upper part of the back wall.
(a) Temperature distribution over
back wall seem from back with radiation
(b) Temperature distribution over
back wall seem from back with no radiation
Figure 11: Temperature differences with and without radiation
Comparing the result of the rotor temperature shows that the temperature rises at the rotor when radiation
is applied to the simulation. In Figure 12 the temperatures are plotted over the rotor to see the impact of the
radiation and it is clear that the radiation increases the temperature of the air. The hot part of the rotor have a
higher temperature when radiation is presented in the model.
27
(b) Temperature distribution over
rotor seem from front
(a) Temperature distribution over
rotor seem from back
Figure 12: Temperature distribution over rotor
4.9.5
Original design
Simulations are done on Munters M X 2 30 desiccant dehumidifier. This is an appliance being produced today
and laboratory tests regarding the temperature can be found in section 4.4
This setup is done as a validation, material of the outer case (the plates) are Aluzink coated sheet as described above in section 4.9.1. The flows are taken from Munters manual Mun (2013). The processes fan is
located at the process outlet, the flow is opposite to the reactivation flow in the rotor. A overview of the flow
can be seen in Figure 13 and the flows are presented in table 6.
Figure 13: Flow overview (Mun, 2013)
Table 6: Base configuration M X 2 30
Process fan
Reactivation fan
Air flow m3 /h
2700
900
Differential pressure Pa
182
92
The temperatures of the back wall is calculated and validated against measurements done by Munters laboratory. Radiation is used and setup with the power calculated in section 4.8.2, since the radiation combined with
the regeneration flow that passed by the heater are heating the surface of the wall. This temperature distribution
is very similar to the temperatures measured. The problem spot is the upper part of the wall which is just after
the heater on the back wall. The flow simulation shows that there are a substantial flow projected on the surface.
In Figure 14 the temperature distribution is shown on the back wall. The temperature is hottest horizontally
after the heater and after the choked area in Figure 10, the later is probably due to the velocity of the air. Since
28
there is so much air passing through that area more heat will be transferred to the back wall. The spot on the
upper part is located just after the heater and is the area of where problem with high temperatures is. Simulation
shows that the radiation from the heater is one of the critical parameters to this hot spot as shown in section
4.9.4, even though the radiation is as calculated earlier in section 4.8.2 a very small portion of the total energy
consumption.
Figure 14: Result of backside wall
Table 7 shows that the average temperature is 67 C and the maximum temperature is 82 C. The maximum
temperature is as discussed earlier after the heater. Tests done by Munters have shown that the temperature
of the back wall can reach temperatures around 80 C and even higher at the upper part of the back wall.
In the simulation the temperature reaches close to this temperature and are therefore assumed to be a good
approximation of the appliance.
Table 7: Temperature extreme points of original back wall
Goal
Backwall Min Temperature
Backwall Avg Temperature
Backwall Max Temperature
Unit
C
C
C
Value
37.35
67.35
82.02
The volume flow rate is as explained earlier important for the heat transferred, in Figure 15, the velocity
will increase with lesser area since the volume flow is set to a constant outlet of 0.25m3 /h. As seen the velocity
is high at the bottom hot spot.
29
Figure 15: Flow trajectories colored after velocity
The temperature distribution over the rotor do have some local temperature rises and the temperature gets
higher in the middle of the rotor as Figure 16 shows. The material of the rotor can handle temporary temperatures reaching 160 C without effecting the lifetime to much. (Petersson, 2014)
Figure 16: Result of temperature over rotor
As seen in Table 8 the temperatures varies over the rotor. The result can be compared with the result in
C and
section 4.4 where the average temperatures are very close
C respectively.
Table 8: Temperature extreme points of original rotor
Goal
Rotor Min Temperature
Rotor Avg Temperature
Rotor Max Temperature
30
Unit
C
C
C
Value
4.9.6
Simulation conclusion
Simulation of the flow shows that there is a quite large amount of air that is projected to the back wall surface.
The flow combined with the radiation create a hot spot on the surface, the temperatures simulated are at the
inside of the isolation. The temperature distribution over the rotor is of interest since a more homogeneous
temperature will give a better moisture wave front in the rotor. If the rotor don’t have a consistent temperature
distribution this will give a decreased performance and less moisture removed at the rotor. Simulations show
that there is a potential improvement in the temperature distributions that may increase the moisture removal
factor (MRF) of the dehumidifier.
The simulation does not show identical similarity with the test results done, this is probably due to other
parameters such as leakage and wrong estimations. For the back wall the agreement is however good , and
the average rotor temperature which is the most important is very close to the real temperature. The leakage
is estimated to be zero in this simulation model although the leakage is not zero and should have a negative
impact on the temperatures. If air escapes it means that some energy escapes and therefore the temperature will
decrease. The estimated values are hard to predict, but the significance of radiation is proven to be important
both in calculations and in simulations although it is not the real value.
31
5 Concept Development
5.1
Specification
Specifications are setup along with Munters R&D department to fulfill the standards for Munters stand alone
as well as from the situation analysis. The concepts must fulfill the criterias to be valid. The technical and
commercial requirements from the product demands will be stated as a product specification usually, but for
now since this is an improvement and not a whole new system, standard components are used if not stated
otherwise. The following criterias are setup in table 9 to for the concept to meet.
Table 9: List of specifications
Desire / Demand
Desire
Desire
Desire
Demand
Demand
Demand
Demand
5.2
Criteria
Decrease local temperature spots on the rotor
Decrease waste energy
Increase lifetime of application
Compact and modular designed
Better or equal general temperature distribution
Design for manufacture
Decrease temperatures on back wall
Concepts
Concepts are made to improve the flow and temperature distribution in the M X 2 30. Concepts will get evaluated
based on the specification list. Information have been gathered internally and externally, using contacts at
Munters and internet to get as good concepts as possible. Concepts are made to improve flow paths, decrease
temperature on the back wall and get a more homogeneous temperature distribution over the rotor as well as
higher temperatures in the air.
5.2.1
Single plate
Single plate concept is a plate installed after the heater to cover the hot spot. A more detailed view of the
installation is seen in Figure 17. This plate is rounded to improve the flow by directing it against the rotor. The
idea is to catch up the heat from the radiation and let the air heat up against the plate instead of heating up the
back wall. The plate is designed to use little material and should be easy to produce.
32
Figure 17: Location of Single plate concept.
Simulations show that the temperature at the upper hot spot showed in Figure 18 is decreased in size and
more heat is going to the single plate, the temperature extremes can be seen in table 10. There are still some
areas with high temperatures before the choked area. Figure 18 shows that the plates takes up a large amount
of heat, this heat is the heat that should get transferred to the upper part of the back wall. The temperature at
the top is lower than the temperature from the design in section 4.9.5.
(b) Temperature distribution over
back wall seen from front
(a) Temperature distribution over
back wall seen from back
Figure 18: Temperature distribution from two angles, front and back side.
Table 10: Temperature extreme points of single plate concept over back wall
Goal
Back wall Min Temperature
Back wall Avg Temperature
Back wall Max Temperature
Unit
C
C
C
Value
31.37
56.99
79.15
The velocity profile is very close to the one seen in the original design, however there are a significant
velocity decrease at the top of the application since there is now a plate that is blocking the flow for going into
33
the corners at the top. Figure 19 shows that there are some stagnation points at the corners, this is not wanted
since the flow should be continuous to decrease the chance of back flows and flows that interrupt the main flow.
Figure 19: Flow trajectories colored after velocity
The temperature distribution displayed in Figure 20 is more homogeneous than the distribution that is
simulated in the original design. The minimum temperature is a little bit higher than the original and will lead
to smaller temperature gradient. The rotors average temperature is a little bit lower than the ones in the original
design, shown in Tables 8 and 11 respectively.
Figure 20: Temperature distribution over rotor
Table 11: Temperature extreme points of single plate concept over rotor
Goal
Rotor Min Temperature
Rotor Avg Temperature
Rotor Max Temperature
34
Unit
C
C
C
Value
5.2.2
Double plates
In order to increase the flow velocity in a attempt to make the flow more turbulent at the rotor to even out the
temperatures the plate in concept Single plate at section 5.2.1 is used together with a bottom plate as illustrated
in Figure 21. The temperature was more even distributed over the rotor in this concept and since it is important
to increase the temperatures over the rotor to increase moisture removal it is of great import to get the air down
to the rotor as fast as possible after the heater.
Figure 21: Location of the upper and lower plate
The temperature distribution of back wall on the Double plate concept still have the same advantage of
blocking the radiation from hitting the back wall. Figures 22a, 22b shows that the upper plate contributes to a
temperature increase at the back wall just after the upper plate.
The average temperature over the back wall is in the Double plate concept higher than the temperature in
single plate concept showed in Table 12 and the distribution is shown in Figure 22. The average temperature is
lower than the original design but has a higher maximum temperature. The radiation is the same as in Single
plate concept, the impact is solely due to the two plates.
35
(a) Temperature distribution over
back wall seem from back
(b) Temperature distribution over
back wall seem from front
Figure 22: Temperature distribution from two angles, front and back side.
The velocity is higher in the Double plates concept as seen in Figure 23. The velocity is especially increased
in the region at the choked area. Temperatures of the back wall is seen in table 12.
Figure 23: Flow trajectories colored after velocity
Table 12: Temperature extreme points of double plate concept over back wall
Goal
Back wall Min Temperature
Back wall Avg Temperature
Back wall Max Temperature
Unit
C
C
C
Value
33.24
60.37
91.09
Table 13 shows the temperature extremes and the average of the rotor is shown for the Double plate concept. The temperatures are slightly higher than the temperatures of single plate and the original design. The
distribution of the temperature is good and covers more area with higher temperatures as seen in Figure 24 than
the original concept.
36
Figure 24: Temperature plot over rotor
Table 13: Temperature extreme points of double plate concept over rotor
Goal
Rotor Min Temperature
Rotor Avg Temperature
Rotor Max Temperature
5.2.3
Unit
C
C
C
Value
Large single plate
The temperatures at the rotor has been successfully increased but there is still parameters to evaluate, one of
them are the size of the plate. Large single plate concept is a larger concept than the Single plate concept in
section 5.2.3. The plate is extended down to the choked area to increase the radiation uptake and improve the
fluid flow. The geometry of the plate is an arc to reduce flow resistance. The plate can be seen in Figure 25.
Figure 25: Location of Large single plate
The temperatures of the back wall in Table 14 shows an average temperature that is 18.7 degrees lower than
the original design. Increasing the size of the plate is very effective to lower the temperatures.
37
(a) Temperature distribution over
back wall seen from back
(b) Temperature distribution over
back wall seen from front
Figure 26: Temperature distribution from two angles, front and back side.
Table 14: Temperature extreme points of back wall
Goal
Back wall Min Temperature
Back wall Avg Temperature
Back wall Max Temperature
Unit
C
C
C
Value
31.68
48.66
80.64
The temperatures are very well distributed over the rotor, see Figure 27. This means that the turbulence is
quite high at the rotor and the fluid is mixed well. There is a concentration of the hot air going thru the rotor
as all the other concept but this hot spot is bigger than the other concepts and has higher temperatures which
means that more heat is transferred to the rotor.
Figure 27: Temperature distribution over the rotor.
Table 15 shows the temperature extremes of the rotor and is revealing that the temperatures is quite high
compared to the original design. The minimum temperature is higher as well which means that there is higher
38
water removal capacity. Investigating the radiation of this concept reveals where the radiation is most concentrated.
Table 15: Temperature extreme points of double plate concept over rotor
Goal
Rotor Min Temperature
Rotor Avg Temperature
Rotor Max Temperature
Unit
C
C
C
Value
The radiation do have a very concentrated temperature area which will be futher investigated in the following concept. The area can be seen in Figure 28
Figure 28: Temperature of fluid over the large plate
5.2.4
Large single plate with fin
The following concept is a modification of Large single plate concept. In order to try to increase the temperature
of the air fins are constructed on the Large single plate concept to take up radiation and transfer the heat to the
air. The location of the plate can be seen in Figure 29, the fins are located at radiation spot showed in the
previous section.
39
Figure 29: Location of Large single plate with fin
In Figure 30 the fin location can be viewed along with the hot spot on the Large single plate.
Figure 30: Fins improvement on the plate
The temperatures on the back wall is a little bit higher than the earlier concept, the heat is more distributed
at the end of the plate as seen in Figure 31. The temperatures of the back wall is shown in table 16.
40
(a) Temperature distribution over
back wall seen from back
(b) Temperature distribution over
back wall seen from front
Figure 31: Temperature distribution from two angles, front and back side.
Table 16: Temperature extreme points of large plate with bottom on back wall
Goal
Back wall Min Temperature
Back wall Avg Temperature
Back wall Max Temperature
Unit
C
C
C
Value
33,25
51,02
93,65
The air temperatures are lower than the concept with no fins and the temperatures at the back wall is higher.
This means less energy to heat the rotor which is the key idea. The temperature distribution is still good at the
rotor and better than the original design as well as the average temperature at the rotor which also is higher than
the original design as seen in table 17 and the distribution over the rotor is shown in Figure 32.
Figure 32: Temperature distribution over the rotor
41
Table 17: Temperature extreme points of Large single plate with fin concept over rotor
Goal
Rotor Min Temperature
Rotor Avg Temperature
Rotor Max Temperature
5.2.5
Unit
C
C
C
Value
Large plate with bottom
The concept Double plates in section 5.2.2 had higher temperature at the rotor than the concept Single plate
in section 5.2.1. This concept is using the same bottom plate to investigate if it is possible to generate a higher
temperature at the rotor. The concept location can be seen in Figure 33. The plate protecting the back wall is
the same used in Large single plate concept at section 5.2.3 since this plate had a positive temperature increase
to the rotor.
Figure 33: Location of the Large plate with bottom
The temperatures at the back wall is higher than the temperatures of the concept Large single plate 5.2.1
but lower than the original design which is positive, data are shown in table 18. The large upper plate is still
taking up much heat from the air and from the radiation sent from the heater. The temperature distribution is
similar to Large single plate concept but have higher temperatures, the cold spot on the back wall behind the
rotor have decreased in size as seen in Figure 34.
42
(a) Temperature distribution over
back wall seem from back
(b) Temperature distribution over
back wall seem from front
Figure 34: Temperature distribution from two angles, front and back side.
Table 18: Temperature extreme points of large plate with bottom on back wall
Goal
Back wall Min Temperature
Back wall Avg Temperature
Back wall Max Temperature
Unit
C
C
C
Value
31,52
50,31
83,52
The temperatures at the rotor is higher than Large single plate concept but not significant, table 19. The
lower plate has low impact on the rotor temperatures if the average temperatures are compared. The temperature
distribution however has changed and been positioned a little lower than Large single plate which is negative
due to the rotation of the rotor. The wet part of the rotor is entering at the y-axis and exits at the x-axis, therefore
it is more of interest with a higher temperature at the entering than the exit. The rotor temperature distribution
can be seen in Figure 35.
Figure 35: Rotor temperature distribution
43
Table 19: Temperature extreme points of large plate with bottom
Goal
Rotor Min Temperature
Rotor Avg Temperature
Rotor Max Temperature
44
Unit
C
C
C
Value
6 Concept selection
The concept selection process uses the specifications in Table 9 in section 6.1 to investigate if the concepts
are worth to develop further and if the concepts are fulfilling all the specifications. There is however another
parameter that is of importance, the cost of the production. The chosen concept is brought to the detail level
design for further investigations and improvements along with production drawings.
6.1
Concept development
6.1.1
Large single plate (modified)
The Large single plate concept is modified to decrease the production cost while trying to replicate the ability as
the concept Large single plate with fin has. The temperature of the air of this concept was increased compared
with the other ones, it seems like if the plate is closer to the heater the air temperature will increase without
affecting the back wall to much. The fins did not get a significant response but the distance to the heater did.
Therefore the plate is simplified and the geometry is changed so the plate is closer to the heater. The arc formed
plate is transformed to a flat plate. This will decrease the material used and ease the production steps since
doing a curvature on a plate is more work than keeping it plain. The concept can be seen in Figure 36.
Figure 36: Location of Large single plate (modified)
The temperature decrease on the back wall is very positive since the average temperature has decreased
with 20.5 C and the minimum temperature has been decreased with 5.4 C . the plate seems to take up much
of the radiation from the heater as seen in 37a and the temperature on the upper part is about 305 K, which is
50 degrees cooler than the original design in section 4.9.5.
45
(a) Temperature distribution over
back wall seem from back
(b) Temperature distribution over
back wall seem from front
Figure 37: Temperature distribution from two angles, front and back side.
Table 20: Temperature extreme points of large plate when modified
Goal
Back wall Min Temperature
Back wall Avg Temperature
Back wall Max Temperature
Unit
C
C
C
Value
31.96
46.85
80.14
The radiation distribution is quite high after the heater, this shows that if the plate is located closer to the
heater it will be hotter. Comparing Figure 38 with the radiation distribution in concept Large single plate with
fin at Figure 30 shows that the area is larger when the plate is closer to the heater.
Figure 38: Radiation distribution with the fluid temperature colored over the flat plate.
Figure 39 shows that the air movement at the upper part is very slow or stands still. This means that the hot
air cannot transfer heat to the outer part as it can in the original design.
46
Figure 39: Velocity plot seen from the side
The average temperature at the rotor is slightly higher than the Large single plate concept as well, which
means that this modification is a success. The distribution over the rotor is pretty homogeneous and few low
temperature spots is located in Figure 40 with the temperatures in table 21.
Figure 40: Rotor temperatures for the Large single plate.
Table 21: Temperature extreme points of large plate when modified
Goal
Rotor Min Temperature
Rotor Avg Temperature
Rotor Max Temperature
47
Unit
C
C
C
Value
6.2
Final concept selection
There are two performance parameters that is of special interest, those are the temperatures of the back wall
which should be low and the temperature at the rotor which is the most important factor and should be high to
increase the moisture removal. A matrix containing the concepts and the ranking of the temperatures is made
to filter out those concepts that come out strong with both a low temperature at the back wall as well as a high
temperature at the rotor.
The concepts are compared to each other as well as compared to the original design. The average temperature is the driving force for the moisture removal of the rotor and gives an estimate whether the concept is
efficient. The whole table can be seen in Appendix A where the ranks for back wall and the rotor is displayed.
The formula for calculating the points is 2xRotor + Backwall, this means that the rank of high temperature
at the rotor is twice as valuable as the back walls rank. This leads to concepts with higher temperatures at the
rotor and lower temperatures at the back wall get higher points. Table 22 shows that the large plates give higher
points than the concepts with smaller plates. The average temperature increase between the lowest and the
highest values is about 1 degree at the rotor and the temperature decrease of the back wall between the original
design and the concept with the lowest temperature (Large single plate (modified)) is 20.5 degrees.
Table 22: Concept weight matrix, full matrix is found in appendix A
Concept
Original Design
Single Plate
Double plates
Large single plate
Large single plate with fin
Large single plate with bottom
Large single plate (Modified)
Average
Avg
Avg
Avg
Avg
Avg
Avg
Avg
Back wall C
67.35
56.99
60.37
48.66
51.02
50.31
46.85
Rotor C
Points
5
5
8
16
12
17
21
In Table 23 the specification is used to see what is left to investigate to fulfill the requirements. The
specification needs to be fulfilled in order to take the concept to the detail design. There are however two
specification points that needs to be evaluated and processed.
1. Increase lifetime of application
2. Compact and modular designed
48
Table 23: Point matrix of concept and specification
Specification
Decrease local temperature
spots on the rotor
Decrease waste
energy
Increase lifetime
of application
Compact and modular
designed
Better or equal
temperature distribution
Design for manufacture
Decrease temperatures
on back wall
Points
Original Design
Single Plate
Double plates
Large single
plate
Large single plate
with fin
Large single plate
with bottom
Large single plate
(Modified)
Weight
0
1
2
3
4
5
6
1
0
1
2
3
4
5
6
1
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
2
0
1
1
1
1
1
1
2
0
1
1
1
1
1
1
2
0
2
1
5
3
4
6
2
0
10
10
20
18
22
28
Increasing the lifetime of the application is a desire and not a demand and the crucial parameter is the
temperature of the rotor. The temperature at the rotor cannot exceed 160 C for a longer time since this will
negatively affect the material of the rotor. None of these concepts exceeds that temperature in the simulations.
In section 4.4 it is seen that there will be hot spots on the rotor as long as the fan is not dragging the
air homogeneously over the rotor. Therefore the temperature distribution over the rotor will not look like the
simulations as long as the air is focused where the fan is located. The temperature of the rotor material cannot
exceed 160 C due to material fatigue of the rotor. It is therefore important to have a homogeneous distribution
over the rotor. In order to fulfill requirement 2, (Compact and modular design) the chosen concept will be
evaluated again in the current model of M X 2 30 at the detail level design in section 7 to reuse the existing
design.
From Table 22 the specification is evaluated and the matrix gives a result of going further to detailed level
design with concept Large single plate (modified).
49
7 Detailed level design
Before the plate can be produced, all dimensions and design requirements need to be met. It is also important
that the plate fulfill the requirements from Munters production specification and quality requirements. The
production of the plate needs to be verified so that Munters production machines can produce the plate.
The material used for the plate is aluminum zink, which is a corrosive resistant material but not corrosive
proof. The material do vary depending on customers demands, if the plate needs to be corrosive proof the
material will be stainless steel.
In the dehumidifier there are holes for other configurations depending on what kind of heater that is in
use.The plate is modified to meet the requirements for the electric heater configuration. This means that the
rivet holes for a gas heater is available for use. This is used as an advantage since there are no requirements
for configurations on the roof of which the plate should be installed onto. On the back wall there is no such
configuration holes as in the roof therefore it requires holes for the rivets. A drawing of the plate can be found
in appendix B.
In Figure 41 the holes are displayed at the roof. The plate is also designed to fit into the beam that goes
vertically down in the middle of the plate. The holes and tolerances are based on Munters productions specification.
Figure 41: Location of configuration holes
50
8 Discussion and conclusions
In section 4.8.1 the energy to heat the air is calculated and with no radiation the temperature rise to 99.5 C
which is a little bit lower than the expected temperature of 100 C. This number is only an estimate since the
density and the specific heat varies with temperature. It is also measured in tests that the heater requires more
energy than expected. The radiation is a small portion of the total energy 3.5 % but it plays a significant role
when deciding what heater to use for the application. Since the
T should be 100 C according to Munters
the power of the heater must exceed the 30kW that it is today. The size of the heater is also important since
it will affect the area of radiation. If the suggested plate doesn’t cover most of the radiation the temperatures
at the back wall will increase which is unwanted and only negative for the application. The plate decrease the
temperature at the hot spot and keeps the energy waste from the heater inside the application which increases
the temperature at the rotor. This is solely a positive affect since the temperature on the rotor is the driving
parameter of desorption process.
The distribution over the rotor depends entirely on the fans location and cone as seen in section 4.4. This is
crucial to have in mind when constructing an application using a suction fan instead of blowing on the regenerative side. Suction fan will reduce the total leakage and a blowing fan will increase the leakage (S.J Slayzak,
2000). The worst case scenario is if the process outlet have a leakage from the regeneration outlet. This should
be avoided since the outlet of the regeneration is very wet and the outlet of the process side is dry and it is put
a lot of energy to make the air dry. Using a blowing fan on the regeneration side can make the distribution over
the rotor more homogeneous and this should be further investigated if a more even distribution over the rotor is
wanted. The blowing fan will cause the air to force itself into the small passages, this is why the regeneration
side should have a suction fan (S.J Slayzak, 2000).
The selection of adsorbent for the rotor is also important, since there are different properties of different
materials. Today a solution of silica gel is used, which is a good adsorbent non corrosive with good adsorption
capability. Hygroscopic salts can improve the moisture uptake by the adsorbent but unfortunately many of
them are corrosive which will affect the production and the application it self. An important factor is also not
the adsorption but desorption. The desorption is equally important as adsorption capability since the material
must be able to give away the moisture to be efficient. It is desirable to have a desiccant material that can be
regenerated at lower temperatures to make alternative energy resources available such as solar power. Also
further work on decreasing waste power should be done to increase the energy efficiency of the dehumidifier.
There is research going on to elaborate and investigate the usage of microwaves which shows a promising result
regarding increasing the regeneration of the desiccant wheel. However, changing regenerating heat source such
as microwaves could result in a benefit of changing the silica gel to another material which maybe have a better
desorption ability with that kind of heating technology. The simulations being developed from data acquired
from elaborations done by Munters are not an exact match of the real world and should therefore not be used
as a answer of how it is but rather be used as a hint of how it appear to be. Since there are parameters being
51
neglected such as the rotation of the rotor and placement of the suction fan, data from the simulations should
be critically looked at and evaluations of parameters are crucial to ensure that the right decision is made.
52
References
Yu.I. Aristov, Restuccia, G. Cacciola, and V.N. Parmon. A family of new working materials for solid sorption
air conditioning systems. Applied Thermal Engineering, 2001.
Yuriy I. Aristov. Challenging offers of material science for adsorption heat transformation: A review. Applied
Thermal Engineering, March 2011.
Fritz Bark. Nationalencyklopedin hydromekanik, 02 2015. URL http://www.ne.se/uppslagsverk/
encyklopedi/l%C3%A5ng/hydromekanik.
Angelo Freni, Alessio Sapienza, Ivan S. Glaznev, Yuriy I. Aristov, and Giovanni Restuccia. Experimental
testing of a lab-scale adsorption chiller using a novel selective water sorbent “silica modified by calcium
nitrate”. International Journal of Refrigeration, May 2010.
Desiccant dehumidifier. Munters Europe AB, 2013.
Bhyrav Mutnuri. Thermal conductivity characterization of composite materials. Master’s thesis, West Virginia
University, 2006.
R Narayanan. Comparative study of different desiccant wheel designs. Applied Thermal Engineering, March
2011.
K.C. Ng, H.T. Chua. C.Y. Chung, C.H. Loke, T. Kashiwagi, A. Akisawa, and B.B. Saha. Experimental investigation of the silica gel±water adsorption isotherm characteristics. Applied Thermal Engineering, June
2001.
Carlos Eduardo Leme Nóbrega. Desiccant-Assisted Cooling Fundamentals and Applications. Springer, 2014.
Jan Petersson. Interview with jan pettersson. Interview, 2014.
Dipendu Saha and Shuguang Deng. Hydrogen adsorption on metal-organic framework mof-177. Tsinghua
Science and Technology, 15, August 2010.
Jung-Yang San. Analysis of the performance of a multi-bed adsorption heat pump using a solid-side resistance
model. Applied Thermal Engineering, March 2006.
J.P Ryan S.J Slayzak. Desiccant Dehumidification Wheel Test Guide. National Renewable Energy Laboratory,
1617 Cole Boulevard, December 2000.
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Ulrich and Eppinger. Product Design and Development. Number ISBN: 978-007-125947-7. McGraw-Hill,
Book, Singapore, 2008.
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L.W. Wang, S.J. Metcalf, R.E. Critoph, R. Thorpe, and Z. Tamainot-Telto. Development of thermal conductive
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54
Appendices
A
Concept selection matrix
Concept
Original Concept
Single Plate
Double plates
Large single plate
Large single plate with fin
Large single plate with bottom
Large single plate (Modified)
B
Average
Avg
Avg
Avg
Avg
Avg
Avg
Avg
Backwall
67.35
56.99
60.37
48.66
51.02
50.31
46.85
Rotor
Drawing
On the following page a drawing of the final concept is found.
55
Rank Backwall
1
3
2
6
4
5
7
Rank Rotor
2
1
3
5
4
6
7
Points
5
5
8
16
12
17
21
C Gantt chart
Figure 43: Planning of master thesis
57