Session F2C-4 HOW TO REDUCE THE COST OF TEACHING PHYSICAL EXPERIMENTATION Jerry K. Keska Department of Mechanical Engineering University of Louisiana-Lafayette Lafayette, LA 70506 [email protected] Abstract Although theoretical and computational tools are inevitable in the teaching of engineering processes, it is generally accepted that experimental approaches, even though they are significantly more costly and time consuming, are far superior. In professional activities, experiments are invaluable necessities when it comes to proving a hypothesis and turning it into a theory or proof-of-concept for new products or technology under development. However, a very important question is how to reduce cost of this hands-on approach to teaching physical experimentation classes. The paper reports the details of the development and implementation of a solution to the problem of how to reduce some of the barriers, especially costs in laboratory classes with hands-on physical experimentation. The solution was used in a two-semester undergraduate class in Instrumentation and Measurements. Application of miniature hardware, construction of electronic measurement systems on prototyping boards, a combination of instructed experiments and open-ended projects resulted in a significant cost reduction. Introduction In the undergraduate teaching process, only solving simple textbook problems that require little, if any, imaginative thinking, diminishes the overall efficiency of the students’ learning. These problems are usually significantly simplified when compared to real-life situations, and more often than not, they have very limited connections to real world problems. In order to increase student interest and the student’s own creative, hands-on, problem solving skills, a physical experimentation class has been developed, which promotes students’ creativity by utilizing openended projects that formulate and investigate realistic, inventive, and complex problems. This approach not only boosts student enthusiasm, it also aligns classroom topics more closely with contemporary standard industrial environments and practices. The most common hurdle in this process is the development of a laboratory and shop base, which is necessary for the constant process of troubleshooting. The difficulty is that this development creates a large financial expense as well as a tremendous increase in the teacher’s responsibilities and time involvement when compared to the demands of a standard lecture or virtual laboratory class. Oftentimes, obstacles like these force engineering educators to make compromises and replace laboratory physical experiments with virtual experiments, which are sometimes performed as blackboard exercises in a lecture classroom. One way to reduce some of the financial burden is by implementing physical experiments on miniature mechanical Proceedings of the 2011 ASEE Gulf-Southwest Annual Conference University of Houston Copyright © 2011, American Society for Engineering Education systems with prototyping sensors and measurement systems as a part of the laboratory class. All of these approaches are extremely attractive in today’s “lean” approach to engineering education. The course development presented here was designed for an undergraduate junior level class that took place over two semesters for four credits and was done in conjunction with a one-hour classroom lecture in mechanical engineering. A slightly modified version of this approach, however, could easily be tailored to all levels of the mechanical engineering technology, or other engineering based curricula. This paper reports the details of an implemented solution to the problem of how to reduce some of the barriers—especially costs—in laboratory classes that include hands-on physical experimentation. The solution was implemented in a two-semester undergraduate class in Instrumentation and Measurements. Application of miniature hardware, construction of electronic measurement systems on prototyping boards, and a combination of instructed experiments and open-ended projects resulted in a significant cost reduction as well as an improvement in teaching quality. Physical Experimentation Although theoretical and computational tools (including virtual tools) are useful in the teaching of engineering processes, it is generally accepted that experimental approaches are far superior, even though they are oftentimes more costly and time consuming. In many cases, experiments are invaluable necessities when attempting to prove a hypothesis and turn it into a theory. Experiments are also necessary when trying to implement a proof-of-concept process or during live tests for a new product or technology. Consequently, it is important for students to conduct physical experiments so that they have hands-on experience with the types of tools used in instrumentation and measurements. By doing these activities, students can gain knowledge about issues such as what sensors and measurements to use, how to develop a feasibility study program, how to conduct computer-based data acquisition and analysis processes, how to analyze and validate experimental data for both deterministic and random processes, how to design experiments, and how to disseminate results. Based on the trend presented in Table 1, the key issue now in physical experimentation is to expose the students to hands-on approaches to acquiring dynamic signals. Dynamic signals are a combination of random and deterministic phenomena that students analyze using computer-aided systems. Students learn to disseminate results, understand and apply the right tools, and implement their knowledge to solve a problem in a cost effective way [1, 2, 4]. In particular, the student needs to understand: a) Why physical experimentation, testing and measurements are crucial in all engineering disciplines. b) How physical experimentation, testing and measurements are related to engineering analysis, design, and product development. c) How to use basic mechanical, electrical, thermal, and fluid measurements for static and dynamic processes of deterministic and random phenomena. by using a hands-on approach. d) How to gather and analyze experimental data of deterministic and random dynamic processes using different levels of mathematical and computational tools. Proceedings of the 2011 ASEE Gulf-Southwest Annual Conference University of Houston Copyright © 2011, American Society for Engineering Education e) How to build and use experimentation tools conducting over ten fully-instructed laboratory experiments, where the lab instruction allows the student to build computer-aided sensors and measurement systems from scratch on a prototyping board or using professional systems. The sequence of experiments gradually develops the student’s knowledge and experience in physical experimentation, testing and measurements. f) How to validate experimental results and, based on defined criteria, allows student to judge the quality of the gathered data and the gathering process. g) How the measurement process error is an inescapable part of the experimentation activities. Students also learn to explain what is acceptable and how to control the limits of acceptability. h) How to incorporate the computer as a universal tool in all processes: design of physical experiments, measurement and data gathering, data analysis, and process of result dissemination (report writing and presentation). i) How to design and build a working prototype of a completed physical system starting with the proposal and progressing through the entire process including the feasibility study and the final presentation of the open-ended project. j) How to generate the basic laboratory and project communication forms. k) How to use the basic capabilities and applications of Computer-Aided Tools including MatLab. To assist students in the effective study of the subject and to provide guided applications, the two volume laboratory manuals were published and made available to students [4]. Due to the importance and necessity of conducting physical experiments, engineering students should become familiar with physical experimentations as early as possible. This early exposure will build up clear connections between theory and experiment, resulting in an understanding of the applied aspects of engineering. In today’s “lean” approach to engineering education and instruction, administrations probably need to increase the willingness to recognize the importance of physical experimentation and the costs, the necessary technical base, and the increasing instructor teaching load required. Also, in physical experimentation, the closed loop between a cause and result is real not imaginary, and a difference must always be tested and corrected, which in many cases requires a significant amount of additional work and effort in comparisons to a standard lecture approach. Experimentation Systems Because the key issue in the physical experimentation is to give students hands-on experience in working with acquired dynamic signals, analyzing and disseminating the results, understanding and applying the correct tools and implementing the knowledge to solve a problem in a cost effective way, the first step is to find how to effectively generate such signals. The second step is to choose the correct approach and to keep the cost as low as possible. The solution is to build a physical generator of signals that are a combination of random and deterministic components (see Figs. 1 - 3). To accomplish this solution, the phenomena of two-phase flow are implemented [3 to 8], where the measured parameter is the spatial concentrations of the twophase flow of air-water mixture in a vertical column using both capacitive and resistive computer-aided measurement systems. This type of physical generator is easily constructed in a Proceedings of the 2011 ASEE Gulf-Southwest Annual Conference University of Houston Copyright © 2011, American Society for Engineering Education laboratory using a vertical column of water with an air source attached to the base. Concentration is changed by regulating the amount of air flowing into the column. In this experiment, a resistive and capacitive sensor is used to collect data and as a concomitant system for data validation. The data collected are analyzed using root mean square (RMS), probability Table 1. Trend in Experimentation Period Signals 1970s - 80s deterministic static 1980s - 90s deterministic dynamic 1990s – 2000s deterministic dynamic Tools calculators computers Instrumentation self contained Sensors Presentation readout and electronic output overhead Documentation mostly manual Reports typewriter and dictaphone self contained and rack readout and electronic output overhead computer manualelectronic word processing computer-aided systems self contained and rack electronic output for DAS 2000s and up composition of deterministic and random dynamic components computer-aided systems mostly rack computer-aided electronic output with DAS computer-aided electronic electronic only word processing word processing only distribution function (PDF), and power density spectrum (PSD) (see Fig. 3). One of the most important parameters in controlling two-phase flow is the void fraction or its complementary parameter, spatial concentration. Started in the 1940’s and continuing up until today, two-phase flow has remained a challenging phenomenon to predict and control because of its random nature. One aspect of the random nature of the signal is the noise component. The noise can be filtered by different types of low-pass filters such a physical filter built with a 741 op-amp, and also by a digital low-pass filter. The acquisition, comparison and calibration of dynamic signals will show the importance of the experimental approach. This process results in information that needs to be validated, analyzed and encourages students to be precise in their studies and experimentation. The experiments can be conducted by four different kinds of two-phase flow systems. A comparison of system parameters for all four two-phase flow experimental systems (Full Research System, Reduced Educational System, Bench Educational System and OEP need to define OEP System) are show in Table 2. Because all four systems are computer-aided systems (CAS), their computer cost was not included in the Table 2. Implementing the low cost criteria, two systems were chosen for completion: Bench Educational System for instructed experiments and the OEP System. This solution does not compromise quality of physical laboratory experiments but significantly reduces cost by miniaturizing full-size systems to benchtop experimental systems and by building electronic systems from “scratch” on prototyping boards. Proceedings of the 2011 ASEE Gulf-Southwest Annual Conference University of Houston Copyright © 2011, American Society for Engineering Education This approach offers the ability to conduct full physical experiments including experimental feedback, understanding of measurement process and data validation, and reduction of necessary shop hardware support. Proceedings of the 2011 ASEE Gulf-Southwest Annual Conference University of Houston Copyright © 2011, American Society for Engineering Education Figure 1: View of Experimental Systems. Top - Reduced Educational System. Middle - Bench Educational System. Bottom – OEP System. Figure 2: First OEP Hardware Project as a Miniature Version of the Bench Vertical Column Proceedings of the 2011 ASEE Gulf-Southwest Annual Conference University of Houston Copyright © 2011, American Society for Engineering Education c v vs. Time Voltage vs. Time 3.6 1 c v [-] V [V] 3.4 3.2 0.5 3 2.8 0 0.5 1 t [s] 1.5 0 2 0 CPSD vs. Frequency 0.5 1 1.5 t [s] CPDF vs. c v 2 Frequency [%] CPSD [-] 1 0.4 0.2 0 0 50 f [Hz] 100 0.5 0 0 0.5 c v [-] 1 Figure 3: Example of Generated Signals Generated . Table 2: Comparison of Experimental Systems System Type Full Research System Reduced Educational System Bench Educational System OEP System Column diameter [mm] 50 3.5 - 10 50 3.5 - 10 Instrumentation Off shelf Off shelf Board built by students Board built by students Sensors System hardware Off shelf Shop build Off shelf Shop build Student build Shop build Student build Shop build Column orientation Vertical only From horizontal to vertical gradually Vertical only System cost $ 28,000 23,000 2,000 From horizontal to vertical gradually 100 OEP Experimentation System After seven instructed experiments, students write a proposal for an OEP, and they also develop and build an apparatus that consists of a 6.35 mm square cross section of clear plastic tube flow channel that serves as both a mechanical and measurement device[4]. The flow channel is Proceedings of the 2011 ASEE Gulf-Southwest Annual Conference University of Houston Copyright © 2011, American Society for Engineering Education mounted on the support wall, which allows it to be rotated about a point from zero to ninety degree. The air-water mixture is then circulated where water is in a closed loop and the air is supplied using a compressor (Bubble Box). After the air passes the flow channel it is released into the atmosphere. The air flow rate is controlled by controlling the voltage powering the compressor. A combination of resistive, capacitive and optical sensors is mounted in the flow channel (Fig 2, 4 and 5). Figure 4: OEP Experimentation System (a) (b) (c) Figure 5: Details of OEP Experimentation System, (a) Flow Channel Inclined at 60° (b) CrossCorrelation Sensors (c) Slug Flow in Flow Channel Proceedings of the 2011 ASEE Gulf-Southwest Annual Conference University of Houston Copyright © 2011, American Society for Engineering Education The second component of the OEP experimentation system is the electronic measurement and signal processing systems with the block diagram shown on Fig. 6. Signal Processing Capacitive Signal AC Bridge Low Pass Filter Flow Channel DC Bridge Resistive Signal DC Bridge Data Acquisition System Optical Signal Computer Aided Experimentation System Cross Correlation System Air Supply Figure 6: Block Diagram of the Experimentation Measurement System Data were collected from three different sensors at the same time, i.e. resistive, capacitive and optical. Calibration values were recorded for air and water only in order to convert voltage signal to concentration signals (cv), as shown in Fig. 6. After that, the cv signals vs. time were used to obtain cumulative power spectrum density (CPSD) and cumulative probability density function (CPDF) plots. An example is shown in Fig. 7. c v vs. Time Voltage vs. Time 3.6 1 c v [-] V [V] 3.4 3.2 0.5 3 2.8 0 0.5 1 t [s] 1.5 0 2 0 CPSD vs. Frequency 0.5 1 1.5 t [s] CPDF vs. c v 2 Frequency [%] CPSD [-] 1 0.4 0.2 0 0 50 f [Hz] 100 0.5 0 0 0.5 c v [-] 1 Figure 7: An Example of Signals Obtained and Analyzed from the OEP Experimentation System Proceedings of the 2011 ASEE Gulf-Southwest Annual Conference University of Houston Copyright © 2011, American Society for Engineering Education The entire OEP experimentation setup is developed and built on a prototyping board by students using simple electronic and mechanical components, as listed in Table 3. The cost of $ 151 represents the most expensive project of the 12 built by students in Fall semester 2010; all 12 projects are shown in Fig. 8. The individual costs ranged from $51 to $ 151. Table 3: List of All Components Used to Build Discussed OEP System. Item ½ x 2 x 4 Birch Plywood Stanley Double Wide Corner Brace Painter’s Cup BubbleBox Air Pump 6’ Aquatic Air Tube Modular IC BreadBoard Socket Universal Soderless Breadboard 100-Piece ¼ Watt Fixed Carbon-Film Resistors 100K-Ohm Linear-Taper Potentiometer Cds Photoresistors (5Pack) Set of 100 Disk Capacitors LM741CN Operational Amplifier (8-Pin Dip) Lambro Industries 4” Galvanized Worm Gear Clamp Real Organized 24” White Double Track Standard Stainless Steel Wood Screws ½” Aluminum Post (2 per) GE 2.8 oz Waterproof Silicone Check Valve Quarter Turn Ball Valve Loctite .85 oz. epoxy Quantity 1 4 1 1 2 2 1 1 1 1 1 1 1 1 1 2 1 1 1 1 Total Price [$] 12.87 15.08 0.98 15.34 7.18 17.98 19.99 6.99 2.99 2.99 5.49 0.99 1.37 6.74 1.67 1.78 3.94 1.99 7.61 5.18 150.98 Figure 8: View of QEP Experimentation Systems Built by Students in Fall Semester 2010 Proceedings of the 2011 ASEE Gulf-Southwest Annual Conference University of Houston Copyright © 2011, American Society for Engineering Education Experimental Results The voltage signals collected from the resistive and capacitive sensors in the calibration process were converted to concentration values and then were analyzed in both frequency and amplitude domains (Fig. 7). Both amplitude domain and frequency domain plots showed differences impacted by different flow conditions (e.g., Figs. 8 to 10). 0.5 CPSD [-] 0.4 0.3 0.2 90 60 30 0 0.1 0 0 10 20 30 40 50 f [Hz] 60 70 80 90 100 Figure 8: CPSD Plots for va of 80 cm/s and Indicated Channel Inclination. 1 0.9 0.8 Probability [-] 0.7 0.6 0.5 0.4 0.3 42.35 cm/s 79.95 cm/s 125.32 cm/s 162.84 cm/s 0.2 0.1 0 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 c v [-] Figure 9: CPDF Characteristics for Flow in Channel Inclined of 90° and Indicated Air Velocities. Proceedings of the 2011 ASEE Gulf-Southwest Annual Conference University of Houston Copyright © 2011, American Society for Engineering Education 1 0.9 0.8 Probability [-] 0.7 0.6 0.5 0.4 0.3 42.46 cm/s 80.14 cm/s 125.17 cm/s 162.88 cm/s 0.2 0.1 0 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 c v [-] Figure 10: CPDF Characteristics for Flow in Horizontal Channel and Indicated Air Velocities. Conclusions Based on experience in the development and teaching of physical experimentation classes, the following conclusions can be derived: 1. Both developed and built experimental bench type systems are characterized by easy operation and calibration processes and for a very low cost it can be build from “scratch” by undergraduate students. 2. These systems generate effectively dynamic signals combining deterministic and random phenomena, validation of data, and are applicable for interfacing into computer-aided physical experimentation systems. 3. The combination of instructed experiments and OEP approaches, using bench type systems, gives students a good opportunity for hands-on learning and applying physical experimentation concepts and tools, how to deal with dynamic data, and how to validate those experimental data. 4. Building and using this OEP system built from “scratch,” students conduct measurements, collect and analyze data and gain hands on experience in the following: calibration process; design and trouble shooting of mechanical and measurement systems; sensor and transducer constructions; experimental data gathering and analysis of deterministic and random signals; measurement of concentration, temperature, displacement, RPMs, pressure, flow rates and velocities, resistance, capacitance, angle, voltage and current; data analysis and validation using concomitant systems; working in teams; report writing and presentation. Proceedings of the 2011 ASEE Gulf-Southwest Annual Conference University of Houston Copyright © 2011, American Society for Engineering Education 5. This approach to miniaturization and student involvement in hands-on experience allows a significant reduction in hardware and shop expenses in the application of physical experimentation in the undergraduate teaching process. 6. The combination of instructed experiments and OEP approaches, using bench type systems, gives students a good opportunity for hands-on learning and applying physical experimentation concepts and tools, how to deal with dynamic data, and how to validate those experimental data. References 1. Patrick F. Dunn, Measurement and Data Analysis for Engineering and Science, 2005, McGrawHill. 2. J.P. Holman, Experimental Methods for Engineers, McGraw-Hill, 2001. 3. Keska, J.K. and Wang G., “Mathematical Model for Pressure Gradient Calculation for Air-Water Heterogeneous Mixture Flow in a Small Square Horizontal Channel Based on the In-Situ Parameters and Flow Pattern Coefficient”, International Journal of Experimental Thermal and Fluid Science, ETF 6736, 2005. 4. Keska, J. K., “Physical Experimentation, Instrumentation and Measurements. Laboratory Manual” Vol. I and II, Lulu Press, 2010. 5. Keska, J. K. and A Chuck Miller, “Experimental Results for Application of Two-Phase Flow in Micro-Heat Exchangers,” Proceedings of FEDSM99 3rd ASME/JSME Joint Fluid Engineering Conference & 1999 ASME Fluids Engineering Division Summer Meeting, pp 1-8. 6. Keska, J. K. and B. E. Williams, "Experimental Comparison of Flow Pattern Detection Techniques for Air-Water Mixture Flow," International Journal of Experimental Heat Transfer, Thermodynamics, and Fluid Mechanics, Vol. 19, pp. 1-12, 1999. 7. Keska, J. K., M.D. Smith, and B. E. Williams, "Comparison Study of a Cluster of Four Dynamic Flow Pattern Detection Techniques," Flow Measurement and Instrumentation, Vol. 10, pp. 6577, 1999. 8. Keska, J. K. and R. D. Fernando, "Average Physical Parameters in an Air-Water Two-Phase Flow in a Small Square-Sectioned Channel," Journal of Fluids Engineering, Vol. 116, pp. 247254, 1994. Proceedings of the 2011 ASEE Gulf-Southwest Annual Conference University of Houston Copyright © 2011, American Society for Engineering Education
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