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Rocket Car driven by the Vaporization of liquid Nitrogen
Rebecca L. Altman
Florida State University
Objective
Friction and Nitrogen Evaporation
The goal of my summer project was to design and create a demonstration for the cryogenics laboratory that
would be able to show the public the fundamentals of low temperature experimentation. I began this project
by performing the past demonstrations and seeing how I could implement those ideas into my assignment.
The three past demonstrations that I performed were: Balloons with gases, making superfluid Helium, and
a Cork Rocket. The first experiment showed how different gases with different boiling points would react
when placed in a liquid Nitrogen bath. The second experiment consisted of using liquid Nitrogen, a vacuum,
and Helium gas to make Helium II (which is also called superfluid Helium). The third experiment consisted
of a rocket with a cork at the end that was filled with liquid nitrogen and then tipped. As the pressure built up
inside, there was enough force to cause the cork to shoot off into the air. Out of all the experiments, this
one seemed like it had the most potential to be exciting, interesting, and educational.
After doing a lot of research, I saw several demonstration videos by Julius Sumner Miller that sparked my
interest. One of these included an experiment where he put dry ice (solid CO2), in a steel tube attached to
a board with wheels. He then told the audience that given time, the dry ice would sublimate and cause the
cork to pop off sending the car into motion. This idea sparked my interest in the possibility of a rocket car
using liquid nitrogen instead of dry ice for the demonstration.
After some test runs, I believe that some of
the information given by the friction test
could have been incorrect. To ameliorate
the car, a tube of water was added to
increase the amount of heat transferred to
the liquid nitrogen. When the warm water
mixes with the liquid nitrogen, it creates a
rapid rate of vaporization of the liquid. This
accelerated discharge of the nitrogen gas
through the nozzle creates enough Impulse
to cause the car to move forward.
Research & Calculations
Before beginning my project I did some research on cryogenics and thermal fluids so that I would have
a general understanding of each. This research included learning about thermal conductivity and expansion,
different types of heat transfer such as Fourier’s Law of Heat Conduction and Newton’s law of cooling, fluid
flow, nozzle behaviors, and how the properties of different materials can effect the above.
The time allowed for the experiment will be ten seconds. The rate of heat transfer given the allotted
time is equal to 5.688 kW. This information is used in Newton’s law of cooling equation to calculate the heat
transfer coefficient. The mass flow rate is then calculated, making is possible to use the pressure restriction
of one atm to compute the velocity of fluid coming out of the orifice. (Eq. 1)
CD = the drag coefficient which is given a constant value of 0.65
Using the basic definition of Impulse, (I = the change in momentum) the impulse is equal to 46.972 N*s.
The force is calculated by using the relationship between force, time, and impulse (F = 4.697 N). (Eq. 2)
(Above) The Rocket Car is ready
to begin so liquid nitrogen is
poured into it via the top.
(Left) The
Rocket Car is
launched by the
liquid nitrogen
inducing an
Impulse that
causes the car to
accelerate.
Nozzle Design
After much debate, I chose to have the nozzle be straight so that the actual construction of the nozzle would
be easier, while still being able to make the demonstration occur. In theory, the converging nozzle would be
the best fit due to the subsonic fluid which would be in motion. The enthalpy of the system would be converted
into kinetic energy, which would cause the velocity to increase. A throat diameter would be a diameter smaller
than the original diameter, which in turn would increase the pressure causing maximum velocity to be reached.
In order to meet pressure restrictions, a converging/diverging nozzle would be needed to gradually reduce the
pressure back to one atmosphere.
Acknowledgements
Dr. Sylvie Fuzier and Dr. Steven W. Van Sciver (mentors)
Scott Maier (Assistance in the Cryogenics Laboratory)
The Cryogenics Department Staff
NHMFL REU Program, (CIRL) Center for Integrated Learning
Applying the weight of the load on the car body, the friction
due to the G-10 surface is calculated from the graphs produced
by the Explorer GLX. Friction is calculated to be very small (0.423 N).
Now it is known that the force created by the impulse will be enough
to over come the forces of friction.
To find the diameter of the nozzle use (Eq. 3), resulting in
= 0.216 inches using (Eq. 4). (After going to the lab and seeing
what was realistic, d = 0.208 in).
(Below) A cylindrical tube filled
with water is placed inside the
aluminum tube and then sealed.
It was determined that this experiment would run best on a
smooth surface so that less force would be needed to move
the car. Since the cryogenics lab has spare G-10 pieces, I
decided that this material would be used as the surface it
would be run on. After running an experiment on the friction
of the G-10 verses the wheels of the car, it was concluded
that friction would be very low due to the smoothness of the
surface material. The friction was determined by using the
Force sensor on the Explorer GLX to give a graph of
velocity. Then using the principles of dynamics, a free-bodydiagram was made to gather the equations necessary to
solve for friction. (It has also been determined that surfaces
with low friction may also be used such as smooth plastic.)
I used Mathcad to conduct the calculations, the Explorer GLX to calculate the friction between the wheels
of the car and the G-10 surface, and the resources in the cryogenics lab to complete the task. I was
successfully able to design a “Rocket Car” that would run on the evaporation of liquid nitrogen. Room
temperature water is mixed with liquid nitrogen at 77 K, creating an expedited evaporation of liquid
nitrogen. The nitrogen gas combined with the water, creates the necessary impulse force to move the car.
Using software provided by Dr. Van Sciver, the amount of heat in the aluminum and liquid nitrogen was
calculated. It was determined that 53.84 kJ of heat would need to be transferred to the nitrogen in order to
evaporate it all (Q = 53.84 kJ). After this was determined, the following steps were taken in order to
calculate the Impulse that would be produced, in addition to the diameter of the nozzle within the pressure
requirement.
Experiment Demonstration
Director: Pat Dixon
Assistant Director: Jose Sanchez
National Science Foundation for funding the REU Program
Dr. Carl A. Moore
Florida State University, Mechanical Engineering Department
d
(Provided the Friction Testing Equipment)
References
Heat Transfer Diagram
Rocket Car Schematic
Barron, Randall F. (1985). Cryogenic Systems (2nd ed.).
New York, NY: Oxford University Press, Inc.
Cengel, Yunus A., & Turner, Robert H. (2005). Fundamentals of
Thermal-Fluid Sciences (2nd ed.).
New York, NY: McGraw-Hill Companies, Inc.
Janna, William S. (1998). Design of Fluid Thermal Systems (2nd ed.).
Boston, MA: PWS Publishing Company
Scott, Russell B. (1988). Cryogenic Engineering.
Boulder, CO: National Bureau of Standards Cryogenic Engineering Laboratory
Scurlock, Ralph G. (Eds.). (1992). History and Origins of Cryogenics
New York, NY: Oxford University Press
Miller, Julius Sumner. Gases and Liquids Part Two
http://www.youtube.com/watch?v=vdujCy6nTSQ Western Video Industries
Wikipedia, The Free Encyclopedia. 17 July 2007, Wikimedia Foundation, Inc.
http://en.wikipedia.org