Final report

Project Overview

Project Overview

Fundamentally, a heat pipe is a device that transmits thermal energy from one point to another. It accomplishes this both through the thermal conductivity of the pipe and through the phase transition of fluid within the pipe. Heat pipes can be used in any application that requires the transfer of heat, though they are used extensively for cooling applications such as CPU heat management, spacecraft radiators, and certain internal combustion engines. 

Source: Benchmark Reviews

An example of a complex heat pipe with radiator fins for computer heat management.

This project will focus on the ability of heat pipes to remove excess heat from a device and radiate it into the atmosphere. In this case, a heat pipe will be designed to remove heat from a small gasoline engine and safely transmit it to a heat sink which will radiate the heat into the atmosphere. This process is especially applicable to the Wankel rotary engine which has notorious problems due to uneven heating of the ignition chamber. Since many small gasoline engines serve stationary purposes with no air flow to help in cooling, heat pipes are a practical method of removing heat from the engine reliably without requiring any extra work.

Source: Cars in Trend

A diagram that displays the workings of a Wankel engine. Note that the combustion always takes place on the right side of the combustion chamber which causes uneven heating.

A heat pipe is a sealed pipe made from a thermally conductive material. Inside, it contains a working fluid which evaporates at the heat source (evaporator) and condenses at the radiator (condenser). In this project, a wick will be used to absorb condensed water on the condenser side and transmit it back to the evaporator side of the pipe through capillary motion. Some heat pipes use gravity or even centrifugal force to accomplish this, however a wick enables the heat pipe to lay horizontally which best suits the application in this project.

Source: Overclock

A diagram that shows the basic cyclical mechanisms of a heat pipe. 

The goal of this project is to create a working heat pipe that can effectively reduce the temperature from a heat source and effectively transmit it into the atmosphere.

Sources
Wu, W., Lin, Y., and Chow, L., "A Heat Pipe Assisted Air-Cooled Rotary Wankel Engine for Improved Durability, Power and Efficiency," SAE Technical Paper 2014-01-2160, 2014, doi:10.4271/2014-01-2160.

Week Nine Update

Week Nine Update

Pipe Sealing

This week, the heat pipe was sealed securely. Sealing the pipe has been one of the largest issues in this project. During every test prior to this, a leak developed that allowed liquid water and vapors to escape the pipe, thus reducing efficiency. This week, we tripled the amount of teflon tape on the threads of the cap and sealed the cap as tightly as possible. We then added additional teflon tape to the joint between the cap and the pipe. This proved to sufficiently seal the pipe and no leaks occurred. The increase in efficiency is apparent in figure 2 below. The pipe was set up like the other previous tests. The evaporator end was at the bottom receiving the heat. The condenser end was at the top away from the heat source. There were three sensors. One at the evaporator end, middle and condenser end (figure 1)

 

Figure 1: Set up of 4th test

Test Four Results

Figure 2: Result of the 4th test

This test shows increased efficiency when compared to the last test. Once a high enough temperature is reached at the evaporator end, that end of the pipe actually begins to cool as water transfers heat to the condenser end and the radiator fins. This represents the cooling of the small engine.

Budget

Table: Required Materials

Category	Cost
1” x 2’ Copper Pipe	$11.63
Aluminum Sheet	$12.45
Copper Cap	$2.62
Copper Adapter	$7.79
Brass Threaded Cap	$10.64
Distilled Water	$0.00
Epoxy Resin	$3.24
Thermal Patse	$4.12
Sponges	$2.16
TOTAL	$54.65

In the weeks following our initial materials acquisition, the only several other expenses were made one was to get sponges to use as a wick for the heat pipe, but those were already calculated for the final report.  The next expense is to get thermal paste and epoxy for the heat pipe was $7.36 raising the total cost of this project to $54.65. There should be no other expenses until the completion of the project. 

References

References

[1]  C. E. Heuer, “The Application of Heat Pipes on the Trans-Alaska Pipeline,” U.S. Army Corps of Engineers, Hanover, NH, Special Report 79-26, 1979.

[2]  W. Wu, Y. Lin and L. Chow, "A Heat Pipe Assisted Air-Cooled Rotary Wankel Engine for Improved Durability, Power and Efficiency", SAE Technical Paper 2014-01-2160, 2014.

[3]  Single Cylinder OHV Air-Cooled Engines, Briggs & Stratton Corp, Milwaukee, WI, 2009.

[4]  G. M. Grover, “Evaporation-condensation heat transfer device,” U.S. Patent 3 229 759, Jan. 18, 1966.

[5]  SMT Component & Assembly, TutorialsWeb, Available: http://www.tutorialsweb.com/smt/smt.htm

Timeline

Table 1: Timeline: The yellow highlights mark the progress of the group until recently. 

Task	1	2	3	4	5	6	7	8	9	10
Research	x	x				x	x
CAD Designing		x	x
Material Acquisition			x
Heat Pipe Assembly			x	x
Theoretical Calculations				x	x
Testing					x		x	x	x
Data Analysis / Experimental Calculations					x	x	x	x	x
Heat Sink Assembly						x	x
Final Report Preparation							x	x	x	x

Timeline Update:

Week 7 was just completed and the pipe assembly and testing is going on as planned for the most part, the process has been slowed because there is also a critical defect in the heat pipe.  Heat sink assembly has also been pushed to week 8, and will be completed before the lab session. Testing will continue, but the pipe is not working with the efficiency originally calculated. The reason for slow progress of optimal results is due to a small leak at the threaded end of the pipe. There is a small gap that leaks water and pressure and in such a delicate system even the smallest gaps can negatively impact results. So this week will be focused on solving the problem with the leak, and assembling the heat sinks.

Week Eight Update

Radiator Fin Attachment

To attach the fins, first the surfaces of the pipe and each fin had to be prepared. Both the pipe and the fin surface were cleaned with scotch brite and methanol to remove any oil or impurities. The surface of the copper pipe was also roughened to give the epoxy more surface area to adhere to. The bases of the fins were first coated with thermal paste, then, they were held into place and secured by rubber bands. Once this was complete, epoxy was applied to the two edges of each fin. Once the epoxy for one fin had set, the next fin was begun. It was discovered that a slight bend in the middle of the bonding surface of each fin created a better fit to the rounded surface of the pipe. The rubber bands were removed after 24 hours once the epoxy had fully cured.

Figure 1: Top isometric view of the fins

Figure 2: Isometric view of the fins

Figure 3: Side view of the fins

The goal for week 8 was to get the pipe completely sealed. During the lab, the group brought the pipe over to the machine shop and got it tightened. There was, however, a little miscommunication in the group and so the pipe was only tightened but the PTFE tape was not replaced. The pipe was then tested without having the PTFE replaced and the following is the result from the test.

Test number 3

The pipe was tested again and the figure below plot out the data recorded. The difference here is that there are fins attached to the condenser end. The figures ( 4 and 5) below show the set up and the plotted result.

Figure 4: Set up to test the heat pipe

Figure 5: Result of test 3

The result, however, does not seem to be much different than the result from week 7. The condenser also barely increased in temperature. Not surprisingly, the pipe was also leaking at the time of testing (figure 6 bellow). The team did not do a good job of securing the pipe and so the reason as to why the pipe does not work is still a mystery and the group cannot move on until the pipe has been secure tightly. The leak, however, did seem to be less than that of week 7. If the group could add more layers of PTFE and tighten the cap more then maybe the cap will be secure and result might change.

Figure 6: Leakage of the pipe.