Group 073-10: Efficient Heat Pipes for Small Scale Industrial/Commercial Applications

Investigating the possibilities of running a project extension to test higher efficiency vacuum heat pipe designs improving the effectiveness of transferring heat over longer distances and complex geometries.

This week in lab the heatsink was turned on the lathe from 2" 6061-T5 aluminum round stock. The finished part deviated slightly from the plans as it was determined that it would be ineffective to build the entire part after a cutting tool failure led to one of the fins breaking. The finished part is composed of only 4 fins compared to the designed 16. A CAD model was drawn up with a drawing sheet to use while machining. Figure 1: Heatsink Drawing w/ Dimensions Other than the tool failure, the machining process when fairly smooth with the completion of a finished part.  Figure 2: Cutting off a blank in the Horizontal Band Saw  Figure 3: Facing the part Figure 4: Fin cutting with a 1/16" parting tool Some tests of the finalized heat pipe were also run this week, it was tested with water and again with acetone. During the test, at about 450 s, the heater at the evaporator end was turned up to a higher setting, because a possible reason for the inefficiency o...

This week in lab the team finished the construction of the final heat pipe design and was able to find a vacuum pump to test how a heat pipe would perform under vacuum. Unfortunately, the results were not promising as the new heat pipe did not nearly work as it was expected to. For the final heat pipe, one end is closed, while the other end is equipped with a valve, as shown below, that can be used to add working fluid and connect to the vacuum pump to create vacuum. After the air is pumped out, the heat pipe is tested with acetone and with water as working fluids. The result is not as well as expected. More experiments will be conducted on this heat pipe next week. The results of the experimentation done are shown below:

This week in lab, the team worked on some more testing and the construction of our final iteration of the heat pipe. A specially designed bushing had to be machined to accept the threads of the 1/8" NPT ball valve. This bushing was then soldered into the copper tube. Another angled test of Prototype 2 was conducted to compare the results from the previous tests. The data is shown below: The graph of this data is shown below: The fluctuation of T1(the temperature at the evaporating end) may be partially due to experimental error. Otherwise, this prototype performed as expected.

This week the team worked on finishing the CAD model for the heat pipe and ran simulations for the heat pipe and condenser. The model represents the heat transfer expected through the heat pipe and condenser. Some finished drawings are also provided with dimensions. Figure 1: Heat Pipe and Heat Sink Assembled Figure 2: Heat Sink Component Figure 3: Thermal Analysis of the Main Body of the Heat Pipe

The team conducted some more tests on Prototype 2 as it was the best performing heat pipe constructed thus far. The test was conducted in the angled orientation as Prototype 2 hadn't been tested in that configuration yet. The results were promising as Prototype 2 exceeded expectations and transferred heat effectively throughout the test. The condenser end increased by 52 degrees over 300 seconds which was an improvement over the horizontal test conducted with Prototype 2. In both tests, the difference between the condenser temperature and the evaporator temperature was calculated and displayed on the graphs. The graph below shows the first test for Prototype 2. To verify our results the test was run a second time but for a longer period of time in order to narrow down on where the heat pipe's maximum operating temperature would be. The results are shown below. For Prototype 2, the effective temperature limit of the heat pipe can be approximated to 125 F without a hea...

It was realized during the testing in Week 4 that a significant design change was required in order to boost the function of the heat pipe. The team assumed that a smaller diameter pipe would improve working fluid circulation at higher temperature values but it was soon discovered that this was not necessarily true. Our results showed a decreased performance with smaller pipe diameters and longer heat pipe lengths. To combat this issue, a redevelopment of the heat pipe design is necessary. One of the vital pieces of a heat pipe is that the interior is in a partial vacuum or the pipe is completely evacuated of air allowing for maximum working fluid circulation. This important component in the design of a heat pipe gives it its function to rapidly disperse heat from one end to the other. As demonstrated in this video . Future heat pipe designs are going to utilize a method to evacuate air from the pipe to provide a near vacuum. The vacuum is essential to higher efficiency heat pipes in a...

This week, prototype 3 and 4 were constructed and tested. As shown in the image below, the shorter one, prototype 4, has a length of 1 foot and the longer one, prototype 3, has a length of 2 feet. The effect of the length of the heat pipe on its efficiency is tested this week. Below is the tables and graphs of the testing done in lab this week. From the test results, it can be concluded that prototype 4 performed better than prototype 3. In 240 seconds, prototype 4 had a temperature increase of 12 degrees, while prototype 3 increased only 2 degrees. A possible reason is that the because the prototype 3 is longer in length, and so heat transfer takes longer. It is also possible due to heat loss along the length of the heat pipe.

Some new design considerations were taken into account in order to test a proposed idea with smaller diameter heat pipes. After doing some basic research it was determined that capillary action has a greater effect the smaller your system gets. Larger diameter heat pipes will still experience capillary action but other factors such as gravity will have different effects on how the working fluid flows in the wick. The diagram in Figure 1 illustrates the proposed problem with larger diameter heat pipes compared to their smaller counterparts. Figure 1: Large and Small Heat Pipe Capillary Force Comparison By reducing the pipe diameter to half of Prototypes 1 and 2, capillary action should be able to happen more efficiently due to surface tension and lower liquid weight (less volume in a smaller pipe). Gravitational effects overcoming surface tension demonstrated in Figure 1 is why we believe that a smaller heat pipe would theoretically run more efficiently. Furthermore, as tempera...

During week 3, the team built and tested the first two prototypes of the heat pipe. The construction of the heat pipes was straightforward as these two prototypes had very little complexity to them. A process of rapid prototyping was utilized to come up with two working devices that would be able to obtain useful data for quick design iterations. Below are two construction photos of the first heat pipe. The first image shows the interior mesh used as a wick and the bottom picture is the crimped pipe end before soldering. A detailed construction log can be viewed on the Heat Pipe Fabrication page. Testing The testing involved using a clamp to hold the pipe in place while hot air was applied to one of the ends of the pipe. Two thermocouple probes were used to measure the change in temperature of the ends of the heat pipe over time. A picture of the apparatus used is shown below: The results for the first prototype show that it was relatively inefficient, due to the fact...

In week 2, the team discussed the timeline and final deliverables of this project. Project Timeline The project timeline is shown below in Table 1. Table 1: Project Timeline The main tasks of the project include research, initial design, ordering of material, generation of a CAD model, construction, testing, design optimization and the final report preparation stage. Research will be done throughout the first few weeks to aid the design, simulation and construction processes. Components are ordered this week, and it will take on average a few days to a week to arrive. We have started to build the CAD model using Autodesk Fusion 360 and Solidworks software. For the construction and testing phase, two prototypes and one final model will be built in the course of six weeks. The first prototype will be constructed in week 3, and tested in week 4. Then, the second prototype will be made in week 5 and tested in week 6. The final model of the heat pipe will be made i...

The primary focus of week 1 was to research the existing designs of a heat pipe, understand the mechanisms at which they operate, and come up with ideas to build an efficient low temperature heat pipe. The main purpose of the heat pipe is to transfer heat from one place to another. Research was conducted on low-temperature applications and the advantage and disadvantage of different designs. After analyzing the information and taking into account the time and budget restriction for this project, an initial design of the heat pipe was generated.  The heat pipe will be made of copper tubing with mesh inside the tubes to serve as a wick. There will also be Aluminum heatsink fins at the condenser end to increase surface area for the spreading of heat to the surrounding. The main tasks include research, initial design, ordering of material, generation of CAD model, construction, testing, and optimization. The design and construction of the heat pipe are limited to a budget of $400 ...