Week 5: April 28, 2016

Greetings Heat Pipe Aficionados!
This week marks a rather impressive jump in progress for the HamPipe. Last weekend, Karen, Noelle, and Mr. Kownurko worked to create a working prototype, named Harold, for the eventual deliverable heat pipe. (Ben would have been there as well, but he had to be at home for Passover). The entire construction process took somewhere between 4 and 5 hours, and there will be a page elsewhere on the blog dedicated to chronicling the step by step directions. The production went extremely well. There were several parts involved between fittings, two different copper tubes, and the braided stainless steel wick material. Though the group was awake for most of Saturday night, we were eventually able to create a working heat pipe.

Karen drilling holes into the inner copper tube. 

Noelle soldering under the careful supervision of Mr. Kownurko.

On Sunday, the group ran several different tests. The first set of tests involved using water as a heat transfer fluid. Later tests involved methanol and acetone as the heat transfer fluids, as we were able to drain the heat pipe through the series of valves on the top. Finally, we tested a higher volume of water in the heat pipe (jumping from 20 mL to 25 mL). There were some setbacks with the testing rig, one of which involved the vice (used to hold the heat pipe at a fixed angle next to the heat source) working as a heat sink. To combat this, we added two pieces of oak wood, one one either side of the heat pipe, which isolated it from the metal of the vice. The rig wasn't perfect, and though we made sure to create a vacuum within the heat pipe during testing, there is always a risk of contamination of the heat transfer fluid inside the tube. For each test, we took temperature at two different points on the heat pipe (close to the heat gun, and further away from it), as well as pressure readings every thirty seconds, and documented until we reached 30 psi. Though we were fairly certain that our solder joints could hold up to 60 psi, we weren't particularly willing to risk the joints failing and spewing 200 degree (F) liquid across the work space and the group itself.

A round of testing: Karen read pressure out to Noelle every 30 seconds, as Noelle recorded both the pressure and the 2 different temperatures on a chart.

Throughout the tests, the group decided that for right now 25 mL of water was the best fit for our heat pipe for several reasons. The first reason is that the water was the least volatile, and maintained a steady pressure that did not pose too much risk to the solder joints. Also, acetone and methanol heated up more quickly initially, but because of the pressure building up so quickly, they were not able to reach as high of a heat as the water. In case you had forgotten, the goal of this particular heat pipe is to be used in cooking (specifically ham), so water also provides a more safe heat transfer fluid. Though there is very low risk of the fluid actually leaking out, during food preparation it is often better safe than sorry. Finally, in tests, the 25 mL of water managed to circulate so well that the temperature at the top of the heat pipe (further from the heat source) was actually higher than the temperature closer to the heat gun, which was pretty amazing to see. The group exited the weekend with an incredible amount of data to input into excel, graph, and analyze, as well as a working heat pipe. This week in lab was therefore mostly dedicated to formatting graphs and charts, and discussing future plans. One option on the table is purchasing a 25-75 mix of ammonia and water, which is likely to be less volatile than the acetone and methanol, but more efficient than water alone. Other discussions centered around whether to build another heat pipe with regular screen instead of braided steel as the wick, or whether to make a final heat pipe the same way, but cap it instead of having the series of valves on the top, or simply cap the existing prototype. The week ahead will contain a good amount of time spent formatting graphs, and creating the portion of the blog which lays out the heat pipe creation process. Ben has also begun working on the draft for the final report, which is due during week 7.

A piece of plain copper tubing, being tested as the baseline on the rig using a vice and a heat gun.