Week 2

Update on Group Roles

We just wanted to give a quick update that we've assigned temporary roles to each group member: Hung will be in charge of the machinery once we all finish the Tier 2 equipment training; Patrick will be in charge of holding the supplies; Jordan will be in charge of changing the blog aesthetic; Wilson will be in charge of facilitating, making sure the group is organized and prepared every week. On another note, we will be rotating who is responsible for writing a blog post each week.

Research and Decisions

For the second week, we continued our research into heat pipes. We've learned that there are a number of things to consider when constructing a heat pipe:

• Heat load/transportation
• Operating temperature
• Pipe material
• Working fluid
• Wick material
• Dimensions of the pipe
• Contact length at evaporating/compensating zone
• Pipe orientation
• Effects of bending/flattening of heat pipes

These specifications must be carefully picked to create an optimally functioning heat pipe; improper modifications can lead to undesirable results, not limited to a waste of resources and time. The table, as follows, shows typical operating characteristics of various heat pipe builds:

Table 1: A table of heat pipes detailing the materials used, their effective temperature, and heat.

Under the assumption that testing will be done using a standard blowtorch as a heat source, the use of most working fluid/pipe material combinations are out of question. Not to mention, we limited our budget to approximately $50. Thus, our decision to choose a copper heat pipe with distilled water (no impurities), as it was one of the cheaper alternatives, was agreed upon as a team.

Steel vs Copper Pipes

Although the use of steel pipes over copper pipes has its advantages, copper pipes usually present better thermal performance overall. In essence, it boils down to the kind of environment in which the heat pipe will be used.

Pipe Dimensions

The diameter and length of the heat pipe affects the rate at which vapor travels. A larger diameter allows for more vapor transportation from the evaporator to the condenser. Generally, large diameter heat pipes are ideal for environments with higher operating temperatures. Based on pipe availability, we decided on a 1/2 inch diameter cross sectional area and will decide on a definitive length upon completion of the mechanical testing and analysis phase.

Wick Material and Pipe Orientation

There are various types of wick structures that can be used for constructing heat pipes, each with their own unique advantages and disadvantages. However, as important as the wick structures are, how the pipe is oriented is equally important. As a team, we've decided on a standard vertical orientation where the condensing end is at the bottom and the evaporating end is at the top. Under these conditions, using a copper wire mesh wick is ideal for reasons that it is most uniform and works best under gravity challenging orientations.