Tutorial

Instructions for Constructing a

Heat Pipe

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Introduction

A heat pipe is a device used to efficiently transfer heat across a distance with minimal loss in order to effectively cool an area. Heat pipes are applied in HVAC systems, computers, or any other systems that generate excess heat that must be cooled. They are typically constructed of a basic pipe capped on both ends, some sort of access point, a working fluid within, and a “wick” structure that assists in the motion of the fluid.

Heat pipes are designed with two of its ends in mind, the vaporizer and the condenser. In Figure 1, the basic operation cycle of a normal heat pipe is shown. Something hot is placed on the vaporizing end of the pipe, which transfers heat to the working fluid within. This fluid then evaporates and travels to the condensing end, where it releases its heat into the environment, condenses back into a liquid, and travels down the wick to start the cycle again.

In this set of instructions, we will be constructing the heat pipe pictured in Figure 2, which is designed to function at temperatures of approximately 900°F.

Figure 1

Figure 2

Materials

Copper Pipe 1" x 2' Threaded Copper Adapter Fitting 1" x 3/4" Teflon Tape Polyethylene Tubing 1" inner diameter Copper Slip Cap 1" inner diameter Female Threaded Brass Ball Valve 3/4" Copper Mesh 5' x 20'

Steps

Installing the internal wick structure
1.Unroll the copper mesh until 2.5 to 3 feet is laid flat on the work area, as in Figure 3.
2.Carefully cut along its width until it is detached from the roll.
3. Next, roll one of the thin ends into a circular shape and insert it into the pipe.
4. Carefully slide it further in until it extends the length of the pipe, and cut off the excess. The inside of the pipe should look like Figure 4.

Figure 3

Figure 4

    Sealing the Pipe

1.     Affix the slip cap and threaded adapter fitting to either side of the pipe. Note that the threads
of the adapter fitting should be pointing away from the pipe.

2.   With a soldering iron, seal the pipe along the circumferences of both the cap and the fitting.

i)       Safety Note: It is advisable to wear heat resistant gloves while soldering to avoid burns.

Figure 5

Creating a Resealable Access Point
1.     A tight seal is necessary for the heat pipe to function, but there must also be a way to access the inside of it in order to fill or drain it of fluid. Ready the brass ball valve, which will be used to accomplish this.
2.     Wrap the threads of the adapter fitting in Teflon tape.
      i)      Pull it taught and wrap 2-3 times as in Figure 6. 
3.     Screw the ball valve on over the tape as tightly as it will go. At this point, the pipe should appear as it does in Figure 7.

Figure 6

Figure 7

Insulating the Pipe
1. If the fluid loses its heat as it travels up the pipe, it may not all condense at the right area and the device will cool the source of heat less efficiently.
2. Cut a 1-foot length of polyethylene tubing and slide it onto the pipe.
     i)      The tubing is weak and can be cut with a box cutter or similar tool.
3. Peel away the plastic lining from the edges in Figure 8 and press them together to create a seal.

Figure 8

Finishing Touches and Use
1. Using a graduated cylinder, measure out 50mL of water
2. Open the ball valve by twisting the lever, pour in the water, and close the ball valve.
3. Suspend the heat pipe over any heat source and observe its heat transfer.

Conclusion

          If you have constructed the heat pipe properly, it should be immediately ready for use without any additional preparations. If you wish to verify that the heat pipe works, construct any vertical testing apparatus such as the one displayed in Figure 9, with a heat source on the bottom and open air on the top, and activate your heat source. If the heat pipe has been improperly sealed, such as by a mistake in Teflon tape wrapping or an open ball valve, you should notice steam or drops of water exiting the pipe at the top. However, if the seal is effective, it should only take a few minutes to measure a substantial difference in temperature with a thermocouple at the top end of the pipe. This indicates that the pipe is transferring heat as intended, and should be effective at up to 900°F.

Figure 9: In this example of a testing apparatus, the heat pipe is clamped to a stand to keep it vertical as the red heat gun blows 850°F air on the base of the pipe.