Last  updated 16/03/2005 21:15:39

Home brew heat-pipe (11/08/2004) and  Zalman Heatpipe HDD cooler (12/08/2004)

The pipe is made from a 280mm length of  10mm diameter copper tube, typically used in micro-bore central heating systems etc.

Heat pipes require a wick to encourage the working fluid to flow back towards the heated end of the pipe. To form a simple wick; I used a ‘star’ washer, slightly larger than the bore of the tube, attached to a rod to score the inside of the tube. After pulling the washer through a few times the inside of the tube has a large number of longitudinal grooves for the water to condense in and flow along.

One end of the tube was then crimped, using a lathe chuck, and sealed with solder. The other is sealed with a short length of copper rod soldered in place, then drilled and tapped to take an M3 screw.

I used about 2 cl of  a 2:1 mixture of water and isopropyl alcohol. (The alcohol helps the water wet the copper and flow better.)  as the working fluid.

To evacuate the heat-pipe I used a small general purpose diaphragm vacuum pump  previously used in a photographic machine.  In order to tighten the sealing screw while connected to the vacuum pump I used a simple ‘T’ piece adapter; a short length of rubber goes over the end of the heat-pipe to one side of the ‘T’ piece,  in the other side of the ‘T’ piece, an ‘O’ ring seals around the shaft of a screw driver while the vacuum pump is attached to the centre of the ‘T’ piece.

Initially the pressure is reduced to about 3psi then the pipe sealed. The crimped end of the pipe is then placed in hot water (~60°C) to check that the pipe is operating. While the end of the pipe is stall hot it is reattached to the vacuum pump and the pressure reduced again (the cool end suddenly becomes very hot).

Testing

To test the operating power of the pipe I attached a high power resister as a heater and a thermocouple to one end and, with an aluminium clamp, a large 1K/W heat-sink to the other end.

To measure the dissipation of the test setup with out any heat-pipe effect, the test setup is placed with pipe vertical and the heater at the top  (the water will run to the bottom of the tube so we will only be measuring the heat lost to the air or by conduction down the copper tube). The power required to raise the temperature of the heated end to the operating temperature is then measured. The test setup is then rotated so that the heat-pipe is just off horizontal (about 5 degrees) with the heated end below the cooled end.

Temp (°C)
over ambient