A different way to Water Cool a Heatsink.

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A different way to Water Cool a Heatsink.

Postby WA2WVL » Fri Apr 04, 2008 10:11 pm

I have been thinking about a solid state KW Linear Amplifier suitable for portable use (such as a DXpedition) and I ran a test as follows:

I mounted 4 high power film resistors on a 7x7 heatsink (with 1 inch fins) and set it in a pan (15x22 inches). Water was added till the water level was up near the top edge of the sink (about 1 inch of water).

A power of 250 watts was applied. The question was how long would it take to boil the water? The answer was forever.

The following data was taken:

6pm (start) 75.7 F water temperature
6:15 89.8 F
6:30 100.4 F
6:45 108.3 F
7:00 115.0 F
7:15 120.0 F
7:30 123.1 F
7:45 125.4 F
8:00 127.4 F
10:00 131.0 F Final temperature (55 C)

A point was reached where the heat lost to the air equaled the power input.

Why 250 watts?
a 1KW class ab linear amp runs at about 50% efficiency so at 1 KW out the heat load is 1 KW. Under voice (SSB) it is less than 500 watts. If you are running contacts, half the time you are listening so 250 watts.
I would not expect anyone to use this technique for a class E amplifier but it is interesting.

Floyd WA2WVL
WA2WVL
Class E Enthusiast
 
Posts: 167
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Location: Homosassa, Fl.

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