[Elecraft] Thermal control for Q1 / Q2 in KPA100?
Mike Harris
mike.harris at horizon.co.fk
Wed Dec 6 10:17:54 EST 2006
G'day,
| The fact that an exhaust fan flow cools objects better than blowing air
onto
| a surface is a bit counter-intuitive because standing in the downstream
side
| of a fan feels cooler to the skin - but that is only because of
evaporation.
| Careful measurement will show that the cooling effectiveness for an
object
| like a heat sink is more effective by moving the heated air away from
the
| object. Getting the heat away is the objective, and blowing on it is
less
| effective than exhausting the heated air.
Never seen a suction cooled external anode HPA, from single 4CX250's to
10kW Klystrons. I've used a small PC fan blowing onto the right hand side
of the heatsink, front to rear, inclined about 45 degrees. During 10-12
hour QRSS beacon runs at 40W o/p the little fan never came on and the
heatsink was room temperature.
A bladed fan is easy to stall if there is any restriction to throughput.
Regards,
Mike VP8NO
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