[Top] [All Lists]

[AMPS] Blowers for finned tubes

To: <>
Subject: [AMPS] Blowers for finned tubes
From: (Dave Kirkby)
Date: Wed, 11 Mar 1998 15:43:47 +0000
> Rich Measures wrote:
> >However, measuring cfm requires elaborate test equipment.

Ian White, G3SEK wrote:

> Actually it's very easy using the method described by K6GT. Simply
> time
> how long it takes for the outlet air to inflate a large, light plastic
> bag. (To measure the inflated volume of the bag, suspend it in a part-
> filled barrel of water, and pour in measured amounts of water into the
> bag until it's just full. The water in the barrel outside of the bag
> supports the weight.)

One way I have measured cfm  is to heat a big (few 100 W) resistor in
the input side of the amp,
then measure the air temperature just before the resistor, and at the
of the anode cooler, with a pair of thermocouples. Flow rate can be

Flow (cfm) = 1.76*power dissipated(W) /increase in temp (deg C)

You can overun the resistor quite a bit, as the cooling air will stop
I ran a 300 W resistor at about 600W or so - cant recall the exact
I recon you need to dissipate at least 10% of the anode dissipation to
get a
sensible temperature rise that can be measured accurately.

Just be careful the resistor is well secured, and can not fly loose.

You should idealy thermally insulate (paper would do) the
grid/cathode compartment, so the heat only escapes up through
the anode cooler, and not out of the amp box.

Instumentation is a bit  more expensive than the method Ian mentions,
I think its easier for big tubes, where the time to fill a bag would be
so short
as to make accurate timing difficult. I used themocouples, since I have
an old
10 input K-type thermocouple thermometer, but a couple of inexpensive
measured on the resistance range of a DVM, should do the job just as

As Ian has said to me in the past, air flow meausrements dont really
need the
highest of accuracy, so perhaps the bag method is better all round.
there are t least two methods of measuring flow that can be done easily
at home.

Any other methods  ??????


FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>