Two good points, but I think you could probably solve both of them by
simply using two flow meters with judicious use of cardboard so that
half the air goes through each one.
John G3UUT
On 13/04/2011 19:04, Ian White GM3SEK wrote:
> John G3UUT wrote:
>> Well that's a relief! I was planning on spending the weekend messing
>> around with bin liners and water butts. It looks like these things are
>> available real cheap on Ebay.
>>
> I'm not sure if a peak flow meter will work, because of the
> back-pressure through the device itself. The bag method may look crude,
> but it has the advantage of a very low back pressure.
>
> To save you from getting cold and wet, a British swing bin bag is about
> 50 litres. (This is probably a Euro standard size, and also a good shape
> for attaching to the outlet vent.)
>
> With care, cardboard and packing tape, you can make volume flow
> measurements within about 10%, which is plenty good enough.
>
>
> 73 from Ian GM3SEK
> http://www.ifwtech.co.uk/g3sek
>
>
>> On 13/04/2011 12 :25, Angel Vilaseca wrote:
>>> An accurate way to measure airflow is to use a peak airflow meter. See
>>> picture here:
>>>
>>> http://en.wikipedia.org/wiki/File:Peak_flow_meter_vert.jpg
>>>
>>> This is a low-cost device used by persons with asthma to self-monitor
>>> their disease. Widely available worldwide.
>>>
>>> 73 de
>>>
>>> Angel Vilaseca HB9SLV
>>>
>>> Ian White GM3SEK a écrit :
>>>> Roger (sub1) wrote:
>>>>
>>>>
>>>>> One other point, I've seen the question raised about how much pressure
>>>>> was a fan generating. For a given tube and existing system you can
>>>>> treat air flow and pressure the same as voltage and current. IF you are
>>>>> getting the required air flow you MUST have the required air pressure.
>>>>> Insufficient pressure and you will have insufficient flow. Get the
>>>>> proper flow and you will have the proper pressure.
>>>>>
>>>>> IF the radiator is plugged or partially clogged you will have high
>>>>> pressure and low flow. But again, it the flow if proper then so is the
>>>>> pressure.
>>>>>
>>>>>
>>>> Air flow rate is what really matters in cooling, and all data sheets for
>>>> air-cooled tubes will state the minimum volume flow rate required.
>>>> Pressure drop is only an indirect way of measuring the volume flow
>>>> rate... and actually a very poor way.
>>>>
>>>> Pressure drop measurements in real amplifiers are very prone to errors,
>>>> because the reading will depend critically on the orientation of the
>>>> manometer pickup tubes relative to the air flow. We have no idea what
>>>> the tube manufacturers did to minimize those errors... or even if they
>>>> were aware of them. Because of all these problems, pressure drop is
>>>> probably the wrong thing for us amateurs to measure.
>>>>
>>>> It's actually MUCH easier to measure the volume flow rate directly. No
>>>> elaborate equipment is needed - simply time how long it takes for the
>>>> outlet air to fully inflate a large, lightweight plastic bag. With a
>>>> little care you can measure the volume flow rate within about 10%, which
>>>> is far more accurate than a pressure measurement.
>>>>
>>>> The original idea came from George Daughters K6GT, and details are right
>>>> here in the AMPS archives:
>>>> <http://lists.contesting.com/archives//html/Amps/1998-03/msg00172.html>
>>>>
>
>
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