[time-nuts] HP5370 power supply measurements

[Tommy Phone]

Some thirty years ago fans for automotive radiator cooling were designed with 7 unevenly spaced blades to reduce the siren effect yet yield comparable air flow. Careful layout and blade sweep back along with an annular ring made it entirely feasible to have a statically and dynamically balanced fan as it came out of the mold. I always wondered why the folks who make these little fans can't figure out how to do that. Maybe getting comparable CFM from a much smaller fan violates some Reynolds number requirement for turbulence control. 

From Tom Holmes, N8ZM

> On Jul 15, 2016, at 3:52 PM, William H. Fite <omniryx at gmail.com> wrote:
> 
> That is, in fact, precisely how you do it.
> 
> 
>> On Friday, July 15, 2016, Orin Eman <orin.eman at gmail.com> wrote:
>> 
>> On Fri, Jul 15, 2016 at 10:55 AM, Poul-Henning Kamp <phk at phk.freebsd.dk
>> <javascript:;>>
>> wrote:
>> 
>>> --------
>>> In message <
>>> CANy2iXq6ONvriDoFgNFkEBQjDKntP7t8KuE7BOUpxJWLCuxLsw at mail.gmail.com
>> <javascript:;>>
>>> , "William H. Fite" writes:
>>>> David Kirkby scripsit:
>>>>> 
>>>>> I often here of people replacing fans with quiter ones, but I suspect
>>> that
>>>>> all they really do is reduce the airflow.
>>>> 
>>>> Not necessarily, Dave. The Austrian company, Noctua, for one, makes
>>>> extremely quiet fans with excellent airflow.
>>> 
>>> ... at zero pressure differential, which is easy to do (Think: ceiling
>>> fan).
>>> 
>>> 
>> 
>> Right.
>> 
>> You have to look at the curves on the data sheet that shows air flow vs.
>> static pressure (and be careful about the static pressure scale).  I found
>> that a 'quiet' fan would often be flowing one tenth as much air as the
>> original fan at the static pressure at which the original fan was rated.
>> 
>> In a given instrument, you may get away with the quieter fan, but how would
>> you tell other than putting a thermometer inside and making a before/after
>> comparison?
>> 
>> Orin.
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> 
> 
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