[TriLUG] OT: the difference between web bulb and dew point temperatures

[Steve Holton via TriLUG]

You might be interested in:

https://www.quora.com/What-is-wet-bulb-temperature-and-why-is-it-measured

https://www.quora.com/What-is-the-practical-meaning-of-wet-bulb-temperature-for-a-human-animal-body

Yes, there are people in this world who know far too much about certain
topics.


On Thu, Dec 21, 2017 at 1:50 PM, Joseph Mack NA3T via TriLUG <
trilug at trilug.org> wrote:

> I have just recently found that wb != dp. (I had assumed they were the
> same.) The definitions are inscrutable and presumably only for those who
> already understand the difference.
>
> The HVAC people know all about this, but when you go to their forums,
> whenever anyone asks for an explanation, they are directed to the
> definitions. Well if the definitions had explained the difference, the
> person wouldn't have needed to ask.
>
> I've plumbed the depths of the people I know and haven't found an answer.
> I know I'm not supposed to ask about non FOSS topics here, but I don't know
> where else to go.
>
> I have a reasonable understanding of how you measure both
>
> o wb - you put a wet sock over a thermometer and blow air over it. The
> temperature of the water drops till (I think) the water vapour pressure of
> the cooled water is the same as the water vapour pressure in the air. So
> the air is moving.
>
> o dew point. you chill the thermometer till water condenses out of the air
> onto the thermometer. I assume the air has to be still for this to work.
>
> I can look up the psychrometric charts to see that the two temperatures
> are different and that dewpoint < wb, but I can't think of a thermodynamic
> way of moving from one to another, like you do when moving around a Carnot
> cycle diagram, which shows the difference between the two situations and
> that shows that dewpoint < wb.
>
> Does anyone know?
>
> (we now return to our regular program of FOSS)
>
> Thanks
> Joe
>
> --
> Joseph Mack NA3T EME(B,D), FM05lw North Carolina
> jmack (at) austintek (dot) com - azimuthal equidistant
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-- 
Steve Holton
sph0lt0n at gmail.com