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re: heat exchanger problem
22 jul 1997
paul milligan pondered briefly, and wrote:
>nick@ufo.ee.vill.edu (nick pine) pondered briefly, and wrote:
>>would someone know how to estimate the latent and sensible heat loss from a
>>150 f 50 cfm airstream saturated with water moving through a horizontal
>>4" diameter x 10' long thinwall pvc pipe submerged in 130 f still water?
> nick, do you accept help from freon pumpers ? :-)
sure... this seems like a typical freon problem, with a different liquid.
i'm interested in how to get useful heat out of compost, using an aerated
closed vessel with recirculating water. compost has about the same heating
value as wood, per pound of dry weight, and about 80% of the heat output
during composting is latent, in the form of warm moist air flowing out of
compost maintained at 50% moisture.
> measure the output ( any two factors, like db & wb ), and run
>the numbers through pmtherm.
i haven't built one of these, and i'd like to be able to predict
performance in advance, and know the effect of varying flow rates,
areas, temperatures, etc...
> or, run your 'nicknumbers' to acheive an estimate of the heat
>transfer, assume output at saturation, and go from there into pmtherm.
"output at saturation" is a helpful clue. can you expand on that? nicknumbers
are based on page 3.4 of the 1993 ashrae hof, which seems to only talk about
sensible heat loss, ie temperature changes, vs phase changes. is there a way
to interpret those calculations in a system with condensation?
> one example - glibly assuming perfect cooling of the air to
>130 f ( not likely ) :
this is interesting. it shows the maximum possible performance, and it
looks pretty good, ie 2.24 tons x 12k btu/hr/ton = 27k btu/hr total,
with 50 cfm of airflow? wow...
>50 cfm in @ 150 f, 100% rh,
>50 cfm out @ 130 f, 100% rh
>
>process cool & dehumid
>tons ( total ) 2.24
>tons (sensible) .29
>tons (latent) 1.95
>lbs h20 / hr 22.72
to me, this represents the output condition that might occur with a
very large heat exchange area, eg 1000' of 4" pvc pipe. i wonder how
that would change with 100' of pipe, or 10' or 1'...
nick
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