|
|
re: question - calculation of convection forces
26 mar 2002
daniel matthews wrote:
>>> i have 10mj/s of energy radiating into [a] via one wall...
>> if the 100 f air is cooled to 77 f near the top of the chimney, eg by
>> an air conditioner in the attic, each cfm of airflow with a temp diff dt
>> (f) moves about dt btu/h, so heatflow cfmxdt = 16.6(10.8)sqrt(10.4)dt^1.5
>> = 34,120k btu/h and dt = 1518 f (wow), so cfm = 16.6(10.8)sqrt(10.4x1518)
>> = 22,529 cfm or 10,632 l/s. that's probably way outside the temperature
>> range of applicability of the formula...
>wow that is a lot of hot air. :o)
yes.
>this technology is low tech but very clever and applicable in the third
>world on different scales...
you might add a windmill to make electrical power. paul gipe's wind power
book says wind power density is 0.05472v^3 w/m^2, where v is in mph, and
the best rotors achieve 40% efficiency (vs the 60% betz limit, which may
not apply for a chimney)... 90% efficiencies for the transmission, generator,
and power conversion make the wind power density 0.01596v^3 w/m^2...
what's the heat-to-electrical power conversion efficiency of a chimney
like this? (hint: grainger's 100 watt ceiling fans move about 25k cfm.)
nick
|
|
