"Rushforth Solar" <ar@...> wrote:
> I would think your quickest
cheapest pool heater would be covering the pool
use with black
plastic.
Clear plastic works better, since it's hard to warm water from
above.
For one thing, warm water rises.
For another,
http://www.rsifibre.com/technical-papers/thermal-diffusivity.php
says
Tr
= (1/a)(2s/Pi)^2ln[8(Ts-Ta)/(Pi^2(Ta-Tb)],
(dividing by (Ta-Tb) on the
right), where
Tr = time to obtain average temp Tb
a = thermal
diffusivity
s = slab thickness
Ts = constant surface slab temp
Ta =
initial slab temp
Tb = average slab temp at time Tr
In their example,
warming a 2" air slab would take 25.3
seconds.
http://en.wikipedia.org/wiki/Thermal_diffusivity says water has
a 0.143x10^-6
m^2/s thermal diffusivity,
So warming a 2" water slab
would take 3920 seconds (65 minutes.)
And warming a 60" water slab would
take 980 hours.
Nick
