Water tank heat loss
Water tank heat loss
(OP)
I have a water tank that is 24" X 96" (711 Liters at 10 Deg. C) wrapped in 2" of foilback insulation and heated by 2, 180w pad heaters. I am wondering at what Temp in Deg.C would this tank freeze?
Any info would be helpfull.
Steviewye.
Any info would be helpfull.
Steviewye.





RE: Water tank heat loss
It seems there is information missing in what you've asked, such as some temperature gradiant on the outside which causes you to need the insulation and the heaters.
Also, is this homework?
Patricia Lougheed
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RE: Water tank heat loss
Thanks.
RE: Water tank heat loss
TTFN
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RE: Water tank heat loss
Thx.
RE: Water tank heat loss
RE: Water tank heat loss
To answer your real quest you must know at least the inout that IRstuff comes up with.
However: Consider your situation: You are asking for free consultancy - all very good. But if somebody helps you - but gives an incroorect answer then what?
Best regards
Morten
RE: Water tank heat loss
I would be happy to be pointed in the right direction. I am more than willing to do my own legwork.
Thx.
RE: Water tank heat loss
Patricia Lougheed
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RE: Water tank heat loss
Assume convective heat transfer coefficient on inside and outside = infinity (conservative)
Assume Insulation value of .3 Btu/hr in/ft2 (probably better, so this is conservative)
I calculate a total area of 53.4 ft2
Assume 1 heater fails (180 W only)
Assume temp must be 20 F above freezing (52 F)
Result: -25 F outside temp will allow water to remain at 52 F with just 1 heater on full time.
RE: Water tank heat loss
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RE: Water tank heat loss
Steviewye.
RE: Water tank heat loss
area of the cylinder
air htc: 25 W/m^2-K
air deltaT = 0ºC - 25ºC
radiative emissitivity = 0.7
surfaceT = 273K
skyT = 220K
The result is 2.9kW of convective loss and 0.6kW radiated loss. There are, of course, lots of caveats, since the emissitivity is unknown, and the htc is a guess. So, then finding a surfaceT that results in 180W (for margin), we get 248K, or -25ºC.
If you use a styrofoam insulation with a thermal conductivity of 0.08 W/m-K, with 2-in thickness, the heat loss for a 25ºC deltaT will be around 180W. Given all the caveats, it looks to be doable, but I would probably go with 3-in thick styrofoam-like insulation. Another insulation option would be htt
TTFN
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