Heat transfer by convection between water in a pool and atmosphere 1

[sizgalil]

Hi,

I am trying to calculate the net heat transfer between an open pool filled with water and the atmosphere. Have taken into account radiation, evaporation.
Having difficulties calculation the conduction from the water to the ground and from the water to the atmosphere. The water is warmer than the atmosphere and the ground.
Can anyone help or send me to a good reference?
Thanks!

 

[CastMetal]

Free heat transfer textbook.

http://web.mit.edu/lienhard/

http://www/ahtt.html

 

[TBP]

The heat loss from the surface is - far & away - the lion's share.

Google the "Burnham Heating Helper". On page 28 is the simple chart & calcs required.

 

[sizgalil]

Thanks.
Downloaded the Burnham helper. Can't find the chart & calcs you've referred to. Do you know in what chapter it appears?

 

[sizgalil]

TBP sorry.
I found the page - 42.

 

[sizgalil]

TBP, when you say the heatloss from the surface includes evaporation, convection, and radiation. Do you know if all these factor are taken in account in the Burnham helper. The book does not mention any details regarding RH or solar radiation?

 

[dalcazar]

Correct me if the assumption is incorrect... But I would assume that natural convection would not play a hugely significant role in the loss of heat to the atmosphere, the boundary layer between the water and the air would be the transfer point of heat, and because evaporation cools the air in the boundary layer, the boundary layer will be colder than the ambient air and thus tend to stick to the boundary, pool in the height differential of ground level and water level, and not convect away from the surface. Thus only forced convection (wind) would be a significant source of heat loss?

Not saying anything anyone has said here is wrong, only bringing up the issue in case it hasn't been considered.

 

[IRstuff]

That's not the way it works. Evaporation cools the water, heats the air. By any measure, heat travels from warmer to cooler.

TTFN

FAQ731-376

 

[TBP]

The pool is a heat exchanger. Like any HX, the two big factors are delta-T and surface area.

There's a table in the Heating Helper that provides factors for wind.

And note that the Heating Helper is just a small, softcover publication for residential/small commercial heating contractors. Having said that, I've used it to help size a couple of pool HXs, supplied from the hot water boiler that heats the house in the winter - it works.

If you need something for an in-depth engineering study of pool heat loss, then the Heating Helper is not the publication you're looking for. If you want to just cut-to-the-chase to the correct answer, well, it's hard to argue with success.

 

[gruntguru]

That's not the way it works. Evaporation cools the water, heats the air. By any measure, heat travels from warmer to cooler.
How does evaporation heat the air? Have you never seen an evaporative air cooler?

Engineering is the art of creating things you need, from things you can get.

 

[IRstuff]

There's a huge difference between cooling down HOT air by transferring the hot air's heat to cooler water, and the OP's "warmer" water losing heat to the air.

TTFN

FAQ731-376

 

[gruntguru]

Evaporation does not "heat" the air. The air in the boundary layer may be warmer (or cooler) than the ambient air but not as warm as it would be if there were no evaporation.

Engineering is the art of creating things you need, from things you can get.