# Heat Transfer Coefficient

Hello,
I have a swimming pool with a waterfall feature.
I need to know how much does the waterfall contributes to cooling the pool.
I tried to use Newton's law of cooling, but I have a problem with the Heat Transfer Coefficient in this case.

Following are the Givens:
Waterfall Width= 5m
Waterfall Height= 1m
Waterfall Thickness= 1cm
Waterfall Flow Rate= 100 m3/Hr
Water Temperature= 26 C
Air Temperature= 20 C

I need to Find Q (in Watts).

Could someone help.
Many Thanks.

Bystander
Homework Helper
Gold Member
One or two "faces" to the "fall?"

russ_watters
Mentor
Welcome to PF.

This isn't an easy problem. The effectiveness of the waterfall in cooling the water in it is pretty difficult to determine. 25%? 50%? Definitely not any better than that, but it depends on factors like geometry and wind. I'd probably guess 25% for a ballpark, if it isn't a dense stream.

What I can tell you is you are using the wrong temperature. A waterfall (cooling tower) will cool the water down to the wet bulb temperature of the air. So that's what you need to calculate your approach against.

An easy way to get the wet bulb temperature is to check the weather at you nearby airport. Every hour (or sooner) they report wind, visibility, cloud coverage, temperature, dewpoint (wet bulb temp), and the altimeter setting. Most airport weather stations have a local phone number you can call just to receive the weather report. These stations are called an AWOS or ASOS.

Hello,
Thank you all, and thanks for pointing out the wet bulb temperature.

The water fall is two faces, so approximate area of both sides is 10 m2.

Thanks