Heat transfer to/from a open topped tank

[friartuck]

Hi clever people

I have what I think is a fairly difficult problem (but I'm hoping you will find it easy)

I have an open topped tank (contains fish in a sea life centre)

The tank I understand is at about 15C and the space varys in temp from 15 to 27C.

The first question is, what will the heat transfer be between the two 'systems'.

I understand that the heat transfer through the tank wall could be simply:

UxAxDT i.e. thermal transfer coefficient x area x temp diff

alternatively I could use tables to give me heat transfer from plane surfaces and look up the heat transfer by convection and by radiation and add them together. (and if my sums were right, I hope the answers would be the same)


BUT, my next question is, what about the actual water surface. What heat transfer will I get there. Can I use the same heat transfer calc metods or is there some evaporation effect to take into account??

I think there are two concerns:

a. What effect is had on the tank i.e. how warm will it get or how cool will it get (the heat gain/loss will need to be catered for by a chiller circuit)

b. What effect is had on the space where the visitors occupy. Will they need extra heating or cooling to cater for the heat transfer.

I'm sure this is a fairly simple question to some of you, after all there are thousands of swimming pools out there


Answers on a postcard please

thanks in anticipation



Friar Tuck of Sherwood

 

[corus]

The problem is more difficult because of the convection that will occur in the water itself, as well as heat loss from evaporation from the surface. If you neglect those factors then you could treat it as a solid body but how accurate your answer would be is another matter.

corus

 

[JStephen]

Check if there's an HVAC forum and repost there. I'm sure lots of HVAC engineers have dealt with the swimming pool problem, and the ASHRAE publications may give detailed loadings for the situation. It may be as simple as giving heating/cooling load per square foot of pool surface or something like that.

 

[owg]

There is a lot of vendor literature on this subject. Look for vendors of immersion heaters. Here is one link that may be helpful.

http://www.engineeringtoolbox.com/38_286.html

.

HAZOP at

http://www.curryhydrocarbons.ca

 

[friartuck]

good one OWG

That tells me the heat lost from a tank (which is part of my problem).

Is there anything on how much heat goes into a tank...I need to keep the fish cool in the summer. The warmth from the space will heat the tank, and in turn, I will need to provide some chilled water to offset the heat gain.

Incidentally, this question is also in the HVAC section, and they are 'head scratching' as well. But I've had some excellent assistance.

Thanks for the help so far. Keep it coming,

Friar Tuck of Sherwood

 

[TD2K]

If you can find a copy of Chromalox's catalogue, the engineering section has a good collection of heat losses including from open tanks.

 

[jrhols]

My good friar:
Heat transfer is ANYTHING but easy, considering the history of manipulations and schemes in the coefficient business.
I hate to break to news or criticize another web site, but I did follow the link to engineering tools another member gave you , and I am compelled by ethical consideration for your situation to tell you that the sample calculation takes a thermal conductivity (70 watts per degree c) for iron which is approximately correct and uses it as a thermal transfer coefficient, coming up with units in square meters after starting with units that are in watts per linear meter. This is a good example of what I dealt with for years as I wrote thermcoat.com about thin coatings and how the thin geometry impacts on their R value. I suggest you use the spreadsheet at that web site and email in any discrepencies you find. It's better than being off by twice the heat in watts and BTU's than other methods will give you, and it has ample validation and cross-calculation.