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Coil in tank: outside heat transfer coefficient

Coil in tank: outside heat transfer coefficient

Coil in tank: outside heat transfer coefficient

(OP)
Hi,

I would like to ask for your opinion in this: i have a tank with water that i need to heat. I have a circular coil inside it. I'm calculatin the area needed to transfer a certain amount of energy a a determined rate. Therefore i'm calculatin the Overall Heat Trasnfer rate, wich is baes on inside and outside heat transfer coefficients and the pipe wall, also.

My problem is:

1) If the fluid is static inside the tank, what should be my outside heat transfer coefficien: ho ??

2) If the water inside the tank has a certain flowrate as shown in the attached ficgure, how can i calculate the heat transfer coefficient, for a circular coil?

Thanks

http://files.engineering.com/getfile.aspx?folder=a76d0ba9-30b4-447f-bf68-b6f26ea90093&file=HX_1.jpg


http://files.engineering.com/getfile.aspx?folder=878cb8de-e9ea-4f65-ad61-b9315fa4a088&file=HX_2.jpg

 

RE: Coil in tank: outside heat transfer coefficient

1)For the tank contents being static, look at natural convection heat transfer for ho.

2)With the tank contents having velocity, look at forced convection heat transfer for for ho.  Is this velocity created by an agitator or external circulation pump?  Correlations for ho under agitation can be found in Perry's and most agitator references books.  
 

Good luck,
Latexman

RE: Coil in tank: outside heat transfer coefficient

(OP)
Dear Latexman,

Thank you for the reply.

Comments:
2) As you can see in my 2nd attached file, the velocity in the tank is imposed by an external circulation pump.
My problem is that usually i calculate heat exchangers considering rectangular pipe arrangementes or "triangular" arrangements. In this case we have a circular coil and the fluid stream crosses it from below. This kind of "object" that is crossed by the stream is new to me and i don't know waht calculations must i do...

I hope i was clear enough.
Thanks

RE: Coil in tank: outside heat transfer coefficient

I tend to treat tank coils as a cylinder in cross flow for heat transfer calculation, and then make sure i specify the coils so that they are at least 2D spaced center to center, prefferably 3, that is usually enough spacing to allow the simplification of just treating it as a single pipe for heat transfer calcs, it will get you quite close in either case.

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