Coil in tank: outside heat transfer coefficient

[mfqd]

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

 

[Latexman]

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

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


Good luck,
Latexman

 

[mfqd]

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

 

[jmiles]

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.