Cooling in tank calculation

[bezar]

Hi

I'm designing a tank with half pipe coil on the outer side of the tank. I want to cool down strawberry juice (jam) with ice water. I'm cooling the jam from 20C to 4C. The heat exchange capaciti of the chiller should be around 5kW.
Can anyone give me a tip on how to calculate the heat exchange area of the tank.

 

[MortenA]

If you ignore HX with the tank and surroundings and assume perfect mixing of the jam then follow these steps:

Your heat transferred from the jam to the icewater will depend on the temperature of the jam

Start with your initial temperature and do an ordinary heat transfer calculation:

Q/t=UAdT

q: enegy J
t: time sec
U: Heat transfer coefficient W/m2/C
A: Heat transfer area
T: Temp C

You can solve this backwards for the first step (T_jam=40 C). Calculate U (this is more tricky and will require some work on your behalf to find out how to calculate U for a agitaed vessel) and then using your value of 5 kW to calculated the required HX area.

Note that as the temperature drops you energy exchange with the jam will reduce - assuming that you cant lower the temperature of the ice water.

Best regards

Morten

 

[bezar]

Thanks a lot for your reply, but I know how to calculate heat transfer. The thing I don't know is how to calculate heat transfer coeficient when I have tank with an agitator.

I reallz never had problems like this becaouse I calculated coeficients for heat exchangers. If you have any clue or direction about heat transfer coeficient calculation for tanks with agitator it would be very helpful.

Best regards

Ivan

 

[Latexman]

bezar,

Perry's Chemical Engineers' Handbook has correlations for heat transfer coefficients for agitated vessels. So do many heat transfer books. My old text by Kern does. It also has the solved differential equations for unsteady-state heat transfer you will need to estimate cool down time. Perry's does too.

Agitator vendors will gladly help you with this estimate, especially if a potential sale is available. Most vendors will give you their book on agitation which will have heat transfer correlations. I know Chemineer and Lightning do. I don't think they show the cool down time equations though.

Good luck,
Latexman

 

[abeltio]

Process Heat Transfer, by Donald Q. Kern covers that case exactly.


saludos.
a.

 

[mechprocess]

Does anyone know how much credit I can take for the tank surface area between halp pipe loops? This program called DeltT takes credit for all the in-between space.

PS Dito on Kerns methods. Kerns rules when it comes to unsteady state batch heating and cooling calculations.