Heat transfer 1

[foote2]

I am trying to determine the amount of heat transferred from a tank of Dia. 9' x lenght 18', containing a fluid at 36 degrees F and a room kept at a temperature of 30.2 degrees F. If anybody out there knows a simple formula or possibly how to find the heat transfer coefficient it would be appreciated.

Thanks Justin

 

[25362]

Do you mean to say the vessel's metal outer surface and the room around it are somehow kept at the constant temperatures you indicated ?

 

[TD2K]

http://www.watlow.com/reference/refdata/0303.cfm

Should give you a starting point.

 

[foote2]

Currently within the room there are six refrigeration units, four of which are working. Right now I have an average room temperature of 31 degrees F. But would like a constant room temperature of 30.2 degrees F. Goal is to determine cooling load and to see if exixting units can accomplish this, so yes the metal outer surface and the room are at a constant temperature of 30.2. The room is enclosed with no windows or doors to the outside.

Thanks Justin

 

[saxon]

foote2, For simple estimation purposes use q=uat.
Where:
q=total heat transmit.,btu/hr
u=ovr-all coeff. of transfer, btu/hr/ft^2/deg.F
a=surface area of body, ft^2
t= Log mean temp. diff. hot/cold fluids.

For the estimation of "u", I take it the fluid in the tank is a liquid and the controlling resistance is a free state convection, use a u value of 1-3. If the fluid giving up heat is not a liquid or is going through a phase change and/or the system is not in a free convection state, this u value will be low.

Hope this helps.
saxon

 

[foote2]

Thanks very much guys and gals, appreciate the help.

Justin

 

[lilliput1]

Use also Q=M x Cp x DT

Heat = Mass x specific heat x temperature change
all in consistent units.

Required time to cool the material down depends on the process of filling & unloading the tanks & thermal conduction properties. Is this a batch process? What fluid is it?
For conduction,the heat transfer coefficient will be mostly the air film which varies with air velocity, surface emmisivity , film position and direction of heat flow. For still air with reflective vertical surface and horizontal heat flow, R = 1.7 or U = 1/R = 0.59
For still air with reflective horizontal surface and heat flow up, R = 1.32 or U = 0.76

By the way, have you tried indexing the thermostat down to 30.2°F & checking with a temperature chart recorder to see if it holds & how long it took to drop for the current mass of products? You may be able to experimentally answer your question.