Heat Exchanger Calc's

[wehber]

Hi,

We are currently putting a package together with a compressor and a gen set and want to cool both units on one cooling circuit. I'm a rusty with thermo so I thought I would turn here. Here are the specs.

Total heat load will be 150,000 BTU/hr

Ambiant temp is 100 F.

We want the coolant out around 120 F.

Using a 60/40 solution of Eth. Gly. and H2O specific heat is around 0.75.

We were thinking of a flow rate of 10 GPM but that along with the size is still TBD.

We would like to find out the temperature of the coolant going into the exchanger. Possibly a way to figure out the unknowns as well. Thanks!

 

[IRstuff]

I suggest that you work with someone in the thermal control unit industry. You're probably going to need a blower to get sufficient air flow across the exchanger.

TTFN

 

[TD2K]

Talk to some suppliers and find out what the typical temperature rise they suggest across the units, that will determine the circulation rate.

Your 120F temperature (out of an air cooler I assume) is reasonable for 100F ambient temperature.

 

[srfish]

The 10 GPM flow and the 150,000 Btu/hr heat duty backs into a temperature change of 37 F. This a large temperature change for this type of application. It will take a large number of tube passes to achieve a reasonable tube velocity.

I suggest a larger flow than 10 GPM.

 

[IRstuff]

We've run a 1 gpm system with 60/40 with a design rating of 10ºC delta temp that works fine with a 400W load. Again, the issue whether you have decent blower and sufficient fin area to remove the heat. Your BTU/hr comes out to 44kW, so a factor 10 scaling in flow and surface area with the same air flow is presumably doable.

TTFN

 

[Diabolico]

You want to use the specific heat equation: Q = m x Cp x DeltaT

Q = Heat load (BTU/hr)
m = mass flow rate (lbs/hr)
Cp = specific heat of coolant
DeltaT = temperature differential between inlet and outlet

From this formula: Tin = Tout + Q/mCp
Tin = 120 + 150000/(10 gpm x 66.4 x .78)
Tin = 156