# Overal heat transfer coefficient: Refrigeration Heat Exchanger

1. Aug 7, 2013

### recreated

Hi There

Does anyone out there know a good estimate or any real values for the total heat transfer area for the hot and cold sides of a domestic refrigeration system? i.e. the sum of the areas of the evaporator and the condenser.

For the Evaporator:
QL=UL.AL.(TL-T1)

AL=heat transfer area of cold side (Low side)=????
UL=overal heat trans. coefficient of cold side.=????
QL=heat removed from cold side = 7.93 KW
TL=refrigerator temp. = 3degs C + 273.15=276.12 Kelvin
T1= Refrigerant evaporating temp. =0degs C + 273.15= 273.15 Kelvin

I am trying to estimate this area so I can calculate the overal heat transfer coefficient which I need for other calculations. So far the outcome of estimating the area and finding the heat transfer coefficient based on it has not been realistic.

If it helps:
The aim of my project is to find the optimal heat transfer ratio between hot and cold side, there is theory on this which I am following, I just need some realistic values for area and heat transfer coefficient. I think it is more logical to estimate the area and find the h.t. coefficient based on that rather than the other way around.

2. Aug 7, 2013

### rude man

Don't know about the evaporator, it's unfortunately hidden, but you can estimate the area of the condenser coil in a refrigerator by measuring the length of one left-to-right run, multiplying by the no. of runs and then by pi*D where D is the diameter of the coil. Add 10% or so for the bends.

3. Aug 7, 2013

### recreated

Thank you. I will try that now. Do you know if the condenser is usually larger or smaller than the evaporator? Or any estimated proportion to use?

I assume condenser area > evaporater area as it has to get rid of heat from the refrigerator & the compressor, but maybe in practise it's different.

4. Aug 7, 2013

### rude man

That seems to be the case. I would estimate the evap coil at 1/7 the area of the condenser. The evap coil is usually small enough to fit in the freezer compartment.

cf. http://www.ebay.com/bhp/refrigerator-evaporator-coil

for examples.

For both coils, extensive heat sink fins are used to dissipate heat (condenser) and draw in heat (evaporator). You would need to take those into consideration. Also, evap coils almost always use a fan to blow the cooled air into the refrigerator. Apparently the newer models put the condenser coil at the bottom & then a fan is probably required there too.

All in all, you're faced with a difficult analysis I think.