the mass flow rate in a heat exchnager

JB1234

Refrigerant-134a is to be cooled by water in a condenser. The refrigerant enters the condenser with a mass flow rate of 6 kg/min at 1 MPa and 70oC and leaves at 35oC. The cooling water enters at 300 kPa and 15oC and leaves at 25oC. Neglecting any pressure drop, determine

(a) the mass flow rate of the cooling water required.
(b) the heat transfer rate from the refrigerant to water.

a)I worked it out and my answer is .35kg/s by using the formula Q=mC(T1-T2)
but the answer is given as 0.486 kg/s

b) still didn't work with it
but the answer is given as 20.35 kJ/s

any help will be appreciated

gneill

What are the thermal properties of the refrigerant? It looks like you'll need the heat of vaporization and specific heats for liquid and vapor states.

JB1234

thnx for the reply

But i dont think that we should find the heat vaporization for liquid and vapor state, because we didn't deal with such thing in class , but we do need to find the specific heat of the refrigerant-134a to be able to use the formula which i post above .

gneill

Then you should supply the value if it is required.

rock.freak667

If you have the refrigerant tables for R-134a, you can alternatively use:

(mΔh)_R134a = (mΔh)_water

JB1234

Thats exactly what i did , i found a table at the end of my book and finally i got the right answer

Thanks for both of you