The mass flow rate in a heat exchnager

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The discussion focuses on calculating the mass flow rate of cooling water and the heat transfer rate in a heat exchanger involving Refrigerant-134a. The refrigerant enters the condenser at 6 kg/min and exits at 35°C, while the cooling water enters at 15°C and leaves at 25°C. Initial calculations yielded an incorrect mass flow rate of 0.35 kg/s, while the correct answer is 0.486 kg/s, and the heat transfer rate is 20.35 kJ/s. Participants emphasize the importance of using specific heat values from refrigerant tables for accurate calculations. Ultimately, one user successfully found the correct values and solved the problem.
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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
 
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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.
 
gneill said:
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.

thnx for the reply

But i don't 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 .
 
Then you should supply the value if it is required.
 
If you have the refrigerant tables for R-134a, you can alternatively use:

(mΔh)R134a = (mΔh)water
 
rock.freak667 said:
If you have the refrigerant tables for R-134a, you can alternatively use:

(mΔh)R134a = (mΔh)water


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
 
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