Question

A dual-fluid heat exchanger has 10 lbm/s water entering at 100 F, 20 psia and leaving at 50 F, 20 psia. The other fluid is glycol entering at 10 F, 22 psia and leaving at 50 F, 22 psia. Find the required mass flow rate of glycol and the rate of internal heat transfer

Answer 1

Answer:

Rate of internal heat transfer = 23.2 Btu/Ibm

mass flow rate = 21.55 Ibm/s

Explanation:

using given data to obtain values from table F7.1

Enthalpy of water at temperature of 100 F = 68.04Btu/Ibm

Enthalpy of water at temperature of 50 F = 18.05 Btu/Ibm

from table F.3

specific constant of glycerin $C_{p} = 0.58 Btu/Ibm-R$

The rate of internal heat transfer ( change in enthalpy )

h4 - h3 = Cp ( T4 - T3 ) --------------- ( 1 )

where ; T4 = 50 F

             T3 = 10 F

             Cp = 0.58 Btu/Ibm-R

substitute given values into equation 1

change in enthalpy ( h4 - h3 ) = 23.2 Btu/Ibm

Determine mass flow rate of glycol

attached below is the detailed solution

mass flow rate of glycol = 21.55 Ibm/s