 31
 2
 Problem Statement

The data below relates to a specific heat exchanger. A reliable colleague has looked up an effectiveness chart and says that the effectiveness in the given operating conditions is 0.82.
For hot fluid: mass flowrate qm= 0.7 kg s 1, specific heat capacity cp=1.8 kJ kg1 K1, inlet temp= 140°C . For cold fluid: mass flowrate qm= 0.6 kg s 1, specific heat capacity cp=4.2 kJ kg1 K1, inlet temp= 15°C . Area of heat transfer surface=14m^2, Overall heat transfer coefficient 360 W m2 K1.
Determine:
i. the two outlet temperatures.
ii. the heat transfer rate.
I've spent ages on this but can't seem to find an equation to find both outlet temperatures! Any help would be greatly appreciated.
 Relevant Equations
 ε=(T_HIT_H2)/(T_HIT_C1 )
Because the specific heat capacity is lower for the hot fluid:
ε=(T_hiT_h2)/(T_hiT_C1 )
0.82=(140T_h2)/(14015)
140T_h2= 102.5
T_h2= 140102.5=37.5°
I'm not sure if I'm actually on the right track here, if I am this is as far as I've gotten. I can't seem to then find an equation to calculate T_c2 other than the equation which my lessons tell me is only used when the specific heat capacity is lower for the cold fluid.
ε=(T_hiT_h2)/(T_hiT_C1 )
0.82=(140T_h2)/(14015)
140T_h2= 102.5
T_h2= 140102.5=37.5°
I'm not sure if I'm actually on the right track here, if I am this is as far as I've gotten. I can't seem to then find an equation to calculate T_c2 other than the equation which my lessons tell me is only used when the specific heat capacity is lower for the cold fluid.
Attachments

39.3 KB Views: 102