Water entering a shell-and-tube heat exchanger at 35°C is to be heated to 75°C by an oil. The oil enters at 110°C and leaves at 75°C. The heat exchanger is arranged for counterflow with the water making one shell pass and the oil two tube passes. If the water flow rate is 68 kg per minute and the overall heat transfer coefficient is estimated from Table 10.1 to be 320 W/(m2 K), calculate the required heat exchanger area.
GIVEN
• One shell pass, two tube passes counterflow heat exchanger with water in shell, oil in tube
• Water temperatures Tw,in = 35°C Tw,out = 75°C
• Oil temperatures To,in = 110°C Tw,out = 75°C
• Water flow rate m n= 68 kg/min = 1.133 kg/s
• Overall heat transfer coefficient (U) = 320 W/(m2 K)
FIND
• The required area (A)
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of water at the average temperature of 55°C (cpw)= 4180 J/(kg K)
For counterflow
The LMTD must be modified according to
F ? 0.80
The rate of heat transfer is
Solving for the transfer area
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