Illustration
A heat transfer fluid is leaving a reactor at a rate of 167 kg/s at 85°C. The fluid is to be cooled to 50°C before it can be recycled to the reactor. Water is available at 30°C to cool the fluid in a 1-2 pass heat exchanger having heat transfer area of 15 m2. The water, which is being used to cool the fluid, must not be heated to above 38°C at the exit of the heat exchanger. The overall heat transfer co-efficient of 400 Kcal/hm2°C can be used for the heat exchanger. The water flows through the shell and the oil flows through the tubes. The specific heat of the fluid may be taken as 0.454 kcal/kg°C. Find out whether the heat exchanger would be suitable for the given heat duty?

Solution:
It is given,

f : hot stream (fluid)

c : cold stream (water)

Energy balance across the heat exchanger will be,

Thus the minimum stream will be the hot stream.

Putting the values in the eq. 8.19,

The area 13.2 m² found is less than the available area (15 m²). Therefore, the given heat exchanger will perform the required heat duty.