Question

The log mean temperature difference for counterflow and parallel flow heat exchanger are identical, when the

A. cold fluid is heated to a certain temperature by condensing steam (isothermal fluid)
B. outlet temperature of both the hot and cold fluid are the same
C. outlet temperature of hot fluid is less than the outlet temperature of the cold fluid
D. none of these statements are valid

Answer 1

The log mean temperature difference for counterflow and parallel flow heat exchangers is identical when the outlet temperature of the hot fluid is less than the outlet temperature of the cold fluid.

Step-by-step explanation:

The log mean temperature difference for counterflow and parallel flow heat exchangers is identical when the outlet temperature of the hot fluid is less than the outlet temperature of the cold fluid (option C).

In a counterflow heat exchanger, the hot and cold fluids flow in opposite directions. The temperature difference between the two fluids decreases along the length of the heat exchanger, resulting in a logarithmic mean temperature difference. Similarly, in a parallel flow heat exchanger, the hot and cold fluids flow in the same direction, but the temperature difference still decreases along the length of the heat exchanger.

Therefore, option C is the correct statement as it satisfies the condition for the log mean temperature difference to be the same in both types of heat exchangers.