Mechanical Engineering - Heat Transfer, Refrigeration and Air Conditioning - Discussion

@All.

Because we are talking about condensers and evaporators here, that means that one of the fluids is undergoing a phase change, which also means that the temperature of that fluid remains constant for inlet and exit, therefore when calculating the LMTD we find that results for counter-current and co-current flow are the same.

@Mechio,

Nowhere in the question, it is written that the temperature of one of the liquids remains same since it only happens during phase change. So the correct answer would be "B".

B is the correct answer.

The correct answer is (A). Since temperature of one of the fluid remains constant during the flow passage, both the parallel flow and counter flow arrangements would give the same values for log mean temperature difference and heating surface area for a specified load.

B is the right answer.

The heat exchange through Evaporator and condenser does not depend on direction of flow.

A condenser or a evaporator can be considered to be either a parallel- or counterflow.

Heat exchanger since both approaches give the same result. Option A is correct.

B is right answer, good explanation @Muhammad Waqas.

For specified inlet and outlet temperatures, the log mean temperature difference for a counter-flow heat exchanger is always greater than that for a parallel-flow heat exchanger. Thus a smaller surface area (and thus a smaller heat exchanger) is needed to achieve a specified heat transfer rate in a counter-flow heat exchanger. Therefore, it is common practice to use counter-flow arrangements in heat exchangers.

Reference: Page 682, Heat Transfer by Cengel 2nd Ed.

Since for evaporator and condenser tm does not depend on direction of flow.