Consider an oil-to-oil double-pipe heat exchanger whose flow arrangement is not known. The temperature measurements indicate that the cold oil enters at 20°C and leaves at 55°C, while the hot oil enters at 80°C and leaves at 45°C.
a. Do you think this is a parallel-flow or counter-flow heat exchanger? Why?
b. Assuming the mass flow rates of both fluids to be identical, determine the effectiveness of this heat exchanger.

A counter-flow heat exchanger is one in which the direction of the flow of one of the working fluids is opposite to the direction to the flow of the other fluid.
In a parallel flow exchanger, both fluids in the heat exchanger flow in the same direction.

Counter flow heat exchanger distributes the heat more evenly across the heat exchanger and allows for maximum efficiency.

The effectiveness of heat exchanger is defined as ratio of actual heat transfer to the maximum possible heat transfer.

Given that the cold oil enters at 20°C and leaves at 55°C, while the hot oil enters at 80°C and leaves at 45°C.

[tex]Effectiveness=\frac{55-15}{80-15}=\frac{40}{65}=0.615[/tex]

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