While the concept of minimum irreversibility is associated with the maximum energy efficiency for energy conversion processes in thermal systems, we have found that it is not quite applicable to the heat exchanger analysis. We have shown that the heat exchanger effectiveness can be maximum, having an intermediate value or minimum at the maximum irreversibility operating point depending on the flow arrangement of the two fluids. Similarly, the heat exchanger effectiveness can be minimum or maximum at the minimum irreversibility operating point. The objective of this paper is to illustrate and discuss such heat exchanger performance and irreversibility trends by combining the temperature difference irreversibility with the $P-NTU$ results for complex flow arrangements.

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