On optimum disposal of waste heat

The irreversibility associated with waste heat disposal across an exchanger represents an inherent trade-off point in the design of power plants. On the one hand, a large degree of irreversibility from a large temperature drop across the heat-transfer surface is detrimental to the thermodynamic efficiency of a cycle that produces waste heat. On the other hand, reduction of irreversibility can be achieved only by employing a larger heat transfer area. Therefore, one expects that there must be an optimum design that maximizes the work output per unit of heat transfer area for a given cycle. The efficiency at this optimum condition should be much closer to efficiencies in comparable cases of “good” design, and it must serve as a much more reasonable yardstick in assesing engineering merit.