Theoretical analysis of a method for segmented heat exchanger design

In the process of the design of heat exchangers, it is difficult to establish the factors governing the optimal points of the design objective functions due to the contradictions and uncertainties of the design objectives. The variation of fluid properties is one of the main factors causing this type of uncertainty. Conventional design methods have not completely solved these problems. In the present work, based on the logarithmic mean temperature difference, a new heat exchanger design method (called the segmented design method) is proposed which takes into account the variation of fluid properties with respect to the temperature. In this method, the whole heat exchanger is first divided into several segments. Then by applying the principle of the conservation of energy and taking into account the initial conditions as well as the connecting conditions of the adjacent segments, the inlet and outlet temperatures of each segment are determined. Finally, the application of the logarithmic mean temperature difference method on each segment defines the heat transfer area.