Thermal Design of Multistream Plate Fin Heat Exchangers—A State-of-the-Art Review

Abstract

Multistream plate fin heat exchangers have replaced two-stream heat exchangers in diverse applications due to their compactness, capacity of handling multiple fluid streams in a single unit, and possibilities of having intermediate entry and exit of the streams. Unique features of such heat exchangers like direct/indirect crossover in temperatures due to several thermal communications among the fluid streams and the dependence of the thermal performance on “stacking pattern” have no equivalent in two-stream modules. As a consequence, an extension of the commonly used design/simulation techniques like ϵ-NTU or the LMTD method, applicable for two-stream exchangers, fails miserably in the case of multistream units. Though several techniques have been suggested over the years, in reality, no universally accepted methodology exists for the “thermal design” of multistream plate fin heat exchangers to date. In this communication, a state-of-the-art review of the thermal design of multistream plate fin heat exchanger is provided. Reported techniques based on heuristics, extension of the analysis applicable for two-stream heat exchangers, differential analysis, network analysis, and rigorous numerical solutions are briefly reviewed. Advantages and limitations of such techniques are also critically judged. The method of “area splitting” and “successive partitioning” proposed by the present research group is also elaborated. Apart from the basic design methodology, the techniques adopted for accounting for variable fluid properties, axial heat conduction in the solid matrix, and thermal communication with the environment have been discussed. Further, the suggested methodologies for optimizing the thermal design are reviewed. Finally, comments have been made indicating the future need of research in this topic.