Physical Dimensions as a Design Objective in Heat Transfer Equipment: The Case of Plate and Fin Heat Exchangers

To incorporate exchanger dimensions as a design objective in plate and fin heat exchangers, a variable that must be taken into consideration is the geometry of the finned surfaces to be used. In this work, a methodology to find the surface geometry that will produce the required heat transfer coefficient and pressure drop to achieve the design targets was developed. The geometry of secondary surfaces can be specified by the fin density, which represents the number of fins per unit length. All other geometrical features, as well as the thermo-hydraulic performance, can be derived from this parameter. This work showed the way finned surfaces are engineered employing generalised thermo-hydraulic correlations as a part of a design methodology. It also showed that there was a volume space referred to as volume design region (VDR) where heat duty, pressure drop, and dimensions could simultaneously be met. Such a volume design region was problem- and surface-specific; therefore, its limits were determined by the heat duty, the pressure drop, and the type of finned surface chosen in the design. The application of this methodology to a case study showed that a shell and tube heat exchanger of 227.4 m(2), with the appropriate fin density using offset strip-fins, could be replaced by a plate and fin exchanger with any combination of height, width, and length in the ranges of 0-0.58 m, 0-0.58 m, and 0-3.59 m. The approach presented in this work indicated that heat exchanger dimensions could be fixed as a design objective, and they could effectively be achieved through surface design.