Analog Simulation Technique for Modeling Parallel-Flow Heat Exchangers

One of the more common methods of determining the dynamic behavior of parallel-flow heat exchangers has been the development of a model for solution on a general-purpose analog computer. Because the analog by its inherent nature can only work with one independent variable (and most mathematical descriptions of a heat exchanger require two independent variables, time and space) the normal procedure has been to lump one of the variables, normally space, and solve continuously with respect to time. However, for large heat exchangers, this can result in a cumbersome analog network due to the number of space lumps required. A technique, time lumping, has been applied to the analog modeling of a heat exchange process to reduce the equipment requirement while at the same time providing models adequate for control studies. The derivation and application of this approach for a sample parallel-flow heat exchanger is presented and compared with a space-lumped solution.