Abstract
In this paper approximate models by the method of weighted residuals (MWR) are given for mono-tubular, parallel, counter and multipass heat exchangers the mathematical models of which are described by the hyperbolic partial differential equations. In a frequency domain study the MWR compares favorably with a finite difference model method in that the results of MWR are accurate and require less computation time. Also, comparison between poles and zeros of MWR models and exact ones shows that approximate poles and zeros do not necessarily approximate only those of the original system near the origin.
Besides the frequency domain the comparison is made by the stability limit of the PI-feedback controled system, where the difference between the exact solution and an approximate one appears clearly. It is shown that the finite difference model with a considerable number of divisions estimates too large a stable area, while MWR models with less number of expansions give a good estimation of the stability limit.
