Flow Passage Arrangement and Surface Selection in Multistream Plate-Fin Heat Exchangers

This paper presents a general design methodology for multistream plate-fin heat exchangers that incorporates the consideration of operability aspects through the manipulation of stream flow passage arrangement. The main features of the design approach are uniform heat load per passage and secondary surface or fin selection. Surface selection is implemented as a means to achieve uniformity in the heat transfer rate of the various streams that take part in the heat exchange process. Uniform heat load content per passage is a design consideration through which an equal number of hot and cold passages is achieved. Under these conditions, the number of passages allocated to a given stream is directly proportional to its heat capacity mass flow rate. A simple model for the steady-state simulation of multistream exchangers is also presented. This model can be used to determine the exchanger response to changes in temperature and flow rate that may take place during operation. Results indicate that flow passage arrangement is a design consideration that can be manipulated to reduce the effect of these types of disturbances upon the target temperatures of specific streams.