PLATE ARRANGEMENT
Comparison of plate heat exchanger plate arrangement to the tube and shell side arrangement in a shell and tube exchanger is charted , the number of passes on the tube side of a tubular unit can be compared with the number of passes on a plate heat exchanger.
The number of tubes per pass also can be equated with the number of passages per pass for the paraflow. However, the comparison with the shell side usually is more difficult since with a plate heat exchanger, the total number of passages available for the flow of one fluid must equal those available for the other fluid to within ±1. The number of cross passes on a shell, however, can be related to the number of plate passes. Since the number of passages/pass for a plate is an indication of the flow area, this can be equated to the shell diameter. This is not a perfect comparison but it does show the relative parameters for each exchanger.
With regard to flow patterns, the plate heat exchager advantage over shell and tube designs is the ability to have equal passes on each side in full counter-current flow, thus obtaining maximum utilization of the temperature difference between the two fluids. This feature is particularly important in heat recovery processes with close temperature approaches and even in cases with temperature crossovers.
Whenever the thermal duty permits, it is desirable to use single pass, counter-current flow for an extremely efficient performance. Since the flow is pure counter-flow, correction factors required on the LMTD approach unity. Furthermore, with all connections located at the head, the follower is easily moved and plates are more readily accessible.
