Heat exchanger network area addition

To this point, it has been assumed that the log-mean tenperature correction factor, F, for all exchangers is the same and equal to 0.8. The reason that F is not assumed to be equal to unity is that, for heat exchangers in most practical applications, the flows of the hot and cold streams are never purely countercurrent. The most common type of heat exchanger in use in the chemical process industries is the shell-and-tube (S T) type. These units are typically made as multiples of the basic 1-shell pass, 2-tube pass (1-2) design. When estimating the fixed capital investment associated with the purchase and installation of the heat-exchanger network, the number of 1-2 S T exchangers is needed in addition to the total surface area of the network. 

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