The tube side of the heat exchanger and its heat exchange area
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Why is the heat exchange area of a 4-pass heat exchanger smaller than that of a 2-pass one?
For the same flow rate: the flow velocity increases, the fluid Reynolds number rises, the convective heat transfer coefficient on the pipe side increases, the overall heat transfer coefficient goes up, and as a result the heat exchange area decreases.
For heat exchangers with the same diameter but different numbers of tube sides, since the partition grooves for these tube sides occupy a portion of the tube sheet area, the more tube sides there are, the larger the area occupied by the partition grooves, and consequently the smaller the available area.
For heat exchangers of the same model, the more tubes there are in the tube side, the larger the area occupied by the partition grooves becomes; as a result, the number of heat exchange tubes decreases, and thus the heat exchange area also reduces.