An analysis is presented for heat exchanger area, tower exit area, and exchanger tube length and number, for heat exchangers in large dry cooling towers, having performance parameters given by powers of Reynolds number, but otherwise under very general cooling-cycle constraints. The calculation method is illustrated for a “spine-fin” heat exchanger which, in a tube size of about 3/8 in., seems capable of achieving low tower size in a practical device. Calculations, over ranges of water pumping power, approach, ITD, number of passes, tube size, tower shape (natural draft) or fan power (mechanical draft), and ambient pressure altitude are shown to be well represented by a chain of powers of these variables, and certain functions of the ratio of real to ideal tower exit area. This ratio is shown to have a best value, depending on the cost coefficients of heat exchange and exit areas, and it is pointed out that typical cost proportions lead to a fluid-mechanical “packaging” problem for the shallow heat exchangers which would be preferred.

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