A simple method for predicting the thermal performance of multistage heat exchangers is proposed. The technique involves an area weighting scheme of the reseated Colburn J factors. The method is developed for, and probably limited to, applications with indirect contact, direct transfer heat exchangers operated in series. However, condensing heat exchangers are amenable to this technique, and thus it offers more flexibility and wider applicability than previously proposed methods. Experimental data for a two-stage, condensing heat exchanger are reported, and the behavior is compared to the predictive scheme with moderate success. While the behavior of multistage heat exchangers may be affected by interstage spacing, the data from the experiments do not allow quantification of the impact of this effect.
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