A hybrid method for the cross flow compact heat exchangers design

Despite their limitations, the cross flow compact heat exchangers are generally modeled by the ε-NTU and LMTD methods and this mainly leads to the absence of effective consideration on the heat transfer geometry at the micro scale. At the same time, numerical analysis applied to compact cross flow heat exchangers, having different and complex finned surfaces respectively at the hot and cold sides, involves high computational costs. A powerful alternative design procedure is here proposed that takes advantage of both numerical and analytical approaches. Hot and cold sides are numerically modeled and predictor functions for heat transfer and fluid dynamic performance are obtained with regression technique, for both sides. The whole cross flow heat exchanger is divided into a set of control volumes, including the fins geometry 3D accurate description of both sides and their separation wall. An analytic iterative method is then used to find a wall temperature distribution throughout and to determine the mass flow rate distributions on both sides starting from the results of the numerical analysis at the micro scale. The multi-scale approach leads to a better accuracy level with respect to the full-scale one and allows to profitably investigate different fins influence on flow distributions, local heat transfer and pressure losses through both sides of the heat exchanger.