Development of Heat and Flow Correlations and Optimization for Corrugated Louver Fin Heat Exchanger

Abstract

The efficiency, heat transfer, and flow characteristics of corrugated louver fin heat exchangers were investigated, and various design parameters were considered to improve their performance. New correlations for the flow efficiency, friction factor f, and Colburn factor j were developed for a variety of geometries. The corrugated fins were optimized using the derived correlations, and the heat-transfer and flow characteristics of the optimized fins were compared with those of fins in a reference configuration. Various turbulence models were first tested against experimental data, and the j and f values predicted by the models were compared with previous correlations. Based on these results, we were able to select a realizable k-ε model. Steady-state two-dimensional results were compared against steady-state three-dimensional results to investigate the three-dimensional effects of the flow around louvered fins. Next, the steady-state results were compared against unsteady results to determine the effects of flow vibrations around the louvered fins. Based on these results, we selected the steady-state two-dimensional realizable k-ε model for further simulations. The results of the numerical model agreed well with the experimental results in the Reynolds number range 700 < Re < 3000, within an error of 17%. Although previous correlations of flow efficiency around corrugated louver fins, which have typically been developed for automotive heat exchangers, predict the flow efficiency well at high velocities, they often underestimate the flow efficiency at lower velocities. The flow-efficiency correlation developed in this study predicted the flow efficiency more generally within an error of 15% in the range 100 < Re < 3000, with Lp sinLα /Fp ranging from 0.3–0.7, where Lp is the louver pitch, Lα is the louver angle, and Fp is the fin pitch. Additionally, general correlations for corrugated louver fins were derived for various geometries. Previous heat-transfer and pressure-drop correlations usually apply for Fp /Lp < 1, and different equations are required for high and low velocities. In this study, new j and f correlations were developed for a wide range of Fp /Lp (i.e., 100 < ReLp < 3000 and 0.8 < Ll /Fl < 0.9, where Ll is the louver length and Fl is the fin length). The design parameters of the corrugated louver fins were optimized using the proposed correlations and numerical simulations. The JF factor of the optimized corrugated louver fins was enhanced by 17% (proposed correlation) and by 10% (numerical simulation), respectively. The streamlines predicted by the optimal configuration were dominant in the direction of the louver and were longer than those in the reference configuration, which improved the flow efficiency. Moreover, the optimized configuration resulted in a longer residence time of air in the louvered fins, resulting in larger heat-transfer rates.