Semi-Empirical 3D Rectangular Channel Air Flow Heat Transfer and Friction Factor Correlations

This paper presents correlations for heat transfer and friction coefficients for combined entry region airflow in 3D rectangular channel as functions of channel depth, Reynolds number, hydraulic diameter, and channel aspect ratio. The correlations were designed to approach known physical limits as the channel aspect ratio and channel depth approach zero, and as the flow becomes fully developed. The curve fits were constructed by bridging continuously between these well known analytical and numerical results for 2D and 3D channels. The RMS value of the curve fits were 1.5 and 2.7% for heat transfer coefficient and friction factor, respectively. These physically-based correlations were created to be applied to the design and analysis of flat tube heat exchanger concepts in parts of the parameter space that lie outside the range of published empirical correlations.