Heat transfer and friction correlations for offset strip fins relative to the offset ratio

Previous studies on the dimensionless Fanning friction factor (f) and Colburn heat transfer factor (j) of offset strip fins have considered an offset ratios of 50. However, most mass-produced offset strip fins have an offset ratio of 30, while a few others have offset ratios of 20 or 10. Thus, previous correlations usually overpredicted j over the entire range of Reynolds numbers for offset ratio of 30 or lower. In this study, we numerically investigated the thermal-hydraulic characteristics of an offset strip fin relative to the offset ratio. In particular, we analyzed the difference in thermal performance subject to the offset ratio based on a 3D computational fluid dynamics analysis. The values of f and j were obtained using eight geometries with different offset ratios. New correlations for f and j were derived from the data obtained through nonlinear regression and multilinear regression. These correlations considered the offset ratio as a variable. Therefore, the heat performance was predicted to be more accurate than the previous correlations. In addition, new correlations could be used to determine the values of f and j using simple calculations.