Parametric study on rectangular finned elliptical tube heat exchangers with the increase of number of rows

The objective of this study is to investigate the performance of rectangular finned elliptical tube heat exchangers (RFETHXs) of low number of rows (N) in turbulent region, with an emphasis on the characteristics with the increase of N. Using 3D numerical simulations based on the validated standard k-epsilon turbulence model, the average thermal-hydraulic characteristics of each row as well as the overall performance along with N are investigated. Then the contribution of each structural factor and the interaction effects between various parameters on the performance are revealed using variance analysis in 4 sub-row-regions. The most significant interaction effect on the performance evaluation criterion (PEC) between structural parameters is confirmed using Response Surface Method (RSM). It is observed that, for the RFETHXs with N > 2, the heat transfer coefficient of the second row of fins is the largest, while those of the first and the last rows remain the smallest two. A 2-row RFETHX has better performance compared to the RFETHXs with larger N. In most cases, the flow and heat transfer of RFETHXs enters fully developed state from the fifth row, but as the transverse tube pitch (P-t) increases or the fin thickness declines, such state is postponed to deeper rows. It demonstrates that significant impact of N on PEC exists in the sub-row-range of 2-3. With the incline of N, the effect of fin pitch (F-p) to j and f decreases while that of P-t increases, and the interaction effect between P-t and F-p to j and PEC becomes more pronounced. This interaction reduces with the increase of frontal velocity. The reason for such interaction is discussed. At last, results of RMS analysis further depict that the interaction effect between P-t and F-p on PEC of a 6-row RFETHX is more significant than that of a 2-row RFETHX. (C) 2018 Elsevier Ltd. All rights reserved.