Three-dimensional numerical simulations are conducted for the air-side steady laminar flow and heat transfer characteristics of the plate fin-and-tube heat exchanger element. The effects of Reynolds number (Re), tube center location (Lc/D), and fin pitch (H/D) are examined. The Re based on the tube diameter and the air inlet velocity varies from 100 to 5000, the tube center location from 0.75 to 2, and the fin pitch from 0.2 to 0.5. The numerical results show that the increase of Re leads to the increase of heat transfer parameters (such as the span-averaged $Nu¯(x)$, the overall average Nusselt number ($Nu¯f$, $Nu¯f,t$) of the fin as well as fin-and-tube, the fin surface average heat bulk $q¯$) and the averaged pressure drop on cross-sectional $P¯(x)$, and the decrease of the friction factor (f) and the fin efficiency (ηf); moreover, the larger Re is, the smaller the influence on these parameters except the $P¯(x)$. Regarding the effect of tube location (Lc/D), the f is almost insensitive to the Lc/D change, and the overall average Nusselt numbers of the fin as well as fin-and-tube increase with increasing Lc/D, but the $q¯$ and the ηf first gradually increase and then decrease. And so consequently, there exist the optimum Lc/D values corresponding to the largest averaged $q¯$ on the fin surface and the largest ηf, respectively. The investigation ascertains that the region achieving the highest average $Nu¯(x)$ is not always holding the largest $q¯(x)$ and/or the largest ηf for a conjugate heat transfer problem. The H/D has a positive impact on the ηf, namely the larger the H/D, the higher the ηf.

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