In this paper, a numerical investigation of air side performance of strip fin surface is presented. Three-dimensional numerical computation was made for a model of a two-row finned tube heat exchanger. The tube configuration is simulated with step-wise approximation, and the fin efficiency is also calculated with conjugated computation. Four types of fin surfaces were studied: A-the whole plain plate fin; B-the strip fin with strips located in the upstream part of the fin; C-the strip fin with strips located in the downstream part of the fin; and D-the strip fin with strips covering the whole fin surface. It is found that the strip fin with strips located in the downstream part of the fin surface (fin C) has higher heat transfer rate than that with strips in the upstream part (fin B) at the same conditions, while the pressure drop of fin C is a bit lower than that of fin B. A comprehensive performance comparison was conducted by using the goodness factor and the pumping power consumption per unit surface area. It is revealed that between the two strip fins the performance of fin C is better than fin B with same strip number. Detailed discussion is provided from the view point of synergy between velocity and temperature gradient. It is shown that the synergy between velocity and temperature field becomes worse in the downstream part of the fin surface, and it is this place that enhancement technique is highly needed. The strip location of fin C just fits this situation. The present numerical work provides useful information on where the enhancement element should be positioned.

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