Optimally staggered arrangement of longitudinally finned flat tubes in laminar forced convection

Abstract

Through Constructal Design, this work investigates the impact of the downstream fin length of longitudinally finned flat tubes in maximizing the heat transfer density and minimizing pressure drop under external laminar forced convection flow.  The flow is assumed to be two-dimensional, steady, and incompressible; a constant Prandtl number defines thermophysical properties. The flow arises due to a pressure drop expressed in the Bejan number. The conservation equations are solved numerically by the finite volume method (FVM) using a commercial CFD package (ANSYS 2021/R2). The range of the longitudinal pitch-to-diameter ratio (SL/D) is considered of 4.0, ST/DT=3.0, θds=0.52, Lu/DT=0.8, and  0.4≤ Ld/DT ≤ 1. Reynolds numbers vary within the range of 200≤Re ≤ 1200 for each downstream fin length. An analysis was conducted on the temperature and velocity contours. The results indicate that the relative gain in the dimensionless overall heat transfer rate, Nusselt number, dimensionless pressure drops, Bejgan number, thermal-hydraulic performance factor, and horsepower is about 15%, 13%, 55%, 74%, 72%and 65%, respectively. Finally, it is concluded that the system with the highest fin length has the highest overall performance of the heat exchanger.