NUMERICAL MODELLING OF FLUID FLOW AND HEAT TRANSFER ACROSS TUBE BANKS

Abstract

1-Jeat transfer across tube banks finds common in industries. It is used to draw off heat from nuclear reactor using coolant and also extensively used across all industries. There are tubes with various cross-sections have been used in heat exchangers, such as circular, elliptical, square and oval. In the present study the hydrodynamics and heat transfer characteristics around tube with elliptical cross-section have been predicted using control volume finite difference method (CVFDM). The present study aims to find out the effect of longitudinal pitch, axis ratio and angle of attack ((x) on the pipe on the heat transfer and flow characteristics. The heat transfer characteristic of cylindrical pipe and elliptical tube was also studied. Reynolds number was defined using diameter and major axis in case of elliptical tube. The elliptical tube was subjected to two different angles of attacks (00 and 900). The present numerical predictions for heat transfer and pressure drop have been first validated with the experimental findings of Ota et al. (1983), where a single elliptical tube was used and air was used as a flowing fluid. The simulations were carried out at different Reynolds number and validated with the experimental work of Ota et al. (1983). The heat transfer from elliptical tube is higher as compared to the circular tube. It was found that heat transfer of elliptical tube when subjected to a = 900, gives higher heat transfer as compared to the elliptical tube with a = 00 and circular tube. Further, it is found that the heat transfer depend upon longitudinal pitch, but up to certain fixed point and that comes out to be 2.5 times the major axis or diameter of circular and elliptical tube respectively. The pressure drop in case of elliptical tube at 90° is higher than that of elliptical tube at 0°. This is because the - separation point gets deferred to downstream of the flow, and less vorticity occurs. Laminar boundary layer develops on the upstream side of the pipe, no matters how much Reynolds number is there.