Influence of Flow Direction on Vortex Flow Structure, Heat Transfer and Performance Improvement in Tube with V-Discreted Baffles

Abstract

Nowadays, the compact heat exchanger is used widely like a radiator, evaporator and condenser of air condition system, cooling device of electronic. Extensive studies have been done on the heat transfer characteristics and flow structure for the heat exchanger with longitudinal vortex generators by numerical method. Periodic laminar flow and heat transfer characteristics in a three-Dimensional (3D) isothermal circular tube wall with 45° in-line V-discrete baffles were investigated numerically. The computations are based on the Finite Volume Method (FVM) and the SIMPLE algorithm has been implemented. The fluid flow and heat transfer characteristics are shown for Reynolds numbers based on the diameter of the tube, Re = 100 to 1200. To generate main longitudinal vortices flows through the tested section, V-discrete baffles with an attack angle of 45° are mounted in tandem with in-line arrangement, pointing downstream (V-Downstream) and pointing upstream (V-Upstream) inserted in the middle of the tested circular tube. Effects of Different Blockage Ratio (b/D, BR) with a single Pitch Ratio (P/D, PR) of 1 on heat transfer and pressure loss in the circular tube are studied. It is apparent that in each of the main vortex flows, longitudinal twisted vortex flows can induce impinging flows on a wall of the inter baffle cavity leading to a drastic increase in heat transfer rate over the circular tube. In addition, the rise in the V-baffle height results in the increase in the Nusselt number and friction factor values. The flow structures, common-flow-up and common-flow-down are appeared by using a baffle with V-Downstream and V-Upstream, respectively. The computational results show that the optimum thermal enhancement factor is around 2.75 at BR = 0.10, Re = 1200 for V-Upstream discrete baffle.