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.
Highlights
The required for more efficient and performance improvement of heat exchanger had been done by increase heat transfer rate with turbulators or vortex generators
Considering at the lower part of a pair of vortex flow, it can be concluded that the V-Upstream case produces two counter-vortex flows having a rotating direction down to the tube wall, called “common-flow-down” while the VDownstream gives opposite rotating flow direction, called “common-flow-up”
Developed periodic laminar flow configurations and heat transfer characteristics in a circular tube fitted with 45° V-Downstream and V-Upstream discrete baffle elements in tandem, in-line arrangements placed on a plate that inserted in the middle of the tested tube have been investigated numerically:
Summary
The required for more efficient and performance improvement of heat exchanger had been done by increase heat transfer rate with turbulators or vortex generators. Were installed into a tube or channel of heat exchanger to increase higher level of turbulence vortex flow and increase degree of impinging jet flow over the walls of the channel. The impinging jet of flow in a heat exchange system can be augmented heat transfer rate and increase in pressure loss. Array of V-shaped baffle were used to insert into the channel or tube in heat exchanger to create impinging jet on the wall leads to the increase in heat transfer rate and efficiencies. The Higher of Blockage Ratio (b/H, BR) of V-baffle give the highest heat transfer rate and provide very enlarge pressure loss. The results showed that the rise of PR leads to the decrease on both pressure loss and heat transfer. Han and Zhang (1992)
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