Amnart Boonloi

Effect of flow attack angle of V-ribs vortex generators in a square duct on flow structure, heat transfer, and performance improvement

A numerical investigation has been carried out to examine the periodic laminar flow and heat transfer characteristics in a three-dimensional isothermal wall square duct with 20° inline V-ribs. The computations are based on the finite volume method, and the SIMPLE algorithm has been implemented. The fluid flow and heat transfer characteristics are presented for Reynolds numbers based on the hydraulic diameter of the square duct ranging from 100 to 2000. To generatemain streamwise vortex flows through the tested section, V-ribs with an attack angle of 20° are mounted in tandem with inline arrangement, pointing downstream (V-Downstream) and pointing upstream (V-Upstream) placed on both the upper and lower walls. Effects of different blockage ratio (b/H, BR)with a single pitch ratio (P/H, PR) of 1 on heat transfer, pressure loss, and performance in the ribbed tube are studied. Apparently in each of the main vortex flows, streamwise twisted vortex flows can induce impinging flows on the walls of the interbaffle cavity leading to drastic increase in heat transfer rate over the square duct. In addition, the rise in the V-baffle height results in the increase in the Nusselt number and friction factor values. The computational results show that the optimum thermal enhancement factor is about 4.2 at BR = 0.20 and 0.15 for the V-Downstream and V-Upstream, respectively.

Effect of Flow Attack Angle for V-Wavy Plate on Flow and Heat Transfer in a Square Channel Heat Exchanger

Effects of flow attack angles of the V-wavy plate on flow and heat transfer in a square channel heat exchanger are investigated numerically. The V-wavy plates with V-tips pointing downstream and upstream called V-Downstream and V-Upstream, respectively, are examined for the Reynolds number in the range of 3000–10,000. The finite volume method with SIMPLE algorithm is selected to solve the present problem. The numerical results are presented in terms of flow and heat transfer visualization. The thermal performance analysis is also concluded in the form of Nusselt number ratio (Nu/Nu0), friction factor ratio ( / ), and thermal enhancement factor (TEF). The numerical result shows that the wavy plate can induce the swirling flow through the test section for all cases. The swirling flow disturbs the thermal boundary layer on the channel wall which is the reason for heat transfer enhancement. In range studies, the heat transfer rate increases around 3–6.5 and 2.8–6 times above the smooth channel for V-Downstream and V-Upstream, respectively. The optimum TEF is found at = 20° and Re = 3000 to be around 2.09 for V-Upstream case.

Thermal Performance Analysis and Empirical Correlations for Laminar Forced Convection over 30° V-Baffled Square Channel

Thermal performance analysis for laminar forced convection in an isothermal wall square channel with 30° V-baffle is presented numerically. The parameters of the V-baffle, blockage ratio (b/H, BR), pitch ratio (P/H, PR), flow direction (V-Downstream and V-Upstream), and arrangement (in-line and staggered), are studied and compared with the previous works, 20° and 45° V-baffle. The Reynolds number based on the hydraulic diameter of the channel (D h ), Re = 100–2000, is used in range study. The results show that the flow configurations of 30° V-baffle are found similar as 20° and 45° V-baffle. The fully developed periodic flow and heat transfer are created around 7th-8th module, while the periodic flow and heat transfer profiles are found at 2nd module in all cases. Except for the periodic concept, the 30° V-baffle can help to reduce the pressure loss around 2.3 times in comparison with the 45° V-baffle at the maximum f/f0 value (BR = 0.3, PR = 1, V-Downstream). The optimum thermal enhancement factor for the 30° V-baffle is found around 4.25 at BR = 0.15, PR = 1, and Re = 2000 for V-Downstream case with in-line arrangement.

3D Simulation on Flow Behavior and Heat Transfer in a Circular Tube with Inclined Different Arrangement of Thin Rib

This work deals with periodic flow, friction loss and heat transfer characteristics in a constant temperature-surfaced circular tube fitted with rib vortex generators (RVG). The computations are based on the finite volume method with the SIMPLE algorithm implemented. The fluid flow and heat transfer behaviors are presented for Reynolds numbers ranging from 100 to 1000. To generate two main vortex flows through the tested section, the 45o RVGs are mounted repeatedly in in-line arrangements on the top and bottom walls and in the central area of the tested section. Effects of different RVG heights, BR in a range from 0.1D to 0.3D with a single pitch of 1.5D on heat transfer and friction losses in the test section are examined. It is apparent that the vortex flows created by the RVG exist and help to induce periodically impinging flows on a sidewall leading to drastic increase in the heat transfer rate over the test section. The computational results reveal that the optimum thermal performance is about 2.38 for using the RVG height of 0.2D for the RVG placed on the tube walls at the highest Re value.