Abstract
The article presents a mathematical study of fully developed periodic laminar flow visualization and heat transfer characteristics in an isothermal wall square-channel fitted with V-shaped baffles on one wall. The computations based on the finite volume method together with the SIMPLE algorithm have been performed. The investigation covers a range of Re based on the hydraulic diameter of the channel, Re = 100-1200. To create a pair of main streamwise vortex flows through the tested section, the V-baffles with the attack angle of 30° with the main flow direction are mounted in tandem and pointing downstream on the lower channel wall only. Effects of different baffle heights and pitches on heat transfer and pressure drop in the channel are examined and the results obtained are compared with smooth channel with no baffle. The numerical result shows that the presence of the V-baffle yields a significant heat transfer enhancement compared with the smooth channel. It is visible that the main vortex flows, a pair of streamwise twisted vortex (P-vortex) can induce impingement flows on the walls leading to a drastic increase in heat transfer rate over the channel. In addition, the increase in the baffle height leads to the rise in the heat transfer and pressure loss while that in the baffle pitch provides the opposite trend. The predicted results expose that the maximum thermal enhancement factors for the V-baffles with BR = 0.3, 0.3 and 0.4; and PR = 1, 1.5 and 2 are, respectively, about 2.44, 2.29 and 2.37 at higher Re.
Highlights
The use of ribs/baffles (Promvonge et al, 2012a; 2012b; Sriromreun et al, 2012) in duct or channel heat exchanger is one of the commonly used passive heat transfer enhancement strategies in single-phase internal flows
It is visible that the main vortex flows, a pair of streamwise twisted vortex (P-vortex) can induce impingement flows on the walls leading to a drastic increase in heat transfer rate over the channel
Numerical computations of laminar periodic flow and heat transfer characteristics in a square channel fitted with 30° V-baffle elements in tandem on the lower wall only are performed
Summary
The use of ribs/baffles (Promvonge et al, 2012a; 2012b; Sriromreun et al, 2012) in duct or channel heat exchanger is one of the commonly used passive heat transfer enhancement strategies in single-phase internal flows. Positioned ribs/baffles in the channels periodically can interrupt hydrodynamic and thermal boundary layers resulting in a greater increase of the heat transfer rate. Investigated on both experimentally and numerically for convection heat transfer in channels with different types of ribs. Karwa and Chitoshiya (2013) experimentally studied of thermo-hydraulic performance of a solar air heater with 60° V-down discrete rib roughness on the air flow side of the absorber plate. They found that the enhancement in the thermal efficiency due to the roughness on the absorber plate is found to be 12.5-20% depending on the air flow rate.
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