Experimental Heat Transfer and Friction in Channels Roughened With Angled, V-Shaped and Discrete Ribs on Two Opposite Walls

Abstract

Experimental investigations have shown that the enhancement in heat transfer coefficients for air flow in a channel roughened with angled ribs is on the average higher than that roughened with 90° ribs of the same geometry. Secondary flows generated by the angled ribs are believed to be responsible for these higher heat transfer coefficients. These secondary flows also create a spanwise variation in heat transfer coefficient on the roughened wall with high levels of heat transfer coefficient at one end of the rib and low levels at the other end. In an effort to basically double the area of high heat transfer coefficients, the angled rib is broken at the center to form a V-shape rib and tests are conducted to investigate the resulting heat transfer coefficients and friction factors. Three different square rib geometries, corresponding to blockage ratios of 0.083, 0.125 and 0.167, with a fixed pitch-to-height ratio of 10, mounted on two opposite walls of a square channel in a staggered configuration are tested in a stationary channel for 5000 < Re < 30000. Heat transfer coefficients, friction factors and thermal performances are compared with those of 90°, 45° and discrete angled ribs. The V-shape ribs are tested for both pointing upstream and downstream of the main flow. Test results show that: a) 90° ribs represent the lowest thermal performance, based on the same pumping power, and is essentially the same for the 2:1 change in blockage ratio, b) low blockage ratio (e/Dh =0.083) V-shape ribs pointing downstream produced the highest heat transfer enhancement and friction factors. Amongst all other geometries with blockage ratios of 0.125 and 0.167, 45° ribs showed the highest heat transfer enhancements with friction factors less than those of V-shape ribs, c) thermal performance of 45° ribs and the lowest blockage discrete ribs are among the highest of the geometries tested in this investigation, and, d) discrete angled ribs, although inferior to 45° and V-shape ribs, produce much higher heat transfer coefficients and lower friction factors compared to 90° ribs.

Numerical study on overall thermal performance in SAH duct with compound roughness of V-shaped ribs and dimples

“…It therefore attained a maximum at a flow attack angle of about 55°. The values of thermo-hydraulic performance parameter determined for the shape of V-shaped ribs combined with dimple ribs have been compared with the values determined for dimple rib shape 23) , V-down rib shape 20) and V-down pattern rib shape. 22) Fig.9 shows the V-shaped ribs combined with dimple ribs shape results in best thermo-hydraulic performance among all the geometries investigated.…”

“…[12][13][14][15][16][17][18][19][20][21][22][23] Taslim et al 20) presented the effect of V-shaped rib roughness with variation of relative rib height, relative rib pitch and flow attack angle on heat transfer and friction factor in a flow through SAH duct. They reported that the V-shaped rib showed higher performance compared to the angled rib.…”

CFD Analysis on the Thermal Hydraulic Performance of an SAH Duct with Multi V-Shape Roughened Ribs

“…Other investigations explored the effect of continuous ribs in various arrangements such as: angled rib [6], V-rib [9,10], discrete V-rib [11][12][13][14][15], multi V-rib [16] and arc-shaped rib [17]. Use of inclined ribs resulted in the improvement of heat transfer as compared to the transverse ribs.…”

“…It was suggested that inclination of the ribs resulted in the generation of secondary flow by the movement of counter-rotating vortices between two consecutive parallel ribs [6], which swept the floor between two ribs, resulting in the increase of heat transfer from the leading end region, whereas a trailing end region produced lower heat transfer coefficients due to accumulation of hot fluid. V-shaped ribs were believed to improve the span-wise distribution of heat transfer by doubling the counter-rotating secondary flow regions [11][12][13][14][15]. Multi V-shaped ribs further improved the thermal performance due to the increase in the density of counter-rotating secondary flow vortices [16].…”

“…This high heat transfer region can be enlarged by breaking a long angled rib into two half-ribs in a V-shape to form two leading ends and a single trailing end (the apex of V facing downstream). Thus, the heat transfer can possibly be further enhanced by using V-shaped ribs [9][10][11].…”