EFFECT OF RIB ATTACK ANGLE ON HEAT TRANSFER AND FRICTION FACTOR IN A SQUARE CHANNEL ROUGHENED BY V SHAPED RIBS WITH A GAP

An experimental study was carried out to investigate the effect of angle of attack on forced convection heat transfer and friction factor of an artificially roughened duct. The test section of the square duct (AR=1) was roughened on its top and bottom wall with V shaped square ribs having a gap on its length. The ratio of the width to height of the duct (W/H) was 1, the relative roughness height (e/Dh) was 0.060, relative roughness pitch (p/e) was 10, relative gap width (g/e) was 1and relative gap position (d/W) was taken as 1/3. The rib attack angle (α) was varied from 300 to 750 . The air flow rate corresponded to Reynolds number (Re) was varied from 5,000 to 40,000. The comparison of heat transfer and pressure drop for various configurations is presented in the form of Nusselt Number and friction factor. The results show that there is significant effect on the Nusselt number and friction factor when the angle of attack has changed. As a result, the maximum enhancement of Nusselt number (Nu) and friction factor (f) were 4.7 and 8.1 times that of smooth duct, respectively. Maximum heat transfer enhancement was associated with ribs of angle of attack of 600 which also produces the maximum friction factor (pressure drop) penalty, in the range of parameters investigated. The thermo-hydraulic performance for all attack angles has also been considered and compared. The result shows that broken V shaped ribs with angle of attack of flow as 600 gave the best thermohydraulic performance of 2.6 times that of smooth duct.