TURBULENT FLOW CHARACTERISTICS AROUND THREE DIMENSIONAL RIBS FOR ENHANCEMENT OF HEAT TRANSFER.

The study deals with the flow characteristics around one of the ribbings on the inside wall which simulates a model of shell-and-tube heat exchanger tube. The rhombic shape ribs were staggered on the wall. The ribbed plates were set on both top and bottom sides of rectangular duct. Reynolds numbers, which based on the average air velocity in the duct and hydraulic diameter, were set at Re equals 1. 0 multiplied by 10**4 and Re equals 3. 0 multiplied by 10**4. Two component velocities, turbulence intensities, and cross correlations of two component velocity fluctuations were measured by a new developed compact two color four beam Fiber LDV probe for the evaluation of turbulent mixing. The results of the detailed flow measurement indicate that the recirculating region behind the rib is reduced with increasing Reynolds number due to increase in the rate of the flow passing by the side of the ribs. Turbulent kinematic energy on the near-wall region behind the rib has a larger value at a lower Reynolds number. A remarkable large peak value of Reynolds shear stress is observed behind the rib at a lower Reynolds number. The characteristics of turbulent flow are well correlated to the tendency of heat transfer enhancement at a lower Reynolds number.