Numerical investigation of heat transfer using impinging jets on ribbed roughened walls

Due to their high heat and mass transfer properties impinging jets have been used in various applications. In this study, the heat transfer and flow of impinging jets was examined numerically using PHOENICS package programme on triangular, square and trapezoidal ribbed surfaces. Investigation was carried out using circular nozzles with a 7x3 rectangular array for Re=3000-10000, H/d=2-8 and dimensionless rib heigth d/e=1.5-3.0. Also examined was the effect of two diffent rib arrangement on heat transfer, where nozzles were directed on ribs, and nozzles were directed between two ribs. In addition, resolutions for smooth surfaces were made for comparison with ribbed surfaces. Low Re number k-? turbulence model has been used during investigations.Firstly, the effect of Re number, H/d and d/e on local Nu number was examined for all rib geometries. In general, it was observed that heat transfer increases with increase in Re number. In addition, it was found that with increase in Re number, difference between maximum and minimum heat transfer has increased. The lowest and highest local heat transfer for all rib geometries was seen when H/d=8 and H/d=4-6, respectively. In general, it has been observed that the rib height had no effect both on local and average heat transfer.Finally, effect of rib arrangement and rib geometry on heat transfer under impinging jets was examined with both local and average Nusselt numbers. Especially at high Re numbers and all H/d values it was oberseved that higher average Nusselt numbers are obtained when the ribs were arranged between two nozzles.