EXPERIMENTAL INVESTIGATION ON HEAT TRANSFER AND FRICTION FACTOR CHARACTERISTICS OF A STATIONARY SQUARE DUCT ROUGHENED BY V AND Lambda-SHAPED RIBS

One of the traditional methods used to improve the efficiency of a gas turbine is to increases the inlet temperature; thereby increasing the power output and in turn, the efficiency. The internal cooling passages of blades are roughened by artificial roughness to improve the cooling performance. The present study investigates the convective heat transfer and friction factor (pressure drop) characteristics of a rib-roughened square duct. The test section of the duct is roughened on its top and bottom wall with V and Lambda-shaped square ribs. In the study, the Reynolds number (Re) varied from 10,000 to 40,000, the relative roughness height (e/D-h) is 0.060, relative roughness pitch (p/e) is 10 and rib attack angle (a) is taken as 450 and 600. The comparison of heat transfer and pressure drop for V and Lambda-shaped ribs is presented in the form of Nusselt Number and friction factor. The results show that the Nusselt number enhancement decreases when the Reynolds number increases. The friction factor ratio is found to increases as Reynolds number increases. The thermal performance decreases when the Reynolds number increases. It seems that the ribs disturb the main flow resulting in the recirculation and secondary flow near the ribbed wall. The heat transfer coefficient and friction factor for all the cases are higher than that of the smooth duct. The V-shaped ribs have higher Nusselt number and friction factor than the Lambda-shaped ribs. It is also concluded that the V-shaped ribs perform better than the Lambda-shaped ribs. Ribs with alpha = 60 degrees produces higher heat transfer and friction factor than alpha = 45 degrees. The results obtained in the study will help the turbine blade designer to design the effective cooling methods to cool the blades.