Experimental investigation of the effects of obstacles in a U-turn channel on heat transfer

The heat transfer enhancement of U-turn channel has been a topical subject for a number of years. This type of designis used on internal cooling of gas-turbine blades, internal cooling of high-speed rotary machine tools and electronic equipment cooling systems. This thesis experimentally investigated the local and averaged heat transfer characteristics in a U- turn channel with the different obstacles. In the experiments, the heating plate was made of stainless steel foil. The foil was electrically heated by means of a high current DC power supply to provide a constant heat flux surface. The heat transfer coefficient was measured by a IR camera positioned on the bottom of the heater assembly vertical to the channel. The local Nusselt number and friction coefficient changes at 5 different points of the return zone between the Reynolds number 4982-40358 were investigated. In this study, theree different obstacles were used. The U-turn channel had an aspect ratio (AR) of 1.0 and a hydraulic diameter (Dh) of 50 mm. The distance of these obstacles from the wall (c)-to- hydraulic diameter ratio (c/W) was fixed at 0, 0,2 and 0,4. According to the results, it was seen that there was a significant increase in heat transfer due to the effect of the obstacles in the U-turn section according to the smooth channel. Value of c/W = 0,4 is better than value of c/W = 0 and c/W = 0,2 for heat transfer. Also the pressure drop effects of all the for obstacles were almost similar.