A study on heat transfer characteristics by impinging jet with several velocities distribution

Impinging jet is well known as the most effective cooling method of a heated surface, since it has a high heat transfer coefficient. In this paper, the heated plate surface is going to be cooled by impinging jet through the heat transfer coefficient enhancement. An air flow with several patterns of velocities is suitable for rapid cooling. Therefore, this method is treated as cooling of thermal systems.The objective of this research consists of improving the heat transfer by air jet flow at proper velocity and adequate distances of collision in order to ensure efficient cooling.In this paper, the measurement of velocity distribution by pitot tube is going to be investigated, the flow visualization by high speed camera and finally the heat transfer characteristics on the heated surface by the impinging jet when changing the distance to the collision plate X/D and the air flow velocities distributions. The experimental results indicate that, the collisions distances X/D = 4, 7 and 9 at velocity 15 m/s compare to others values have the highest heat transfer coefficient rate

Augmentation of Heat Transfer in a Tube with a Blade Wheel at Inlet

This paper shows how the heat-transfer coefficients along heated tubes are affected by the clearance against the tube wall, the inlet angle and the widths of various types of blade wheels which are propelled by an internal flow in a circular tube and inserted at the inlet in order to augment heat transfer along the tube. The maximum and averaged heat-transfer coefficients in the region from blade position to far downstream were 3.0 and 2.2 times those in smooth duct respectively, for air ranging in Reynolds number from 15000 to 60000. Moreover, the performance evaluation was carrid out under the condition of fixed pumping power, and it was found that the performace ratio depends more on the inlet angle and the width of the blde than clearence, and the ratio is larger than one