Experimental Research on the Cooling Characteristics by Swirling Impinging Jet from a Nozzle with Internal Thread

To achieve high-efficiency cooling performance and good uniformity of impinging jet, a new type of nozzle structure is proposed. The new nozzle has four circumferential spiral channels symmetrically distributed inside a normal smooth nozzle, similar to an internal threads. The influences of this nozzle on heat transfer characteristics of impinged surface under different helix angles(0°, 15°, 30°, 45°), Reynolds numbers (6 000-30 000) and impact distances (1 to 8 times the equivalent diameter) were studied experimentally. And the heat transfer rule of the impinged surface was revealed. The experimental results indicate that a big helix angle can enhance slightly the heat transfer coefficient on the impinged surface. Compared with the conventional impinging jet from the smooth circular hole and the hole with four straight channels, the swirling impinging jets from the designed nozzles are effective to enhance the overall heat transfer coefficient on the impinged surface under the same conditions. At the impact distances of 2 times and 4 times the equivalent diameter, Nusselt numbers of the 45-degree thread hole are 7.4% and 11.4% higher than that of conventional impinging jet at the stagnation area, respectively. The heat transfer coefficient on the impinged surface is non-linearly increased with the increase of Reynolds number. The maximal value of Nusselt number under a relative large Reynolds number occurs at the location of 0.7 times the equivalent diameter outside the stagnation point. With the increase of the impact distance, the effect of the swirling flow on the target surface heat transfer is weakened or even disappeared. © 2018, Editorial Office of Journal of Xi'an Jiaotong University. All right reserved.