การเพิ่มการถ่ายเทความร้อนบนพื้นผิวของกลุ่มเจ็ทพุ่งชนโดยติดตั้งปลอกท่อเหนี่ยวนำอากาศ

Abstract

Recently, jet impingement has been studied by many researchers especially focusing on heat enhancement on an impingement surface. In previous work, mounting an expansion pipe or an air-induced duct at nozzle exit can enhance heat transfer on the target surface. However, a single impinging jet was only focused. Therefore, the purpose of this research is to investigate the effects of mounting air-induced ducts on flow and heat transfer characteristics of impinging jet array. Jets discharging from pipe nozzle with fully developed flow impinged normally on the target surface for cooling. Pipe nozzles having d=17.2 mm of diameter were arranged in 5 rows x 5 columns with an in-line configuration, and air-induced ducts were mounted at the end of each nozzle. The parameters studied were varied including: (1) the length of air-induced duct (L) at L/d=2, 4, 6 and (2) the inner diameter of an air-induced duct (D) at D/d=2, 4, 6, (3) the jet-to-plate distance (H) at H/d=2, 4, 6, 8, (4) the jet-to-jet distance (S) at S/d=4, 6, 8, and (5) Reynolds number of the jets at Re=10,000, 20,000, 30,000 and 40,000. The conventional impinging jets were also performed with the same mass flow rate for benchmarking. The temperature distributions on the impingement surface were measured by using an infrared camera for evaluating heat transfer coefficient. Flow characteristics were simulated using computational fluid dynamics (CFD) with V-f turbulence model. Results showed that the ambient air was induced into the air-induced duct. An entrainment of induced air became greater when the duct was longer, and the entrainment area was expanded when the diameter of the duct was enlarged. This influenced on a heat transfer enhancement of impinging jets with mounting air-induced duct which was greater than the case of conventional impinging jets, especially at the condition of the narrow jet-to-jet distance and the large jet-to-plate distance. Finally, the heat transfer correlation of the impinging jet array mounting air-induced duct was performed under the parameter studied