Experimental investigation on heat transfer of HEMJ type divertor with narrow gap between nozzle and impingement surface

摘要

In order to explore the possibility of improvement of the He-cooled modular divertor with multiple jet cooling (HEMJ) concept including optimization of design parameter, an experimental study on heat transfer performance of the HEMJ divertor was performed by means of helium loop at Georgia Tech, in which the pressure, flow rate and temperature of helium pressure is up to 10 MPa, 8 g/s and 300 degrees C, respectively, under heat flux of 6 MW/m(2) loaded by means of induction heater. Although the non-dimensional distance between jet nozzle and impingement surface H normalized by typical nozzle diameter D, HID is 0.9 in the reference design of HEMJ, heat transfer experiments were carried out under the condition of HID = 0.5 and 0.25 to enhance the heat transfer performance. In the case of HID = 0.25, the averaged Nusselt number was increased by about 20% from the value for HID = 0.5 in the case that the jet temperature less than 100 degrees C. By contraries, the averaged Nusselt number was decreased with increase in jet temperature which is larger than 200 degrees C in the HID = 0.25 case. It is expected that the degradation of heat transfer performance with increasing the jet temperature is caused by the re-laminarization occurred near heat transfer surface. (C) 2015 Elsevier B.V. All rights reserved.