Experimental study on the heat transfer characteristics of a micro scale impinging jet

Abstract

Heat transfer to a single, axisymmetric impinging jet was studied using a thermal chip. The design and fabrication for the thermal chip with arrays of temperature sensors using diode and heaters is presented. The parameters varied in the testing were jet diameter (0.1mm, 0.2mm, 0.5mm and 1mm), Reynolds number (1000, 5000, 10000) and dimensionless jet-to-target spacing, H/d (2.5, 5, 7.5, 10, 20). The tests were performed using air as the working fluid. Results are presented in the form of local heat transfer coefficients as a function of dimensionless radial distance from the stagnation point, r/d. The local heat transfer coefficient calculations account for lateral conduction within the thermal chip, which, in contrast to conventional practice, has been shown to be non-negligible. Local heat transfer coefficients has been determined that (i) the Nusselt number attains its maximum value at H/d < 8, which is identical result as that of a macro scale, (ii) increasing the Reynolds number yields higher Nusselt number, as expected (iii) the smallest jet diameter yielded the largest heat transfer coefficient for a given Reynolds number.