Numerical analysis of cooling of a hot plate by an array of submerged microjets

The effect of a distance between a nozzle and hot plates on flow and heat transfer characteristics was investigated numerically for an array of submerged air microjets. Considered numerical model consisted of 16 microjets, arranged in the regular array of 44. The compressible steady state air flow, including turbulent effects, was model applying the SST k- turbulence model. Numerical simulator was developed in the ANSYS Workbench environment. During analyses the jet diameter-based Reynolds number and jet pitch to jet diameter ratio were equal to Red = 1100 and s/d = 31.25, respectively, while the distance between the nozzle and hot plates to jet diameter ratio was set to H/d = 3.125, 25 and 50. In terms of heat transfer, the best distance-to-jet diameter ratio was found to be H/d = 25. Increase of this ratio resulted in more uniform distribution of temperature and heat transfer coefficient on the hot surface and drop in cooling performance. The effect of lateral flow on adjacent jets was the most significant for H/d = 3.125 and decreased with rise in this ratio. NUMERICAL MODEL OF AN ARRAY OF SUBMERGED MICROJETS The considered geometry consisted of a space where the air jets which were generated in orifices were developed, impinged on the heater surface and then flow out through lateral openings – see Fig. 1. The nozzle plate consisted of 64 orifices of diameter and x and y pitches equal to d = 0.16 mm and sx = sy = 5 mm, respectively. It gave the jet pitch to jet diamter ratio of s/d = 31.25. In simulations only one fourth of the geometry presented in Fig. 1a was considered due to symmetry. The geometrical model with symmetry planes, orifices and air outlets is shown in Fig. 1b. (a) (b) FIGURE 1. Schematic of cooling system with the jet array: (a) sketch with dimensions and highlighted area considered in the modeling, (b) top view of the geometrical model of space between the nozzle and hot plates with boundary conditions Nozzle plate