Flow boiling characteristics in expanding type structured heat sinks for different roles of gravitational force

Abstract

The orientation of the devices that must be cooled can change depending on the application requirements. Orientation-based variations can influence the physical mechanism regarding the coolers. Therefore, here, saturated flow boiling in the structured (expanding micro pin-finned with staggered array) micro heat sink is investigated under different angles. Positive and negative orientation of the heat sink have influence on the possible contribution of the gravitational effects. Experimental range includes three angular positions (+30°, 0°, -30°), two mass velocities (G=105 and 210 kg m-2 s-1) and a large heat flux interval (194 - 366 kW m-2). Inlet and ambient temperatures are constant at approximately Ti = 73°C and Ta = 24°C, respectively. It is concluded that optimum thermal performance is got for the horizontal orientation (0°) for both the mass flux values. The wetting process as well as balance of the gravitational force (related to liquid flow) and buoyancy force (related to the vapor flow) plays a key role on the thermal performance. Both the relevant forces are related to inclination angle. The pressure drop at the condition of ϕ = 0° is relatively higher than those of the others (ϕ = +30° and -30°).