Effect of liquid splattering on thermal performance of jets and sprays over plain and pillared surfaces

Abstract

A comparative study of liquid jet and spray is explored over plain and pillared copper surfaces with coolant flow (water) ranging over 3000 < Re < 10500, and heat fluxes up to the critical heat flux limit. Liquid jets and sprays are hydrodynamically characterized using high-speed videography and the phase-Doppler particle analyzer system. The interaction of liquid jets and sprays with the respective metallic substrates is experimentally investigated and strong liquid splattering is observed over the pillared surfaces at higher coolant flow rates. The resulting splattering mass fraction is measured over a range of coolant flow rates and radial positions of the nozzle. Subsequently, the effect of splattering on heat transfer performance is compared for various heat flux conditions by measuring the steady-state surface temperature. Heat transfer coefficient is found to be a strong function of coolant flow rate, operating heat flux conditions, and splattered mass fraction. Significant differences are not seen in these quantities between the liquid jet and spray for a plain surface. However, spray cooling clearly shows superior heat transfer enhancement over a liquid jet for a pillared surface where the critical heat flux limit is significantly delayed. The apparent advantages of heat transfer performance enhancement with patterning of surfaces are not always guaranteed, and the design consideration must address the coolant interaction with it to ensure a net advantage, which may get diminished due to liquid splattering induced by the interaction of the coolant with the patterned surface.