An experimental study on two-phase flashing R134a spray cooling performance with multiple nozzles

Low-boiling-point R134a spray cooling effectively reduces surface temperatures rapidly, with applications in chip cooling, automotive air conditioning, and laser biomedicine. Multiple nozzles have a larger spray coverage and liquid film spreading area compared to a single nozzle, allowing for enhanced convective and phase-change heat transfer, leading to large-area uniform cooling and flexible adjustment of cooling capacity. An experimental apparatus for cryogen spray cooling was set up to analyze the effects of various factors, including nozzle inner diameter, spray distance, spray pressure, spurt duration, and cooling substrate, on the surface heat transfer characteristics. The results indicate that the lowest surface temperature is primarily influenced by the nozzle inner diameter and spray distance, while the peak heat flux is mainly affected by the spray distance and the cooling substrate. The heat flux with copper surface is ∼38 times that of an epoxy resin block (qmax = 8179.94 kW/m2). Nozzle diameter has the most significant impact on the uniformity of surface cooling, whereas spray pressure and duration have the weakest effects on surface heat transfer characteristics. When the cooling substrate is an epoxy resin block, appropriate spray conditions (Nozzle diameter D = 0.4 mm, spray pressure P = 1.9 MPa, spray distance H = 10 mm, and spurt duration ts= 50 ms) allow droplets to fully atomize and distribute reasonably across the surface, achieving the lowest cooling temperature (Tmin = −40.13 °C) and the highest heat flux (qmax = 217.76 kW/m2) as well as realizing a longer effective cooling time.