Multi-nozzle spray cooling for high heat flux applications in a closed loop system

A modified R134a closed loop spray cooling system is used to investigate the spray cooling thermal performance of a multi-nozzle plate. The nozzle plate consists of six jet-swirl nozzles, covering a sprayed area of 1 × 2 cm². The nozzles are customized in the 1.9 mm thick nozzle plate, so that they are flushed with the plate surface. The spray height from the plate to the impact area of 8.8 mm is determined by the spray angle and coverage area. Power input to the heater copper block was set to obtain a heat flux variation from 35 to 165 W/cm². The differential pressure across the nozzle plate ranged from 3.87 to 4.74 bar. Temperatures at a particular heat flux, under steady state conditions, were collected over a range of flow rates for analysis on the thermal performance of spray cooling using the multi-nozzle plate. The highest heat transfer coefficient of 39,000 W/m² K was observed at heat flux of 145 W/cm² with a surface temperature of 48 °C. The incidence of critical heat flux can be observed when the power input causes the heat flux to reach above 165 W/cm². A generalized correlation is developed for the dimensionless heat flux as a function of dimensionless mass flow rate, and wall superheat degree, along with the Weber number and the Jacob number.

► Self-designed multi-nozzle plate for spray cooling in a closed loop system.
► R134a refrigeration closed loop system was utilised for the test setup.
► Spray cooling heat transfer characteristic can be classified into 2 regions.
► Observation of critical heat flux at heat flux above 165 W/cm2.
► A generalized dimensionless heat flux correlation has been developed.