Spray Cooling Droplet Impingement Model

Abstract

Spray Cooling is one of the leading techniques proposed for rejection of high heat flux levels necessary in future aircraft and spacecraft electronics and weapons packages. Experimental research and computational CFD require significant amounts of time to setup and execute to completion. Therefore, a faster Monte Carlo based simulation has been proposed, in order to aid in the development of differing spray cooling conditions and applications. MATLAB has been used to model the surface impingement behavior of several hundred thousand spray droplets exiting a Spraying Systems FullJet 1/8-G spray nozzle. Previously measured Phase Doppler Anemometry measurements were used to match the droplet diameter and radial flux distributions of the simulation to actual spray conditions. Typical spray characteristics for the Spraying Systems nozzle are: a flow rate of 1.05x10 -s m 3 /s, a normal droplet velocity of 12 m/s, a droplet Sauter mean diameter of 48 m, and heat flux values ranging from 50-100 W/cm 2 . These spray conditions result in the following nondimensional parameters: We, 300-1350, Re, 750-3500, and Oh, 0.01-0.025. The simulation produces a surface map depicting different heat transfer regions present on the heater surface; these include: undisturbed thin liquid film, fresh liquid craters, boiling craters and dried out craters. A combination of flow boiling and liquid convection was used to calculate heat transfer values based on the distribution of liquid on the heater surface. For one assumed heater power and spray flow rate, the simulation produced a Nusselt number of 22.3, while experimental efforts produced a Nusselt number of 55.5 for the same heater power level and one spray flow rate.