Experimental investigation of droplet dynamics and heat transfer in spray cooling

Experimental investigation on droplet dynamics and heat transfer in spray cooling was conducted. Water and water solutions with different surfactant additions (sodium dodecyl sulfate) were used to cool a 10 mm in diameter, horizontal copper surface. A multi-nozzle spray system was constructed for studying the effects of mass flux on spray cooling. This multi-nozzle system provides a variable mass flux spray from 0.156 to 1.20 kg/m(2) s with a diameter and velocity variation less than 20%. The incoming and outgoing droplets were characterized in situ with a newly developed laser phase-Doppler anemometry (PDA). It was found that, the heat transfer process in spray cooling can be divided into four regimes using the expulsion rate defined as the ratio of local outgoing to incoming mass fluxes. The advantage of the surfactant addition in spray cooling has also been investigated. Besides adding surfactant results in relative small diameters for both impinging and expulsing droplets, the slope of the droplet expulsion rate at the transition to the critical heat flux (CHF) regime also changes sharply with surfactant addition which results in a almost constant heat removal rate near the CHF regime. This character may provide an additional safety mechanism for a heat transfer device to avoid burnout. (C) 2003 Elsevier Inc. All rights reserved.