CRITICAL HEAT-FLUX LIMITS FOR A HEATED SURFACE IMPACTED BY A STREAM OF LIQUID DROPLETS

An experimental apparatus has been constructed to allow investigation of heat transfer from a horizontal, upward facing, heated surface impa cted by streams of monodisperse water droplets of varying size and imp act frequency. Droplet diameters between 2.3 and 3.8 mm were used, wit h drop frequencies varying from 2 to 15 droplets per second. The dropl et impact velocity was 1.3 m/s. Critical heat flux, surface superheat, droplet size, and frequency were the primary measured data. Heat flux es as high as 325 W/cm2 were achieved with wall superheats of only 24- degrees-C. The liquid film thickness produced upon droplet impact is s hown to be a key factor in these experiments, and the importance of in vestigating the wetted area is highlighted. The effectiveness of dropl et impact cooling using droplets with diameters on the order of millim eters is shown.