Experimental and Numerical Studies of Mist Cooling with Thin Evaporating Subcooled Liquid Films

Wetability;Saturated liquid films cooling;Subcooled liquid films cooling;Enhancement ratio;Heat transfer enhancement;Ultra thin liquid films;Evaporative cooling;Two-phase forced convection;Two-phase flow cooling;Electra laser;KRF lasers;High average power lasers;Spray mist cooling;Nozzle generated mist cooling;Dispersed flow

Novak, Vladimir ; Mechanical Engineering

University:Georgia Institute of Technology

Department:Mechanical Engineering

关键词: Wetability;    Saturated liquid films cooling;    Subcooled liquid films cooling;    Enhancement ratio;    Heat transfer enhancement;    Ultra thin liquid films;    Evaporative cooling;    Two-phase forced convection;    Two-phase flow cooling;    Electra laser;    KRF lasers;    High average power lasers;    Spray mist cooling;    Nozzle generated mist cooling;    Dispersed flow;   

Others  :  https://smartech.gatech.edu/bitstream/1853/10528/1/novak_vladimir_200605_phd.pdf

美国|英语

来源: SMARTech Repository

【 摘 要 】

An experimental and numerical investigation has been conducted to examine steady, internal, nozzle-generated, gas/liquid mist cooling in vertical channels with ultra-thin, evaporating subcooled liquid films. Interest in this research has been motivated by the need for a highly efficient cooling mechanism in high-power lasers for inertial fusion reactor applications. The aim is to quantify the effects of various operating and design parameters, viz. liquid atomization nozzle design (i.e. spray geometry, droplet size distribution, etc.), heat flux, liquid mass fraction, film thickness, carrier gas velocity, temperature, and humidity, injected liquid temperature, gas/liquid combinations, channel geometry, length, and wettability, and flow direction, on mist cooling effectiveness.A fully-instrumented experimental test facility has been designed and constructed. The facility includes three cylindrical and two rectangular electrically-heated test sections with different unheated entry lengths. Water is used as the mist liquid with air, or helium, as the carrier gas. Three types of mist generating nozzles with significantly different spray characteristics are used. Numerous experiments have been conducted; local heat transfer coefficients along the channels are obtained for a wide range of operating conditions. The data indicate that mist cooling can increase the heat transfer coefficient by more than an order of magnitude compared to forced convection using only the carrier gas. The data obtained in this investigation will allow designers of mist-cooled high heat flux engineering systems to predict their performance over a wide range of design and operating parameters.Comparison has been made between the data and predictions of a modified version of the KIVA-3V code, a mechanistic, three-dimensional computer program for internal, transient, dispersed two-phase flow applications. Good agreement has been obtained for downward mist flow at moderate heat fluxes; at high heat fluxes, the code underpredicts the local heat transfer coefficients and does not predict the onset of film rupture. For upward mist flow, the code underpredicts the local heat transfer coefficients and, contrary to experimental observations, predicts early dryout at the test section exit.