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Title:Heat transfer during spray water cooling using steady experiments
Author(s):Zhou, Xiaoxu
Advisor(s):Thomas, Brian G.
Department / Program:Nuclear, Plasma, & Rad Engr
Discipline:Nuclear Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Spray cooling
Heat transfer
Induction heating
Spray heat transfer coefficient
Abstract:Spray water cooling is widely used in many industrial processes to control heat removal from a hot material surface. In order to control heat transfer rates and obtain desired surface temperature distributions, a deeper understanding of fundamental spray cooling dynamics and more accurate estimation of spray heat transfer rates is needed. In this thesis, a new technique combining experiment and computational modeling has been developed for measuring the steady-state heat transfer extracted locally by water sprays or air-mists impinging on the surface of a hot metallic sample. The experimental apparatus was developed by A. C. Hernandez B., H. Castillejos E, and F. A. Acosta Gat CINVESTAV, Mexico, and is designed to be able to employ spray water to cool the metallic sample accommodated inside a copper coil with an alternating current as induction heating goes on inside the sample. Control of total input power from the wall maintains each desired sample thermocouple temperature. A computational model developed using the commercial finite-element package COMSOL Mutiphysics uses a two-dimensional axisymmetric model of the electromagnetics and heat-conduction equations to balance the heat extracted from the sample surface by the boiling water droplets. Measurement of the RMS current flowing through the copper coil enables the model to estimate the heat extracted to the cooling spray by matching the sample thermocouple temperature measurement. Heat transfer coefficients and fluxes are quantified for spray cooling of a platinum sample at temperatures ranging from 100-1200C, using typical air-mist nozzles and conditions relevant to steel continuous casting, and also compared with transient measurement results of spray cooling and Nozaki empirical correlation. The results reveal the flexibility of the technique to investigate different aspects of spray cooling. The spray heat transfer coefficients extracted range from 1 kW/m2K to 27kW/m2K, and heat fluxes rang from 0.5MW/m2 to 5MW/m2 as the sample surface temperature varies from 80oC to 1185oC Heat removal hysteresis exists during the spray heating-cooling cycle. The Leidenfrost temperature is found to be around at 850oC.
Issue Date:2010-01-06
Rights Information:Copyright 2009 Xiaoxu Zhou
Date Available in IDEALS:2010-01-06
Date Deposited:2009-12

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