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An investigation of heat transfer in spray cooling

University of British Columbia

Spray water fluxes .and heat-transfer coefficients have been measured for some commercial spray nozzles, with a view to generating reliable and accurate data for the design of spray chambers of continuous casting machines. Sprays produced by both full cone and vee-jet nozzles have been investigated. The distribution of water in the sprays has been measured for different spray pressures and distances from the nozzle, by measuring the amount of water arriving at collector tubes inserted in the sprays. Thermocouples embedded in a heated stainless 'heat transfer probe' allowed the temperature transients within the probe to be measured during the spray cooling of these probes. Analysis of these transients by a solution to the 'Inverse Boundary Value Problem' allowed the calculation of the heat-transfer coefficients and surface heat fluxes as a function of the surface temperature of the cooled surface of the probe The results of this investigation indicate that the most important variable affecting the heat-transfer coefficient is the local water, flux at the cooled surface. The coefficients have also been determined to be temperature sensitive even at surface temperatures in excess of 800 °C. For the same value of water flux, neither the nozzle type nor the spray pressure has a strong influence on the heat-transfer coefficients. Correlations of the form [equation not included] have been obtained between the heat-transfer coefficients and spray water fluxes for different surface temperatures The for of the correlation obtained when the effect of surface temperature between 800 and 1000°C was included is [equation not included] where p(3) is negative. This showed that the operating boiling process in the present spray cooling experiments was unstable film boiling, causing scatter in the data.

Text

2010-03-29

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http://hdl.handle.net/2429/22968

Materials Engineering

University of British Columbia

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