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A study of boiling heat transfer on a hot steel plate cooled by an inclined circular bottom water jet Chester, Noel Leslie

Abstract

Controlled cooling on the runout table is a crucial component in the production of advanced high strength steels since there is a direct correlation between the cooling path experienced by the steel and its final mechanical properties. Recent trends are towards enhanced cooling of the steel so that complex dual phase microstructures can be obtained. Cooling of the steel on the runout table is usually achieved via impinging water jets on both the top and bottom of the strip, which can lead to significant heat transfer enhancement. The purpose of this study is to develop a fundamental understanding of bottom jet impingement cooling of hot steel plates. Specifically, this research has focused on the role bottom jet nozzle inclination angle and water flow rate have on the effectiveness of heat extraction on a hot steel plate. The methodology undertaken for this research involved carrying out experiments using a pilot scale runout table with both stationary and moving plates. Volumetric flow rates, strip speeds, and inclination angles were in the range of 35- 55 l/min, 0-1 m/s, and 10-30°, respectively. Experimentally, each plate was instrumented with numerous sub-surface thermocouples installed approximately 1 mm from the impingement surface. Temperature measurements were taken at the impingement point and several streamwise distances from the impingement point in all directions. Using the above measurements in conjunction with an Inverse Heat Conduction (IHC) model allowed the calculation of boiling curves or heat fluxes as a function of plate surface temperature and time. From the above measurements, transient cooling data on the hot steel plate by bottom jet impingement has been analysed.

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