This study experimentally investigated the hydrodynamics and heat transfer characteristics of a circular water jet impinging on a moving hot metal sheet as fundamental research on pipe-laminar cooling. The circular jet was issued from a 5-mm-diameter pipe nozzle. A 0.3-mm-thick sheet made of stainless steel was adopted as the test sheet. In the experiment, the liquid flow formed by the jet impingement was observed by flash photography, and the temperature profile on the underside of the moving sheet was measured by infrared thermography. The initial temperature of the moving solid was varied from 100°C to 500°C. The mean velocity at the nozzle exit ranged between 0.4 m/s and 1.2 m/s. The moving velocity of the solid was set to less than or equal to 1.5 m/s. The estimated heat flux profile on the cooled surface was found to be strongly dependent on the initial temperature of the sheet. When the initial temperature of the sheet was relatively low, a bow-shaped high heat flux region appeared in the upstream of the jet impact point. At higher temperatures, the heat flux area existed only in the jet impact regions. The heat flux increased with increasing initial sheet temperature, reached peak values, and then decreased drastically. The sharp decrease in the heat flux, which was due to the formation of a vapor layer, was influenced by the jet velocity and/or the sheet velocity.
The heat transfer characteristics of a circular water jet impinging on a moving hot solid were investigated experimentally. In the experiments, distilled water at room temperature was used as the test coolant. The circular jet issued from a 5-mm-diameter pipe nozzle, fell vertically downward, and impinged on a horizontal moving sheet made of 0.3-mm-thick stainless steel. The initial temperature of the sheet, the jet velocity, and the moving sheet velocity were varied systematically. The initial temperature of the moving sheet was set to 100, 150, 200, or 250°C. The mean velocity at the nozzle exit was 0.4, 0.8, or 1.2 m/s, and the moving velocity was 0.5, 1.0, or 1.5 m/s. Observations made using flash photography and thermography showed that the location of the front edge of the liquid film formed upstream of the jet impact point depends on all of these factors. The local heat flux is very small in the dry area, increases steeply near the front edge of the liquid film, and reaches a peak. If the distance between the front edge of the liquid and the jet impact point is relatively large, a second peak appears near the jet impact point. An experimental correlation was developed for predicting peak heat fluxes near the front edge of the liquid, although it has no theoretical background. The correlation agrees moderately well with the experiments.
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