Heat transfer characteristics of a pipe-laminar jet impinging on a moving hot solid

Abstract

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.