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.

Boiling Heat Transfer Characteristics of Vertical Water Jet Impinging on Horizontally Moving Hot Plate

“…22) The experimental method used here was similar to that in our past work 22) for the downward jet, so that a direct comparison of the cooling characteristics of the downward-and upward-impinging jets could be conducted. The test coolant was water at 17°C and the test solid was a thin stainless steel sheet.…”

“…Note that the point showing the "maximum heat flux" did not necessarily coincide with the center of the jet impact point. 22) Figure 4 shows the maximum heat flux under varying experimental conditions. The data for downward jets 22) are also plotted for reference.…”

“…22) Figure 4 shows the maximum heat flux under varying experimental conditions. The data for downward jets 22) are also plotted for reference. We discuss here the results for upward jets, and the results for the downward jets are considered in the subsection 3.4.…”

“…They reported that overall cooling efficiency improved in the case of the moving plate than the stationary one. Fujimoto et al [21][22][23] studied the hydrodynamics and the heat transfer characteristics of downward circular jets impinging on a hot moving stainless steel sheet by means of flash photography and thermography. The effects of varying jet velocity, and the moving velocity and temperature of the solid were investigated.…”

“…A comparison of the results for the upward-and downwardimpinging jets was carried out under the same impact velocity V i , and jet impact diameter d i . In our previous work, 22) the inner diameter of the pipe nozzle was d 0 = 5 mm and the nozzle-to-plate spacing was H = 40 mm. The mean jet velocity at the nozzle exit was set to 0.4, 0.8, and 1.2 m/s.…”