Transient Boiling Heat Transfer Characteristics of a Moving Hot Surface during Two-fluid Flat Spray Quenching
Hiroshi Niitani, Yuichi Mitsutake
In the hard cooling process of steel, heat flux and temperature fluctuations are so large due to the wetting that it is difficult to measure unsteady cooling phenomena. In this study, we experimentally analyzed the detailed heat transfer behavior of continuous casting secondary cooling of a moving system using the improved IHCP (Inverse heat conduction problem) analysis with the Laplace transform technique developed in the previous paper. The test piece was a SUS304 rotor with a thickness of 10 mm and an outer diameter of 136 mm, which was heated to 880°C, rotated at a peripheral speed of 0.9 to 8.0 m/min, and cooled from above with a flat air mist spray. Thermocouples were installed at two points 1.5 mm and 3.5 mm from the surface. As a result of the analysis, under the conditions of the film boiling region, the surface heat flux qw could be expressed as qw / qw,peak = (W / Wpeak)0.57 using the spray water flux W. However, after the start of wetting, cooling continued even on the downstream side in the moving direction where the water droplets did not collide directly. In the nucleate boiling region and the film boiling region, the average heat flux when passing through the spray did not change due to the change in casting speed. However, the wetting start temperature became higher as the casting speed becomes slower.
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