Infrared camera-based analysis of heat flux distribution in film boiling of water flow over a moving steel sheet

Abstract

The film boiling of free-surface water flow over a moving hot steel sheet is a common occurrence in the run-out table (ROT) cooling process used in hot rolling mills in the steel industry. Engineers seek to optimize cooling operations, necessitating the comprehension of forced convective heat transfer characteristics between cooling water and hot steel sheets in the film-boiling regime. In this study, we developed an experimental methodology using an infrared camera to evaluate the heat flux distribution along a moving solid with a high spatial resolution. Specifically, a 0.5-mm-thick test sheet made of stainless steel was subjected to cooling by a water film flowing at 0.72 m/s. The surface heat flux was measured while varying the velocity of the test sheet (0.5, 1.0, and 1.5 m/s), temperature of the test sheet (450-590℃), and water temperature (30-60℃). The study revealed that the heat flux was highest in the region where the water first contacted with the moving solid and then decreased downstream. The peak values of the surface heat flux depended on the water temperature, but were almost independent of the moving velocity. We compared the results with the similarity solutions for single- and two-phase boundary layer theories to gain insights into the heat transfer mechanism and to discuss the effects of varying the examined parameters. In addition, we developed a correlation formula to predict the heat flux profile in the first contact region.