Abstract
The cooling process of a hot steel plate by a cylindrical water flow was studied experimentally and analytically in this paper.
The cooling characteristics were examined on the basis of cooling curves obtained under various experimental conditions. A numerical model was built up to calculate the relation between temperature and time at a given point of the steel plate during cooling. Then, the heat transfer coefficient on the water cooling zone was found out so that the cooling curve calculated by the numerical model became equal to the experimental result.
The main results obtained in this paper are as follows:
(1) The heat transfer coefficient on the water cooling zone may be considered to be proportional to square root of the difference between the plate surface temperature and the water temperature; α ∝ (θs-θw)1/2 where, θs, θw: The temperature of the plate surface and the cooling water, respectively.
(2) The black zone is formed on the initially hot red plate surface, as soon as the water strikes the plate. The radius of the black zone expands approximately in proportion to square root of the cooling time.
(3) The theoretical cooling curves were found to match with the experimental ones by the appropriate combination of the heat transfer coefficient on the water cooling zone and the growth rate of the zone. Here, α=500 (θs-θw)1/2 as the heat transfer coefficient (kcal/m2h°C) and Rw=RB+10.0 as the water cooling radius (mm) were used in this calculation, where RB indicates the black zone radius.
