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A software to simulate the solidification, heat transfer and water flowrate distribution in slab continuous casting was developed by establishing a mathematical model for the heat transfer and solidification in medium thickness slab casting. This model was validated by pin shooting and surface temperature measurement experiments. A reasonable target surface control temperature was found by testing the high temperature mechanical properties of Nb bearing ship plate steel, and then the water flowrate of each loop of the secondary cooling zone was determined by the software. The influence of uneven secondary cooling in the slab width direction on the quality of the slab was also investigated, which provided data for the optimisation of the secondary cooling of the slab caster. On the basis of the above research, an optimisation scheme for a secondary cooling system was proposed. Experimental results showed that the quality of the slab was significantly improved after optimisation. The centreline macrosegregation was reduced, and the ratio of equiaxed grains was increased by 3?18%. In addition, the transverse cracking of the slab was almost eliminated. List of symbolsa, b constant (a is 15?8847, and b is 0?011495) c specific heat capacity of steel, J kg 21 uC 21 c s , c l , c sl specific heats of solid steel, liquid steel and steel in the mushy zone, J kg 21 uC 21 c w specific heat capacity of water, J kg 21 uC 21 E elastic modulus, GPa f s solid phase fraction g gravity constant (9?8 N kg 21 ) h heat transfer coefficient, W m 22 uC 21 h w , h n complex heat transfer coefficients on the broad and narrow surfaces of slab, W m 22 uC 21 H the distance between meniscus and force bearing point, m L f latent heat, J kg 21 L m effective length of mould, m L the distance between meniscus and microunit, m q heat flux, W m 22 -q average surface heat flux, W m 22 Q m water flowrate of mould, kg s 21 S eff effective cooling region of mould, m 2 t temperature, uC t b , t w , t e temperatures of strand surface, cooling water and environment, uC T l , T s liquidus and solidus of steel, uC v casting speed, m min 21 W the flux of cooling water, L m 22 s 21 DP ferrostatic pressure, N m 22 DT w temperature difference between inlet and outlet water of mould, uC Dx, Dy mesh size of slab in its width and length directions (8 and 4 mm in this paper) e radiation coefficient (0?8 in this paper) l thermal conductivity coefficient, W m 21 uC 21 l s , l l , l sl thermal conductivity coefficients of solid steel, liquid steel and steel in the mushy zone, W m 21 uC 21 m Poisson's ratio r density of steel, kg m 23 s Stefan-Boltzmann constant (5?67610 28 W m 22 K 24 ) t time, s

Fluid flow plays a significant role in the continuous casting of molten steel. In this paper, two Reynolds Averaged Naiver-Stokes (RANS) models and a Large Eddy Simulation (LES) model were comparatively employed to characterize the fluid flow inside a dissipative ladle shroud and a tundish. LES model was proved to be powerful to characterize the turbulence structure inside the ladle shroud. The effect of meshing density on the computational accuracy was considered using the LES model. The fine-mesh model can capture multiscale vortices inside the ladle shroud; while, the coarse-mesh model disables the LES to obtain the detailed flow information. The experiment of particle image velocimetry (PIV) was used to verify the flow field obtained by the LES model inside the tundish. The PIV and the LES results agree well in terms of flow pattern and velocity vector.