| In this thesis, the wide slab continuous caster mold(220×(1350～2300)mm~2,300×(1500mm～2300)mm~2)is researched which is made by the Bao Steel corporation in China, the fluid flow and temperature distribution was simulated and mathematical model was established by using the commercial software FLUENT and some mathematic methods such as continuity equation,momentum equation and energy equation. Simulation research on the fluid flow and the heat transfer behavior of molten steel in mold was also included. In addition, because of the surface longitudinal cracks when casting, the key problem which lies on optimization of structure parameters of nozzle was analyzed.The research results showed that surface longitudinal cracks in the wide slab surface with the original submerged entry nozzle (SEN) were mainly caused by the weak upper flow circulation in the mold, the slow heat exchange near the meniscus and the non-uniform melting of the mold powder. Therefore, the five new nozzles were designed by changing the shape of the nozzle. And the two best nozzles were chosen by the numerical simulation. The modified SEN with smaller outlet thickness, 15°downward port angle and convex bottom was designed to the mold of thickness of 220mm.The nozzle of mold of thickness of 300mm was modified with 15°downward port angle and flat bottom.What's more, the fluid flow of molten steel was stable and the temperature distribution was uniform when the optimization nozzle was used. The optimization nozzle could be improved the wide slab quality. The experiment result had indicated that, the slag distribution was uniform after the use of optimization nozzle. The surface longitudinal crack decreased for more than 30% and the rejection rate of slab was 0. The trial results also showed that the optimum SEN presented a better application effect.
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