The quality of the half products is conditioned by the conditions of cooling of molten steel during its transfer through the various exchangers and in particular the mold. The latter constitutes the first phase where molten steel starts to be solidified. The instantaneous solidified crust must be sufficiently thick to contain liquid steel and to avoid the phenomena of opening under the effect of the ferrostatic pressure. Among the recurring concerns of the steel industry is the appearance of the mastery of content inclusions in metallic alloys. Despite the dramatic increase in the cleanliness of steel, it still happens now that macro-inclusions (accidental) are found in the metal. The objective of this work is to demonstrate the influence of the nozzle geometrical modification of the flow structure and the behavior of the particles in the mold of the casting machine. The obtained results show the advantage of an inclined nozzle because it makes it possible to widen the recirculation zone what supports the increase in the residence time of the particles on the one hand and the formation of a solidified crust sufficient thick on the other hand. Numerical tests of the particles behavior (Al2O3) showed the advantage of using the geometric shapes of well designed nozzles. Due to symmetry, only half of the area is considered.