In this work, we numerically study laminar flows in forced convection in a U -shaped channel. Our study was based on a finite volume method by the fluent code carried out for a Reynolds number varying in the range 100<Re<700, and the Rayleigh number Ra=105 and Prandtl number Pr=0.72. As a function of the Reynolds number, the results obtained are presented in the form of the thermal and dynamic field, the variation of the Nusselt number and the variation of the speed and average temperature at

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... e outlet of the channel as a function of Re also. We see a significant improvement in heat exchange along all the walls of the channel as the number increases Re.