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The preparation of micron-sized spherical particles by the Pulsed Orifice Ejection Method (POEM) is a typical unconstrained heat transfer and solidification process, and the prepared spherical particles have the characteristics of uniform particle size, high roundness and consistent thermal history. The heat transfer mechanism dominated by convection and radiation is crucial for the preparation technology, solidification process and microstructure control. According to the preparation process, heat transfer and solidification characteristics of micron-sized spherical metal particles by POEM, a numerical calculation model of heat transfer and solidification in a three-dimensional spherical coordinate system is established in this paper. The proposed model considers the behavior of the convection and radiation heat transfer of pure Cu particles in the unconstrained solidification process, and adopts the temperature recovery method to deal with the latent heat of pure metal solidification. The temperature variation and distribution of spherical particles at different solidification stages are calculated, and the temperature gradient, cooling rate, liquid-solid interface movement and solidification rate during the solidification process are also investigated. In addition, the convective and radiative heat transfer and their contribution are simulated and analyzed, and the effects of different preparation processes on the convective heat transfer of the particles are explored. The results provide references for the optimization of the preparation and the regulation of the solidification process of micron-sized spherical particles by POEM.