importance for obtainment of high rates of monomer consumption. However, if particle fragmentation takes place in an uncontrolled way, undesirable production of polymer particles with poor morphological properties and small diameter (fi nes) can occur, leading to operational problems and production of off-spec materials. [1][2][3] Polyolefi ns can be produced commercially in slurry, solution, bulk, and gas-phase processes. One of the main advantages of gas-phase processes is the possibility to operate the process continuously in agitated tank reactors. However, temperature control is normally less efficient in gas-phase than in liquid-phase processes, due to the combination of high rates of reaction, reduced heat capacity of the gas and higher mass and heat transfer resistances between the continuous gas phase and the polymer particles. This characteristic property of gasphase reactors may impose the use of lower specifi c heat generation capacity, higher residence times, and longer grade transition periods, when compared to liquid-phase processes. Despite that, gas-phase polymerization reactors can be very effi cient and present high operational fl exibility, justifying the signifi cant industrial interest in these processes. It is particularly important to note that the solid polymer material can be easily separated Computational fl uid dynamics (CFD) is used to study the gas-particle heat transfer in gasphase olefi n polymerizations. Particularly, the effects of particle rotation on the gas-particle heat transfer coeffi cient and internal particle temperatures are evaluated, showing that particle rotation can exert a signifi cant impact on observed temperature profi les, so that this effect should not be neglected during detailed CFD process simulations. As a consequence, particle rotation can lead to particle cooling and development of spherical gradient symmetry, validating the use of simpler modeling schemes that are based on reaction-diffusion in symmetrical spherical geometry.

uncontrolled particle fragmentation and possible temperature runaway. Proper fragmentation of catalyst particles can ensure the achievement of high particle porosity and high exposure of catalyst active sites, which are of essential importance for obtainment of high rates of monomer consumption. However, if particle fragmentation takes place in an uncontrolled way, undesirable production of polymer particles with poor morphological properties and small diameter (fi nes) can occur, leading to operational problems and production of off-spec materials. [1][2][3] Polyolefi ns can be produced commercially in slurry, solution, bulk, and gas-phase processes. One of the main advantages of gas-phase processes is the possibility to operate the process continuously in agitated tank reactors. However, temperature control is normally less effi cient in gas-phase than in liquid-phase processes, due to the combination of high rates of reaction, reduced heat capacity of the gas and higher mass and heat transfer resistances between the continuous gas phase and the polymer particles. This characteristic property of gas-phase reactors may impose the use of lower specifi c heat generation capacity, higher residence times, and longer grade transition periods, when compared to liquid-phase processes. Despite that, gas-phase polymerization reactors can be very effi cient and present high operational fl exibility, Computational fl uid dynamics (CFD) is used to study the gas-particle heat transfer in gasphase olefi n polymerizations. Particularly, the effects of particle rotation on the gas-particle heat transfer coeffi cient and internal particle temperatures are evaluated, showing that particle rotation can exert a signifi cant impact on observed temperature profi les, so that this effect should not be neglected during detailed CFD process simulations. As a consequence, particle rotation can lead to particle cooling and development of spherical gradient symmetry, validating the use of simpler modeling schemes that are based on reaction-diffusion in symmetrical spherical geometry.