The temperature variations during the conversion of an oxygen carrier particle exposed to high intensity solar heat flux are assessed as a function of time with an unsteady-state model. The conservation equations of energy and mass are solved simultaneously using an appropriate numerical technique, whose reliability was assessed by comparison with the available experimental and numerical data from the literature. This model was used to study the effect on the particle conversion and maximum temperature of various operating parameters i.e. particle size, external heat and mass transfer, radiation heat flux intensity, CH₄ mole fraction and surrounding temperature. The numerical results show that exposing the particle to high flux solar radiation decreases the conversion time and increases the particle temperature. The calculations indicate that a higher Nusselt number results in a lower temperature rise of the particle and a lower conversion time. The calculations also show that, convection is the dominant mechanism of particle cooling, despite the high temperature of the particle surface. ; Mehdi Jafarian, Maziar Arjomandi, Graham J. Nathan