This paper presents a computational study on the inter-phase heat transfer inside a conical fluidized bed reactor when hot air is introduced through the bottom inlet. Two different diameters, 2.0mm and 4.0mm glass particles are used as the first and second solid phase and hot air is used as the third phase. A gas–particle heat transfer and particle–particle heat transfer are investigated by using computational fluid dynamics. Euler–Euler two-fluid model is used to describe dynamics of particles and fluid flow in the reactor. We observe that gas–particle heat transfer coefficient is large when solid particle is small. This is the same tendency as the gas–particle heat transfer coefficient when cold air is introduced among hot particles. Particle-to-particle heat transfer depends much on the superficial velocity at the inlet.