This study aims at determining the effects of the initial distance between two particles on the sweeping of the thermal boundary layers that form along the heated surfaces of a straight channel as the fluid and particles flow downstream. The focus is on the transient, start-up flow that evolves from a quiescent state, in which fluid and the two particles are still in the channel at a uniform temperature, with the surfaces of the channel set at a different isothermal condition as the flow begins. Preliminary numerical results reported here compare the convection effects of the two particles, with different initial distances, to the convection effect obtained for the clear (of particles) case. The results indicate and enhancement of the average Nusselt number along the channel of up to 27 % and an increase in the average heat flux of up to 10 % when the particles are present. Also, it is found the convection enhancement increases with the distance between the particles, up to an optimal distance beyond which increase flattens out. This optimal distance between particles is determined here to equal six times the diameter of the particle. Finally, the location of the particles in the channel has no effect on the localized heat transfer process observed around them, provided the particles have the same distance between them.