Comparative Analysis of Heat-Transfer Efficiency in Round and Flat Continuous Diffusers

Numerical simulation of flow and heat transfer in round and flat continuous diffusers with a smooth surface is performed using a three-parameter differential RANS turbulence model supplemented by a transfer equation for the turbulent heat flux. A comparative analysis of local and integral characteristics of the flow and heat transfer shows that, at the same opening angle, the Nusselt number in a round diffuser is higher than in a flat diffuser, and this excess increases with increasing opening angle. However, the Reynolds analogy factor for a round diffuser is slightly higher than for a flat diffuser due to the higher value of the friction coefficient in a round diffuser. It is shown that, with an increasing Reynolds number, the Reynolds analogy factor, both current and averaged over the diffuser length, slightly decreases. The Nusselt number averaged over the length also decreases, while the averaged friction coefficient remains practically constant.