Investigation of Energy Loss Mechanisms in Cyclone Separators

Based on the transient Navier-Stokes equation of an incompressible Newtonian fluid, a vorticity form of the mean mechanical energy equation is derived which is suitable for strongly swirling flow or vortex flow, and reveals the mechanism of mean mechanical energy losses in cyclone separators. Results show that the mean mechanical energy losses in cyclone separators are mainly caused by mean viscous dissipation, turbulent diffusion, and turbulent energy production in a steady turbulent flow. Order-of-magnitude analysis indicates that the rate of local turbulent energy production and mean viscous dissipation is related to the local turbulent Reynolds number at each point in cyclone separators. A large local turbulent Reynolds number designates the turbulent energy production as the primary contributor to mean mechanical energy losses, whereas in the case of a small turbulent Reynolds number the order-of-magnitude quotient between the two quantities decreases, indicating the increased significance of the mean viscous dissipation contribution to mean mechanical energy losses. A combination of theoretical analysis and LDV experimental results indicates the mean viscous dissipation is larger in the quasi-forced vortex region and the boundary layer than in other regions of cyclone separators. The energy losses are mainly caused by turbulent energy production in a majority of the regions (except in the laminar sublayer very close to the wall), especially the largest energy losses in the central quasi-forced vortex region. Hence, decreasing turbulence is an effective approach for drag reduction in cyclone separators.