MOVEMENT OF THE PARTICLES ON THE ROTARY HEAT EXCHANGERS

Experiments with cones rotating in air, with the angle at vertex of cone β = 120º and β = 180º shown that with frequency Ω ≥ 2,5 Hz the projection of particles trajectories on horizontal plane (particles diameter d ≈ 0,1 mm) is close to logarithmic spirals. Analysis of this approximation function and results of the physical simulation, which allow to determine the coefficient of near-surface resistance C_D^* shown that particles does not slide or roll on the cone surface. Average distance between particles and surface less, but commensurable with the thickness of stationary near-surface velocity layer. The thickness of stationary near-surface velocity layer at least ten times more than dimensions of the particles. Particles are “jumping” on the solid surface, the height of this “jumps” is approximately equal the displacement thickness of the velocity layer. Particles’ transference on the normal to surface and their unidirectional rotation lead to mass exchange between the layers of the viscous fluid, therefore, intensify the heat abstraction from hot surface to air and particles. This factors lead to reduction of the heating time and increase of flash-products quality.

Keywords:
rotary heat exchanger, dehydration, thermal decomposition, boundary layer, coefficient of resistance, centrifugal force.
УДК 532.526.2 + 533.6.12

MOVEMENT OF THE PARTICLES ON THE ROTARY HEAT EXCHANGERS