Particles Heat Treating in a Pulsating Gas Stream

Abstract

The subject of the paper is the application of pulsating flow to the particles heat treating. Pulsation influence mechanisms are segregated by the author into two groups: quasi – steady – state (when, at every point in time, an instantaneous value of the heat transfer rate may be calculated with the equations obtained for steady-state conditions) and unsteady – state which includes the remainder. It is shown that, depending on the process parameters, pulsations can increase, not influence, or even reduce heat transfer. Resonance phenomena and large size particles, for which the influence of gravity is substantial, receive special attention. The heat transfer intensification may be achieved due to increases in both heat transfer coefficient and particle residence time. Longitudinal pulsations (when the pulsation and main flow velocities have the same direction) may be preferable in the unsteady-state range of parameters. Transverse pulsations (when the pulsation velocity is perpendicular to the main flow) can be more effective in the quasi – steady – state range. Nonuniformity of heat treating in pulsating flow, influence of the main flow turbulence, trigger effects, and different methods of pulsation generation, including pulsating combustion, are discussed. In conclusion some recommendations are given for designing practical processes.