Heat transfer characteristics of high-temperature particle population in ultra-dilute phase: Particle-fluid-surface heat transfer during falling

Abstract

In dry centrifugal granulation technology, the liquid slag is granulated in the granulator to produce a particle population with a high-temperature dilute-phase distribution. During the falling process, inadequate heat transfer can cause the droplets to fail to solidify completely, greatly reducing the safety of the heat recovery bed operation. In this work, A heat transfer model for a particle population of ultra-dilute phase slag was developed, to investigate the particle-fluid-surface heat transfer characteristics of the particle population around the tube, and obtain the changing law of particle population cooling and tube surface heat transfer characteristics. The conclusions of the study show that the fluid flows close to the tube, which is due to particle perturbation. The separation point is to be shifted back, from 180°∼210° to the top 90°∼120°, resulting in a local heat transfer coefficient maximum at the upper of the tube. The amplitude of the fluctuations in the local heat transfer coefficients exhibits the dominance of the different heat transfer types, the percentage of radiant heat transfer is above 60% in all cases. The extended particle residence time can effectively increase the particle cooling rate, the particle cooling rate is above 230 K/s. This study reveals the heat exchange mechanism between the gas-solid phase of the ultra-dilute particle population and the horizontal tube during the falling process, positive performance of horizontal tubes on heat transfer to particle populations was confirmed. Combined heat transfer between the surfaces of dilute-phase particle populations is proposed as a new research content in the field of high-temperature melt granulation, expanding the prospects of industrial applications of combined heat transfer between the surfaces of fluid-solid multiphase flows.