Research On Movement And Thermal Conductivity Of Particulate Matter In Externally Heated Rotating Device

Particulate matter has attracted much attention due to its wide application in chemistry,minerals,food,medicine and other fields.The externally heated rotary device is also a kind of commonly used equipment for the heat treatment of the particulate matter in industrial production.The unit operation,which involves the movement and heat transfer process of particulate matter in an externally heated rotary device,is an important part of industrial production and has an important impact on the quality of the final product.In this paper,the bi-disperse spherical particles and monodisperse columnar particles in the rotary device are taken as the research object.And the numerical simulation of the movement and heat transfer process of the particulate matter in the externally heated rotary device is carried out by coupling the discrete element method(DEM)with a conductive heat transfer model.The Lacey mixing index is used as the evaluation index of the particle mixing effect.And the average particle temperature,the standard deviation of the particle temperature,the effective heat transfer coefficient and the heat transfer rate are used as the evaluation indexes of the heat transfer effect of the particle bed.The effects of moving baffles with different lengths on the movement and mixing of bi-disperse spherical particles were analyzed.The effects of rotating speed of the rotary device,the number and height of fixed right-angle baffle,particle volume,and filling rate on the heat transfer characteristics of monodisperse colurnnar particles in an externally heated rotating device were analyzed.The effects of moving baffles with different lengths on the mixing and heat transfer of monodisperse columnar particles in extermally heated rotary devices were analyzed.In the bi-disperse spherical particle system,when the rotation speed of the rotary device is 15 r/min,the fluctuation amplitude of average particle velocity increases as the length of the moving baffle increases.Adding the moving baffle and fixed baffle in the rotary device can enhance particle mixing,but compared with fixed of equal length,the moving baffle can better enhance particle mixing.And the optimal dimensionless length of the moving baffle is 1/3.When the rotation speed of the rotating device is 60 r/min,the influence of the moving baffle on the average velocity fluctuation tends to be more random.And only the moving baffle with a dimensionless length of 1/4 can enhance particle mixing.At both rotational speeds,the moving baffle causes the average particle velocity to fluctuate more sharply.In the monodisperse columnar particle system,reducing the rotation speed of the rotary device,increasing the number of the right-angle baffle,increasing the height of the right-angle baffle,reducing the volume of the particles,and reducing the filling rate all can make average particle temperature rise faster and enhance the uniformity of the temperature distribution of the particle bed.Various factors mainly optimize the heat transfer by increasing the contact area between the particles and the rotating device or reducing the heat capacity of the particles in the rotary device.Reducing the rotation speed of the rotary device,increasing the number of the right-angle baffle,increasing the height of the right-angle baffle,reducing the volume of the particles can increase the contact area between the particles and the rotating device.And reducing the filling rate can reduce the heat capacity of the particles in the rotary device.When the rotation speed of the rotary device is 15 r/min or 60 r/min,adding a moving baffle to the rotating device can inhibit the mixing of the monodisperse columnar particles.However,the mixing of particles at low speed is better than that at high speed.At both rotational speeds,the inhibition of the moving baffle on the heat transfer between the particles and the rotary device also gradually becomes stronger as the length of the moving baffle increases.But the heat transfer rate at low speed is higher than that at high speed.