Particle Heat Transfer Characteristics Research Articles

Discrete element method study of the mixing and heat transfer behaviour of a binary‐size granular system in a rotating drum

AbstractUnderstanding the internal solid motion and heat transfer behaviour within rotating drums is paramount for their design and operation across various industries. The discrete element method (DEM) is utilized to elucidate the general flow, mixing, and heat transfer characteristics of particles within rotating drums. Following model validation, this study delves into the mixing behaviour and heat transfer patterns of binary‐size particles in the rotating drum, while also assessing the impact of size ratio and rotating speed. The findings reveal that variations in particle size result in noticeable radial segregation, consequently affecting the heat transfer dynamics of solid phase within the system. Higher rotating speeds enhance mixing and dispersion of solid phase but lead to a decrease in the averaged particle temperature. Furthermore, the heat flux exhibits a negative correlation with particle size. Distinct heat transfer behaviours are observed among particles of different sizes in both active and passive areas, with larger particle size ratios exacerbating segregation, potentially impacting final product quality. In summary, these findings offer crucial insights into heat transfer phenomena in rotating drums, aiding in the design and operation of apparatus.

Numerical investigation on the heat transfer of particle arrays in supercritical water

The heat transfer characteristics of particles in supercritical water (SCW) are the research foundation for the development of the technology of coal gasification in SCW. The study encounters two challenging problems: the complexity of particle spatial distribution and the special variation of SCW properties. Therefore, this work focuses on contrasting the particle interaction characteristics between in SCW and conventional fluid, instead of the direct study of particle clusters in SCW. Research is conducted by the particle-resolved numerical simulation method. In the simulations, the SCW inflow is 973 K and 25 MPa which is a usual operating condition, and all particle surface temperatures are constant and uniform with the values of 300 K, 672 K and 973 K which are respectively below, at and beyond the pseudocritical temperature zone. The side-by-side and streamwise distributed arrays, which are simple but representative, are adopted as the research objects firstly. The effects of particle number and inter-particle distance on heat transfer are studied. Results indicate that the effects of particle interaction on heat transfer under all heat transfer states are similar in the side-by-side array; while only the effects under the pseudocritical and supercritical states are similar in the streamwise array. Then the structured packed array is adopted, and the effects of void fraction (ε) under different heat transfer states are studied. Moreover, a new correlation dependent on ε and Re is built for predicting the ratio of the Nu of a particle in the structured packed array and that of a single particle.

Numerical study of blockage and arching behavior of particle with different shapes in packed bed

Blockage has a significant impact on the flow and heat transfer characteristics of particles in discharging process and can affect the system security seriously. In this study, the discrete element method (DEM) was adopted to analyze the discharge flow of pebbles, ellipsoids, and cubes. The mechanism of blockage formation is the mechanical interaction between particles. With the increase of axial force, the frequency of the blockage increases. High probability of blockage formation arises when the local axial velocity difference dvzl is less than 0.075, while a large local difference in axial velocity (dvzl≥ 0.075) can efficiently avoid blockage. With the increase of the bottom cone angle α of the geometric of the packed bed, blockage during particle flow can be avoided. When α increased to 60°, the particles of Rd less than 0.248 can be discharged smoothly. In addition, the coefficient of friction μ between particles, the ratio of particle diameter to discharge orifice diameter Rd and the aspect ratio Ra of non-spherical particles are all factors influencing the formation of blockages. The critical conditions for particle blockage formation were proposed. For actual working condition of engineering, the application of Rd less than 0.24 and μ less than 0.4 can effectively avoid blockage formation and ensure relatively safe operation for spherical particle systems. For ellipsoidal particles, low aspect ratio (Ra≤4) can effectively avoid blockage.

Numerical simulation of gas–solid heat transfer characteristics of porous structure composed of high-temperature particles in moving bed

Blast furnace slag is the main by-product of ironmaking, and its waste heat recovery is essential for energy saving. As an excellent gas–solid reactor, moving bed has wide application prospects in waste heat recovery. Nevertheless, most researchers are currently keen on the thermal characteristics of fluidized bed. There is no clear conclusion for gas–solid heat transfer mechanism of moving bed, especially the heat transfer characteristics of particles with multiple particle size distribution. Therefore, in this paper, a CFD-DEM coupling method is used to simulate waste heat recovery process of the blast furnace slag in the moving bed. The gas–solid heat transfer characteristics of a porous structure composed of different particle size distribution systems were studied. The results show that the binary particle size mixing system has the best heat transfer effect. Moreover, the waste heat recovery rate decreases with the increasing initial temperature and mass flow rate of particles, while increases with the increasing bed height and gas flow rate. Based on these results, an empirical correlation of the comprehensive heat transfer coefficient is obtained using the dimensional analysis. The study clarifies multiphase flow and heat transfer characteristics in the moving bed of the porous structure composed of high-temperature slag particles with multiple particle size distribution, and provides a theoretical basis for the next-step development of a high-efficiency gas–solid heat transfer moving bed.