Numerical study of natural convection effects on effective thermal conductivity in a pebble bed

New Formula for Direct Prediction of the Effective Thermal Conductivity of the Ellipsoidal Granular Bed at High Temperatures

“…According to the given conditions in the literature, , the ETC of the bed was computed by using our model, and the results for the bed containing interstitial air that is static and with natural convection are plotted in Figure b,c, respectively. The x -axis is the average temperature of the granular bed [ T bed = ( T h + T c )/2].…”

“…The x-axis is the average temperature of the granular bed [T bed = (T h + T c )/2]. The scatters are the results calculated based on our model, and the solid lines are from the data of Bu et al 21,33 As shown in Figure 8b,c, the computed results of our model are in good agreement with the data of Bu et al, 21,33 and little error exists for k λ , k c , k r , and k eff . Therefore, k λ , k c , and k r can be calculated independently to obtain the ETC of the granular bed (Section 2.3), and the model and computational method in this paper are verified and are valid to calculate the ETC of the granular bed.…”

“…Martis and Annabattula further used DEM to investigate the ETC of the bed composed of multisize spherical particles and presented the analytical expression for particle–particle conduction. Bu et al studied the ETC induced by interstitial fluid convection and particle–particle radiation in a spherical granular bed, and they found that the natural convection enlarges the ETC in the bulk region but can be ignored when the temperature is over 600 K. Cheng and Yu proposed a new macroscopic approach to evaluate the steady-state radiation heat transfer in a packed bed of uniform spheres, and the results indicate that the mean heat flow between particles mainly depends on the bed temperature and related material properties.…”

Thermal conductivity modeling of monodispersed microspheres using discrete element method

“…In this work, we aim to carry out a systematic study on monodispersed spherical particles within a wide range of particle size, temperature and gaseous pressure to evaluate the random particle packing structure derived from a DEM model and to quantify the contribution of different heat transfer pathways. Although the effects of the parameters (particle size, temperature, pressure) have been investigated separately in several earlier studies 23,28,29 , the limited range of values in each of these studies and the different experimental conditions across different studies still inhibited effective validation of the DEM model and quantification of contributions of different heat transfer mechanisms.…”

An experimental/numerical hydrothermal-Second law analysis of a finned/tubular heat exchanger using Bhatnagar–Gross–Krook Lattice Boltzmann (BGKLBM) and rheological-thermal behavior of Fe2O3-water

“…The main objective of this work is to study the effect of fluidsolid thermal conductivity ratio on the natural convection and entropy generation. Bu et al (2020) conducted a numerical analysis on natural convection influence over the effective thermal conductivity within a pebble bed. The results declared the concise effect of natural convection in the pebble temperature in solid form and considerable effect on fluid form.…”