Effect of Pebble Size Distribution and Wall Effect on Inner Packing Structure and Contact Force Distribution in Tritium Breeder Pebble Bed

Abstract

In the tritium breeding blanket of nuclear fusion reactors, the heat transfer behavior and thermal-mechanical response of the tritium breeder pebble bed are affected by the inner packing structure, which is crucial for the design and optimization of a reliable pebble bed in tritium breeding blanket. Thus, the effect of pebble size distribution and fixed wall effect on packing structure and contact force in the poly-disperse pebble bed were investigated by numerical simulation. The results show that pebble size distribution has a significant influence on the inner packing structure of pebble bed. With the increase of the dispersion of pebble size, the average porosity and the average coordination number of the poly-disperse pebble bed gradually decrease. Due to the influence of the fixed wall, the porosity distribution of the pebble bed shows an obvious wall effect. For poly-disperse pebble bed, the influenced region of the wall effect gradually decreases with the increase of the dispersion of pebble size. In addition, the gravity effect and the pebble size distribution have an obvious influence on the contact force distribution inside the poly-disperse pebble bed. The majority of the contact force are weak contact force that is less than the average contact force. Only a few of pebbles have strong contact force that is greater than average contact force. This investigation can help in analyzing the pebble crushing characteristics and the thermal hydraulic analysis in the poly-disperse tritium breeder pebble bed.

Sulfur Dioxide Promoted Mercury Fast Deposition over a Selenite-Chloride-Induced Surface from Wet Flue Gas

“…As shown in Figure S8, with the reaction tube increased from 6 mm ( D / d = 3–6) to 20 mm ( D / d = 10–20), the induction time gradually reduced to about 20 min. Moreover, a lower D / d ratio will give rise to a higher flow velocity along the wall and decrement in efficiency . The breakthrough ratio of reaction with a 6 mm tube increased to 11% after 120 min, while those of 10 and 20 mm tubes kept the entire mercury removal.…”

Adsorption of Gaseous Mercury for Engineering Optimization: From Macrodynamics to Adsorption Kinetics and Thermodynamics

“…Moreover, the mercury removal declined from nearly 100% to 93.6% within a 600 min adsorption (see the inset in Figure f). The porosity near the wall was higher because the particles contact the confining wall only at a point, while with the wall distance increased, the porosity became smaller. , It resulted in a higher flow velocity along the wall, which is the so-called wall effect. The porosities of packed reactors in the experiments were measured as 24.63%, 19.49%, 17.08%, and 16.80% at the tube diameters of 6, 10, 20, and 30 mm, respectively.…”

Effects of the Aspect Ratio and Cross-Sectional Area of Rectangular Tubes on Packing Characteristics of Mono-Sized Pebble Beds

“…The packing characteristics of randomly packed pebble beds are influenced by many factors, such as container dimension and shape, pebble size distribution, and packing mode [28][29][30][31][32][33][34][35][36][37][38]. Since most pebble beds are confined by a cylindrical wall in many applications, the packing structures of cylindrical beds have been widely investigated [17][18][19]23].…”

“…Several equations were also proposed to predict the local porosity distributions in three defined zones in a square pebble bed. Gong et al [7,8,32] and Taguchi et al [48] investigated the packing fraction and the local porosity distribution in cylindrical and cubic pebble beds. A similar porosity distribution was obtained in a cubic pebble bed.…”