• Energy Research
• Closed Access close
• Restricted close
• Embargo close
• AU close
• Tsinghua University close

Abstract As an important class of particle flows in industrial applications, hopper flows, particularly those using pebbles (diameters dp ~O(10-2) m), play a significant role in nuclear reactor engineering, e.g. HTGR and ADS reactors. However, the features and influencing factors of the binary mixture discharge have not yet been widely investigated. In this study, the discrete element method (DEM) simulation was adopted to analyze the discharge flow of binary mixtures consisting of ellipsoids and spheres in a hopper. After a model validation, the effects of particle aspect ratio (Ra, the ratio of the major axis to the minor axis) of ellipsoids and component ratio (Rn, the ratio of the ellipsoid number to the sphere number) of ellipsoids to spheres were analyzed. Flow patterns were visualized by colored pebble stripes according to pebbles' initial heights. Particle discharge flow rates were computed to examine their relations to particle aspect ratios and component ratios. The force structure and distributions of the binary mixtures were also explored. Results showed that pebble stripes followed quadratic function profiles. Adding ellipsoids was advantageous for particles discharging at lower particle aspect ratios (Ra≤2), while impedimental at large particle aspect ratios (Ra≥3). The discharge flow rate was inversely proportional to the particle aspect ratio at fixed component ratios, and linearly proportional to the 1/4th power of the component ratio at fixed particle aspect ratios. In addition, the discharge flow rate showed low sensitivity to the initial packing states of particles when the particle aspect ratio and component ratio were fixed.

Abstract The core of pebble bed type reactor (HTGR) is a packed bed composed of spherical pebbles (fuel element and graphite moderator). The restitution coefficient is an important parameter which is directly related to the flow of the core pebbles and affects the motion trajectory and stacking state of the fuel pebbles. Herein, Discrete Element Method (DEM) is used to simulate pebble flows within a thin pebble bed. The packing peaks, apex angles, trajectory and velocity deviations, residence time and residence ratios are analyzed in details. The influence of restitution coefficient on the motion characteristics of pebble flow are studied based on the trajectory of fuel pebble. A new evaluation criterion for the uniformity of pebble flows is put forward, and its influencing mechanisms are explored. The relationship between the restitution coefficient and pebble motion is proposed, which can help understand the flow uniformity of fuel pebbles in nuclear reactor core.

This work discusses and proposes the construction principles of particle concentration-based mixing indices for a general particle system. The principles proposed herein follow the criteria and adv...

Microelectronic circuits are often damaged by surges. Surge protection for microelectronic circuits has some special requirements that are different than those for electrical equipment. The approach that the surge invades microelectronic circuits is studied in this paper. The surge withstand capability of some typical serial communication integrated chips, the behaviors of voltage-limiting components, and the influence of the connecting capacitance of a voltage-clamping device on digital signals are studied. Then, a design method of surge suppressor for communication systems is proposed.

In conjunction with a TiO2 protective layer and FeNiCoOx electrocatalyst, a graphene/Si heterojunction photoanode is demonstrated as a new type of Si-based buried junction with high photovoltage for solar water oxidation.

Particle swarm optimization (PSO) is a population-based evolutionary technique. Advancements in the PSO development over the last decade have made it one of the most promising optimization algorithms for a wide range of complex engineering optimization problems which traditional derivative-based optimization techniques cannot handle. The most attractive features of PSO are its algorithmic simplicity and fast convergence. However, PSO tends to suffer from premature convergence when applied to strongly multi-modal optimization problems. This paper proposes a method of incorporating a real-valued mutation (RVM) operator into the PSO algorithms, aimed at enhancing global search capability. Three variants of PSO algorithms are considered. The resultant hybrid PSO-RVM algorithms are experimentally investigated along with the PSO variants and an existing PSO with Gaussian mutation using six typical benchmark functions. It is interesting to see that the effectiveness of RVM varies for different PSO variants as well as different kinds of functions. It has been found that one of the hybrid algorithms, CBPSO-RVM, which is an integration of the PSO with the constriction factor and inertia weight (CBPSO) and the RVM operator, exhibits significantly better performance in most of the test cases compared to the other algorithms under consideration. Furthermore, this algorithm is superior to most of the existing algorithms used in this study when applied to two practical ED problems with non-smooth cost function considering the multiple fuel type and/or valve-point loading effects.

Anaerobic digestion is recognized as a good and promising method for energy recovery from sewage sludge, but it is difficult to select a suitable process from various conventional and emerging technical options. In this study, five processes including mesophilic and thermophilic anaerobic digestion (CAD and TAD), mesophilic and thermophilic high-solids anaerobic digestion (HSAD and THSAD) and anaerobic digestion with thermal hydrolysis pretreatment (THPAD) are compared using life cycle environmental and economic assessment. Particularly, the uncertainty derived from variable sludge organic content and biogas production is analyzed. The results showed that energy output should be the most sensitive factor determining the assessment results. For common high-organic-content sludge, thermophilic processes like THSAD and TAD lead to the least environmental impact while THSAD and THPAD exhibit the best economic performance. Compare with CAD, THSAD have 44% less environmental impact and 118% higher net present value (NPV) for a project with treatment capability of 100 t dry solids per day. However, for low-organic-content sludge, high-solids processes like THSAD and HSAD are much better than the others mainly owing to their less consumption of thermal energy. Using this kind of feed sludge, THSAD can bring 40% less environmental burden and 31% more NPV than CAD.