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The novel shape-stabilized phase change material (PCM) has the following salient features: large apparent specific heat for the phase change temperature region, suitable thermal conductivity, and the ability to keep the shape stabilized when it undergoes a phase change. In this technical brief, we put forward a kind of shape-stabilized PCM floor that is able to absorb solar radiation energy in the daytime and to release the heat at night in winter. The thermal performance of a prototype room using such a floor was studied. The experiments show that the mean indoor temperature of a room with the PCM floor is about 2°C higher than that of the room without a PCM floor, and the indoor temperature swing range is obviously minimized. Therefore, installing shape-stabilized PCM in a room may increase the degree of thermal comfort and reduce space heating energy consumption in winter. In addition, the experimental results provide data for modeling and simulation research for such PCM floor systems.

Abstract The subcritical multiplication factor k s with the existence of external source neutrons is important for the evaluation of the neutron multiplication M, especially in the accelerator-driven system (ADS) performance assessment. The effective multiplication factor k eff calculated from the traditional source iteration method in Monte Carlo codes can’t fully describe the subcritical system, acquiring the spurious neutron flux distribution. A direct Monte Carlo method called modified source iteration method by external source is introduced to calculate the subcritical multiplication factor k s directly, acquiring the real neutron flux at the same time. Compared with Monte Carlo fixed source calculation, the modified source iteration method has a great advantage in calculating the subcritical multiplication factor k s and its statistical error directly, especially for systems with complex geometry and a variety of fissile materials where much post-processing work on the tally results from fixed source calculation is needed. Moreover, much calculation time can be saved through this method when obtaining the subcritical multiplication factor k s with similar precision. This method has already been implemented in Reactor Monte Carlo code RMC including parallel calculation capability and can be effectively applied to the analysis of accelerator driven subcritical system (ADS).

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.

The goal of nanotechnology is to build nanodevices that are intelligent, multifunctional, exceptionally small, extremely sensitive and have low power consumption. When the nanodevice is required for applications such as in vivo biomedical sensors, a nanoscale power source is required. Although a battery or energy storage unit is a choice for powering nanodevices, harvesting energy from the environment is an essential solution for building a “self-powered” nanodevice/nanosystem, [ 1 , 2 ] which is an integration of nanodevice(s) and nano-enabled energy scavenging technologies. [ 3 ] Previously, nanogenerators (NGs) have been demonstrated that can convert mechanical energy of low (order of Hz) and high (around 50 kHz) frequencies into electricity by means of piezoelectric zinc oxide nanowires (NWs). [ 4–6 ] A single silicon NW-based heterostructure has been used to fabricate solar cells that are effective for driving an NW-based pH sensor or logic gate. [ 2 ] Still, the most abundant energy available in biosystems is chemical and biochemical energy, such as glucose. In this paper, we report an NW-based biofuel cell (NBFC) based on a single proton conductive polymer NW for converting chemical energy from biofl uids, such as glucose/blood, into electricity, using glucose oxidase (GOx) and laccase as catalyst. The glucose is supplied from the biofl uid and the NW serves as the proton conductor. Although the electrolyte solution is a choice for transferring proton, it is essential to develop a proton conductive NW in some cases, such as the case in Figure S3c (see Section III of the Supporting Information (SI)), in which the anode and cathode solution are separated. A net current is generated

Integration of heat and electricity supply improves the overall energy efficiency and system operational flexibility. The renewable powered heat-electricity energy system is a promising way to set up residential energy supply facilities in remote areas beyond the reach of power system infrastructures. However, the volatility of wind and solar energy brings about the risk of supply inadequacy. This article proposes a data-driven robust method to quantify two measures of such a risk in the stand-alone renewable powered heat-electricity energy system. The uncertainty of renewable generation is modeled through a family of ambiguous probability distributions around an empirical one based on the Wasserstein metric; then, the probability of heat and electricity load shedding during a short period and related penalty cost are discussed. Through a polyhedral characterization of renewable power feasible region, the load shedding probability under the Wasserstein ambiguity set comes down to a linear program. With a piecewise linear optimal value function of the penalty cost, its expectation under the worst case distribution in the Wasserstein ambiguity set also gives rise to a linear program. The proposed method requires moderate information on renewable generation and makes full use of available data, whereas sustains computational tractability. The evaluation result is robust against the inaccuracy of renewable power distributions. Case studies demonstrate the effectiveness of the proposed approach.

The DC distribution system is an important development direction of the distribution system, which can improve the reliability and the quality of the power supply, and support the new energy, the energy storage, the electric vehicles, and the flexible access of AC and DC loads to grid. To realize the demonstration application of the DC distribution technology, China’s first demonstration project of the medium voltage DC distribution network will be built in Zhuhai, Guangdong Province to support the construction of the city energy internet. First, this paper analyzes the demand of the DC distribution network project, and puts forward the construction content and construction target. Then, it designs and analyzes the electrical connection mode, system operation mode, and startup and shutdown mode of the DC distribution network, and proposes the overall project construction plan. Finally, it conducts the specific project design and analysis, which mainly include the selection of equipment such as inverters, DC transformers and DC circuit breakers, the design and analysis of the DC control and protection system, the design and analysis of the over-voltage protection and the configuration scheme of the lightning arrester, and analysis of the system transient characteristics. The design and analysis of the engineering program is a combination of China’s distribution network engineering practice and technical characteristics, which lays a solid foundation for the advancement of the DC power distribution technology in China, and has reference value and demonstration effect for the design and construction of other projects.

Abstract The optimization model of the district heating system for an N-floor building is set up. The mass flow rate and thermal conductance distributions are optimized for prescribed total mass flow rate and prescribed total thermal conductance respectively by the Newton method. Two numerical examples are presented, and the effects of the parameters, such as the heat load, its distribution and the room temperature, on the optimal results are discussed. It is shown that for a three-floor building with two users on each floor, larger heat load requires larger mass flow rate on the corresponding floor when the total mass flow rate is prescribed. Putting the user of larger heat load nearest to the upstream flow reduces the total mass flow rate for fixed total heat load on the floor. For the three-floor building with one user on each floor, larger thermal conductance of the corresponding heat exchanger is required for the room with higher temperature when the total thermal conductance is prescribed. With fixed total heat load of two floors, distributing more heat load to the room with lower temperature reduces the total mass flow rate.

Abstract The automotive operating protocols is a comprehensive expression of a country or a region’s road, climatic environment and driving habits. It is the foundation of energy consumption, test method and limit method for automobile products. It has direct impact on R & D, production and government access management of enterprises. For fuel cells vehicles, the lifetime is one of the main factors restricting their commercialization. Furthermore, the lifetime evaluation methods and its standard specifications of vehicular proton exchange membrane fuel cell are the critical factors to its technological development, but there is no authoritative recognized life evaluation method and test protocols so far. A logical fuel cell durability test protocol is the fundamental for developing the fuel cell life evaluation methods. A review on the state-of-art in the world for fuel cell accelerated test protocols was given, the research circumstances of different universities and research institutions in China, America, the European Union, Japan and so on are analyzed and summarized in detail. Then the essential characteristics and applicable environments of a comprehensive and effective durability test protocol are summarized based on the analysis and demonstration of the existing durability test protocols in literature. The work in this paper focuses on the research of durability test protocols of the fuel cell stack for the first time. The final conclusion will provide theoretical basis for establishing fuel cell durability test specifications and proposing life evaluation methods, and make a contribution to the long life research of vehicular fuel cells.

With the rapid development of the Inner Mongolia power grid, especially wind power capacity continuing to increase, its randomness and volatility put forward higher requirements on the grid to run scheduling. faced of the multi-level, multi-scale, multi-object complex grid, it is the problem to be solved — how to make full use of adjustable system resources and means of automation equipment, optimizing the operating status of the grid to achieve the coordination of the active and reactive optimization and distribution to ensure the safety of the grid. stability, economic operation. In view of the existing operating and scheduling technologies of Inner Mongolia power grid and drawing on the idea of hybrid control system, this article proposes a control strategy of machine net coordination and optimization based on layered event-driven control. This strategy takes into account indicators as economy, safety and quality of the system. It establishes a layered event driven control model to realize layered management and regulation of the whole system. It can automatically judge and select the optimal (or quasi optimal or appropriate) control mode, thus ensuring the sound dynamic quality of the entire power system while improving its stability and reactive power flow to reduce the network loss. Based on the control theory system, we conducted simulation analysis of Inner Mongolia power grid. The result reveals that the control strategy can not only keep contact line exchange power and central node voltage within permitted range, but also improve the economy and safety of the system. The simulation analysis proves that our control strategy can guarantee the safe, sound and economic operation of the system. It can elevate the automatic control level of Inner Mongolia power grid and guide fine adjustment of active and reactive power.