Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

How to effectively utilize low and medium temperature energy is one of the solutions to alleviate the energy shortage and environmental pollution problems. In the past twenty years, because of its feasibility and reliability, organic Rankine cycle has received widespread attentions and researches. In this paper, it reviews the selections of working fluids and expanders for organic Rankine cycle, including an analysis of the influence of working fluids' category and their thermodynamic and physical properties on the organic Rankine cycle's performance, a summary of pure and mixed working fluids' screening researches for organic Rankine cycle, a comparison of pure and mixture working fluids' applications and a discussion of all types of expansion machines' operating characteristics, which would be beneficial to select the optimal working fluid and suitable expansion machine for an effective organic Rankine cycle system.

A review of working fluid and expander selections for organic Rankine cycle

Annual Energy Outlook

Developing thermoelectric materials with superior performance means tailoring interrelated thermoelectric physical parameters – electrical conductivities, Seebeck coefficients, and thermal conductivities – for a crystalline system. High electrical conductivity, low thermal conductivity, and a high Seebeck coefficient are desirable for thermoelectric materials. Therefore, knowledge of the relation between electrical conductivity and thermal conductivity is essential to improve thermoelectric properties. In general, research in recent years has focused on developing thermoelectric structures and materials of high efficiency. The importance of this parameter is universally recognized; it is an established, ubiquitous, routinely used tool for material, device, equipment and process characterization both in the thermoelectric industry and in research. In this paper, basic knowledge of thermoelectric materials and an overview of parameters that affect the figure of merit ZT are provided. The prospects for the optimization of thermoelectric materials and their applications are also discussed.

A review on thermoelectric renewable energy: Principle parameters that affect their performance

The process chain of energy conversion from primary energy carriers to final energy use is subject to several losses. Especially in end use, vast amounts of converted energy occur as waste heat, which is often released to the environment. In terms of raising energy efficiency and reducing the energy consumption, such waste heat needs to be used. To date, some studies or investigations about industrial waste heat of selected countries have been carried out, but other sectors like commerce were not considered. Therefore, this work presents a novel top-down approach for the estimation of waste heat potential of the most common sectors of end use (transportation, industrial, commercial and residential) including electricity generation on a global scale. It also deals with the temperature distribution of this unused energy. The evaluation reveals that 72% of the global primary energy consumption is lost after conversion. In further detail, 63% of the considered waste heat streams arise at a temperature below 100 °C in which electricity generation has the largest share followed by transportation and industry.

Estimating the global waste heat potential

This paper developed 3D product models of motorcycle and engine by UGNX as well as virtual prototyping by ADAMS program with road roughness generated by MATLAB. Under the straight-line running condition, the dynamic responses of motorcycle multibody system to both road and engine excitations were compared with those to only road excitation in terms of vertical acceleration response, amplitude frequency response and power spectral density. The comparisons of simulation data showed that the response due to flat road excitation was around 20 Hz, while that to the combined excitations was in a wide frequency band, of which the major components focused on 10 Hz, 15 Hz, 35 Hz, 70 Hz, 100 Hz and even higher frequencies, reflecting the characteristics of engine excitation based on its unbalanced inertia force and torque. It is concluded that the high fidelity virtual prototyping can simulate the dynamics of motorcycle product well in investigating the vibration and ride comfort performance.

Dynamic response of functional virtual prototyping of motorcycle under combined excitations

Simulation Research of the Structural Downsizing of SCR Reactor

The organic Rankine cycle (ORC), as the most promising technology for engine waste heat recovery, has many configurations available to match the complicated engine waste heat conditions. This paper is aimed at revealing the characteristics of the engine waste heat condition for which different ORC configurations are matched so as to give selection guidance. The engine waste heat sources are characterized by the exhaust gas temperature (300°C-650°C) and the heat ratio of the high temperature waste heat to low temperature waste heat (0.5-1.5). Four mostly investigated configurations including the single-loop ORC, the cascade dual-loop ORC, the dual-pressure ORC, and the CO2 transcritical Rankine cycle (CTRC) are selected and modified to enable efficient utilization of all waste heat sources. Their thermodynamic performance is optimized for different waste heat characteristics. The results show improvements in net power for all configurations when exhaust gas temperature and heat ratio rise from 300°C, 0.5, to 650°C, 1.5, respectively, of which the high-temperature split CTRC (HTS-CTRC) recorded the largest increase of 183.58%, while the split regenerative ORC (SR-ORC), dual-pressure ORC (D-ORC), and split cascade ORC (SC-ORC) increased by 17.41%, 23.71%, and 35.45%, respectively. Two selection maps are established to provide general references for quickly selecting the configuration according to different waste heat characteristics whatever the engine type and operating conditions.

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Comparison Study of Four Typical ORC Configurations for Different Waste Heat Characteristics of Engine

A double-working-medium expander used for a two-stage organic Rankine cycle, comprising a cylinder body, a rotor disposed inside the cylinder body and provided with a plurality of slip sheets in a radial direction of the cylinder body, and a rotary shaft fixedly connected to the center of the rotor, wherein, the cylinder body is of an annular structure formed by two semi-oval structures which are in butt joint with unequal semi-major axes and equal semi-minor axes; the outer peripheral surface of the rotor can be rotationally tangent to the inner peripheral surface of the cylinder body at the butt joint position of the two semi-oval structures of the cylinder body; a low-temperature cycle volume for expanding the low-temperature working medium with a large flow and a small expansion ratio and a high-temperature cycle volume for expanding the high-temperature working medium with a small flow and a large expansion ratio are formed among two sides of the rotor and the cylinder body, respectively; and, a first fluid inlet and a first fluid outlet, which are arranged on the wall of the cylinder body, are communicated with the low-temperature cycle volume, and a second fluid inlet and a second fluid outlet, which are arranged on the wall of the cylinder body, are both communicated with the high-temperature cycle volume. In the present invention, two working mediums in the two-stage organic Rankine cycle can do expansion work in an expansion mechanism.

Gequn Shu

Papers

Dynamic response of functional virtual prototyping of motorcycle under combined excitations

Simulation Research of the Structural Downsizing of SCR Reactor

Comparison Study of Four Typical ORC Configurations for Different Waste Heat Characteristics of Engine

Double-working-medium expander used for two-stage organic Rankine cycle