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

Potential of carbon dioxide transcritical power cycle waste-heat recovery systems for heavy-duty truck engines

Performance comparison of 2-methylfuran and gasoline on a spark-ignition engine with cooled exhaust gas recirculation

Effect of lubricating oil on the particle size distribution and total number concentration in a diesel engine

Preliminary tests on dynamic characteristics of a CO 2 transcritical power cycle using an expansion valve in engine waste heat recovery

Waste heat recovery (WHR) is one of the most useful ways to improve the efficiency of internal combustion engines, and an electricity-cooling cogeneration system (ECCS) based on Rankin-absorption refrigeration combined cycle for the WHR of gaseous fuel engines is proposed in the paper. This system can avoid wasting the heat in condenser so that the efficiency of the whole WHR system improves, but the condensing temperature of Rankin cycle (RC) must increase in order to use absorption refrigeration system, which leads to the decrease of RC output power. Therefore, the relationship between the profit of absorption refrigeration system and the loss of RC in this combined system is the mainly studied content in the paper. Because the energy quality of cooling and electricity are different, cooling power in absorption refrigeration is converted to corresponding electrical power consumed by electric cooling system, which is defined as equivalent electrical power. With this method, the effects of some important operation parameters on the performance of the ECCS are researched, and the equivalent efficiency, exergy efficiency and primary energy rate are compared in the paper.

Gequn Shu

Papers

Potential of carbon dioxide transcritical power cycle waste-heat recovery systems for heavy-duty truck engines

Performance comparison of 2-methylfuran and gasoline on a spark-ignition engine with cooled exhaust gas recirculation

Effect of lubricating oil on the particle size distribution and total number concentration in a diesel engine

Preliminary tests on dynamic characteristics of a CO 2 transcritical power cycle using an expansion valve in engine waste heat recovery

Analysis of an electricity-cooling cogeneration system for waste heat recovery of gaseous fuel engines