Quantitative assessment of energy changes in underground coal excavations using numerical approach

Coal burst is caused by a dynamic and unstable release of energy within the overstressed rock mass/coal during the mining process.Although the occurrence of coal burst is a result of the complex impacts of many factors,a major component of coal burst mechanism is associated with energy storage and release.This study reviewed the sources of energy that can contribute to a coal burst,principally strain and potential energy stored in the coal mass around excavations,and radiated seismic energy released by geological discontinuities.The energy balance concept proposed by[1]was utilised in numerical modellings to compute the radiated seismic energy in a modelling system and the kinetic energy of ejected rock/coal for a given burst scenario.The modelling results showed that the strain energy density(SED)around excavations increases with increasing mining depth and the maximum SED area migrates deeper into the coal.For the effect of geological features on both roadway and longwall face,the coal burst risk proneness can be assessed considering the proposed energy terms.According to the results of energy changes in excavations,the modelling predicts that for depths of ejection 2 m and 3 m the kinetic energy of a burst increases as the mining depth increases from 100 m to 1000 m,but for depth of ejection 1 m only increases until mining depth reaches 700 m and then decreases.The proposed energy-based model indicators can deepen the understanding of energy changes and the associated coal burst risks for different mining conditions.

Energy Security and Climate Change in the European Union,China and Latin American Relationships:Major Challenges and Areas of International Cooperation

The author discusses the subject in both ecological and political perspectives based on a most comprehensive,authoritative and updated bibliography.Hence,Latin America and the Caribbean(LAC) is as much diversified as there are sub-regions and regional organizations in geopolitical and geo-economical terms and often dialectic regarding energy security,climate change and LAC ties with Europeans and China and so is the tripartite relations with the rest of the world so far as energy security and climate cha...

Entropy change-induced elastic softening of lithiated materials

To understand the ＂elastic softening＂ of Li-Si alloys for the development of Li-ion batteries, the effect of stress-induced change of entropy on the mechanical properties of lithiated materials is examined within the theories of thermodynamics and linear elasticity, An approach is presented whereby the change of Gibbs free energy is governed by the change of the mixture entropy due to stress-induced migration of mobile atoms, from which the contribution of the change of the mixture entropy to the apparent elastic modulus of lithiated materials is determined. The reciprocal of the apparent elastic modulus of a lithiated material is a linear function of the concentration of mobile Li-atoms at a stress-free state and the square of the mismatch strain per unit mole fraction of mobile Li-atoms.

China and the United States’ Critical Roles in Tackling Climate Change and Shaping the International Regimes

This paper argues that major powers can play critical roles in a complicated regime system,as evidenced by China and the U.S.which have had pivotal influence in the construction of the post-2020 climate regime.China and the U.S.have participated in multilateral consultations beyond the scope of the United Nations Framework Convention on Climate Change(UNFCCC)while making use of many political platforms,such as Asia-Pacific Economic Cooperation(APEC),G20,and informal meetings and dialogues to bridge the gap among various approaches to mitigating climate impacts.China-U.S.bilateral cooperation has incorporated energy and climate issues into the strategic and economic dialogue(S&ED)and launched other schemes,such as EcoPartnerships and wide-ranging dialogues and initiatives on clean energy/clean vehicles.These schemes support the reconciliation of ideas related to domestic abatement policies in the areas of energy,climate change,and environmental protection.Since the Trump administration came to power in 2017,the bilateral cooperation at national level has been retreated significantly and therefore slowdown the UN’s institutional response to climate change.At the stage,the U.S.may not be able to play a critical role in shaping the regime,yet China is regarded to be the most important player in negotiations under the Paris Agreement.

Long-term Energy Demand and CO_2 Problem in the PRC

The long-term energy demand in China and the-Chinese share in global CO2 emission are forecasted on the basis of scenarios of population growth and economy development up to 2050 proposed in view of the interaction of energy, economy, environment and social development. The total energy demand in 2050 will reach 4.4~ 5.4 billion tce. It is shown in energy supply analysis that coal is China’s major energy in primary energy supply. The share of CO2 emission in the future Chinese energy system will be out of proportion to its energy consumption share because of the high persentage of coal to be consumed. It will reach about 27%. The nuclear option which would replace 30.7% of coal in the total primary energy supply will reduce the share by 9.8%. So the policy considerations on the future Chinese energy system is of great importance to the global CO2 issues.

Theory and Practice of High-Level Sprint Training Based on Accurate Sectional Timing

There is an obvious gap in sprint level at home and abroad,and there are different opinions on the reasons.According to the analysis,physical energy and its distribution in each segment are the main factors restricting the sprint performance in China.Different from middle and long-distance running,we must rely on accurate sectional timing technology to master the law of speed-physical energy change in the process of sprint.Each stage is an integral part of the whole dash process,and each part restricts each other.Each stage has a relative best achievement.Simply pursuing the optimal state of segment is not only not helpful to the final result,but also counterproductive.

Parallel Integrated Model-Driven and Data-Driven Online Transient Stability Assessment Method for Power System

More and more uncertain factors in power systems and more and more complex operation modes of power systems put forward higher requirements for online transient stability assessment methods.The traditional modeldriven methods have clear physical mechanisms and reliable evaluation results but the calculation process is time-consuming,while the data-driven methods have the strong fitting ability and fast calculation speed but the evaluation results lack interpretation.Therefore,it is a future development trend of transient stability assessment methods to combine these two kinds of methods.In this paper,the rate of change of the kinetic energy method is used to calculate the transient stability in the model-driven stage,and the support vector machine and extreme learning machine with different internal principles are respectively used to predict the transient stability in the data-driven stage.In order to quantify the credibility level of the data-driven methods,the credibility index of the output results is proposed.Then the switching function controlling whether the rate of change of the kinetic energy method is activated or not is established based on this index.Thus,a newparallel integratedmodel-driven and datadriven online transient stability assessment method is proposed.The accuracy,efficiency,and adaptability of the proposed method are verified by numerical examples.

Fusion curves and thermodynamic properties of carbon tetrachloride,chloroform,bromoform and silicon tetrachloride at pressure up to 3500 MPa

The fusion temperature as a function of pressure for carbon tetrachloride, chloroform, bromoform and silicon tetrachloride at pressures up to 3500MPa has been determined. The experimental data were fitted by the equation Tfus=T0（1 ＋ Δp/a1）^a2 exp（-a3Δp） and the changes of the maolar enthalpy and molar internal energy on fusion were calculated using the parameters of the fitted equation. Comparisons with the data from the literature show that the experimental data, parameters of fitted equations, changes of the molar enthalpy and molar internal energy are reliable.

Dynamic Characteristics of Single-frequency Signal after Modulated by Feedback Control System

In order to study the dynamic characteristics of the single-frequency signal through the nonlinear control system,the system control mode,the outer excitation patterns of the model and the amplitude are investigated by using the methods of the nonlinear dynamical analysis. The time-domain diagram,power spectrum,phase diagram and the largest Lyapunov exponent obtained from the process of the signal propagate through different control module are given. The researches on different control systems demonstrate that: after single-frequency signal goes through the nonlinear controller,it is still non-chaotic although the output contains more frequency components; but with the feedback and the external perturbation,the output is a continuous broadband spectrum and the result shows that there is chaos. The energy of the input signal reduces with some appropriate parameters. Therefore,the control system of the nonlinear feedback is a good way to broaden the spectrum of output with inputting a single-frequency signal.

New Method Proving Clausius Inequality

It is impossible that proving the internal energy change has the relations with volume and pressure. About the second law of thermodynamics, many mistakes of formulations need to be put right and modified, and many new concepts are surveyed too. The equality and inequality on the ratios of internal energy change to temperature and work to temperature are discussed. The relation between the reversible paths and their realistic paths is also researched. In an isothermal process, the internal energy change for the gases is equal to zero, but the internal energy change is not equal to zero for the phase transition or chemical reaction. The Clausius inequality can be derived from the equation calculating the internal energy change in mathematics;it is the new method proving the Clausius inequality. These change laws of thermodynamics could be applied to the gravitational field and mechanical motion and so on.

Preparing and Studying of Phase Change Energy Storage Materials

The thermal energy storage phase change material used for building has been prepared with a few of fatty acids based on the principle of binary low eutectic point. The thermal behaviors such as phase transition temperature and enthalpy of compound energy storage material are researched through differential scanning calorimeter(DSC) and scanning electron microscope(SEM) . The results show that the thermal energy storage phase change composite material can be used in the wall panels well as its higher latent heat.

Thermodynamics of Phase Equilibria in FeO-TiO2-Al_(2)O_(3)System

This scientific paper discusses the information on the structure of the three-component system FeO-TiO_(2)-Al_(2)O_(3),which is necessary for the creation of heat-resistant oxide materials.The structure of binary systems:FeO-Al_(2)O_(3),FeO-TiO_(2),and Al_(2)O_(3)-TiO_(2)is described,and the data on the FeO-TiO_(2)-Al_(2)O_(3)system are presented.The thermodynamic data of all compounds of the system are given,on the basis of which the change in the Gibbs free energy in the temperature range of 800-1900 K for twenty-one exchange reactions was calculated.It has been established that the triangulation of the FeO-TiO_(2)-Al_(2)O_(3)system changes in five temperature ranges:up to 1408 K(TiO_(2)exists in the polymorphic modification-anatase),1408-1537 K(TiO_(2)exists in the polymorphic modification-rutile and pseudobrookite is stable),1537-1630 K(thialite is stable),1630-2076 K(rearrangement cannot occur)and above 2076 K(the presence of the stoichiometric compound Al_(4)TiO_(8)is allowed).Two-phase equilibria up to 1408 K are stable:Al_(2)O_(3)-FeTiO_(3),FeTiO_(3)-FeAl_(2)O_(4),and FeAl_(2)O_(4)-Fe_(2)TiO_(4);in the temperature range of 1408-1537 K:FeAl_(2)O_(4)-TiO_(2),FeAl_(2)O_(4)-FeTi_(2)O_(5),FeAl_(2)O_(4)-FeTiO_(3),and FeAl_(2)O_(4)-Fe_(2)TiO_(4);in the temperature range of 1537-1630 K:FeAl_(2)O_(4)-TiO_(2),FeAl_(2)O_(4)-FeTi_(2)O_(5),FeAl_(2)O_(4)-FeTiO_(3),FeAl_(2)O_(4)-Fe_(2)TiO_(4),and FeAl_(2)O_(4)-Al_(2)TiO_(5);in the temperature range of 1630-2076 K:FeTi_(2)O_(5)-Al_(2)TiO_(5),Al_(2)TiO_(5)-FeTiO_(3),FeTiO_(3)-Al_(2)O_(3),FeTiO_(3)-FeAl_(2)O_(4),and FeAl_(2)O_(4)-Fe_(2)TiO_(4);over 2076 K:FeTi_(2)O_(5)-Al_(2)TiO_(5),FeTi_(2)O_(5)-Al_(4)TiO_(8),Al_(4)TiO_(8)-FeTiO_(3),Al_(4)TiO_(8)-Fe_(2)TiO_(4),Al_(4)TiO_(8)-FeO,and Al_(4)TiO_(8)-FeAl_(2)O_(4).

Thermodynamic Modeling of MgO-Al_(2)O_(3)-TiO_(2) System

This scientific paper gives consideration to the information on the structure of the triple component system,in particular MgO-Al_(2)O_(3)-TiO_(2) that serves as a basis for the production of thermal resistance materials.The structure of such binary systems as MgO-Al_(2)O_(3),Al_(2)O_(3)-TiO_(2),MgO-TiO_(2) was described and the data available for the MgO-Al_(2)O_(3)-TiO_(2) system were given.Thermodynamic data on all the system compounds were also presented and used for the computation of a change in the free Gibbs energy in the temperature range form 800 K to 1900 K for the basic exchange reactions.It was established that the triangulation of the MgO-Al_(2)O_(3)-TiO_(2) system was changed in the three temperature intervals:in the temperature range lower than 1537 K TiO_(2) existed as the polymorphous modification,i.e.anatase;in the temperature range from 1537 K to 2076 K TiO_(2) existed as a polymorphous modification in form of rutile and tialite was stable;and at the temperatures above 2076 K the availability of stochiometric compound of Al4TiO_(8) was possible.In the temperature range lower than 1537 K the two-phase equilibra of Al_(2)O_(3)-MgTi2O_(5),Mg-MgALCU MgTiO_(3)-MgAl_(2)O_(4),and Mg_(2)TiO_(4)-MgAl_(2)O_(4) were stable;in the temperature range from 1537 K to 2076 K the two-phase equilibria of MgTigO_(5)-AlgTiO_(5),MgTiO_(3)-Al_(2)TiO_(5),MgTiO_(3)-Al_(2)O_(3),MgTiO_(3)-MgAl_(2)O_(4),and Mg_(2)TiO_(4)-MgAl_(2)O_(4) were stable,and above 2076 K the MgTi_(2)O_(5)-Al_(2)TiO_(5),MgTi_(2)O_(5)-Al_(4)TiO_(8),Al_(4)TiO_(8)-MgTiO_(3),Al_(4)TiO_(8)-Mg_(2)TiO_(4),Al_(4)TiO_(8)-Mg0,and Al_(4)TiO_(8)-MgAl_(2)O_(4) systems were stable.

China-Brazil Forum on Climate Change and Energy Technology Innovation

The China-Brazil Forum on Climate Change and Energy Technology Innovation opened in Tsinghua＇s Main Building on January 14, 2009. Mr. Samuel Pinheiro Guimaraes, Brazilian Vice-Minister for Foreign Issues, Professor Luiz Pinguelli Rosa, Federal University of Rio de Janeiro, Director of COPPE, and representatives from Brazil＇s Embassy in China attended the Forum.

A one-step method for producing microencapsulated phase change materials

This short communication reports our recent work on the synthesis and characterisation ofmicrocapsules of phase change materials using silica as the shell material through a one-step method. The method uses no surfactants or dispersants for stabilising the capsules. The results show that the one-step method allows the tuning of the size and polydispersity of the capsules, and the use of different core materials. Analyses of the capsules show that they contain about 65% phase change materials. The results also suggest no need for a stabilising agent due to self-stabilisation by the amine groups. Further work is underway to investigate the mechanical and thermal properties of the microcapsules and the scale-up of the method.

Multi-walled carbon nanotubes added to Na_2CO_3/MgO composites for thermal energy storage

Na2CO3/MgO composites with added multi-walled carbon nanotubes （MWCNTs） were prepared and tested as phase change materials （PCMs） for thermal energy storage. Na2CO3/MgO composite PCMs were prepared and their chemical compatibility and thermal stability were studied. MWCNTs introduced with Na2CO3/MgO composite PCMs were also investigated and scanning electron microscopy （SEM） characterization was used to demonstrate the uniform dispersion of MWCNTs in Na2CO3/MgO composite PCMs. The composites with added MWCNTs still display good thermal stability with mass losses lower than 5%. Introducing MWCNTs into composite Na2CO3/MgO PCMs by material formation/calcination signifi.cantly enhances the thermal conductivity of the composite PCMs. The thermal conductivity of the composite PCMs was found to increase with an increase in the weight fraction of the added MWCNTs and an increase in the testing temperature. This study may present a promising way to prepare high temperature phase change materials with superior properties such as improved thermal stability.

Carbonate-salt-based composite materials for medium- and high-temperature thermal energy storage

This paper discusses composite materials based on inorganic salts for medium- and high-temperature thermal energy storage application. The composites consist of a phase change material （PCM）, a ceramic material, and a high thermal conductivity material. The ceramic material forms a microstructural skeleton for encapsulation of the PCM and structural stability of the composites; the high thermal conductivity material enhances the overall thermal conductivity of the composites. Using a eutectic salt of lithium and sodium carbonates as the PCM, magnesium oxide as the ceramic skeleton, and either graphite flakes or carbon nanotubes as the thermal conductivity enhancer, we produced composites with good physical and chemical stability and high thermal conductivity. We found that the wettability of the molten salt on the ceramic and carbon materials significantly affects the microstructure of the composites.

Scenario analysis of energy-based low-carbon development in China

China＇s increasing energy consumption and coal-dominant energy structure have contributed not only to severe environmental pollution,but also to global climate change. This article begins with a brief review of China＇s primary energy use and associated environmental problems and health risks. To analyze the potential of China＇s transition to low-carbon development,three scenarios are constructed to simulate energy demand and CO2 emission trends in China up to 2050 by using the Long-range Energy Alternatives Planning System（LEAP） model. Simulation results show that with the assumption of an average annual Gross Domestic Product（GDP） growth rate of 6.45%,total primary energy demand is expected to increase by 63.4%,48.8% and 12.2% under the Business as Usual（BaU）,Carbon Reduction（CR）and Integrated Low Carbon Economy（ILCE） scenarios in 2050 from the 2009 levels. Total energy-related CO2 emissions will increase from 6.7 billion tons in 2009 to 9.5,11,11.6 and11.2 billion tons; 8.2,9.2,9.6 and 9 billion tons; 7.1,7.4,7.2 and 6.4 billion tons in 2020,2030,2040 and 2050 under the BaU,CR and ILCE scenarios,respectively. Total CO2 emission will drop by 19.6% and 42.9% under the CR and ILCE scenarios in 2050,compared with the BaU scenario.To realize a substantial cut in energy consumption and carbon emissions,China needs to make a long-term low-carbon development strategy targeting further improvement of energy efficiency,optimization of energy structure,deployment of clean coal technology and use of market-based economic instruments like energy/carbon taxation.

1.54 μm photoluminescence enhancenment of Er^(3+) -doped ZnO films containing nc-Ge: joint effect from Er^(3+) local environment changing and energy transfer of nc-Ge

ZnO films containing Er and Ge nanocrystals(nc-Ge) were synthesized and their photoluminescence(PL) properties were studied. Visible and near-infrared PL intensities are found to be greatly increased in nc-Ge-containing film. Er-related 1.54 μm emission has been investigated under several excitation conditions upon different kinds of Ge, Er codoped ZnO thin films. 1.54 μm PL enhancement accompanied by the appearance of nc-Ge implies a significant correlation between nc-Ge and PL emission of Er^(3+). The increased intensity of 1.54 μm in Ge:Er:ZnO film is considered to come from the joint effect of the local potential distortion around Er^(3+)and the possibleenergy transfer from nc-Ge to Er^(3+).

Performance of a collector-storage solar air heating system for building mechanical ventilation preheating in the cold area

The application of solar thermal energy to preheat cold fresh air for mechanical ventilation could save a lot of energy and ensure the stable operation of the ventilation system.In this paper,a kind of collector-storage solar air heating system(CSSAHS),in which the thermal storage unit(TSU)is characterized by a dual S-channel for heat transfer,is proposed and the mathematical model for the integrated system was established.The model including the TSU,solar air collector,heat recovery device,and the fan was verified by an experimental study set up in a typical cold city in China.The model has been verified by experiments.The simulation results demonstrate that fresh air is the most important factor affecting storage/release efficiency.The increasing rate of heat release efficiency in the range of fresh air temperature-6-18°C is about 1.58%/°C.The solar heat collector area and the size of the TSU suitable for representative cities in cold regions are optimized based on multi-condition simulation analysis.The CSSAHS can preheat fresh air for 5 h after heat storage and the release efficiency is between 52 and 74%.Compared with other systems,the energy-saving rate of the CSSAHS is 26.5-33.3%in cold winter,and the heat supply ratio of the TSU is 24.4-35.1%.