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Abstract Expanded graphite (EG) is considered as a promising supporter for phase change material (PCM) due to its unique porous structure and excellent heat transfer ability. In the study, EG with different mass fractions (9 wt.%, 13 wt.%, 16.67 wt.%, and 20 wt.%) was respectively blended with MgCl 2·6H2 O. The thermal conductivity data of composite PCMs with 9 wt.%, 13 wt.%, 16.67 wt.%, and 20 wt.% of EG was respectively measured to be 0.942 W/m K, 1.053 W/m K, 1.354 W/m K and 1.658 W/m K. DSC analysis showed that 16.67 wt.% of EG decreased the degree of supercooling by 29.4 °C and that the addition of 3.0 wt.% SrCO 3 further decreased the degree of supercooling by 17.9 °C. The maximum encapsulation weight percentage of MgCl2·6H2O reached 83.33 wt.% after 30 phase change cycles without significantly reducing its latent heat value, exhibiting the relatively stable thermal reliability.

Abstract A “permeability equilibration time” is typically assumed in interpreting permeability measurements – indicating that equilibration has been reached and both sorption-induced changes in deformation and their impact on permeability evolution have ceased. However, for extremely low matrix permeability (tight) dual porosity rocks, this “permeability equilibration time” may easily exceed the time interval between two consecutive permeability measurements – invalidating the interpretation of a steady permeability if the non-steady state conditions are not correctly accommodated. This is especially important where pressure diffusion from fracture to matrix results in a non-monotonic and non-asymptotic approach to a steady permeability, but instead contains multiple stages, plateaus and permeability reversals. We validated this hypothesis through experiments and analysis. Experiments measured the non-monotonic and scale-dependent deformations of fracture and matrix and linked these directly to the dynamic evolution of reservoir permeability. These laboratory strain measurements were integrated with numerical analyses to explore how mass and stresses transferred between matrix and fracture and were coupled under conditions of constant confining pressure. Strain gauges were distributed to directly measure stress transfer between matrix and fracture and interrogated deformation at different scales and at different proximities to control fractures. The prismatic sample of coal was tested under freely expanding boundary conditions. Optical microscopy and X-ray CT imaging were used to define the fracture distribution throughout the sample with mercury intrusion (capillary) porosimetry (MICP) constraining the pore size distribution and enabling independent estimation of matrix permeability. A numerical model was built and verified by matching measured strains and then applying this to model the evolution coal permeability from initial to ultimate equilibrium. Both the experimental and numerical results show that the final equilibrium state (pressure, stress and mass contents) for the matrix system extends to months rather than hours and suggests that some current permeability data may therefore reflect a non-equilibrium permeability state. Results also show that during this non-equilibrium condition, the swelling of the matrix near the fracture will cause not only compaction and narrowing of the fracture, but also shrinkage of the matrix that is distant from the fracture under constant confining pressure condition. Both experimental and numerical results demonstrate that the evolution of non-equilibrium strain/permeability is determined by the matrix-fracture interactions, including sorption-induced swelling/shrinking, through transient stresses in matrix and fractures. And that these non-equilibrium stress transfers determine the dynamic permeability evolution during gas extraction (e.g., CH4) or injection (e.g., CO2) at reservoir scale for tight dual porosity rocks (e.g., coal and shale).

Abstract Unconventional natural gas, including coalbed methane and shale gas, has become important natural gas resources. Coal and shale reservoirs are characterised by low porosity and low permeability and difficult for gas production. These reservoirs are also considered as fractured reservoirs, i.e. the natural fracture/cleat system in coals and bedding direction microfractures in shales. Permeabilities of these reservoirs are sensitive to stress change. During gas production, the pressure drawdown significantly increases effective stress, and thus decreases the absolute permeability. The relationship between permeability and stress is characterised by fracture compressibility, which is difficult and costly to be obtained from the field, but can be acquired easily from laboratory measurement. In this review article, the laboratory methods to obtain fracture compressibility were reviewed. Literature data on fracture compressibility for coals and shales were collated and the relationships between fracture compressibility and pressure, stress and rock properties were discussed. It is found that fracture compressibility is higher for coals than for shales, and the fracture compressibility for proppant supported fracture is even lower than that for the same shale or coal. Moreover, fracture compressibility is variable depending on gas type, gas pressure, and stress. Fracture compressibility has no correlation with absolute permeability in general, but has a weak positive correlation for the same sample.

Aqueous energy storage devices attract increased attention due to their high safety, low cost, and easy maintenance. However, the low energy density caused by the narrow electrochemical stability window (ESW) of aqueous electrolytes severely restricts their widespread applications. Herein, a new type of “small‐molecule crowding” electrolyte of 95EG‐H2O (95 wt% ethylene glycol [EG]) is proposed for the first time. Significant enhancement of water molecular stability is accomplished through the engineering of a hydrogen bond network. The small‐molecular crowding agent (EG) not only expands the ESW to 3.2 V, but also endows the electrolyte with low viscosity. As a proof‐of‐concept device, the symmetry carbon‐based supercapacitor using the newly developed electrolyte exhibits a so far record‐high operating voltage of 2.8 V, a high energy density of 58.7 Wh kg−1 at a power density of 1.4 and 30.3 Wh kg−1 at a power density of 42 kW kg−1, and a durable lifespan exceeding 20 000 cycles at a current density of 5 A g−1.

The production of synthesis gas has gained increasing importance because of its use as raw material for various industrial syntheses. In this paper synthesis gas generation during the reaction of a coal/methane with steam and oxygen, which is called the co-gasification of coal and natural gas, was investigated using a laboratory scale fixed bed reactor. It is found that about 95% methane conversion and 80% steam decomposition have been achieved when the space velocity of input gas (oxygen and methane) is less than 200 h(-1) and reaction temperature about 1000 degrees C. The product gas contains about 95% carbon monoxide and hydrogen. The reaction system is near the equilibrium when leaving the reactor. (c) 2007 Elsevier Ltd. All rights reserved.

Abstract The compressed air storage connects charging and discharging process and plays a significant role on performance of Adiabatic Compressed Air Energy Storage (A-CAES) system. In this paper, a thermodynamic model of A-CAES system was developed in Matlab Simulink software, and a dynamic compressed air storage model was applied in the simulation, revealing the influence of time-varying temperature and pressure of air on performance indicators, e.g., roundtrip efficiency and energy density. The analysis results can be used as an explanation of the contradicting conclusions on system efficiency from other articles, as well as a reference in the design and operation of an A-CAES plant. There exists an optimal after-throttle-valve pressure when applying energy density as objective function with constant expander inlet pressure. A relatively higher heat transfer coefficient between atmosphere and air in storage tank results in more stored air in charging process and more released air in discharging process, which are of great benefit for A-CAES system in terms of energy density. The dynamic performance characteristic of compressed air storage can affect design capacity of first heat exchanger of expansion train and moreover, reduce roundtrip efficiency and energy density of A-CAES system.

Abstract A new skeletal mechanism of n-butane is developed for describing its ignition and combustion characteristics applicable over a wide range of conditions: initial temperature 690–1430 K, pressure 1–30 atm, and equivalence ratio 0.5–2.0. Starting with a detailed chemical reaction kinetic model of 230 species and 1328 reactions (Healy et al., Combust. Flame, 2010), the directed relation graph method is applied as the first step to derive a semi-detailed mechanism with 134 species. Then, the reaction path analysis in conjunction with temperature sensitivity analysis is used to remove the redundant species and reaction paths simultaneously under the condition of low-temperature and moderate-to-high temperatures, respectively. Finally, a skeletal n-butane mechanism consisting of 86 species and 373 reactions can be obtained. Mechanism validation indicates that the new developed skeletal mechanism is in good agreement with the detailed mechanism in predicting the global ignition and combustion characteristics. The new skeletal mechanism is further validated using extensive available literature data including rapid pressure machine ignition delay time, shock-tube ignition delay time, laminar flame speed, and jet-stirred reaction oxidation, covering a large range of temperatures, pressures, and equivalence ratios. The comparison results demonstrate that a satisfactory agreement between predictions and experimental measurements is achieved.

AbstractA solution‐processed acceptor‐π‐donor‐π‐acceptor (A‐π‐D‐π‐A) type small molecule, namely DCATT, has been designed and synthesized for the application as donor material in organic solar cells. The fused aromatic unit thieno[3,2‐b]thiophene (TT) flanked with thiophene is applied as π bridge, while 4,8‐bisthienyl substituted benzodithiophene (BDT) and 2‐ethylhexyl cyanoacetate are chosen as the central building block and end group, respectively. Introduction of fused ring to the small molecule enhances the conjugation length of the main chain, and gives a strong tendency to form π–π stacking with a large overlapping area which favors to high charge carrier transport. Small‐molecule organic solar cells based on blends of DCATT and fullerene acceptor exhibit power conversion efficiencies as high as 5.20 % under the illumination of AM 1.5G, 100 mW cm−2.