High Temperature Field Research Articles

Investigation of structural, optoelectronic and thermoelectric properties of GaCuX2 (X = S, Se and Te) chalcopyrites semiconductors using the accurate mBJ approach

Ternary chalcopyrites have recently been the focus of scientists due to their optoelectronic and thermoelectric application as solar energy converters, nonlinear optical devices and detectors. In the present study, we used the first principle calculations based on the density functional theory (DFT) to explore the structural, optoelectronic and thermoelectric properties of GaCuX2 (X = S, Se and Te). The electronic band structure, density of states and optical properties were investigated using the modified Becke Johnson (TB-mBJ) approximation. These materials were discovered to be direct band gap semiconductors in this study, which agrees well with previously reported results. When compared to GaCuS2 and GaCuTe2, GaCuSe2 has a smaller gap value, due to the lower chemical bonding nature of Ga and Se atoms. The density of states of these three ternary chalcopyrites, as well as their optical properties including dielectric functions, optical conductivity and absorption coefficient have also been examined and discussed in details. The maximum reflectivity occurs at 13.5 eV, which exists in the ultra-violet region, showing that investigated materials can be employed to shield high frequency ultraviolet radiations. The calculated maximum refractive index static value varies from 1.5 to 5.5 eV, predicting that the materials under consideration can be used in a vast range of optoelectronic applications, especially in the visible range. GaCuS2 shows high refraction among these compounds. Finally, the thermoelectric properties of these materials, such as the Seebeck coefficient, the power factor and figure of merit, are analyzed using the semi-classical Boltzmann theory as executed in the BoltzTraP code. The high Seebeck coefficient and figure of merit values reveal that these systems belong to a new class of high-efficiency thermoelectric materials (TE) for high-temperature application fields. These findings are likely to open up new route for researchers looking into the potential areas of application of these compounds in thermoelectric and optoelectronic devices.

Spark plasma extrusion of binder free hydroxyapatite powder

Abstract This work explores the possibility of manufacturing dense and nanocrystalline hydroxyapatite (HA) large monoliths by spark plasma extrusion (SPE). This method combines uniaxial mechanical compression, high temperature, and electromagnetic field to promote the extrusion and sintering of HA powder in one single step. The results show that the binder-free extrusion of pre-compacted HA powder is feasible at a temperature similar to the temperature at which nanocrystalline HA shows superplastic behavior. The extrusion continues throughout the sliding and rotation of the particles, and also due to the grain boundary sliding, up to the point where no more material is available, thus producing monoliths of nearly 30 mm in length and 10 mm in diameter. The dehydration and smooth surface of the powder appear as paramount factors to facilitate the HA extrusion without additives. The extruded HA preserved the stoichiometry and nanometric grain size and exhibited preferential microstructural alignment in the direction of extrusion. The material experiences local thermal and pressure gradients during extrusion, producing different densification and hardness along its length. The SPE of HA will benefit the healthcare field by offering new processing approaches of bone substitutes and osteosynthesis devices.

A Facile Method for Fabricating a Monolithic Mullite Fiber-Reinforced Alumina Aerogel with Excellent Mechanical and Thermal Properties.

Alumina aerogels are considered to have good application prospects in the high-temperature field. In this study, monolithic mullite fiber-reinforced alumina aerogels with excellent mechanical and thermal properties were synthesized via a facile method without the use of any chelating agents. This method successfully avoids the introduction of impurities during the use of catalysts and chelating agents while greatly reducing gelation time, and thus helps mullite fibers to uniformly disperse in the sol. The compressive stress at 80% strain of the obtained mullite fiber-reinforced alumina aerogels was as high as 16.04 MPa—426% higher than that of the alumina aerogel without the addition of mullite fibers. Regarding thermal properties, the shrinkage of the mullite fiber-reinforced alumina aerogels (AM) samples was less than 1% after heat treatment at 1300 °C for 2 h. Furthermore, the rear-surface temperature of the AM samples burned by a butane blow torch was only 68 °C. These outstanding properties make AM samples promising for application in thermal insulation materials in high-temperature fields such as aerospace and industrial thermal protection in the future.

Multiscale-Band K-Distribution Model for Molecules in High-Temperature Gases

Radiation heat transfer plays a dominant role in high-temperature flow field. Rapid and reliable calculation of spectral radiation properties is beneficial for thermal analysis and detection of radiation target. In this paper, a multiscale-band k-distribution model is proposed for the study of radiation properties in high-temperature gases. The accurate absorption coefficients are firstly calculated using the line-by-line model. The slope of the accurate absorption coefficient line and its slope threshold are then extracted and analyzed, which act as a basis to divide the absorption coefficient line into multiple segments. For different segments, different bandwidths are chosen for the corresponding band k-distribution model. In the model, the 7-point Gauss–Lobatto method is employed to obtain the optimized absorption coefficients. These optimized absorption coefficients formed the absorption coefficient database. The radiation intensities of gases are finally calculated and analyzed based on the optimized database. Experimental results suggest that the multiscale-band k-distribution model can improve the efficiency up to 35% compared with the widely used narrow-band k-distribution model. Simultaneously, the relative calculation error is less than 5% compared with the most accurate line-by-line model.

Sustainability and financial assessments and double-criteria optimization of a novel power/hydrogen coproduction scheme using solar power and compressed air energy storage cycle

The use of solar energy is vital for the future of meeting the energy demand in the world. Different high- or medium-temperature solar-based power plants have been introduced and examined; however, the low exergetic performance of the solar power-to-electricity process is the principal defect. Although using thermal energy storage in such plants leads to continuous production throughout the day, it also increases the rate of exergy destruction. To improve this deficiency, the present study suggests and studies the simultaneous use of thermal energy storage and compressed air energy storage technologies in a high-temperature soar-based coproduction system by considering a multi heat recovery technique. In this regard, the operation of the system is divided into three periods of the day, namely, storing (low-radiation mode), charging (high-radiation mode), and discharging (night times). Hence, a Brayton cycle equipped with a high-temperature solar field using heliostat mirrors is established. In addition, an organic Rankine cycle is employed for heat recovery. In addition, a low-temperature electrolyzer is utilized for hydrogen generation. The ability of the suggested framework is investigated from the exergetic, sustainability, and financial aspects and is optimized by an advanced evolutionary algorithm. The optimum state indicates that the objective functions, i.e., exergetic round trip efficiency and unit cost of the system, are 26.17% and 0.159 $/kWh, respectively. Furthermore, the electricity capacity and hydrogen production rate are obtained at 7023 kW and 627.1 kg/h, respectively. Moreover, its sustainability index and exergoenvironmental impact index are found at 1.66 and 2.30, respectively.

On the possibility of technosphere safety by superionic

The purpose of this article is an attempt to substantiate the possibility of using a new technology for cleaning the industrial atmosphere in a separate workshop of the Taldykorgan battery plant "Kainar AKB", which produces, in particular, powerful batteries for K–700 tractors for agriculture. The innovative technology of air purification proposed by us in the technosphere of the manufacture of batteries for the agricultural production complex is based on the use of transport ion-conducting properties of solid electrolytes made of stabilized zirconium dioxide. The traditional methods of industrial atmosphere purification in enterprises and factories known to us, in our opinion, are morally outdated in terms of bulky external dimensions, noise generation, and need for systematic maintenance. The installation developed by us from a superionic conductor is devoid of these disadvantages, it is low-inertia, does not create a noise effect, compact and small-sized. Our ion conducting solid electrolyte is a ceramic material in the form of pipes, test tubes, tablets, initially containing impurity cations of lower valence, such as calcium, yttrium, scandium, in comparison with zirconium. Actually, these impurity cations create the presence of vacancies or holes in the solid cubic structure of zirconium dioxide. Only oxygen anions will be transported through these vacancies under the effect of external factors, high temperature, and DC electric field. The research method is based on the measurement of the electromotive force, which is recorded at the boundary section: air/superionic/air, which is uniquely mathematically related to oxygen concentration in air stream.

Robust quantum entanglement and teleportation in the tetrapartite spin-1/2 square clusters: Theoretical study on the effect of a cyclic four-spin exchange

The whole entanglement measure so-called geometric Π4 average of tangles and bipartite entanglement of the antiferromagnetic spin-1/2 XXX Heisenberg model on a tetranuclear square cluster with cyclic four-spin interaction are rigorously examined by the help of thermal negativities. The model comprises two nearest-neighbor exchange couplings J1 and J2 such that J1≫J2. When the cyclic four-spin exchange is zero, the maximum value of whole entanglement Π4 is achieved at low enough temperatures and relatively high magnetic fields (B≈J1). Also, maximum bipartite entanglement between pair spins with exchange coupling J1 is achievable at high temperature and high magnetic field. This quantity remains alive for sufficiently high temperature and high magnetic field values comparable with the relevant exchange coupling J1. A nonzero value of the cyclic four-spin exchange notably enhances the degree of the whole entanglement, while it weakens the bipartite entanglement degree. We demonstrate that the whole entanglement reaches an unconventional minimum at a special parameter region of cyclic four-spin exchange almost ten order of magnitude smaller than J1, where the system is in a quantum antiferromagnetic state. The real complex [Cu4L4(H2O)4](ClO4)4 as a strong antiferromagnetic tetranuclear square compound provides us an experimental representative to estimate the strength of the whole and bipartite entanglements at high enough temperature. It is demonstrated that the entanglement negativities of this complex are yet depend on the considered cyclic four-spin interaction even though its magnitude is significantly smaller than J1. We realize that the possibility of quantum teleportation through a couple of discrete Cu4II complexes would solely happen for the magnetic fields lower than a critical value. It is also demonstrated that enhancing the cyclic four-spin exchange results in diminishing the average fidelity. Moreover, we conclude that the quantum Fisher information investigated for the pair of spins with exchange interaction J1 reaches its minimum close to the critical magnetic field at which a ground-state phase transition occurs from highly entangled state to separable one.

Study on the Structure, Magnetic Properties and Mechanism of Zn-Doped Yttrium Iron Garnet Nanomaterial Prepared by the Sol-gel Method.

To explore the effect and mechanism of bivalent ion doping on yttrium iron garnet (YIG), Zn-YIG (Zn-doped YIG) nanoparticles with a size of 60~70 nm were prepared by the sol-gel method. It was proven that Zn ion doping resulted in lattice expansion and internal stress due to crystallite size shrinkage. A Raman spectroscopic analysis proved the influence of Zn doping on the crystal structure and peak intensity by analyzing Raman vibration modes. The characteristics and chemical mechanism of mass loss and phase evolution in each temperature region were explored through TG-DSC measurements. Moreover, it was revealed that the antiferromagnetic coupling, pinning mechanisms and particle aggregation lead to coercivity, exhibiting different variation trends. A saturation magnetization (Ms) curve variation mechanism was further revealed, which was due to the thermal effects, super-exchange effect, and coupling effect between sub-lattices. Meanwhile, the influence of the thermal effect on Ms and its mechanism were explored by spin theory, and it was proven that it was mainly caused by the random arrangement of magnetic moments and thermal vibration. These results provide theoretical support for the wider application of YIG devices in microwave and high-temperature fields.

Significantly improved high-temperature charge-discharge efficiency of all-organic polyimide composites by suppressing space charges

In order to satisfy the miniaturization trends of power electronic devices and safe operation in harsh environments, high-temperature dielectric polymers with excellent energy density and great reliability are desired in advanced electronic and power systems as electrostatic capacitors. Herein, the all-polymer dielectric composite films, consisting of ferroelectric polymer poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) as filler and linear polymer polyimide (PI) as matrix, were fabricated by in situ polymerization method for electrostatic energy storage scenarios. Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) results indicated that the P(VDF-HFP) was successfully compounded into the PI matrix. The dielectric permittivity of PI/P(VDF-HFP) energy storage composites was enhanced, while the breakdown strength and electrical resistivity values were wrecked slightly with enhancive mass fraction of P(VDF-HFP). Consequently, the discharged energy density (Ud) of PI-10, PI-20 and PI-30 were 2.60, 2.90, and 3.16 J/cm3 at 30 ℃ and 400 MV/m, respectively, which were 1.05, 1.17 and 1.27 times than those of neat PI film (2.48 J/cm3). Notably, an interesting phenomenon was observed that the charge-discharge efficiency (η) of all-organic composites was dramatically improved situated in high-temperature conditions. When the mass ratio of P(VDF-HFP) to PI was 1:4, the corresponding Ud and η of PI-20 could be significantly improved to 2.25 J/cm3 and 76.9% at 382 MV/m and 150 ℃, which were 6.7 and 10.5 times than those of neat PI film (0.336 J/cm3 and 7.3%) at 300 MV/m, respectively. Impressively, PI-30 film delivers an enhanced Ud of 1.81 J/cm3 and η of 71% at 200 ℃ and 308 MV/m. The significant improvement in the efficiency of composites under high-temperature environment is attributed to the suppression of space charges, which was verified by the TSDC results. In addition, the all-polymer composites exhibited outstanding cycling stability under harsh conditions of high temperature and high electric field. Our fabricated PI/P(VDF-HFP) composite films present potential energy storage applications in the high temperature environments with demand for flexible dielectric materials with upgraded permittivity, excellent energy density as well as reliable cycling stability.

On-Line Detection of Demagnetization for Permanent Magnet Synchronous Motor via Flux Observer

Demagnetization in permanent magnet synchronous motor (PMSM), caused by high temperature or inverse magnetic field, may increase loss and torque ripple, and even degrade the system stability in severe cases. On-line detection can identify the incipient demagnetization of permanent magnets (PMs), as well as providing reference for subsequent fault-tolerant control, so as to avoid further demagnetization. Therefore, an on-line demagnetization detection method is proposed in this paper by using flux observer. First, an observer is established in the three-phase stationary reference frame by taking the stator currents and the amplitudes of the fundamental and harmonic components of flux as state variables. Then, three demagnetization indexes are presented to evaluate the properties of PMs based on the observed flux information. The proposed method can directly track the amplitude of harmonic flux and evaluate the severity of the demagnetization more comprehensively. Simulation and experimental results demonstrate the effectiveness of the proposed method.

Specific-Ion Effects Unveil a Route for Modulating Oxidatively Triggered Acid Systems for Reservoir Applications.

On-demand in situ preparation of industrially relevant organic acids, namely, methanesulfonic acid, triflic acid, and trifluoroacetic acid, is demonstrated in this study. Sodium and potassium bromate were found to selectively oxidize a series of ammonium salts NH4X, where X = OMs, OTf, or OTFAc, with characteristic clock reaction behavior. The redox system undergoes rapid acid formation following an extended induction time at 150 °C and is identified as a potential candidate for high-temperature oil field chemistry applications where on-demand acid placement is required. Although the reaction kinetics for acid formation from NH4X salts where X = Cl, Br, F, or SO42- follows a pKa trend, the rates of formation of the organic acids are much slower and deviate from this trend. Furthermore, we demonstrate that the rate of acid formation can be modulated by the addition of alkali metal salts, with the strongest effect observed from LiBr. Spectroscopic studies implicate the formation of lithium bromate ion pairs that slow or altogether inhibit the oxidation of NH4+. Additionally, the presence of Br- alters the reaction path, eliminating the clock behavior and creating a pathway for Li+ to strongly inhibit the redox reaction. From these studies, a method for slowing ammonium oxidation under reservoir conditions to sufficiently delay acid formation until the precursors are placed in the zone of interest is identified.

Influencing factors and experimental study on electrothermal high temperature field of the outburst coal in China

In this study, we proposed a method to solve the problems of low permeability of the outburst coal seams and gas extraction in China. We used heating cables to heat outburst coal seams and increase the gas desorption capacity of coal seams to prevent outbursts. An experimental cement tank was constructed to investigate the influence of the heating temperature, cable layout and thermal insulation conditions in the cement tank on the electrothermal high-temperature field characteristics of the outburst coal sample. The following results were obtained: The effective heating radius of the heating cable was 800 mm ≤ R < 1,000 mm. As the heating time increased, the temperature of the coal sample in the cement tank first increased rapidly and then became stabilized. The same heating time, The coal sample temperature of the cement tank in the third experimental scheme is the highest When the heating temperature was 300°C, the maximum coal sample temperature was 107°C. The stable temperature of the coal sample in the cement tank was considerably higher under thermal insulation conditions than under no-thermal insulation conditions.

Simulation and experimental study of uniformity of temperature field of electrically heated water

With the aim of investigating the non-uniformity of the temperature field of electrically heated water in a horizontal stationary circular tube, we numerically simulated the axial and radial temperature fields in a horizontal circular tube using the Fluent CFD package. We then designed a sectioned grouping heating scheme based on a two-position controller for experimental verification. The results show that the axial temperature in the tube is non-uniform if the tube is not placed horizontally. In the heating stage, uniform heating of the entire tube surface leads to significant vertical temperature stratification, with higher temperature in the upper part and lower temperature in the lower part of the circular tube. However, heating only the lower half of the tube's surface can reduce the temperature difference between the upper and lower layers from more than to less than, effectively improving the uniformity of the temperature field. During steady-state operation, due to the limitations of the two-position controller algorithm, the radial temperature deviation rises to a maximum of for the sectioned grouping heating mode. Compared with the whole-tube uniform heating mode, the grouping heating mode, especially the four-group heating mode, has obvious advantages with regard to the time to reach steady-state and the uniformity of the steady-state temperature field. This paper provides a reference for the design of heating schemes for horizontal isobaric closed circular tubes with high precision, minimal overshoot and good temperature field uniformity.

Numerical performance assessment of double-shell targets for Z-pinch dynamic hohlraum

A Z-pinch dynamic hohlraum can create the high-temperature radiation field required by indirect-drive inertial confinement fusion. A dynamic hohlraum with peak radiation temperature over 300 eV can be obtained with a >50 MA Z-pinch driver according to the scaling law of dynamic hohlraum radiation temperature vs drive current. Based on a uniform 300 eV radiation temperature profile with a width of 10 ns, three double-shell capsules with radii of 2, 2.5, and 3 mm are proposed, and the corresponding fusion yields from a one-dimensional calculation are 28.8, 56.1, and 101.6 MJ. The implosion dynamics of the 2.5 mm-radius capsule is investigated in detail. At ignition, the areal density of the fuel is about 0.53 g/cm2, the fuel pressure is about 80 Gbar, and the central ion temperature is about 4.5 keV, according to the one-dimensional simulation. A two-dimensional simulation indicates that the double-shell capsule can implode nearly spherically when driven by the radiation field of a Z-pinch dynamic hohlraum. The sensitivities of the fusion performance to the radiation temperature profiles and to deviations in the capsule parameter are investigated through one-dimensional simulation, and it is found that the capsule fusion yields are rather stable in a quite large parameter space. A one-dimensional simulation of a capsule embedded in 50 mg/cm3 CH foam indicates that the capsule performance does not change greatly in the mimicked environment of a Z-pinch dynamic hohlraum. The double-shell capsules designed here are also applicable to laser indirect-drive inertial fusion, if a laser facility can produce a uniform 300 eV radiation field and sustain it for about 10 ns.

Polymer composites with high energy density and charge–discharge efficiency at high temperature using aluminum oxide particles

Polymer-based dielectric capacitors with excellent elevated-temperature capacitive performances are highly demanded in next-generation electronic power systems. Here, we design an effective and low-cost way to fabricate high-temperature polymer capacitors via adding Al2O3 nanoparticles (NPs) into polyetherimide (PEI) nanocomposites. Benefited from good thermal stability, high thermal conductivity of Al2O3 NPs and high glass transition temperature of PEI, the Joule heat caused by high temperature and large electric field, dissipate quickly. Therefore, the nanocomposites present low dielectric loss and superior high-temperature capacitive properties. Consequently, even at 150 °C, the Al2O3 NPs/PEI nanocomposite delivers still slim electric displacement-electric field (D-E) loops, small remnant electric displacement (Dr), and large maximum electric displacement (Dmax). Thus, it results in an ultra-high discharged energy density (Ue) of 6.68 J cm−3, which far exceeds the state-of-the-art polymer and polymer composites, and high efficiency (η) of 84.77% at 150 °C. This work addresses the paradox that large Ue and high η cannot be simultaneously achieved in high-temperature polymer composites.

Investigation on effect of semiconducting screen on space charge behaviour of polypropylene‐based polymers for HVDC cables

High voltage direct current (HVDC) power transmission cable is critical for realising sustainability through renewable energy revolution. Eco-friendly thermoplastic polypropylene (PP)-based polymers/nanocomposites are regarded as promising candidates for replacing current thermoset crosslinked polyethylene (XLPE) cables. As an essential component of the extruded HVDC cable for improving conductor/insulation interface and suppressing charge injection to insulation at high DC electrical stresses, developing semiconducting (SC) screens that are compatible with PP-based insulation is of similar importance but has not been well studied yet. This work aims at designing PP-based semiconducting screens and investigating space charge behaviours of SC/PP/SC sandwich specimen to unfold the effect of semiconducting materials, bonding methods, applied DC electric field, and temperature on charge injection, accumulation, transportation, and dissipation in PP-based insulation. Although conventional thermal, mechanical, and low field electrical characterisations demonstrated that all of the developed semiconducting materials meet the performance criteria of commercial semiconducting materials, their space charge and local electric field distribution varied significantly at high DC fields. Compared with the traditional non-bonded configuration used at lab-scale, charge injection was enhanced in hot-pressed SC/PP/SC samples with tightly bonded interfaces, which better reflects the real situation in extruded cables. High temperature further intensified charge injections. Besides, our results also revealed that high temperature and electric field strongly influence charge mobilities and consequently their distribution and local electric field in PP-based insulations.

Flexible nanocomposite paper with superior fire retardance, mechanical properties and electrical insulation by engineering ultralong hydroxyapatite nanowires and aramid nanofibers

With the increasing popularity of modern electronic devices in the fifth-generation (5G) era, high-performance and high-safety electrically insulating materials with good mechanical flexibility and strength, high thermal stability and fire resistance are urgently needed. Herein, we report a highly flexible, thermally stable, and fire-retardant nanocomposite paper with high dielectric breakdown strength and mechanical strength by synergistically integrating one-dimensional ultralong hydroxyapatite (HAP) nanowires and aramid nanofibers (ANFs) through the vacuum-assisted filtration process. The as-prepared HAP/ANF nanocomposite paper has a nanowire/nanofiber networked framework and a layered structure, and exhibits high tensile strength (73.5 MPa), fracture strain (7.4 %), folding durability (1396 times under a loading weight of 9.8 N), excellent flexibility, and good processibility. Notably, the HAP/ANF nanocomposite paper has a superior dielectric breakdown strength (92.4 kV mm−1), high thermal stability and flame retardancy in comparison with the commercial Nomex T410 electrical insulation paper. The multifunctional HAP/ANF nanocomposite paper is promising for applications in miniaturized and flexible electronic devices, high-voltage electrical insulation equipments, and fire-retardant and high-temperature fields.

Studying magnetic-polaron cooper-pair-breaking effects in Bi2Sr2CaCu2O8+δ by femtosecond photoexcitation

The relation between magnetism and superconductivity, whether magnetism is beneficial to superconductivity or they permit co-existence and competition, has been a long debate in the high-temperature superconducting field. Here, to explore this odd issue, we study the relaxation dynamics of photoinduced magnetic-polaron and superconductivity quasiparticles by an ultrafast time-resolved optical reflectivity technology in Bi2Sr2CaCu2O8+δ . When the pump fluence is less than 7 mW, time-resolved reflection spectrum ΔR(t)/R 0 is dominated by the superconducting component. It is noteworthy that a large of photoinduced magnetic-polaron component can cause the inhibition of the superconducting component when the variable pump fluence is more than the value 7 mW. It can be attributed to the strong photoinduced magnetic-polaron Cooper-pair-breaking mechanism. Further studies have shown that the photoinduced magnetic-polaron Cooper-pair-breaking mechanism is similar to the pair-breaking effect caused by the magnetic impurity Fe in the Bi2Sr2CaCu2O8+δ superconductor, although the forms of their action are different.

Numerical Simulation of Seepage-Heat-Solid Coupling of Gas Seepage in Prepumped Boreholes under Electrothermal High Temperature Field

In order to verify the law of coal bed gas desorption and permeability under electrothermal high-temperature field, by establishing the mathematical model of gas seepage-heat-solid coupling, and taking gas drainage working face in Guizhou as an engineering example, the characteristics of the high-temperature field of coal under different heating hole temperatures are simulated. The COMSOL software is used to simulate the high-temperature field characteristics, thermal damage, and permeability of coal under different heating hole temperatures. The numerical simulation results show the following:(1) the influence trend of a high-temperature field on coal thermal damage and permeability is consistent, when the heating temperature is higher than 600°C, the thermal damage and permeability of coal seam change suddenly and increase with the increase of temperature. (2) When the temperature of a heating hole is 200-800°C, the gas permeability in the damaged area increases with the increase of temperature. When the heating temperature is greater than 600°C, the radial and axial permeability around the heating hole will increase. (3) Compared with the experimental data obtained by the existing researchers, the simulation results of coal permeability under the electric heating high-temperature field have a high consistency with the experimental results of Junrong and others.

Graphene-based deep eutectic solvent nanofluids with high photothermal conversion and high-grade energy

The photothermal properties of nanofluids have been the focus of direct absorption solar collectors (DASCs). At present, there are few studies on the application of nanofluids in high temperature field. Liquids with low specific heat capacity can reach higher temperatures under the same solar radiation, which broadens the application of nanofluids at high temperatures. In this work, urea/choline chloride (ChCl) deep eutectic solvent (DES) is proposed as a new base fluid. Compared with water, urea/ChCl DES has high boiling point and small specific heat capacity, which exhibits better photothermal performance in DASCs. DES is prepared by heating method and its photothermal conversion efficiency reaches high value of 56.9%, which is 36.4% and 11% higher than that of water and ethylene glycol (EG), respectively. Experimental studies reveal that the photothermal conversion efficiency of 40 ppm graphene DES nanofluid can be as high as 94.3%, and its maximum temperature can reach 115 °C when the solar radiation is raised to 2000 W•m−2. In addition, graphene DES nanofluids demonstrate great stability with no settling within 45 days. This research demonstrates that DES nanofluids have the high energy grade, which expands the scope of its application.