Heat Coefficient Research Articles

Construction of different metamorphic degree coal models and corresponding adsorption characteristics based on molecular simulation

Coal samples with different metamorphic degrees have different gas-adsorption capacities. Most of the existing studies analyze differences in gas-adsorption characteristics from a macro perspective, based on experimental methods, and there has been limited research on the micro level. Using industrial and elemental analyzes, Fourier-transform infrared spectroscopy, 13C-NMR, and X-ray photoelectron spectroscopy, we tested and analyzed the molecular-structure characteristics, such as elemental composition, atomic ratio, and functional-group type and distribution, of three coal samples: anthracite (WYM), coking coal (JM), and lignite (HM), with different metamorphic degrees and constructed their macromolecular-structure models. The carbon contents and densities of the models were consistent with the measured values. We also constructed a coal matrix model using a molecular simulation based on the constructed coal molecular model. By comparing and analyzing the trends of adsorption amount, isosteric heat, and selective adsorption coefficient, we explored the differences in the adsorption characteristics of single and binary mixtures on coals with different metamorphic degrees. The adsorption of CH4 and CO2 on the coal matrix conformed to the Langmuir adsorption model. With increasing metamorphic degree, the adsorption amount increased in the order WYM > JM > HM, and the adsorption capacity of the coal matrix for CO2 was higher than that for CH4. The isosteric adsorption heat of CH4 was proportional to the degree of coal metamorphism; however, its relationship with pressure was not clear. Under different temperature and pressure conditions, the selective adsorption of CH4/CO2 on coal with various metamorphic degrees decreased with an increasing CO2 molar ratio. Conditions of 303.15 K (30 °C), 2–4 MPa, and CH4/CO2 = 0.1 were more conducive to the competitive adsorption of CO2 than that of CH4.

Seasonal performance comparison analysis of the roll-bond photovoltaic thermal heat pump system in a multi-energy generation: An experimental study

Solar photovoltaic thermal heat pump systems contribute significantly to the building industry's goal of energy efficiency and “carbon neutrality” by producing multiple types of energy from the intensive use of solar energy to meet the varied and dispersed energy requirements of modern buildings. An experimental investigation of the roll-bond photovoltaic thermal heat pump system powered by a roll-bond photovoltaic thermal unit is presented in this study, together with the system's precise operating principle and the structural design of the unit. The theoretical underpinnings of experimental research are discussed, including the establishment of test platforms and error analysis, as well as the method for evaluating system performance, which includes solar power, heating, and cooling. Following that, continuous experiment monitoring under various weather conditions in Dalian is carried out throughout the year, which serves as the basis for system performance evaluation and comparison, with a focus on heating, power, and cooling. Comparison analysis results show that the heating and power generation performance in the summer season is the highest, with an average photovoltaic efficiency of 13.6% and an average heating coefficient of performance of 6.16, which is followed by the transition season and winter season, with an average photovoltaic efficiency and heating coefficient of performance of 11.9% and 6.05, 10.2% and 4.54, respectively. However, the performance of power and heating cogeneration in summer conditions fluctuates due to variations in solar radiation intensity. Furthermore, the system can run in cooling mode during the night, on overcast days, and on rainy periods to generate cooling capacity. The cooling performance is the highest during clear nighttime, followed by the overcast nighttime and overcast daytime, with an average cooling coefficient of performance of 2.99, 2.66, and 2.12, separately. Rain, as a cooling water source, significantly improves system cooling performance. The results show that the proposed roll-bond photovoltaic thermal heat pump system can generate high-efficient multi-energy under a variety of weather conditions while remaining stable over time, providing a valuable practical feasibility reference for renewable energy utilization in buildings in northern China.

Determination of thermophysical characteristics in a nonlinear inverse heat transfer problem

This paper presents a detailed and developed method for finding soil nonlinear thermophysical characteristics. Two-layer container complexes are constructed. The side faces of which are thermally insulated, so that one can use the one dimensional heat equation. In order not to solve the boundary value problem with a contact discontinuity and not to lose the accuracy of the solution method, a temperature sensor was placed at the junction of the two media, and a mixed boundary value problem is solved in each region of the container. In order to provide the initial data for the inverse coefficient problem, two temperature sensors are used: one sensor was placed on the open border of the container and recorded the temperature of the soil at this border, and the second sensor was placed at a short distance from the border, which recorded the air temperature. The measurements were carried out in the time interval (0,4tmax). At first, the initial-boundary value problem of nonlinear thermal conductivity equation with temperature dependent coefficients of thermal conductivity, heat capacity, heat transfer and material density is investigated numerically. The nonlinear initial-boundary value problem is solved by the finite difference method. Two types of difference schemes are constructed: linearized and nonlinear. The linearized difference scheme is implemented numerically by the scalar Thomas’ method, and the nonlinear difference problem is solved by the Newton’s method. Assuming the constancy of all thermophysical parameters, except for the thermal conductivity of the material, on the segment (0,tmax), the quadratic convergence of Newton’s method is proved and the thermal conductivity is calculated, while the solution of the linearized difference problem was taken as the initial approximation for the Newton’s method. By freezing all other thermophysical parameters, and using the measured temperatures in the segment (tmax,2tmax), the coefficient of specific heat of the material is found. Proceeding in a similar way, using the initial data on the segment (2tmax,3tmax), the density of the soil is determined. Also, based on the measured initial data on the segment (3tmax,4tmax), the heat transfer coefficient is determined.Based on the experimentally measured data, at each time interval, the corresponding functional is minimized using the gradient descent method. The differentiation of a nonlinear difference problem with respect to the desired parameter method is used to find the gradient of the functional. This method allows you to find the functional gradient and the damping coefficient of the gradient descent in an explicit form. In this case, the compilation and solution of the conjugate problem, which is a frequently used method for solving the inverse problems, is not needed.The performed numerical calculations show that for small time intervals the solutions of the linearized difference problem differ little from the solution of the nonlinear difference problem (1 - 3%). And for long periods of time, tens of days or months, the solutions of the two methods differ significantly, sometimes exceeding 20%. In addition, all thermophysical characteristics (8 coefficients) were found for a two-layer container with sand and black soil. Also the dependence of the temperature difference at the boundary between the environment and the soil for the heat transfer coefficient was shown.

A Numerical Intuition of Activation Energy in Transient Micropolar Nanofluid Flow Configured by an Exponentially Extended Plat Surface with Thermal Radiation Effects

In recent times, heat and mass transportation have had some of the most recognized and attractive research areas in computational fluid dynamics. It is useful in the modeling of the flow of nuclear reactors, bioinformatics, the medical discipline, etc. Driven by the execution of the flow in the manufacturing application, the goal of the present analysis is to explore the novel effect of micropolar fluid configured by an exponentially elongated sheet positioned horizontally in a porous channel. The impact of activation energy, internal heating, and heat and mass transfer features are integrated into the revised flow model. A mathematical framework for different flow fields is developed in order to highlight the significant aspects of the thermal and concentration slip effects evaluated on the extended plat surface, with the aid of appropriate transformation factors to diminish the nonlinear fundamental flow equations (PDEs) to a system of (ODEs). Precise numerical treatment for a wide range of pertinent parameters is adopted to solve the nonlinear system through a built-in algorithm in the MATHEMATICA platform. The features of prominent emerging parameters against various flow fields are viewed and addressed through plotted visuals. The influence of the factors on skin friction, heat, and mass coefficients offered through 3D animation is evaluated. The temperature profile improves with ascending values of Brownian parameter and thermophoretic diffusion force but diminishes with subject expansions in Prandtl number and thermal slip parameter. It has been noticed that the concentration outlines increase for reaction rate and activation energy parameters but dwindle for expending values of porosity parameter, Lewis number, and concentration slip parameter. Skin fraction values increase due to the growing nature of the micropolar and second-grade fluid parameters. Nusselt numbers upsurge for increasing thermophoretic diffusion parameters while exhibiting a declining trend for Brownian motion parameters.

CH4 adsorption and diffusion characteristics in stress-loaded coal based on molecular simulation

The Variety of roof stress during mining was one of the main factors affecting the adsorption and diffusion characteristics of coalbed methane. CH4 adsorption and diffusion characteristics in micro- and meso-pores of coal under different stress loading were simulated in this study by means of molecular mechanics and molecular dynamics. Firstly, the micro- and meso-pores of coal with four different slit widths (10 Å, 20 Å, 50 Å, and 80 Å, respectively) were established. Then, the stress-strain characteristics of the frameworks under different stress loading were studied by applying uniaxial stress. Finally, the CH4 adsorption and diffusion characteristics in different stress-deformed frameworks were investigated. Under the action of stress loading, the mesoporous framework showed a stronger deformation tendency. This process can be divided into the deformation occurring in the coal molecule and the slit. The energy evolution of coal framework under stress presented an exponential decay trend, which resulted in a decreasing trend in the adsorption amount of CH4 in the framework. Under the loading of 10 GPa external stress, the CH4 absolute adsorption amount in the four frameworks decreased by 65.21 %, 65.21 %, 68.07 %, and 70.98 %, and the excess adsorption amount decreased by 54.33 %, 69.07 %, 69.75 %, and 73.85 %, respectively, compared with the initial framework (σ = 0 GPa). The absolute adsorption amount and self-diffusion coefficient of CH4 both increased with the increasing slit width. In the compression stage of the framework, the heat released by CH4 adsorption showed a decreasing trend, and the self-diffusion coefficient of CH4 showed an increasing trend. However, in the stage of slit compression, the adsorption heat and self-diffusion coefficient tended to increase and decrease, respectively. By analyzing the diffusion types of CH4 in micro- and meso-pores, it was found that, in micropores, transitional and Knudsen diffusion were dominant, while in mesopores, transitional and Fick diffusion were dominant. This study can provide theoretical reference for coal seam gas pre-extraction engineering.

Modified stability analysis of double‐diffusive convection in viscoelastic fluid layer saturating porous media

AbstractThe present analysis mathematically investigates the thermohaline convection problem in viscoelastic fluid layer saturating porous media by utilizing the modified Boussinesq approximation. By performing linear stability analysis, the Darcy–Rayleigh numbers for stationary and oscillatory modes of convection are derived. The effects of different parameters describing the problem are studied numerically. In nonlinear stability analysis, the heat and mass transfer rates in the form of Nusselt and Sherwood numbers, respectively, are obtained for oscillatory convection using the derived Ginzburg–Landau equation. From the results, it is observed that overstability is the preferred mode of instability in linear stability. It is found that in linear double‐diffusive convection problems, the stress relaxation imparts a destabilizing effect whereas the strain retardation time, the coefficient of specific heat variation due to temperature, and the concentration gradient have a stabilizing effect on the system's stability. The numerical values of heat and mass transfer rates varied with the coefficient of specific heat showing that the heat transport decreases while the mass transport increases. Also, the stress relaxation time, the concentration gradient, and the gravity modulation's amplitude increase while the strain retardation time decreases the heat and mass transfer rates. The wavelength of oscillations remains unaltered with the variation of specific heat variation due to temperature. The modulation frequency does not affect the heat/mass transfer rate; though, the wavelength of oscillations decreases with increasing frequency.

Optomechanical squeezing with pulse modulation.

Quantum control technology provides an increasingly useful toolbox for quantum information tasks. In this Letter, by introducing a pulsed coupling to a standard optomechanical system, we show that stronger squeezing can be obtained with pulse modulation due to the reduction of the heating coefficient. Also, the general squeezed states, such as the squeezed vacuum, squeezed coherent, and squeezed cat states, can be obtained with their squeezing level exceeding 3 dB. Moreover, our scheme is robust to cavity decay, thermal temperature, and classical noise, which is friendly to experiments. The present work can extend the application of quantum engineering technology in optomechanical systems.

Transcutaneous Pulsed RF Energy Transfer Mitigates Tissue Heating in High Power Demand Implanted Device Applications: In Vivo and In Silico Models Results.

This article presents the development of a power loss emulation (PLE) system device to study and find ways of mitigating skin tissue heating effects in transcutaneous energy transmission systems (TETS) for existing and next generation left ventricular assist devices (LVADs). Skin thermal profile measurements were made using the PLE system prototype and also separately with a TETS in a porcine model. Subsequent data analysis and separate computer modelling studies permit understanding of the contribution of tissue blood perfusion towards cooling of the subcutaneous tissue around the electromagnetic coupling area. A 2-channel PLE system prototype and a 2-channel TETS prototype were implemented for this study. The heating effects resulting from power transmission inefficiency were investigated under varying conditions of power delivery levels for an implanted device. In the part of the study using the PLE setup, the implanted heating element was placed subcutaneously 6–8 mm below the body surface of in vivo porcine model skin. Two operating modes of transmission coupling power losses were emulated: (a) conventional continuous transmission, and (b) using our proposed pulsed transmission waveform protocols. Experimental skin tissue thermal profiles were studied for various levels of LVAD power. The heating coefficient was estimated from the porcine model measurements (an in vivo living model and a euthanised cadaver model without blood circulation at the end of the experiment). An in silico model to support data interpretation provided reliable experimental and numerical methods for effective wireless transdermal LVAD energization advanced solutions. In the separate second part of the study conducted with a separate set of pigs, a two-channel inductively coupled RF driving system implemented wireless power transfer (WPT) to a resistive LVAD model (50 Ω) to explore continuous versus pulsed RF transmission modes. The RF-transmission pulse duration ranged from 30 ms to 480 ms, and the idle time (no-transmission) from 5 s to 120 s. The results revealed that blood perfusion plays an important cooling role in reducing thermal tissue damage from TETS applications. In addition, the results analysis of the in vivo, cadaver (R1Sp2) model, and in silico studies confirmed that the tissue heating effect was significantly lower in the living model versus the cadaver model due to the presence of blood perfusion cooling effects.

Thermodynamic performances analyses and process optimization of a novel AA-CAES system coupled with solar auxiliary heat and organic Rankine cycle

An AA–CAES–SAH–ORC system for cascade utilization of energy is proposed based on the AA–CAES–SAH system. The position of the solar auxiliary heat is rearranged, and the exhaust air of air turbine is used as heat source of the organic Rankine cycle. Energy and exergy efficiencies, conversion coefficient of electricity storage, and potential coefficient of waste heat are selected as evaluation indicators to analyze the influence of different operating parameters on the thermodynamic performances, which is then compared with those of the AA–CAES–SAH system. Maximum energy and exergy efficiencies are selected as the objective functions for process optimization to reveal the optimal operating parameters and the best thermodynamic performances of the system. The results show that the four evaluation indicators of the AA-CAES-SAH-ORC system are better than those of the AA-CAES-SAH​ system. The AA-CAES-SAH-ORC system has better thermodynamic performances when the total pressure ratio of compressor unit, the temperature of thermal conductive oil heated by solar energy, the mass flow rate of air in the energy release process, and the temperature of exhaust gas in the air turbine are lower When the compression ratio of the low and high pressure stage compressors are 9.402 and 7.871, the expansion ratio of the high and low pressure stage air turbines are 9.099 and 9.990, the maximum energy and exergy efficiencies of the AA-CAES-SAH-ORC system are 64.71% and 71.88%, respectively.

Сушка растительных материалов, обработанных низкотемпературной плазмой

Efficient production requires reliable scientific foundations for new energy-saving technologies and drying processes that are able to transform plant materials into functional products. Mathematical modeling and control can provide efficient drying of cold plasma pretreated plant materials and predict its results.
 The present research featured raw potatoes and apples that underwent an electrophysical treatment by atmospheric pressure plasma in an air gas medium. The Luikov drying model served as the main model of heat and mass transfer as a system of coupled differential equations of humidity and temperature potentials. The mathematical modeling procedure and the program code were implemented in the MathCAD software.
 The cold plasma pretreatment proved to decrease the drying time. A greater disintegration index resulted in a shorter total drying time. The mathematical modelling of the heat and mass transfer processes almost coincided with the experimental results. The analysis of kinetic transfer coefficients of heat, moisture, and pressure potentials made it possible to develop a control parameter of the drying process of plant materials enti tled as the disintegration index.
 The proposed mathematical model explained the emerging effects, while the refined kinetic coefficients supported by experimental data clarified the processes in the drying material.

Comparative studies on superconductivity in Cr3Ru compounds with bcc and A15 structures

Chromium (Cr) is a transition metal element with 3d orbital electrons. In most compounds containing Cr, due to the correlation effect, twofold features, namely localization and itinerancy are expected. The localization gives rise to a magnetic moment, while the latter exhibits as the effective coherent weight for conductivity. Here we report the physical properties of Cr3Ru compounds with body-centered cubic (bcc) and A15 structures by using multiple experimental tools. The resistivity measurements show sharp superconducting transitions at = 2.77 K and = 3.37 K for the bcc and A15 structures, respectively. A high residual resistivity exists in both phases. Magnetization measurements also show rather narrow superconducting transitions, with a clear hump feature in the intermediate temperature region (about 150 K), which may be ascribed to the remaining antiferromagnetic spin fluctuations. A pronounced second peak effect has been observed in magnetization hysteresis loops in the superconducting state only for samples with bcc structure. The specific heat coefficient reveals a clear jump at critical temperatures (). We find that s-wave gaps can be adopted to fit the low temperature specific heat data of both samples yielding ratios of about 3.6, indicating a moderate pairing strength. Interestingly, the Wilson ratios are 3.81 and 3.62 for the bcc and A15 phases, suggesting a moderate correlation effect of conducting electrons in the normal state. Besides, for samples with A15 structure, another specific heat anomaly occurs at about 0.85 K and is sensitive to magnetic fields. In addition, by applying high pressures, both systems will exhibit an enhancement of with a rate of about 0.019 K GPa−1 and 0.013 K GPa−1 for the bcc and A15 phases, respectively. Our combinatory results point to unusual behavior of both superconducting and normal states in these two Cr based alloys.

Thermodynamic analyses of a novel ejector enhanced dual-temperature air source heat pump cycle with self-defrosting

Previous studies have pointed out problems with the dual-temperature air source heat pump. Thus, this paper proposes a novel dual-temperature air source heat pump cycle with a self-defrosting method for simultaneous production of heat sources at different temperatures. An ejector was added to the novel system, which reduced the heat transfer temperature difference of the low-temperature condenser and the utilization of multiple heat sources. In addition, a new type of defrosting, which utilizes the heat from the hot liquid refrigerant to defrost the evaporator using two evaporators and a four-way valve, is used to reduce the energy needed for defrosting and decrease temperature fluctuations. Thermodynamic modeling using the energetic and exergetic analysis method was employed to evaluate the modified cycle performance and compare it with that of the basic heat pump cycle. Eco-friendly refrigerants, such as R134a, R600a, R290, and R1234yf, were adopted as the working fluid. The simulation results show that the heating coefficient and exergy efficiency in the proposed cycle were improved by 29.34% and 43.52%, respectively, compared with those of the standard cycle under typical operating conditions. Among the refrigerants, the eco-friendly refrigerant R600a exhibited the best performance under various operating conditions. Moreover, the COP in the new system was 20.72–44.47% higher than that of a traditional system, and the exergy efficiency improvement was 29.70–49.19% compared to the standard system. In summary, this study confirms the performance enhancement potential of an ejector-based dual-temperature air-source heat-pump cycle and provides theoretical support for its practical implementation.

Gas Fluxes and Steady State Saturation Anomalies at Very High Wind Speeds

AbstractGas exchange at high wind speeds is not well understood—few studies have been conducted at wind speeds above 20 ms−1 and significant disagreement exists between gas exchange models at high wind speeds. In this study, noble gases (He, Ne, Ar, Kr, and Xe) were measured in 35 experiments in the SUSTAIN wind‐wave tank where the wind speeds ranged from 20 to 50 m s−1 and mechanical waves were generated as monochromatic or with a short‐crested JONSWAP frequency spectrum. Bubble size spectra were determined using shadowgraph imagery and wave statistics were measured using a wave wire array. The steady state saturation anomalies and gas fluxes initially increased as wind speeds increased but then leveled off, similar to prior studies of heat and momentum flux coefficients. Noble gas fluxes and steady state saturation anomalies are correlated most strongly with bubble volumes for the less soluble noble gases and with wind speed and wave Reynolds number for the more soluble noble gases. In the JONSWAP experiments, significant wave height was the most important predictor for gas steady state saturation anomalies with correlation coefficients of greater than 0.92 for He, Ne, and Ar (P < 0.05). Furthermore, invasion fluxes were larger than evasion fluxes when other conditions were similar. Taken together, these lab‐based experiments suggest more attention should be paid to parameterizations based on wave characteristics and bubbles and that current wind‐speed based gas exchange parameterizations should not be applied to conditions with very high wind speeds.

Numerical Study of Heat Transfer Characteristics in High Pressure Steam Turbine During Stop Unit Process with Sliding Pressure

During maintenance of the turbine and its auxiliary equipment, which requires a stop of the turbine oil system equipment and an open turbine casing, the first stage metal temperature requirement must be below 150°C. The normal stop unit method with natural cooling takes about 14 to 17 days. In order to speed up the cooling time to 5 days, a forced cooling turbine is needed using the stop unit method with sliding pressure. The heat transfer that occurs in the high-pressure turbine during the stop unit process with sliding pressure was investigated using the numerical method of CFD simulation. The 2D geometry design was made from high-pressure turbine cutouts images. Then meshing was made. The solver stage and the post-processing stage were set. The simulation was running in a steady state and followed by transients. The validation method was to compare the first stage metal temperature parameter between the actual process and the results of the CFD simulation at a load of 350 MW, then re-simulate it at 500 MW and 645 MW. The stop unit process with sliding pressure starting at 645MW resulted in the best final cooling compared to the stop unit at 500 MW and 350MW loads. By increasing the main steam flow, the resulting cooling increases. By increasing the value of the fluid flow velocity, the Reynolds number increases, so the convection heat coefficient also increases.

Finite Element Analysis for Rocket Motor Case Under Internal Pressure and Thermal Loads

Rocket motor combustion chamber need to contain very high pressure and temperature due to burning of rocket fuels. Although for small rocket the burning time in the combustion chamber are short about 1 to 5 seconds it is very important to make sure that the combustion chamber can hold the pressure and heat produced by the burning of the fuels. Even with a very strong material of combustion chamber and the analysis proof that the chamber is able to stand the high pressure produced there are high probability of structural failure due to the increase of temperature due to heat into the combustion chamber wall since the increasing temperature of the combustion chamber wall will decrease the strength of the material. In this study the thermal analysis was done using ANSYS software with various thickness from CC 2.5, CC 3.5 and C.C 5.0 in two condition which are the stress due to static stress and the stress due to static stress and thermal stress. The propellant properties, pressure applied, chamber temperature and heat coefficient are the same in all cases. Then the results for the different thickness stress at the wall are plotted and compared. The study shows that the results due to then static stress and overall stress with different combustion chamber thickness for the radial stress show no significant differences. While the hoop stress and von-Mises stress due to static stress are maximum at inner wall and decrease as the direction of the wall increase from the inside. In other cases where the static and thermal stress are applied, the highest stress is at the outer wall of the cylinder. The higher combustion chamber thickness, the lower hoop stress and von-Mises stress need applied to the combustion chamber wall. Thus, results in higher safety factor for the higher combustion chamber thickness.

Thermodynamic analysis of a modified vapor-injection heat pump cycle using an ejector

This paper presents a modified sub-cooler vapor-injection (MSV) cycle with an ejector for air source heat pump applications. The added ejector is used to realize two condensation temperatures for the cycle by using its pressure lift ability and effectively improve cycle performance. The cycle performances are evaluated through thermodynamics methods and compared with those of a basic sub-cooler vapor-injection (BSV) cycle. The results show that compared with the BSV cycle, the heating coefficient of performance (COPh), the volumetric heating capacity and the exergy efficiency of the MSV cycle are increased by 10.1%, 6.3% and 14.1% under a typical operating condition, respectively. The COPh of the MSV cycle using three low-GWP substitutes (R1234yf, R1234ze(E) and R32) are compared with R134a. The results indicate that among them, R1234ze(E) is the most promising refrigerant for improving MSV cycle performance while replacing R134a. It can be concluded that the MSV cycle has a better heating performance by the introduction of the ejector, and thus could offer potential benefits for applications in air source heat pumps.

Explorations on properties of ε′ phase and new crystalline phase of Fe3Ge alloy under high pressures

We calculated the lattice dynamics, elasticity, electron spin polarizability P(EF), and electron specific heat coefficient γ of the L12-Fe3Ge crystalline alloy under high pressure using first-principles method based on density functional theory. By comparing the lattice dynamics and elasticity of the ferromagnetic and non-magnetic systems, it can be found that the spontaneous magnetization of the system induces the dynamic stability of the system at low pressure (less than 6 GPa). Furthermore, the magnetostriction induced by the spontaneous magnetization enhances the elastic modulus of the system. With the increase of pressure, in the pressure range of 130-290 GPa where the spin magnetic moment of the system decreases sharply, the elastic modulus exhibits an abnormal behavior, which leads to double peaks in Poisson's ratio v and Pugh's ratio B/G, correspondingly, double valleys appear in shear modulus G, Young's modulus E and Debye temperature ΘD, which are associated with dynamic instability in the 130-290 GPa. Finally, for the phonon spectrum at 260 GPa with a significant imaginary frequency, the metastable orthogonal Fmmm structure is obtained using the soft mode phase transition theory. After comparing the enthalpy differences with different structures, it is found that the ferromagnetic Fmmm structure is a metastable phase, which is dynamic stable at 0 GPa and 260 GPa.

Investigating the limits of superconductivity in UTe2

Spin-triplet bulk superconductors are a promising route to topological superconductivity, and UTe2 is a recently discovered contender. The superconducting properties of UTe2, however, vary substantially as a function of the synthetic route, and even nonsuperconducting single crystals have been reported. To understand the driving mechanism suppressing superconductivity, we investigate UTe2 single crystals grown close to the nonsuperconducting boundary (growth temperature ∼710 ∘C) through a combination of thermodynamic and x-ray diffraction measurements. Specific heat measurements reveal a sharp decrease in the superconducting volume and a concomitant increase in the residual specific heat coefficient close to the nonsuperconducting boundary. Notably, these crystals are inhomogeneous and show an apparent double transition in specific heat measurements, similar to samples grown at much higher temperatures (∼1000 ∘C). Our single crystal x-ray diffraction measurements reveal that there are two important tuning parameters: uranium vacancies and the atomic displacement along the c axis, which shows a twofold increase in samples with a reduced superconducting volume. Our results highlight the key role of local disorder along the uranium-uranium dimers and suggest that the apparent double superconducting transition is more likely to emerge close to the superconducting limits of UTe2.

A high-temperature heat pump for compressed heat energy storage applications: Design, modeling, and performance

The current paper presents the design and performance of a high-temperature heat pump (HTHP) integrated in an innovative, sensible, and latent heat storage system. The HTHP has been designed to work between a heat source from 40 to 100 °C and a heat sink above 130 °C. An initial refrigerant analysis has revealed that R-1233zd(E) is the best candidate to meet the required performance and environmental considerations. The first part of this paper deals with the sizing and selection of the main components while discussing the challenges and working limits. A numerical model is also presented and validated. The second part of the paper is dedicated to develop parametric studies and performance maps under different operating conditions. The results show that the current HTHP, at a source temperature of 80 °C, consumes from 3.23 to 9.88 kW by varying the compressor’s speed from 500 to 1500 rpm. Heat production is achieved in the form of latent heat (7.40 to 21.59 kW) and sensible heat (from 6.35 to 17.94 kW). The heating coefficient of performance (COPHTHP) is around 4.

Coupled modeling of peatlands carbon cycle and carbon dioxide emission from their peat deposits

COmplex Model of BOg LAndscapes (COMBOLA) is a set of dynamic models of carbon and nitrogen turnover, net ecosystem exchange, water balance, heat and water transport, generation and transfer of CO2 and CH4 in a peat deposit on a number of time scales. Combined modeling of carbon turnover and carbon dioxide emission from peat deposits on an annual time scale is carried out as part of COMBOLA for several bog landscapes in Western-Siberian south taiga. One-dimensional vertical reaction-diffusion model for carbon dioxide emission from peat deposit is combined with compartment carbon cycle model allowing estimate both bog type vegetation changes and greenhouse gases balance under probable climate change or perturbations initiated by human activities. Water table level (WTL) separating aerobic peat layer from the anaerobic one is calculated by means of the whole peat layer depth and its water balance relations. Minimal statistical information is used for calibrating temperature dependencies together with coefficients of heat and water transfer equations. The stationary states of carbon cycle are accompanied by steady average profiles of carbon dioxide concentration and can loose stability under human or climatic perturbations. The model dynamics is simulated with several climatic projections of the IPSL atmospheric circulation model for 21st century with anthropogenic scenarios RCP-2.6 and RCP-8.5.