Increase In Specific Heat Capacity Research Articles

Spent ion-exchange resin as a new aggregate to enhance specific heat capacity of composite building materials: A case study on gypsum plaster

Spent ion exchange resin (SIER) is a by-product derived from drinking water treatment plants, possessing intriguing physicochemical properties that render it a promising ingredient for composite building materials. Surprisingly, there has been a luck of research investigating its impact on the performance of such materials. This study addresses this gap by characterizing unfired and fired gypsum-based composites with varying SIER weight ratios (10–50 wt%) and firing temperatures (300, 600, and 900°C). X-ray diffraction, scanning electron microscopy, and the hot disk method were employed to explore the effects of SIER on the composites’ thermal-mechanical features. The results revealed the significance of SIER as a promising waste-based aggregate to enhance the specific heat capacity (cp) of gypsum-based composites. With increasing SIER content and firing temperature, the composites demonstrate improved cp, reduced thermal conductivity, and decreased compressive strength. Both unfired and fired composites exhibited an increase in cp, up to 74.4% and 331.8%, respectively. The composite material achieved a noteworthy reduction in thermal conductivity, reaching 0.132 W/m.K, and a specific heat capacity increase to 4491.35 J/kg.K, which surpasses that of the control sample by more than four times (1040 J/kg.K). These newly developed composites hold significant promise as thermal energy storage materials for low-temperature building applications.

Recent Advances in Molten Salt-Based Nanofluids as Thermal Energy Storage in Concentrated Solar Power: A Comprehensive Review.

This study critically reviews the key aspects of nanoparticles and their impact on molten salts (MSs) for thermal energy storage (TES) in concentrated solar power (CSP). It then conducts a comprehensive analysis of MS nanofluids, focusing on identifying the best combinations of salts and nanoparticles to increase the specific heat capacity (SHC) efficiently. Various methods and approaches for the synthesis of these nanofluids are explained. The article presents different experimental techniques used to characterize nanofluids, including measuring the SHC and thermal conductivity and analyzing particle dispersion. It also discusses the challenges associated with characterizing these nanofluids. The study aims to investigate the underlying mechanisms behind the observed increase in SHC in MS nanofluids. Finally, it summarizes potential areas for future research, highlighting crucial domains for further investigation and advancement.

Specific Heat Capacity of Solar Salt-Based Nanofluids: Molecular Dynamics Simulation and Experiment.

In this study, a nanofluid composed of molten solar salt (MSS) and 1.0% SiO2 nanoparticles by mass was created and analyzed using differential scanning calorimetry (DSC) to determine its specific heat capacity (SHC). The SHC of the nanofluid was found to be significantly higher than that of pure MSS. The average increase in SHC of the nanofluid with 1.0% SiO2 nanoparticles (NPs) loading was found to be 15.65% compared with pure MSS. The formation of nanostructures after doping with NPs may increase the SHC of molten salt (MS) nanofluids, according to certain published research that included experimental confirmation. Nevertheless, no thorough theoretical or computational studies have been conducted to verify the experimental findings related to MSS nanofluid. Molecular dynamics (MD) simulations were conducted in various simulation boxes for different cases to verify the experimental findings and investigate the mechanism behind the enhancement of SHC caused by the addition of SiO2 NPs in eutectic MSS. The simulations used pure MSS and mixtures containing NaNO3 nanostructures bonded with SiO2 NPs. The highest SHC increase of 25.03% was observed when the simulation box contained 13.71% NaNO3 nanostructures by weight. The incorporation of NaNO3 nanostructures increased the surface area and total surface energy, leading to a positive effect on the SHC of the MSS nanofluid. However, the decrease in the base molten salt's SHC had a slight negative impact on the overall SHC of the MS nanofluid.

Thermal Storage Performance of a Shell and Tube Phase Change Heat Storage Unit with Different Thermophysical Parameters of the Phase Change Material

The thermal storage performance of shell and tube phase change heat storage units is greatly influenced by the thermophysical parameters of the phase change material (PCM). Therefore, we use numerical simulations to examine how the thermal storage capability of shell and tube phase change heat storage units is affected by thermophysical parameters such as specific heat capacity, thermal conductivity, and latent heat of phase change. The findings indicate that while the rate of temperature increase and the rate of the PCM melting both slow down as specific heat capacity increases, the overall heat storage increases. Within the specified range of parameters, the average rate of heat storage increases by approximately 4% for every 50% increase in specific heat capacity. The PCM’s rate of temperature rise slows down and its overall heat storage capacity rises throughout the middle stage of the phase change heat storage process as the latent heat of phase change grows. The average heat storage rate increases by approximately 6% and 22% for every 50% increase in latent heat and thermal conductivity, respectively. Notably, when the thermal conductivity is enhanced by a factor of 1.5, the average heat storage rate experiences an almost 50% increase. The thermal conductivity of the PCM has a negligible impact on total heat storage. The choice and use of the PCM in shell and tube phase change heat storage heat exchangers has a theoretical and empirical foundation thanks to this work.

Effect of temperature on thermal properties and residual strength of coal gangue concrete

Key factors for assessing the high-temperature resistance of coal gangue concrete are high-temperature residual strength and thermal properties. The high-temperature residual strength, high-temperature thermal conductivity, high-temperature specific heat capacity, and high-temperature density of concrete with various coal gangue coarse aggregate replacement ratios were tested using experimental methods in this paper to study the high-temperature resistance of coal gangue concrete. Thermal density and high-temperature residual strength tests took into account influencing factors like the water-cement ratio (0.50, 0.45, 0.40), aggregate replacement ratio (0, 25 %, 50 %, 75 %, 100 %), and temperature variation (room temperature, 200 °C，300 °C，400 °C，500 °C，600 °C，700 °C，800 °C), while thermal properties tests considered the effects of various coarse aggregate replacement ratios and temperatures. The study showed that when the temperature rises, coal gangue concrete's thermal density falls, mass loss rises, residual strength declines, thermal conductivity rises, and its specific heat capacity fluctuates. At temperatures between 20 °C and 400 °C, concrete's residual strength decreases with an increase in the coal gangue coarse aggregate replacement ratio, while thermal conductivity and specific heat capacity increase. At temperatures between 500 °C and 800 °C, however, concrete's residual strength slightly improves with an increased coal gangue coarse aggregate replacement ratio, while mass loss changes more. The research finally provides the formulae for calculating the high-temperature residual strength and thermal properties of coal gangue concrete based on the test results.

Microstructure, thermophysical properties and neutron shielding properties of Gd/316 L composites for spent nuclear fuel transportation and storage

In this paper, (0.5–5.0 wt%)Gd/316 L composites were prepared by vacuum arc melting, and the microstructure, thermophysical properties, and neutron shielding properties were analyzed deeply. The results showed that the Gd/316 L composites started solidification in primary ferrite mode and terminated solidification by a peritectic-type reaction forming (Fe, Ni, Cr)3Gd that is rich in Ni and Gd. In the peritectic-type reaction, local convection in the Ni-rich and Gd-rich peritectic liquid phase leads to the formation of multiple variants of (Fe, Ni, Cr)3Gd. The higher the Gd content, the greater the amount of (Fe, Ni, Cr)3Gd and ferrite, and the harder it is to keep the austenitic matrix of 316 L stainless steel. The solidification temperature range of Gd/316 L composites is 1074–1460 °C, which severely limits the ability to further process it by high-temperature deformation techniques such as hot rolling or hot forging. (Fe, Ni, Cr)3Gd preferentially nucleates and grows in the triangular region of austenite grain boundaries at 1074 °C. At 50–500 °C, with increasing Gd content, thermal expansion and thermal diffusion coefficients become decrease, and thermal conductivity and specific heat capacity increase. The trend of thermophysical property changes is favorable for SNF transportation and storage applications. The thermal neutron shielding properties of 1.0 wt%Gd/316 L composite is comparable to that of 4.45 wt% B content boron steel and 15 wt%B4C/Al composite. The Gd content in Gd/316 L composites material should not exceed 2.5 wt%. If the Gd content continues to increase, it is of little significance to improving shielding properties and material thinning. A shielding thickness of 3 mm is more appropriate for Gd/316 L composites. Too thin would not provide sufficient mechanical properties and increase processing and manufacturing costs.

Dependence evaluation of factors influencing coal spontaneous ignition

AbstractCoal spontaneous combustion is determined by a variety of factors. Testing can describe the changes incoal spontaneous combustion with various factors, however, the dependence of spontaneous combustion on various factors is unclear. Therefore, reliability theory was used to deduce the functional relationship of the dependence of coal spontaneous combustion on various factors, and construct a model algorithm for predicting the probability of occurrence of coal spontaneous combustion, which is adopted to evaluate and rank the degree of influence of various factors on coal spontaneous combustion. Effective prevention methods are proposed by strengthening the role of the most important factors. The results show that, by taking the duration of coal heating to 150°C as the measurement standard of coal spontaneous combustion, the duration of the initial stage of coal heating increases linearly with the increase of specific heat capacity, thermal conductivity, and moisture content of coal. With the increase of oxygen concentration, oxidation rate, and initial temperature of the coal, the duration of the initial stage of coal heating decreases exponentially. With the increase of gas flow seepage velocity in the coal body, the duration of the initial heating stage changes in a parabolic manner. At the same time, the probability of spontaneous combustion decreases exponentially with the increase of specific heat capacity and moisture content of the coal. The probability of coal spontaneous combustion increases linearly with the increase of coal thermal conductivity, oxygen concentration, gas seepage velocity, and rate of oxidation. The dependence of coal spontaneous combustion probability on different factors can be expressed as follows: coal temperature > gas seepage velocity > specific heat capacity > oxidation rate > oxygen concentration > moisture content > thermal conductivity.

Effect of Nano Ni Particles on the Microstructure and Thermophysical Properties of Sn-Bi-Zn Heat Transfer and Heat Storage Alloys.

The specific heat capacity plays a crucial role in influencing the heat transfer efficiency of materials. Considering the relatively low specific heat capacity of metals, this study focuses on investigating the impact of second-phase nano Ni particles on the microstructure and thermophysical properties of the alloy matrix. The alloys' phase compositions and microstructures were examined using X-ray diffraction phase analysis (XRD), electron probe micromorphology analysis (EPMA), and X-ray fluorescence spectroscopy (XRF). Furthermore, the thermophysical properties of the alloys were comprehensively analyzed through the employment of a differential scanning calorimeter (DSC) and the laser flash method (LFA). The addition of second-phase nanoparticles significantly increased the specific heat capacity of the alloy in the liquid state; however, the phenomenon of nanoparticle agglomeration diminishes this improvement. The analysis of the specific heat enhancement mechanism indicates that ordered states are formed between the second-phase solid nanoparticles and the melted metal in the liquid state. With the increase in temperature, the destruction of these ordered states requires additional heat, resulting in the increase of specific heat capacity.

Identification of invisible fatigue damage of thermosetting epoxy resin by non-destructive thermal measurement using entropy generation

To quantify carbon fiber-reinforced plastic (CFRP) fatigue, herein, we investigate the relationship between fatigue and an epoxy resin used in CFRPs. Generally, fatigue is related to the entropy, which comprises the mechanical entropy, calculated from the dissipated energy and temperature, and thermal entropy, calculated from the relationship between specific heat capacity and temperature. According to previous studies, mechanical entropy generation and thermal entropy generation are equal. Herein, 100 cyclic loading tests are conducted on epoxy resin specimens consisting of 4,4’-DDS and bisphenol a diglycidyl ether. The dissipated energy is determined based on stress – strain curves, and mechanical entropy generation is quantified. An equation for the relationship between the specific heat capacity and temperature is developed based on the Debye model, and the increase in specific heat capacity is calculated for equal mechanical and thermal entropy generations. Generally, differential scanning calorimetry is used for specific heat capacity measurements; however, because these measurements are performed by cutting the specimen, a nondestructive measurement method is required. In this study, the specific heat capacity is measured using lock-in thermography (LIT), and the measured and estimated values are comparable. Thus, fatigue can be estimated by quantifying the thermophysical properties, and the lock-in thermography method is a suitable thermophysical property measurement method for this application.

Thermo-physical properties and thermal energy storage performance of two vegetable oils

Sensible heat storage materials are cheaper than latent heat storage materials for small storage volumes. Vegetable oils are cheap and readily available sensible heat storage materials produced locally in most countries in Sub-Saharan Africa. In this paper, the refractive indices, sound velocities, densities, specific heat capacities, and thermal conductivities of Sunflower oil and Roki oil (a blend of Palm oil and Sunflower oil) are determined experimentally. These two vegetable oils are locally produced in Uganda. Isentropic compressibility and thermal expansion coefficient are derived from the physical properties for the first time. The results show the refractive index, sound velocity, density, and thermal conductivity decrease with the increase in temperature, whereas isentropic compressibility, thermal expansion coefficient, and specific heat capacity increase with the increase in temperature for both oils. Roki oil shows higher thermal conductivity values than Sunflower oil at various temperatures. Additionally, an experimental setup to compare the performance of Roki oil and Sunflower oil as sensible heat storage materials for domestic medium temperature applications is presented. Roki oil and Sunflower oil are experimentally compared using charging and discharging experiments. The charging/heating cycles are first simulated with electrical energy followed by experimental tests with solar energy using parabolic dish solar cookers. The thermal comparison is made in terms of the temperature profiles during charging, discharging and heat utilization processes. During charging, the results show that Roki oil attains higher maximum temperatures (170–233 °C) compared to Sunflower oil (160–210 °C). Roki oil shows higher temperatures (71–78 °C) during cooling compared to Sunflower oil (67–76 °C). Roki oil shows higher heat utilization temperatures compared to Sunflower oil. The results provide insights on the utilization of locally available materials in Uganda as sensible heat thermal energy storage which are cheaper than commercial solar heat transfer oils.

Experimental investigation on rock thermal properties under the influence of temperature

The rock thermal parameters is of basic interest in geophysical, underground and engineering applications. The most relevant properties are thermal conductivity, specific heat capacity and thermal diffusivity. The present paper focuses on thermal properties of several rock types and minerals under the influence of temperature. On one hand, we provide a detailed review of rock thermal parameters and available correlations, and on the other hand, a series of laboratory measurements are presented and data are analyzed. For specific heat capacity measurements at atmospheric pressure and over a temperature range from 20 to 600 °C, the Differential Scanning Calorimetry (DSC) method is used and an indirect method is proposed. The results demonstrated an increase of specific heat capacity with a second order polynomial regression. The thermal conductivity and thermal diffusivity were investigated between 20 and 180 °C using the Hot Disk method. A logarithmic decrease with temperature was observed. In addition, a simple and inexpensive apparatus for measuring thermal conductivity at room temperature (20.0 ± 0.2 °C) is described and the results are compared with the commercial device. The results showed good performance with the estimated errors below 10%. To improve the applicability of the obtained results, empirical equations are developed to predict the thermal properties as a function of temperature and other physical properties. It was observed that the empirical relationships and the predicted values by the proposed equations are in agreement with the experimental data and with literature. Research results in this paper can be used as a support for rock engineering and a solution of a range of scientific and applied problems.

Design of Radially Variant Phase‐Change Material Composites

Phase‐change materials (PCMs) and high‐conductivity elements can be combined to form highly compact and efficient composite heat sinks. However, the design challenge presented by thermal composites composed of PCMs and high‐conductivity elements remains unresolved. Herein, design guidelines are presented for radially varying cylindrical PCM composites. Numerical and analytical techniques are utilized to explore the utility and limits of optimal composite designs selecting for 1) temperature minimization, 2) specific effective heat capacity maximization, and 3) volumetric effective heat capacity maximization. Significant increases in each metric are observed when implementing radially variant designs in cylindrical geometries, especially for metrics of heat capacity. Furthermore, a hybrid approach to variant composite design is presented, allowing for the balancing of different design objectives. The utilization of a variable design under high heat flux (10 ± 1.4 W cm−2) and short melting periods (up to 50 s) is experimentally demonstrated, directly resulted in a 65% decrease in total system mass and a 200% increase in specific heat capacity while maintaining strong temperature dampening performance. In a second case study, a 23% decrease in mass is demonstrated while maintaining strong specific heat performance, emphasizing the broad utility of this approach.

Effect of Morphology and Concentration of Two Carbon Allotropes on the Enhancement of Specific Heat Capacity of Eutectic Molten Salt

Abstract This study aims at investigating the effect of nanoparticle morphology and concentration on the specific heat capacity of a molten salt used as thermal energy storage material in concentrated solar power plants. Binary carbonate salt eutectic (lithium carbonate and potassium carbonate at a molar ratio of 62:38, respectively) is used as the base material. Two different carbon allotropes, graphite nanoparticles (Gp) and carbon nanotube (CNT) are used as dopants to look into the morphological effect on specific heat (Cp). A series of experiments are carried out to systematically investigate the effect of nanoparticle concentration by varying the mass percentages of carbon allotropes (2 wt.%, 4 wt.%, and 6 wt.%) in the base material. The specific heat capacity of the samples is measured both in solid (250 °C and 400 °C) and liquid phases (520°–560 °C) using a differential scanning calorimeter (DSC). The results show a maximum enhancement of 35% in Cp for 6 wt.% Gp -based salt in the liquid phase. CNT-based nanomaterials exhibit a maximum enhancement of 20% for 4 wt.% CNT inclusion in the liquid phase. The superior performance of Gp compared to CNT and mass concentration-controlled specific heat is explained using field emission scanning electron microscope (FESEM) and energy-dispersive X-ray spectroscopy (EDS) analysis. FESEM and EDS analysis confirm the presence and the composition of the compressed layer, respectively. These layers are considered to be responsible for the anomalous increase in specific heat capacity at different mass concentrations for the carbon allotropes.

Determination of thermal conductivity, thermal diffusivity and specific heat capacity of porous silicon thin films using the 3ω method

Here the thermal transport properties of low thermal conductivity porous silicon thin films attached to high thermal conductivity silicon substrates are studied using the 3ω method implemented over the 100 Hz to 33 kHz frequency range. The thermal conductivity and thermal diffusivity of the films are extracted using temperature impedance monitoring of electrical contacts deposited on films, combined with an extended-frequency, multi-layer thermal model. From the extracted thermal conductivity and diffusivity of the films, the heat capacity could be determined. Validation of the approach is performed using the known properties of thick substrate glass and SU-8 layers spun on silicon substrates, the latter ranging in thickness from 1.35 to 12.5 µm. The technique was then applied to porous silicon films with porosities ranging from 45% to 77%. The extracted thermal properties for as-fabricated films show a reduction of thermal conductivity and diffusivity from 1.7 to 0.15 W/mK and 1.9 to 0.2 mm2/s, respectively as the porosity increases. After passivation by annealing in nitrogen and at 600 °C, the same films exhibited higher values of thermal conductivity and diffusivity ranging from 2.7 to 0.7 W/mK and 2.5 to 0.65 mm2/s. The ability to extract both thermal conductivity and thermal diffusivity for these films removes the need to make assumptions around specific heat capacity, commonly made during analysis of porous media. These results show for the first time a monotonic increase in specific heat capacity of porous silicon films as a function of porosity.

Effect of La and Sc Co-Addition on the Mechanical Properties and Thermal Conductivity of As-Cast Al-4.8% Cu Alloys

The effects of La and La+Sc addition on mechanical properties and thermal conductivity of Al-4.8Cu alloy were comprehensively studied. The as-cast samples were characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and first-principles methods. The results reveal that the grain morphology of Al-4.8Cu alloy changes from dendrite to fine equiaxed grain with La, La+Sc addition. The average grain size of Al-Cu-La (Al-4.8Cu-0.4La) and Al-Cu-La-Sc (Al-4.8Cu-0.4La-0.4Sc) decreased by 37.2% (70.36 μm) and 63.3% (119.64 μm) respectively compared with Al-Cu (Al-4.8Cu). Al-Cu-La has the highest elongation among the three which is 34.4% (2.65%) higher than Al-Cu. Al-Cu-La-Sc has the highest ultimate tensile strength and yield strength which are 55.1% (80.9 MPa) and 65.2% (62.1 MPa) higher than Al-Cu, respectively. The thermal conductivity of Al-Cu-La and Al-Cu-La-Sc is 10.0% (18.797 W·m−1·k−1) and 6.5% (12.178 W·m−1·k−1) higher than Al-Cu alloy respectively. Compared with Al-Cu, Al-Cu-La has less shrinkage and porosity, the presence of Al4La and AlCu3 contribute a lot to the decrease of specific heat capacity and the increase of plasticity and toughness. The porosity of Al-Cu-La-Sc does not significantly decrease compared with Al-Cu-La, the presence of Al3Sc and AlCuSc bring about the increase of specific heat capacity and brittleness.

Superior thermal energy storage performance of NaCl-SWCNT composite phase change materials: A molecular dynamics approach

Molten salts are attractive candidate materials used for effective thermal energy transfer and storage, which can be applied in the concentrating solar power (CSP) system at high temperatures for efficient and continuous solar energy utilization. In this paper, in order to improve the thermal performance of NaCl based molten salt, the NaCl and single walled carbon nanotubes (NaCl-SWCNT) based composite phase change materials (CPCM) were proposed and designed by composition design strategy of materials. The thermal properties and the microstructure of CPCM systems were investigated by means of molecular dynamics (MD) simulation at nanoscale. The thermal properties including density, melting point, self-diffusion coefficient, thermal conductivity, melting enthalpy and specific heat capacity were predicted, the simulation results are in good agreement with the available experimental data, and the mechanism of desirable thermal performance enhancement was revealed from the microscopic point of view. It was found that the addition of SWCNT can effectively reduce the melting point of molten salts, so as to control the working temperature range of molten salts. With the increase of the SWCNT mass fraction, the thermal conductivity and specific heat capacity increase significantly with the maximum enhancement of 38.59% and 5.87%, respectively, but the melting enthalpy decreases by 36.37%. The above phenomena can be attributed to the variation of atomic energy from nanoscale. This study is expected to provide possible guidance on the design and application of molten salts based PCMs for thermal energy storage at high temperatures.

Effects of coflow velocity and coflow moisture contents on the formation and emissions of CO/NO in non-premixed impinging flames

The emission characteristics of non-premixed impinging flames are investigated using PIV experiments and numerical simulations. Different coflow conditions are conducted to focus on the pollutant emissions with the flame-wall interaction. Results show that flame dynamics obtained from experiments are in good agreement with that calculated from numerical simulations, and flame instability is intensified in near wall region in large coflow velocity case. In addition, the increase of coflow velocity may promote CO production, especially in low mean mixture fraction region (0.07-0.26). The distribution of CO is dispersed in large coflow velocity case, which is related with a strong convection and diffusion process. Besides, it is found that the decrease of flame temperature and the large wall quenching distance is observed with the increase of coflow moisture content, which is associated with the weakened combustion progress and the migration of reaction zone due to the decrease of O2 concentration in coflow mixture and the increase of specific heat capacity. The decrease distribution of local emission indexes of CO and NO is also shown in high coflow moisture content case, which can weaken the production of CO, thermal NO and prompt NO, and accelerate the consumption of NO. Moreover, CO reduction occurs mainly in high CO concentration region, while NO reduction is observed in the whole flow field. Results indicate that small coflow velocity and high coflow moisture content are beneficial to supress pollutant emissions, which can provide reference data for the optimization of clean combustion devices.

Supercritical CO2Heat Recovery System Finds Application in Oil and Gas Operations

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 197965, “Transforming Waste Heat to Electric Power in Oil and Gas Compression Systems Using Supercritical Carbon Dioxide,” by Thomas Soulas, Siemens, prepared for the 2019 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 11-14 November. The paper has not been peer reviewed. The complete paper describes an advanced Rankine cycle process-based system that converts waste heat into usable electrical power to improve the efficiency of gas-compression stations on gas-production platforms and pipelines. Instead of steam, this system uses industrial-grade carbon dioxide (CO2) in the supercritical state as the working fluid. Introduction Globally, rejected heat is estimated to correspond to approximately 65% of net energy input across the industrial infrastructure, with numbers varying from 60 to 70% depending on the region. Considerable waste heat is ejected from equipment such as the gas turbines commonly used in mechanical drive applications found in the compression processes of gas-production platforms and transmission pipelines. Recently, a technology that supports energy recovery from heat rejected from a broad range of industrial processes has become available to the oil and gas industry. The system recovers usable, but often wasted, heat and converts it into higher-value, usable electrical power. While most gas turbine heat-recovery systems use a bottoming steam cycle to improve thermal efficiency, the system described in the complete paper is based on an advanced Rankine cycle process. With revenue and cost predictability, the technology generates power at a competitive installed cost and delivers an estimated 10% increase in baseline efficiency for a gas-compression station to reduce effectively the overall cost of electricity. The main innovation of the technology lies in the selection of CO2 as the working fluid. Advantages of CO2 in Heat-Recovery Cycles CO2 has relatively moderate conditions for the supercritical state, with a critical pressure of 1,071 psi and a critical temperature of just above 88°F. With an approximately 50% increase in specific heat capacity at approximately the critical point and likely cycle conditions, and a reduced compressibility factor near the critical point, CO2 is ideally suited to recover heat energy across a broad range of temperatures and sources such as those found in exhaust gas streams.

Tuning the electronic, mechanical, thermal, and optical properties of tetrahexcarbon via hydrogenation

Recently, Tetrahexcarbon (TH-carbon), a new two-dimensional(2D) carbon allotrope, has been identified with an intrinsic direct bandgap, which makes it promising for practical applications in optoelectronic devices. Using first-principles calculations, we examined the possibility of manipulating the physical and chemical properties of TH-carbon sheet by controlled hydrogenation. We systematically studied pristine TH-carbon and its hydrogenated derivatives with various configurations such as single- and double-sided hydrogenation. Our study revealed their stability in energetic, dynamic, thermal, and mechanical aspects. Depending on the hydrogen coverage and configurations, we observed the tunability of the phononic and electronic bandgap, and the direct-indirect-direct bandgap transitions. These results suggest the plausibility of modulating its electronic properties by hydrogenation. The heat transport in TH-carbon is anisotropic. A significant decrease in thermal conductivity was observed in the fully hydrogenated TH-carbon. The thermal conductivity in TH-carbon can be controlled by the sp3 C–H low conduction domains. A notable increase in specific heat capacity was observed in hydrogenated derivatives of TH-carbon, which would make them useful in nanoscale engineering of thermal transport. The hydrogenation was found to reduce the in-plane stiffness and Young’s modulus, but increase the ultimate strength. These findings would provide important guidelines for practical applications of TH-carbon.

Experimental study on thermal and mechanical properties of cemented paste backfill with phase change material

The structural safety and thermal properties of cemented paste backfill (CPB) are the key factors to realize geothermal exploitation by using CPB. In this paper, taking the gold tailing-based consolidated backfill body as research object, thermal conductivity, specific heat capacity, density and compressive strength of backfill body were tested by changing the proportioning of backfill materials, the effects of slurry concentration, cement-tailing ratio, phase change material (PCM) addition and other factors on thermal and mechanical properties of backfill body were analyzed. The results show: for backfill body without paraffin, the larger the slurry concentration or cement-tailing ratio, the better the thermal conductivity, specific heat capacity, density and compressive strength. The addition of PCM, paraffin, makes the structure of backfill body lose, and thermal conductivity, density and compressive strength decrease, the average reduction rate is 25.6 %, 12.3 % and 18.7 % respectively, but specific heat capacity increases, the average growth rate is 12.5 %. The increase of specific heat capacity and the existence of phase-change latent heat make backfill body have better heat storage performance. When paraffin is added to backfill body, the larger the cement-tailing ratio, the higher the increase degree of compressive strength with increasing slurry concentration; the higher the slurry concentration, the more obvious the effect of increasing cement-tailing ratio on improvement of compressive strength. Therefore, the weakening of mechanical properties for backfill body caused by the addition of PCM can be improved by increasing slurry concentration or cement-tailing ratio appropriately. The research results provide basic data for the research on thermal and mechanical properties of backfill body with PCM, and also provide theoretical reference for the research on technical system of ore deposit-geothermal collaborative mining, which is mainly based on thermal storage backfill body.