Thermal Conductivity Of Mixtures Research Articles

Effect of phase change materials on thermophysical properties of asphalt mixtures and snow melting performance

The increased Thermal Conductivity and Thermal Diffusion Coefficient of asphalt mixtures means that the material is able to conduct and disperse heat more efficiently. In winter, this property can be used to accelerate the melting process of snow and ice, reducing the risk of road sliding due to snow and ice build-up. In this study, the thermal conductivity, thermal diffusion coefficient, and specific heat capacity of phase change asphalt (PCA) mixtures were investigated using a transient flat-plate heat source method. Analysis was performed with a thermal constant analyzer, a custom-designed thermal conductivity experiment, and a differential scanning calorimeter. Additionally, a phase change asphalt mixture thermoregulation rutting plate was prepared to evaluate its thermoregulation and snow and ice resistance under actual winter and indoor conditions. Results indicated that the thermal conductivity and thermal diffusion coefficient of PCA mixtures were superior to those of conventional asphalt mixtures. Notably, the specific heat capacity of these mixtures increased significantly within the phase change temperature range. The integration of phase change materials enhanced heat transfer within the asphalt mixtures, allowing for a delayed cooling process when temperatures decreased, with the maximum cooling range observed to be 2.8°C. Snow melting tests confirmed the early snowfall efficacy of the phase change asphalt mixture rutting plate, effectively achieving minimal snow accumulation and demonstrating the capability of 'melting light snow.'

Flow-Independent Thermal Conductivity and Volumetric Heat Capacity Measurement of Pure Gases and Binary Gas Mixtures Using a Single Heated Wire.

Among the different techniques for monitoring the flow rate of various fluids, thermal flow sensors stand out for their straightforward measurement technique. However, the main drawback of these types of sensors is their dependency on the thermal properties of the medium, i.e., thermal conductivity (k), and volumetric heat capacity (ρcp). They require calibration whenever the fluid in the system changes. In this paper, we present a single hot wire suspended above a V-groove cavity that is used to measure k and ρcp through DC and AC excitation for both pure gases and binary gas mixtures, respectively. The unique characteristic of the proposed sensor is its independence of the flow velocity, which makes it possible to detect the medium properties while the fluid flows over the sensor chip. The measured error due to fluctuations in flow velocity is less than ±0.5% for all test gases except for He, where it is ±6% due to the limitations of the measurement setup. The working principle and measurement results are discussed.

Thermal conductivity of MX80 powders-granules mixture and its prediction for high-level radioactive waste repository

Bentonite granules and their mixtures with powders are considered to be a preferred sealing material for filling gaps between buffer layer and surrounding rock in high-level radioactive waste (HLW) repository. Due to continuous release of decay heat from nuclides, thermal conductivity of bentonite granules must be assessed. In this study, the effects of water content, dry density, temperature on the thermal conductivity in the directions parallel (λpar) and perpendicular (λperp) to the bedding plane of MX80 powders-granules mixture (PGM) were investigated by thermal probe technique. Test results showed that the thermal conductivity of powdered bentonite (PB) was higher than that of PGM and λpar was higher than λperp. With increasing water content, the difference rate (δPSD) in thermal conductivity between PB and PGM increased, and anisotropy coefficient α (a ratio of λpar to λperp) decreased, while the effects of dry density and temperature on δPSD and α were not obvious. The factor importance was analyzed, and results showed that the effects of water content, dry density, temperature, and particle size distribution decreased successively. A modified geometric mean (MGM) model for predicting thermal conductivity of PGM with temperature is proposed and it predicted thermal conductivity of MX80 PGM well.

The effect of special additives on the physico-mechanical properties of mixtures used for the manufacture of cores by the cold-box-amine-process

The article presents an analysis of the effect of various special additives on the physical and mechanical properties of sand‑resin mixtures used for the manufacture of cores by the cold‑box‑amine process. Two groups of additives that have the most significant effect on the thermal conductivity of mixtures were studied: additives containing metals or their oxides and carboncontaining additives and composites. The influence of these additives on the tensile strength of the mixtures in the cured state, on their gas content and gas permeability was determined, the results obtained were compared with the characteristics of the reference mixture made without the use of additives.

Thermal Conductivity of Liquid Mixtures: Model of the Dependence on Concentration

Thermal Conductivity of Liquid Mixtures: Model of the Dependence on Concentration

Thermal conductivity of ethylene glycol and water binary mixtures at evaluated temperature and pressure

Binary mixtures of ethylene glycol and water are widely used as working fluids in many areas, and the study of thermal conductivity is crucial in the determination of the heat transfer properties of related systems. In this paper, the thermal conductivity of these binary mixtures at a series of ethylene glycol concentrations (0 to 100 wt%) is measured experimentally using a transient hot-wire system at evaluated temperature and pressure range from 293–533 K and 0.1–15.0 MPa. Moreover, the experimental data are fitted into an equation as a function of temperature, pressure, and concentration, the average absolute deviation and maximum deviation between fitted values and experimental data are 0.29 % and 1.05 %, respectively, which shows that this equation describes our data very well. Furthermore, available experimental data in the literature are collected and the comparisons between literature data and our data are analyzed, our data agree well with most literature data. This work is expected to promote the use of binary mixtures of ethylene glycol and water as heat transfer working fluids in industries.

Thermal Conductivity of Binary Mixtures of 1,1,1,2-Tetrafluoroethane(R-134a), 2,3,3,3-Tetrafluoropropene (R-1234yf), and trans-1,3,3,3-Tetrafluoropropene (R-1234ze(E)) Refrigerants.

A total of 2160 thermal conductivity data points, measured using a transient hot-wire instrument, are reported for binary mixtures of R-134a, R-1234yf, and R-1234ze(E) refrigerants from 200 to 340 K to pressures of 12 MPa for mixtures containing R-1234yf and to 50 MPa for R-134a/1234ze(E) mixtures. Data are reported at compositions of approximately (0.33/0.67) mole fraction and (0.67/0.33) mole fraction for each binary mixture investigated. The estimated relative expanded uncertainty of the thermal conductivity measurements is less than 2%. The data are used to refit binary interaction parameters for the Extended Corresponding States (ECS) model implemented in REFPROP (version 10.0). Additionally, the data in this study are used to assess the performance of a generalized entropy scaling model for refrigerants. Finally, the strengths and weaknesses of the ECS and entropy scaling models are compared.

Thermo-physical studies and corrosion analysis of caprylic acid–cetyl alcohol binary mixture as novel phase change material for refrigeration systems

This study aims to prepare a stable caprylic acid (CA) and cetyl alcohol (CAL) organic binary mixture as a solid–liquid phase change material (PCM) with a phase transition temperature in the range for exotic chilled refrigeration. A detailed study was carried out on the thermo-physical properties, thermal reliability and corrosion analysis of the prepared binary mixture. The result showed that the binary mixture of caprylic acid–cetyl alcohol (CA–CAL) with a eutectic point at 85:15 molar mass ratio is suitable for medium-range refrigeration application. The determined onset melting/freezing temperature with differential scanning calorimetry (DSC) was 10 °C/8.9 ± 0.1 °C with a phase transition enthalpy of 154.1/153.3 ± 1% J/g. The binary mixture thermal conductivity measured in the solid phase (at 0 °C) and liquid phase (at 20 °C) was (0.288 ± 0.028) and (0.156 ± 0.007) W/(m⋅K), respectively. Moreover, the thermal reliability test result of the prepared binary mixture under accelerated thermal cycling for 500 melting/freezing cycles showed a maximum of 10.1% deviation in thermal properties, which was in the acceptable range for organic binary PCM. The prepared PCM was found to be compatible with stainless steel and aluminum over an extended period of time, based on corrosion tests conducted on aluminum, copper and stainless steel over a period of 84 days. According to this study, the binary combination CA–CAL as PCM is a potential candidate for cold chain food transportation, supermarket cold cabinets, and other refrigeration applications.

Experimental Investigations on the State-Dependent Thermal Conductivity of Sand-Rubber Mixtures

Soil-rubber mixtures are potential construction materials for use in civil engineering applications such as the thermal insulation layer for buried pipelines in the permafrost zone and underground energy storage systems. Currently, however, the thermal conductivity of soil-rubber mixtures in various stress, saturation, and void ratio conditions is not fully understood. In this study, a stress-controlled apparatus based on the thermal needle probe technique was developed. It was employed to study the influence of the aforementioned factors on the thermal conductivity of sand-rubber mixtures. Thirty-four tests were completed with a wide range of net stresses (0–600 kPa), initial degrees of saturation (0%–100%), void ratios (0.45–0.95), and rubber contents (0%, 10%, and 20%). Three replicates were used in each condition. The results showed that the thermal conductivity was strongly dependent not only on void ratio, rubber content, and degree of saturation but also on net stress. For instance, the thermal conductivity of a dry sand-rubber mixture increased by 30% when the stress increased from 0 to 600 kPa. This increase in thermal conductivity can mainly be attributed to an increase in interparticle contact area, accounting for about 25% of the 30% increase; the reduction in void ratio played a minor role. A semiempirical equation was proposed to calculate the thermal conductivity of sand-rubber mixtures at different stress levels.

Low-Temperature Performance of Asphalt Mixtures Modified by Microencapsulated Phase Change Materials with Various Graphene Contents

Microencapsulated phase change materials (PCMs) added to conventional ones can store excessive heat energy and reduce thermal stresses. In this study, melamine–formaldehyde resin phase change microencapsulated PCMs, with different contents of graphene (CG), were added to asphalt mixtures, in order to reduce their low-temperature cracking, induced by thermal stresses. Low-temperature and heat-conducting/storing performance of the obtained mixtures was examined via beam bending tests, semi-circular bending low-temperature performance tests, thermal conductivity tests and volume-specific heat capacity tests. Besides, the prepared asphalt mixtures’ water stability and high-temperature stability values were obtained via freeze-thaw splitting and wheel tracking tests. The low-temperature performance of PCM-modified asphalt mixtures was evaluated via their bending strain energy densities, with one of the PCM-modified asphalt mixtures, namely CGMFPCM3, synthesized by the authors, was 1.7 times higher than that of the common asphalt mixture. Although the dynamic stability of all three PCM-modified mixtures was deteriorated by 68, 50, and 20% compared to the common one, that of CGMFPCM3 still complied with the standard requirement. Thermal conductivity and volume-specific heat capacity of the asphalt mixture at 278.15 K was enhanced by 5 and 43%, respectively, after adding CGMFPCM3. It is recommended for reducing the temperature variation-induced cracking in the asphalt pavement. Thermal conductivity and volume-specific heat capacity can be used for evaluating the temperature-regulating performance of asphalt mixtures.

Replication Data for: Thermal conductivity of binary sand mixtures evaluated through full water content range

Replication Data for: Thermal conductivity of binary sand mixtures evaluated through full water content range

Thermophysical Properties of Nanoferrofluid (Fe3O4 –Acetone/Znbr2) as a Working Fluid for Use in Absorption Refrigeration Applications

In this paper, thermophysical analyses were achieved for the mixture of (Fe3O4-acetone/ZnBr2) refrigeration working solution and examine its efficiency characteristics as a nanoferrofluid for use in absorption refrigeration applications driven by different low temperatures sources. Where it shows an investigation of the chosen nanoferrofluid containing the preparation, stability, structure, and properties. The reasons behind choosing Fe3O4 nanoparticles are that acetone is a good dispersivity medium for this kind of nanoparticles, also, their excellent thermophysical properties and magnetic property which give an ability to utilize them combined with applying an external magnetic field as a method for long and acceptable suspension stability of these nanoparticles in the base fluid thus enhancement in the heat transfer process in the generator of Absorption Refrigeration System (ARS). As a multi-factor experimental study, the experiments are designed to visually inspect the suspension nanoparticle's stability in the base fluid. Then presenting the thermophysical analysis of different properties of the mixture (thermal conductivity, density, dynamic viscosity, and specific heat capacity). The results elucidate that the studied nanoferrofluid has good dispersion and an enhancement in thermal conductivity that reaches 10.179 % at 0.2 (wt.%) of nanoparticle concentration. Also, by increasing nanoparticle concentration, the density increased, heat capacity decreased, as expected, and viscosity significantly increased.

Thermal conductivity of bentonite-graphite mixture and its prediction for high-level radioactive waste repository

Thermal conductivity of buffer material is crucial for the design and performance assessment of high-level radioactive waste (HLW) repository. Large amount of decay heat will increase the maximum temperature in bentonite buffer, which threatens the safety of HLW repository. One possible method to relieve such problem is adding graphite to bentonite for increasing its thermal conductivity. Therefore, the thermal conductivities of a bentonite with different graphite contents were measured by the heat flow meter method and the results showed that the thermal conductivity was a function of graphite content, water content and void ratio, while the temperature had ignorable influence for dry bentonite or bentonite-graphite mixture. The volume fraction of air and degree of saturation were strongly linear with the thermal conductivity. Based on experimental data, the Cote-Konrad model, geometric mean model and two Maxwell-like models were introduced and improved, and the suggested predictive methods proved to be effective by literature data.

Combustion in Ni–Al system with Cu additive (powder or rod) Experiment and mathematical model

Experimental studies were carried out with theoretical calculations of wave synthesis in the Ni–Al–Cu system were performed using the mathematical model developed. Approximate analytical formulas were obtained for synthesis performance evaluation. The inverse problem method was used to get kinetic constants that determine process dynamics based on the experimental data and analytical relationships. It is shown that the combustion front propagation velocity increases monotonically with an increase in the reaction sample relative density in the range of relative density values of 0.4 to 0.6. The depth of copper melt penetration from the center of the sample into the nickel-aluminum matrix depends on the relative density of the sample and copper wire diameter: higher densities and larger diameters lead to an increase in the liquid-phase impregnation area. The rate of nickel and aluminum powder frame wetting with copper melt is limited by the synthesis wave speed. Based on the experimental data and analytical ratios, we estimated the effective kinetic constants describing the high-temperature synthesis of the Ni + Al reaction mixture in the presence of copper additives. The thermal effect of the NiAl intermetallic formation reaction and the preexponential factor in the chemical transformation equation are calculated, the exponent value in the ratio for the mixture thermal conductivity is established; a constant determining the process of nickel-aluminum matrix impregnation with copper melt is found. The macroscopic approach used to analyze the NiAl intermetallic synthesis makes it possible to determine all the desired physicochemical characteristics and model parameters. The mathematical model is suitable for predictive estimates and experimental data analysis in the macroscopic approximation. Approximate analytical formulas are obtained for calculating the NiAl intermetallic synthesis characteristics. They allow for calculating the through channel characteristics and can be used in the design of NiAl products.

Influence of Freeze–Thaw Cycles on Thermal Conductivity, Water Permeability and Mechanical Properties of Asphalt Mixtures

This research studied the effect of freeze–thaw cycles on the thermal conductivity, water permeability and mechanical properties of asphalt mixtures in the cold region. Three types of asphalt mixtures, namely a stone mastic asphalt (SMA) mixture, dense graded asphalt concrete (AC), asphalt-treated base (ATB) mixture, were produced in the laboratory. The thermal conductivity test and water permeability test were used to study the thermal conductivity and water permeability of asphalt mixtures, respectively. Meanwhile, the uniaxial compression test and indirect tensile test were carried out to investigate the mechanical properties of asphalt mixtures. The results showed that with the increase in the number of freeze–thaw cycles, the thermal conductivity and mechanical properties of all asphalt mixtures were weakened, while the water permeability of them was improved. In addition, the effect of freeze–thaw cycles on the thermal conductivity and mechanical properties of ATB mixture was more significant than that of SMA mixture and AC.

Densities, Viscosities, and Thermal Conductivities of the Ionic Liquid 7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium Acetate and Its Mixtures with Water

7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium acetate (mTBD acetate) is a protic ionic liquid that is being investigated for use in industrial processes, such as for producing textiles from cellulose. To aid in designing such processes, we have measured the densities, viscosities, and thermal conductivities of mTBD acetate and aqueous mixtures containing mTBD acetate. We also investigated how excess amounts of mTBD or acetic acid affect the density, and found that in general an excess of either component decreases the density. However, when no water is present, the sample with excess acetic acid actually has a slightly higher density than when there is an equimolar amount of acid and base. The maximum density occurs when some water is present (around 30–40 mol%). We also modeled the density data using the ePC-SAFT equation of state and provide simple correlations for calculating the viscosity and thermal conductivity of these mixtures.

Thermal Conductivity of Pure Fluids and Multicomponent Mixtures Using Residual Entropy Scaling with PC-SAFT—Application to Refrigerant Blends

The statistical associating fluid theory (SAFT) was used to predict the thermal conductivity of multicomponent mixtures, through the concept of residual entropy scaling. The concept suggests that t...

Experimental Research on the Thermal Conductivity of Binary Mixtures with a Biodiesel Compound Ethyl Laurate + Three Alcohols (1-Propanol, 1-Butanol, and 1-Pentanol)

Biodiesel is recognized as a powerful substitute for diesel fuel. The alcohol can be blended with diesel or biodiesel for certain property improvements. In this research, the liquid thermal conduct...

Ab initio Investigation of Interfacial Thermal Transport for HMX‐PVDF Interface

AbstractThe theoretical investigation of heat dissipation for polymer‐bonded explosives (PBXs) is in high demand in explosive design in terms of safety and realibility, particularly as lack of effective experimental measurements. Here, we investigate the fundamental understanding of thermal transport across the heterogeneous interface between HMX and PVDF, by using the diffuse mismatch model and anharmonic inelastic model. This work explores the interfacial thermal conductance via ab initio calculation and derived phonon dispersions, phonon group velocities. For HMX‐PVDF interface, it is shown that low‐frequency phonon modes (especially lower than 10 THz) and two‐phonon elastic processes play dominant roles in the interface thermal transport. Furthermore, we present the calculated interfacial thermal conductance as a function of temperature. The thermal conductivity of mixture HMX‐PVDF system is analyzed with an effective medium approximation model. From these calculations, we give the thermal transport properties predictions of PBX for thermal conductivity enhancement and provides fundamental microscopic insights into phonon transport physics in PBX.

The Emergent Behaviour of Thermal Networks and Its Impact on the Thermal Conductivity of Heterogeneous Materials and Systems

The properties of thermal networks are examined to understand the effective thermal conductivity of heterogeneous two-phase composite materials and systems. At conditions of high contrast in thermal conductivity of the individual phases (k1 and k2), where k1 << k2 or k1 >> k2, the effective thermal conductivity of individual networks of the same composition was seen to be highly sensitive to the distribution of the phases and the presence of percolation paths across the network. However, when the contrast in thermal conductivities of the two phases was modest (k1/k2 ~ 10−2 to 102), the thermal networks were observed to exhibit an emergent response with a low variability in the effective thermal conductivity of mixtures of the same composition. A logarithmic mixing rule is presented to predict the network response in the low variability region. Excellent agreement between the model, mixing rule and experimental data is observed for a range two-phase porous and granular media. The modelling approach provides new insights into the design of multi-phase composites for thermal management applications and the interpretation or prediction of their heat transfer properties.