International Journal of Thermophysics最新文献

This work presents a fundamental equation of state for calculations of the thermodynamic properties of R-1132(E), which is a potential refrigerant for residential or mobile air conditioners. The equation of state has a functional form expressed explicitly in the Helmholtz energy with temperature and density as the independent variables, and the form is fitted to consistent experimental datasets, including the critical parameters, vapor pressure, saturated liquid and vapor densities, ((p, rho , T)) behavior, vapor-phase sound speed, and ideal gas isobaric heat capacity. The equation of state is valid between temperatures from 240 K and 400 K, with pressures up to 6.5 MPa. In this range, expected relative uncertainties at the 95 % confidence interval ((k=2)) are 0.1 % for liquid densities, 0.4 % for vapor densities, and 0.1 % for vapor-phase sound speeds, except at the saturation states and in the critical region where larger deviations of up to 2 % are possible in densities due to higher experimental uncertainties. The uncertainty in calculated vapor pressures is 0.15 % above 275 K, which is larger at lower temperatures due to their small values. Various plots of derived properties from the equation of state show that the equation exhibits qualitatively correct behavior over wide ranges of temperature and pressure.

The paper outlines the essential conditions required to achieve measurements of low uncertainty for the thermal conductivity of solids using the transient hot-wire technique. The paper aims to provide rigorous guidelines for the correct implementation of this technique for solids. For solid materials, the study shows that an uncertainty of as little as ± 1 % is attainable across a broad temperature range by employing the finite element method to solve the pertinent heat transfer equations within the experimental setup. Importantly, the paper discusses the necessary steps to verify that the experimental conditions conform to the theoretical model.

In an office building equipped with a Variable Air Volume (VAV) system, this paper introduces a novel method for controlling the minimum supply airflow fraction in each zone’s VAV box, having a capability to consider indoor CO₂ level and energy consumption. The EnergyPlus simulation using the medium office prototype model was employed, which evaluated the performance of the energy and CO₂ concentration for five VAV box airflow control strategies. The paper focuses on CO₂ concentration-based airflow control method and compares it with other four methods including conventional single-max, reduced minimum single-max, demand-controlled ventilation(DCV), and dualmax control methods according to guidelines and common practices. The newly proposed control strategy directly correlates the minimum airflow fraction to CO₂ concentration. A general trend emerged when comparing CO₂ concentrations—lower minimum airflow fractions were associated with higher concentrations. The proposed control method effectively maintained low CO₂ concentrations and enabled a lower airflow fraction contributing to energy consumption reduction. It was confirmed that heating energy consumption in climate zone 4A, 5B, and 6A showed a maximum saving of approximately 30% compared to the conventional single-max and dual max control strategies. It was found that cooling energy consumption in climate zone 4A and 6A can achieve a maximum saving of approximately 10% compared to the conventional control strategies. The proposed CO₂ concentration-based control logic is promising as it not only improves the indoor air quality lowering the CO₂ concentration in the occupied spaces, but also contributes to HVAC energy savings.

The current study contributes to research on some thermophysical properties of ternary aqueous mixtures containing glycerol with 1,2-ethanediol, 1,2-propanediol, or 1,3-butanediol and their corresponding binary mixtures. Experimental measurements concerned density and refractive index at various temperature and under atmospheric pressure. PC-SAFT was applied successfully for predicting liquid density for the mixtures and different mixing rules of refractive index were used for modeling the experimental values of refractive index. The experimental data were also used to calculate the excess molar volumes, (V_{123}^E), and refractive index changes on mixing, (Delta n_{D,123}), for the ternary systems. These were subsequently compared to results obtained with a variety of semi-empirical methods using binary system results. On the other hand, the following derived properties were computed for each binary mixture, based on temperature and glycerol concentration: excess molar volumes, (V^E), partial molar volumes, (overline{V}_i), apparent molar volumes, (V_{theta i}), partial molar volumes at infinite dilution, (overline{V}_i ^{infty }), excess partial molar volume at infinite dilution, (V_i ^{E infty }), isobaric thermal expansions, (alpha), excess thermal expansions, (alpha ^E), and refractive index deviations, (Delta n_D). Infrared spectroscopy analysis was also carried out at atmospheric temperature and pressure. Infrared spectroscopy analysis was also carried out at ambient temperature and pressure. All the measured and calculated properties demonstrate a significant impact of molecular structure, including the size, shape, and length of the carbon chain. As expected, the infrared spectra of these mixtures show a strong potential for hydrogen bonding.

The efficient heat dissipation capacity of phase-change cooling offers a reliable solution for cooling high heat flux devices. Nevertheless, the evolution of phase-change fluid frequently encounters volatile states, resulting in considerable pressure fluctuations. This paper seeks to enhance the pipes active cooling efficiency of phase change by examining the weight ratios of pipe structural parameters on heat transfer, pressure drop, and comprehensive performance. Simulation model based on the Volume of Fluid (VOF) methodology was constructed to investigate the heat transfer and pressure reduction performance of the pipes. A comprehensive performance factor that considering both pressure drop and heat transfer characteristics was developed. The contributions of pipe structural parameters to the objective functions of pressure drop, heat transfer, and comprehensive performance are evaluated using a combination of orthogonal experiments and the Signal-to-Noise ratio (SNR) function. The accuracy of the numerical model was validated using quartz lamp thermal experiments. The findings suggest that when formulating the objective function based on comprehensive performance, the principal influencing factor for micro-pipe is wall thickness, accounting for up to 42.7 %. Conversely, for mini-pipes, the primary influencing factor is coolant flow velocity, contributing 43 %. Due to the effects related to size, the factors influencing the overall performance of micro/mini-pipes differ. They are primarily influenced by alterations in vapor volume fraction generated by phase change inside the pipeline. This study proposes an evaluation method considering multiple factor levels, furnishing crucial technical support for phase-change heat transfer technology.

This paper presents the results of thermal conductivity characterization of six high oleic soybean oil (HOSO) and four high oleic canola oil (HOCO)-based hybrid nanofluids formulated with four types of nanoparticles (Graphene nanoplatelet (xGnP), TiO₂, MoS₂, and Al₂O₃) at nanoparticles wt% concentration from 1 % to 7 % in 1 % increment using the two-step method for use in MQL machining of difficult-to-cut metals. Thermal conductivity of the formulated hybrid nanofluids were measured using Thermtest Transient Hot Wire Liquid Thermal Conductivity Meter at temperatures from 25 °C to 75 °C in increment of 10 °C. Obtained results showed that thermal conductivity of all nanofluids decreases linearly with temperature, while the thermal conductivity enhancement increases nonlinearly with increase in wt% concentration, following second order polynomial. At 7-wt% nanoparticle concentration, hybrid nanofluids xGnP-TiO₂/HOSO gave the highest thermal conductivity enhancement (109.73 % and 103.31 % at 25 and 75 °C) followed by xGnP-TiO₂/HOCO (101.36 % and 97.52 % at 25 °C and 75 °C), xGnP-MoS₂/HOCO (101.36 % and 97.52 % at 25 °C and 75 °C), xGnP-MoS₂/HOSO (96.3 % and 96.89 % at 25 °C and 75 °C), xGnP-Al₂O₃/HOCO (91.62 % and 83.23 % at 25 °C and 75 °C), xGnP-Al₂O₃/HOSO (91.25 % and 83.23 % at 25 °C and 75 °C). xGnP hybrid nanofluids are recommended for MQL machining. TiO₂–MoS₂/HOSO, TiO₂–MoS₂/HOCO, MoS₂–Al₂O₃/HOSO, TiO₂–Al₂O₃/HOSO hybrid nanofluids gave the lowest thermal conductivities and are not recommended as base fluids due to their insignificant thermal conductivity enhancement. Thermal conductivity of the hybrid nanofluids is lower than that of mono-nanofluids, but there are other inherent properties that could be beneficial.

Microwave resonators are a technology with the potential to automate the rapid acquisition of vapour-liquid equilibrium data in multicomponent mixtures. However, the re-entrant resonators commonly used for fluid characterization have limited ability to mix or drain adequately due to the bulbs and narrow gaps used within the sample volume to spatially distribute the sensing regions with intense electric fields. This work describes a novel composite cavity combining two toroidal split-ring resonators and a cylindrical resonator, each sealed and partially filled with the polymer PEEK, to spatially separate sensing regions whilst maintaining an unobstructed sample volume. This unique design also allows for the total sample volume to be an order-of-magnitude smaller than conventional microwave cavities, without significantly increasing the resonant frequencies. Mass transfer between phases is facilitated by mechanical agitation, reducing equilibration time. Finite element analysis (FEA) is used to model how the dielectric interfaces within the cavity perturb electric field distributions. This model is used to interpret measurements of two-phase propane to quantify liquid volume fraction and phase dielectric permittivities.

Using efficient building materials with high thermal inertia maintains indoor thermal comfort while reducing energy demand and energy savings. In this study, we developed and characterized the thermophysical and chemical properties of a novel Biosourced Composite Phase Change Material prepared using the shape-stabilized method for energy storage and improving the energy efficiency of buildings in arid climates. The physico-chemical compatibility between RT28 HC and the selected matrix was verified by Fourier Transform Infrared Spectroscopy and X-Ray Diffraction techniques and observed with Scanning Electron Microscope. The Differential Scanning Calorimeter results indicated that the composite material including 50 wt. % RT28 HC has a melting temperature and latent heat property of 31.5 °C and 128.3 J⋅g⁻¹, respectively. Thermogravimetric measurements confirmed the thermal reliability of the biosourced composite material for building applications. The thermal conductivity of RT28 HC incorporated into the biosourced composite material, including 10 wt. % of graphite, was improved by 305 %. Thermal performance tests the potential of the composite material to improve the thermal performance of walls subjected to the thermal conditions of the arid zone climates were implemented using a trombe wall. Thermal performance results revealed that integrating composite material plates reduced the internal and external faces of the trombe wall temperatures by 7 °C and 14 °C, respectively. Integrating the biosourced composite material into the wall increases its thermal inertia and stabilizes the interior temperature within the comfort temperature range. Thermal performance tests confirm the biosourced composite material’s efficacy in improving thermal comfort, as well as its potential application for thermal energy storage in buildings.