Journal of Thermal Analysis and Calorimetry最新文献

The use of next-generation refrigerant fluids is preferred to improve the global environment’s livability. In this context, the thermodynamic properties of R466A, a new-generation refrigerant with low ozone depletion potential and global warming potential, have been modelled using various methods. Linear regression, artificial neural network (ANN), and gene expression programming (GEP) models were used to predict R466A’s temperature–pressure relationship in the saturated liquid–vapor phase and its enthalpy-entropy relationship in the superheated vapor phase. The models’ performance was evaluated based on statistical parameters such as the determination coefficient (R²), mean absolute error, and root mean square error (RMSE), and compared with actual values. The research results indicate that the GEP model achieved the lowest RMSE values for predicting thermodynamic properties in the saturated vapor phase. On the other hand, ANN models were found to be more suitable for estimating properties in the superheated vapor phase. The R² values for ANN models ranged from 0.999 to 0.986, whereas GEP models exhibited R² values between 0.999 and 0.982. Despite slightly lower performance compared to some ANN models, GEP models employed explicit equations.

In the early research process, the ideal gas was taken as the research object, but in practice, the working fluid was all non-ideal gas, so it is of great significance to study performance of actual internal combustion engine with non-ideal gas. This study utilizes an irreversible Diesel cycle model, which has been established in the previous literature, and considers various irreversible loss terms and specific heat model of non-ideal gas working fluid, to perform cycle performance analysis and multi-objective optimization. Compression ratio ((gamma)) is taken as optimization variable to optimize efficiency ((eta)), dimensionless power ((overline{P})), dimensionless power density ((overline{{P_{{text{d}}} }})) and dimensionless ecological function ((overline{E})). The results show that there are optimal (gamma) s to maximize the four-objective functions ((eta_{max }), (overline{P}_{max }), (overline{{P_{{text{d}}} }}_{max }) and (overline{E}_{max })); with the rises of irreversible loss terms, the (eta_{max }), (overline{P}_{max }), (overline{{P_{{text{d}}} }}_{max }) and (overline{E}_{max }) all drop. As freedom degree of monatomic gas changes from 1 to 3, only (eta_{max }) drops and the other three-objective functions rise. When (overline{P} - eta - overline{E} - overline{P}_{{text{d}}}) is optimized and (gamma_{{{text{opt}}}}) is mainly concentrated between 3.6 and 5.3, the calculation results of (overline{P}_{{}}) are distributed between 0.85 and 1. The calculation results of (eta) are distributed between 0.46 and 0.52. The calculation results of (overline{E}) are distributed between 0.6 and 1. The calculation results of (overline{{P_{{text{d}}} }}) are distributed between 0.9 and 1. When (overline{P} - eta - overline{E} - overline{P}_{{text{d}}}) and (overline{P} - overline{E} - overline{P}_{{text{d}}}) are optimized, deviation indexes obtained by using LINMAP decision-making are the smallest and the best among all optimization results. Multi-objective optimization algorithm is an optimization method to solve multiple conflicting objectives by simulating the competition mechanism in nature. It can find a balance point among multiple objective extremes and thus improve comprehensive performance of Diesel cycle.

A stationary, symmetrical hemispherical solar collector with helical risers is experimentally investigated. Pure water and Ag-CuO/water hybrid nanofluid are used as the working fluid. The nanoparticle's volume fractions are 0.1 and 0.3%, and the flow rates of the working fluid are 1, 1.5, and 2 Lmin⁻¹. A total of 9 tests have been conducted in 9 consecutive days during August 2022. All tests were performed according to ASHRAE standards. The main novelty of this study is the practical use of hybrid nanofluid and helical risers in a solar collector with hemispherical geometry. According to the results, a hemispherical solar collector exhibits hopeful and favorable thermal efficiency due to its particular shape and the unique arrangement of its helical risers. The results show that with the increase in flow rate, the temperature difference between the inlet and outlet of the hemispherical solar collector and the heat exchanger inside storage tank decreases, while the thermal performance of the solar collector increases. Also, when the concentration of nanoparticles increases, the temperature difference between the inlet and outlet of the collector, and the thermal efficiency, increases. The results show that the maximum thermal efficiency of the solar collector is 86.8% and the maximum average temperature of the fluid around the heat exchanger in the storage tank is 79.8 °C, and these results are related to the hybrid nanofluid with a volume fraction of 0.3% and a flow rate of 2 Lmin⁻¹.

To address the issue of low efficiency in cooling heat exchangers at the deeper ends of mine fans, we propose a micro-unit approach for arranging the cooling water flow path within the heat exchanger. This method involves subdividing the heat exchanger into micro heat transfer units and determining the heat transfer characteristics of each individual unit through theoretical calculations and software simulations. Utilizing a computer program, these micro units are systematically arranged and combined to exhaust all possible cooling water flow paths. The ultimate objective is to derive the optimal structural arrangement of the cooling water flow path within the heat exchanger, with the goal of achieving the most efficient heat transfer effect. The findings reveal that the optimized structure, obtained through the micro-unit optimization method, achieves an average air outlet temperature of 311.65 K. This temperature is lower than that of the typical current-flow structure (311.88 K) and the typical counter-flow structure (311.68 K), indicating a superior heat transfer effect. Further examination demonstrates that the average air outlet temperature across all counter-flow structures is 311.68 K, which is notably lower than the average air outlet temperature of 311.90 K observed in the current-flow structure. This highlights the enhanced heat transfer effectiveness of the counter-flow structure. This novel method for optimizing the heat exchanger flow path applies the concept of finite element analysis to the optimization process, reducing computational and experimental costs. This approach is significant for improving the efficiency of heat exchangers.

The electrochemical properties, heat production properties and safety of lithium-ion batteries are significantly affected by the ambient temperature. In this paper, a combination of experimental and simulation methods is used to reveal the differences of the battery thermoelectric coupling characteristics under wide temperature range environment (from − 20 ℃ to 40 ℃) by taking 21,700 cylindrical ternary lithium batteries as examples. We design the battery model characterization method, carry out the battery charging and discharging characteristics experiments under different ambient temperatures, extract the respective modeling key parameters, reveal the differences of parameters under different temperatures, and construct the battery thermoelectric coupling model under wide temperature range environment. Simultaneously, we utilize the model constructed above to conduct simulations and experimentally verify battery thermal performance. By comparing experimental data acquired through infrared thermography and K-type thermocouples with simulation outcomes, we find the error to be below 5%. Unlike the homogeneous heat source model, the model constructed in this paper can simulate the uneven temperature field. In comparison to both equivalent circuit models and electrochemical-thermal coupling models, it involves fewer computations. It considers both the precision of simulating battery thermal performance and practicality for market-oriented popularity, which lays the foundation for research and market-oriented popularity related to battery thermal management design under wide temperature range environment.

Energy storage has been proposed as a promising solution to reduce the mismatch between the energy supply and demand. Research on thermochemical sorption energy storage (TSES) has demonstrated considerable interest in thermal energy storage system and heat transforming processes used in applications of solar energy storage, space heating, industrial heat recovery, and heat upgrade during the past 20 years. TSES is the only promising method to store energy for long-term/seasonal periods without any energy losses. However, TSES system is more complex and thus has not yet been developed commercially. So, more efforts are required to bring this technology to the market. TSES is the most recent thermal energy storage technology in recent decades, and it is still under investigation in laboratories. Sorption materials are the basis for developing TSES systems; however, it has the drawbacks of agglomeration and swelling; to address this issue, porous heat transfer matrixes using expanded natural graphite (ENG) have recently been proposed for improving mass and heat transfer by solidified composite adsorbents. So, the techniques of making composites of inorganic salts for TSES systems are presented in detail. Different from previous reviews, this review article focuses on various solid–gas thermochemical seasonal sorption and resorption energy storage systems based on metal halide–ammonia and consolidated composite metal halide–ammonia working pairs. This paper provided a state-of-the-art review on the progress of the latest studies and projects of theoretical and experimental chemisorption energy storage systems. Basic concepts, Clapeyron diagram, and selection criteria of storage materials of TSES systems were also presented.

According to review of the literature, the influence of nanoparticle diameter with irregular shapes on viscosity requires further research since there is no relation between particle size and nanofluid stability. In this study, SiO₂/EG–water-based nanofluid samples were prepared, and their viscosities were experimentally determined. SiO₂ nanoparticles had sizes of 7, 15, and 40 nm, and the base fluid was a 50% ethylene glycol and 50% water mixture. Nanofluid samples were prepared using a two-step technique. Viscosity change was measured every 10 °C from 20 to 60 °C. The maximum viscosity values were observed for 7, 15, and 40 nm particles over an entire concentration range. Considering all measurements, the highest viscosity increase was 60.51% for 3% SiO₂ (7 nm) at 60 °C, and the lowest viscosity change was 7.72% for 1% SiO₂ (40 nm) at 40 °C. The most stable sample of the current study was 1% SiO₂ (15 nm), and its Zeta potential was − 35.6 mV. Finally, a new empirical equation that included temperature, particle diameter, and concentration terms is suggested to predict dynamic viscosity, with R²_adj = 0.98. It was also compared with previous correlations.

In this work, the impact of lab synthetic addition agent, CSH-PCE nanocomposites (CPNs), on the early hydration property of the ternary binder containing Portland cement, limestone, and calcined coal gangue was investigated. CPNs were added in partial substitution of Portland cement by mass at 0%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5% and 3.0%. X-ray diffraction (XRD), isothermal calorimetry, mercury intrusion porosimetry, and scanning electron microscopy were used to characterize the hydration and hydrates of the CPNs-modified pastes systematically. The workability and compressive strength of this ternary system was also studied. The obtained results indicated that the use of CPNs continuously improved the workability of the ternary mortar. The compressive strength of the ternary mortar increased with CPNs additions until the threshold limits of 3.0% and 2.5% before and after 12 h, under which the strength values were even higher than the reference OPC mortar at each age. Isothermal calorimetry results indicated that CPNs promoted cement hydration and produced more hydrates, which were also verified by the qualitative XRD analysis. This promotion effect leads to significant reduction in porosity as well as densification in microstructure within the ternary paste, ultimately resulting in enhanced early-age compressive strength. These findings provide valuable insights for designing lower carbon footprint ternary blends incorporating calcined coal gangue and limestone while maintaining comparable early-age compressive strength to traditional cement.

The objective of this research study is to enhance the performance of a flat plate collector by using various cooling fluids, as an increase in solar panel temperature can decrease its efficiency. The experiment utilized three different fluids: distilled water, zinc sulfide nanofluid, and copper zinc sulfide nanofluid. FTIR analysis revealed a pronounced peak at 1133 cm⁻¹, indicating the presence of Cu²⁺ ions in ZnS. Three key parameters were systematically examined to optimize the solar panel's energy gradient and temperature variance. The flow rate of the cooling fluid varied from 0.5 to 2.0 L min⁻¹. Notably, the use of copper zinc sulfide nanofluid resulted in improvement in the energy gradient, reaching a peak value of 1112 W m^–2. The temperature difference showed a significant increase, peaking at 4.73 °C when using CuZnS nanofluid at a flow rate of 1.5 L min⁻¹. The incorporation of copper particles in the nanofluid notably enhanced the thermal conductivity of the cooling fluid. This improvement significantly boosted the efficacy of heat transfer processes, thereby increasing the overall efficiency of the solar panel system.

This study investigated the effect of neodymium (Nd) on the crystal structure and magnetocaloric properties of lanthanum–strontium manganites (La_0.7−xNd_xSr_0.3MnO_3, 0 ≤ x ≤ 0.4), synthesized by assisted high-energy ball milling. Rietveld analysis from X-ray diffraction disclosed that Nd³⁺ did not promote crystallographic phase transitions. The rhombohedral crystal structure remained in the R-3c space group for all the compositions, with slight changes in lattice parameters. The defect model allowed the quantification of the Mn⁴⁺ occupancy, which is in the range from 0.20 to 0.26 mol, for 0.1 and 0.4 mol of Nd³⁺, respectively. The presence of Mn⁴⁺ promoted further ferromagnetic interactions, increasing systematically the saturation magnetization, from 65 A·m²·kg⁻¹ to 73 A·m²·kg⁻¹, and a diminution in the Curie temperature from 364 to 255 K, for 0 and 0.4 mol of Nd³⁺, respectively, obtained by temperature-dependent magnetization measurements. The doped manganite with 0.35 mol of Nd³⁺ showed a maximum of entropy change of 3.73 Jkg⁻¹ K⁻¹ at 1.8 T near room temperature, with a relative cooling power of 82 Jkg⁻¹ and temperature-averaged entropy change, TEC(3) and TEC(10), of 3.53 and 3.06 Jkg⁻¹ K⁻¹, respectively. It is demonstrated that the presence of Nd³⁺ modulates the Curie temperature near room temperature and enhances the magnetocaloric properties at low magnetic fields, making these manganites a promising material for magnetocaloric applications.