Journal of Thermal Analysis and Calorimetry最新文献

Magnetic nanofluids play a crucial role in enhancing thermal properties, providing a promising pathway for optimizing energy supply systems and improving heat transfer efficiency. Beyond advanced thermal management, these innovative fluids showcase potential applications in the medical field, underscoring their versatility in addressing challenges across various industries. In this review, emphasis is placed on the nature and philosophy of magnetic field effects on the thermophysical properties, explaining basic mechanisms and investigating implications across applications. Under magnetic influence, particles align, forming clusters and chains, influencing thermal conductivity, viscosity, and specific heat capacity. Temperature variations serve a vital function, impacting the fluid’s response to magnetic fields. Brownian motion, affected by these fields, contributes to controlled particle motion, while agglomeration tendencies under magnetic conditions further shape thermal properties. In this review, several key findings about the behavior of magnetic nanofluids are revealed. For example, it is found that by increasing the magnetic field intensity at a constant shear rate, the viscosity first reaches a plateau and then decreases with further increases in field intensity. Furthermore, below/above the Curie temperature, the alignment of magnetic nanoparticles increases/decreases, influencing thermal expansion coefficient. This review presents two novel aspects that have not yet been compiled coherently elsewhere: firstly, an in-depth description of the nature and mechanisms of the magnetic field’s effect on thermophysical properties, and secondly, an examination of the rarely investigated properties of thermal expansion coefficient and specific heat capacity.

Studies are underway to apply phase change materials (PCMs) to buildings to reduce energy consumption. PCMs can be expected to achieve energy savings by exploiting their high latent heat capacity and time-lag phenomenon, slowing down the heat transfer within the structure, and accumulating and releasing latent heat. This study analyzed the appropriate melting point and energy-saving effects based on changes in external climate conditions, attachment location, and PCM properties (thickness and thermal conductivity) through building energy simulations. Climate data were quantitatively categorized into climate zones based on heating degree hours, cooling degree hours, and insolation, and a total of 14 climate zones were proposed. The appropriate melting point based on climate was evidently more effective for cooling than for heating, and external attachment was proved to be more advantageous. As the thickness increased, the appropriate melting point decreased, and the energy-saving effect remained effective. The thermal conductivity increased with the graphite content by 0.90–2.37%, and the appropriate melting point also changed by 0.72–0.91 °C. As the thermal conductivity increased, heat was rapidly transferred within the PCM, altering its energy-saving effect by 0.18–3.35%.

For the semi-batch isoperibolic homogeneous exothermic reaction, the dosing rate is an effective method to control the exothermic rate. In this work, the esterification of propionic anhydride and sec-butanol is taken as an example to obtain the heat of reaction by considering the heat of mixing effect. The effect of dosing rates on reaction temperature and heat transfer efficiency are investigated for the semi-batch reaction system. The dosing rate is optimized by kinetic-free thermal runaway criteria based on Ψ number and the ν_ADaREκ-X_ac,max & Ry_min-Wt plots. The effect of cooling jacket temperature on the optimal dosing rates calculated by the criteria is investigated. The obtained results have been compared with the boundary and temperature diagrams criterion. The results show that safe operation conditions can be approximately obtained when lack of kinetic information for semi-batch reaction process. This work can provide a guidance which can facilitate the optimization of dosing rate to improve reaction efficiency and prevent thermal runaway.

Spill fire, a kind of common fire accident, has the characteristics of strong sudden occurrence and fast spread rate, so there has been widespread concern about it. Compared with pool fire, there is limited research on spill fires now. In order to study the process of fire spread and combustion on sand substrate, a series of experiments were designed to investigate the effect of sand particle size on the spread and heat transfer of the continuous ethanol spill fire. The flame spread distance, substrate temperature, and penetrating heat radiation were measured. The resistance effect of sand, spread distance and rate, and steady linear burning rate were analyzed. Moreover, heat loss was also calculated. The results show that sand can effectively impede the development of spill fire. On the one hand, dry sand has strong capillary action, which makes most of the fuel adsorbed upward by the sand layer after entering the flow trough. Therefore, sand has obstructive capacity on the spread of liquid fuel, thereby shortening the spread distance of spill fire. On the other hand, sand has strong thermal conductivity, which can reduce the stable burning area of spill fire by increasing the total thermal feedback of spill fire and improving the steady burning rate of fuel. However, if the particle size of sand is too small, the liquid fuel will spill from the sand surface. In this case, the resistance effect of sand on the spread of liquid fuel will weaken. Therefore, sand with appropriate particle size should be selected for spill fire in practice.

This study aims to theoretically analyse the flow and heat transfer characteristics of ethylene glycol ((text{C}_{2}text{H}_{6}text{O}_{4}))-based nanofluid containing magnetite ((text{Fe}_{3}text{O}_{4})) nanoparticles squeezed between two parallel disks with magnetic effect. The governing nonlinear partial differential equations are transformed into nonlinear ordinary differential equations by employing a set of suitable similarity transformations. Further, by adopting the homotopy perturbation method (HPM), an approximate solution to the considered model is obtained. The solutions are compared with the classical finite difference method (FDM) and are in good agreement. The current study mainly emphasizes the analysis of velocity profile, skin friction coefficient, temperature distribution curve, and Nusselt number for different pertinent parameters. The findings in this study highlight the role of applied magnetic field in modifying the flow and heat transfer characteristics of the nanofluid, notably showing that an increase in the concentration of magnetite nanoparticles correlates with higher skin friction at the disk surfaces and enhances the Nusselt number, reflecting improved heat transfer performance. This underscores the potential of magnetite-enhanced nanofluids in enhancing the efficiency of thermal systems.

In this study, the energetic and exergetic performance of a household refrigerator with a unique compact heat exchanger composed of a mini-channel flat tube condenser and offset strip fins (OSF) is investigated experimentally by considering varying amounts of R600a (48–64 g) and capillary tube lengths (2800, 3300, and 3800 mm). The experiments have been performed for two refrigerators involving two different innovative condensers composed of mini-channel flat tube and offset strip fins which have varying orientations instead of conventional wire-on-tube condensers. The experiments were conducted in a climatic chamber at a temperature of 25 ± 0.5°C. According to the standard of IEC 62552:2015, the target temperatures of the fresh food and freezer compartments are set at 4°C and −18°C, respectively. Specific and relative exergy destructions of each component, total exergy destruction, the coefficient of performance, and second-law efficiency of the overall system with two different mini-channel condensers are reported for varying amounts of refrigerant and capillary tube lengths. The major concern of the investigation is to reveal the key components contributing to the degradation of the overall performance of the unique design. It is observed that the evaporator, which has a ratio of 52–69% in total exergy destruction within all investigated cases, is the most exergy destructive component and the exergy destruction of the evaporator decreases when the amount of R600a increases. The mini-channel condensers are the second exergy destructive components with a ratio of 19–22%. As an important outcome of this unique design’s investigation, exergy destruction of the condenser and compressor does not show a monotonic change with respect to the refrigerant amount and capillary length. Besides, the highest coefficient of performance and second-law efficiency are obtained when the amount of R600a is 48–50 g in all three capillary tube lengths.

In the field of food research, the determination of the heats of combustion (Δ_cH) of the nutrients is essential to estimate the amount of energy obtained by metabolizing during digestion. Here, we have developed six novel QSPR models to predict this thermodynamic property of different families of organic compounds. The models were developed using the experimental data set of 215 compounds (71 organic acids, 28 amino acids, 37 amines and amides, 31 sulfur compounds and 48 heterocyclic compounds). About 16,000 molecular descriptors were calculated to represent the molecular structure of the compounds. The QSPR models resulted to be simple MLRs with a maximum of three variables, facilitating the interpretation and comparison with existing models in the literature. The statistical parameters exhibited excellent predictive capacity and robustness of the models obtained. The correlation coefficients of the selected models were major to 0.8 and the root means square error minor to 0.1. These results suggested that the models could be utilized for the prediction of the Δ_cH of other compounds that could be present in the foods.