Journal of Thermal Analysis and Calorimetry最新文献

In the current articles, a numerical approach is developed to analyze the unsteady freezing process within a wavy container embedded with porous foam. The incorporation of porous foam, along with the addition of nanoparticles and radiative cooling, significantly accelerates the solidification process. These methods enhance thermal conduction within the system, which in turn improves the efficiency of cold energy storage, making them highly beneficial for applications requiring rapid cooling. The governing equations are derived by incorporating source terms related to the freezing, and the Galerkin technique is employed to solve these equations. The use of an adaptive grid technique ensures accurate representation of the moving solid–liquid interface, or ice front, during the simulation. Validation results demonstrate excellent agreement with experimental data, underscoring the importance of using adaptive meshing in capturing the transient dynamics of the freezing process. The findings reveal that the insertion of porous foam declines the needed time about 81.14%, significantly boosting the overall efficiency of the system. Furthermore, the utilizing nano-powders decline freezing time about 6.87%. Additionally, incorporating radiative cooling into the system further speeds up the freezing process by around 10.86%. These improvements highlight the combined benefits of using porous materials, nanotechnology, and radiative cooling for optimizing cold energy storage systems. The reduction in freezing time demonstrated in this study, particularly the 81.14% improvement with porous foam insertion, represents a noteworthy step forward in cold energy storage technology.

In order to reduce size and cost, the heat transfer (HT) capacity of conventional heat exchanger (HE) must be increased. Addition of nanoparticles (NPs) into parent fluids is a potentially effective method of improving HT at a manageable pressure drop. The present study was focused on the comparative analysis of thermal performance factor (TPF) between CuO–water nanofluid (NF) and ZnO–water nanofluids on double-pipe heat exchanger (DPHE) at four volume fractions (0.005%, 0.02%, 0.04%, and 0.07%) in the Reynolds number (Re) range of 5500–15000. The experiment was performed for single-phase fully developed flow in turbulent regime. The maximum enhancement in Nusselt number (Nu) for CuO–water NF was observed as 12.58% higher than ZnO–water NF for volume fraction (VF) of 0.07% at Re = 5000. Maximum augmentation in friction actor was recorded for CuO–water NF as 14.55% superior than ZnO–water NF for VF of 0.07% at lowest Re of 5500. At a Re of 5500, the maximum TPF value for CuO–water NF was found to be 2.61% greater than ZnO–water NF for 0.07% of VF. In order to develop better understanding of the behaviour of NFs, ZnO and CuO-NPs were characterized in the laboratories using XRD, HRTEM, EDS, and FTIR analysis. An empirical correlation for both Nu and friction factor (ƒ) has been developed within the range of given parameters using regression analysis.

This work aims to improve the efficacy of phase change material (PCM)-based shell-and-tube-type latent heat thermal energy storage (LHTES) systems utilizing differently shaped fins. The PCM-based thermal process faces hindrances due to the lesser thermal conducting property of PCM. To address this issue, the present problem is formulated by adopting the concept of conducting fins. The geometry comprises concentric cylinders, in which the inner cylinder carries the heat transfer fluid (HTF), whereas the outer cylinder contains PCM. Four number fins of different shapes are attached outside the HTF carrying cylinder. The enthalpy–porosity approach is used for modeling the phase change and heat transfer. The investigation is conducted numerically utilizing the finite volume-based numerical technique for the range of control variables such as the shape of the fins (straight, curved, and wavy fins) and various temperatures of the HTF. Furthermore, all the results are assessed with the results of no-fin case. The results show that the melting time drops markedly by 122.2% using a curved fin. This paper shows the capability of geometry modification in enhancing the heat energy storage rate of thermal energy storage systems. The PCM-based latent heat thermal energy storage (LHTES) unit is very effective for sustainable energy solutions through storing and releasing of renewable energy following the supply and demand cycle. Therefore, the outcome of the present study will enrich the knowledge on the design of efficient and compact thermal energy storage systems.

This research investigates the thermodynamic characteristics of solar ponds as industrial-scale freshwater production and solar energy storage systems. The study focuses on a solar pond utilizing saline wastewater as a heat transfer medium. Experimental findings reveal density variations within the wastewater, ranging from 1.09 to 1.27 (g{cm}^{-3}), and viscosity ranging from 0.96 to 1.13 (cP). Additionally, the wastewater exhibited a heat capacity between 3.163 and 3.142 (kJ{kg}^{-1}{K}^{-1}). Operational data indicate peak solar radiation and evaporation rates in June, with a corresponding freshwater production of approximately 5 L per day. Ambient temperature analysis revealed July as the warmest month and January as the coldest. Theoretical temperature predictions aligned closely with experimental observations, with maximum and minimum effluent temperatures occurring in July and December, respectively.

Coal spontaneous combustion (CSC) is a major issue in the coal mining industry and poses a significant threat to the safety of coal production. To address this problem, various technologies for CSC prevention and extinguishing have been developed. Despite this, a bibliometric and systematic review of CSC prevention and extinguishing technologies (PAETs) is currently lacking. To bridge this gap, a scientometric analysis of the bibliographic data in this field is conducted to identify current popular technologies and challenges, including statistics and analysis of the number of publications, institutions, journals, and research hotspots. Also, the paper divides CSC-PAET into two categories: wind flow control methods and fire prevention and extinguishing medias. It also provides detailed information on the research status, fire extinguishing principle, application effect, advantages, and disadvantages of each category. Finally, based on the findings and limitations of the published literature, this paper recommends that future research should focus on the microscopic mechanism of CSC reaction, strengthening the development of fire prevention and extinguishing medias and intelligent equipment, and realizing the dynamic identification, analysis and control of the whole mine fire prevention and extinguishing system, which is helpful for researchers and engineers in the field.

Fluid flow across a rotating disk has significant technical and industrial applications, including rotors, turbines, fans, centrifugal pumps, spinning disks, viscometers, etc. The impact of different-shaped nanoparticles immersed in the fluid controlled the thermophysical characteristics of the fluid, which were utilized in several sectors to accelerate thermal advancement. In the present problem, the tri-hybrid nanofluid flows over a rotating disk with three different shapes, namely spherical, cylindrical, and platelets, respectively, for Al₂O₃, multi-layered carbon nanotubes, and graphene nanoparticles immersed in the base fluid water. Under convective conditions, the tri nanofluid’s thermal expansion is more significant when combined with Joule heating, Cattaneo-Christov heat flux, and nonlinear thermal radiation. The Galerkin Finite Element Method is used to solve the simplified form of PDEs after a similarity transformation is introduced to convert them into ODEs. The skin friction coefficient and the heat transfer rate are subjected to a quadratic regression analysis; the results are shown in tables. Compared to the base fluid, the Nusselt number reveals an improvement of around 5.72% for nanofluid, 7.35% for hybrid nanofluid, and 17.18% for tri-hybrid nanofluid when the strength of radiation parameter and Brinkman number is raised. Platelet-shaped nanoparticles observed a significant tendency to enhance the rate of heat transfer, which is more prominent for the tri-hybrid nanofluid than the hybrid and mono nanofluids. Each graph features a comparison of ternary hybrid, hybrid, and mono nanofluid with other significant physical parameters. It was noted that the entropy of the system significantly intensified with Reynolds number and temperature ratio, while it was controlled by radiation parameters. The uses of ternary nanofluids include energy storage devices, adsorbents, sensors, imaging, catalysts, therapeutic activity, and more.

The aim of this study is to evaluate the performance of engines and the produced emissions by adding diethylene glycol dimethyl ether (DGM), an oxygen-rich additive with a high cetane number, into n-pentanol and diesel fuel blends. Using pure diesel (OXG0) as the benchmark, five fuel blends were tested in a single-cylinder compression ignition engine. While always keeping a diesel ratio of 70%, the blends displayed a range of DGM content ranging from 5 to 20%. Analysis showed that by 1.27% in contrast to pure diesel, the mix of 70% diesel, 10% n-pentanol and 20% DGM (OXG4) enhanced brake thermal efficiency (BTE). Moreover, OXG4 was shown to be efficient in lowering CO and NO_x emissions under all load conditions, therefore demonstrating its ability to control negative emissions. Still, when the DGM content rose, CO₂ emissions clearly started to rise—probably because of improved combustion efficiency. Furthermore, the study showed that compared to OXG0 other blends—OXG1, OXG2 and OXG3—often produced greater brake-specific fuel consumption and slightly worse BTE. The findings highlight the feasibility of DGM as a suitable additive to enhance diesel fuel blends to get better emission characteristics without appreciably compromising engine performance.

The current work focuses on simulating the freezing through a complex porous geometry using an adaptive grid approach. This simulation incorporates the impacts of radiation and the application of hybrid nano-powders to derive the final model. The governing equations are solved using the Galerkin method, with two unsteady terms in the energy equation discretized through an implicit technique. The validation of the simulation code shows excellent agreement with the previous studies, confirming the accuracy of the model. Notably, the outcomes reveal a substantial reduction in freezing time when using hybrid nanomaterials compared to pure water, with the latter taking approximately 106 times longer to freeze. Additionally, the presence of radiation accelerates the freezing process, reducing the time required by a factor of 1.25 compared to the absence of radiation. The combination of porous foam further enhances the system’s performance, reducing freezing time by approximately 79.92%.

In order to improve the utilization rate of solar energy, a new type of photo-thermal phase-change microcapsules PCM@SA@PDA was successfully prepared with n-docosane (C-22) as core material and sodium alginate (SA) and polydopamine (PDA) as composite wall material. Here, SA capsules were formed by cross-linking of metal ions to envelop and prevent the leakage of melted C-22 (PCM@SA). Dopamine was self-polymerized on the surface of PCM@SA microcapsule; thus, efficient light absorption was achieved for photo-thermal transformation. The chemical structure, thermal properties, light absorption properties and photo-thermal conversion properties of the prepared microcapsules were analyzed and characterized. Based on the study of the effect of different contents of C-22 core materials on the thermal storage performance of PCM@SA, the optimal addition amount of C-22 was determined to prepare photo-thermal phase-change microcapsules. Compared with the PCM@SA, the photo-thermal phase-change microcapsule PCM@SA@PDA still showed good stability and heat storage performance. Their melting heat enthalpy was about 152.5 J g⁻¹, and they also showed better photo-thermal conversion performance. Combining C-22, SA and PDA to prepare photo-thermal conversion phase change energy storage materials, the method was characterized by strong adaptability, simple operation, low production cost and high economic benefits, which could not only further improve the stability of the composite material, but also increase the photo-thermal conversion efficiency of the system. Therefore, this composite material integrating active light absorption, conversion and storage functions would have higher solar energy utilization rate and broader application prospect.

In this investigation, Galerkin technique was utilized as a reliable method for simulating transient phenomena, to model the unsteady discharging process. The use of an adaptive grid further bolsters the reliability of the numerical simulation, a feature substantiated in the subsequent sections. The study centers on two pivotal factors: the powder diameter (dp) and their concentration (ϕ). With rise in ϕ, there is a significant 41.2% enrichment in the discharging rate. Significantly, the incorporation of nanotechnology has proven to be a game changer, resulting in a notable 41.2% improvement in the discharging rate. The effect of dp is interesting, demonstrating a dual impact on freezing time—initially decreasing by 19.95% and later increasing by 49.18%.