Thermal Science and Engineering Progress最新文献

A supercritical carbon dioxide (sCO₂) to aviation kerosene fuel heat exchanger is an important part of the power and thermal management system (PTMS) of hypersonic vehicles. This study developed a numerical model for a sCO₂-fuel airfoil-fin printed circuit heat exchanger (AF-PCHE) used in the PTMS. Moreover, four parameters were optimized with the comprehensive performance coefficient (JF) as an optimization objective, including airfoil horizontal spacing (L_h), airfoil vertical spacing (L_v), the height of cold-side channel (H_c,rp3), and the height of hot-side channel (H_c,CO2). The results indicated that the most significant parameter affecting the JF was the H_c,CO2, followed by the H_c,rp3. The optimized structural parameters were L_h = 12.6 mm, L_v = 5.26 mm, H_c,rp3 = 1.05 mm, and H_c,CO2 = 1.36 mm. The significance order of the single-factor effects of the JF was H_c,CO2 > L_v > H_c,rp3 > L_h. The JF of the optimized design was increased by 24 % compared to the original design of the AF-PCHE.

The paper proposes a framework based on deep learning, transfer learning, and multi-objective optimisation to model and optimise heat transfer in smart city infrastructure to make them energy efficient and thermally comfortable. The framework in the paper contains a building thermal dynamics prediction model developed using hybrid CNN-LSTM on an extensive dataset (12.56 metric tonnes) of Indian buildings covering various characteristics, which is then fine-tuned with data from five major Indian cities. This predictive framework has a high generalisation capability of energy consumption and predicting indoor temperature profiles with the mean absolute errors (MAE) of building energy consumption ranging from 8.7 to 12.3 kWh and indoor temperature as 0.6 to 1.1 °C, respectively. Transfer learning is considerably improving the performance of the proposed model in newly added cities, which improved the MAE in the training cities (New Delhi and Mumbai) by 3.6 % and reduced the R^2 to 10.7 %. The multi-objective optimisation involving decision-making processes resulted in energy savings of 15.7 % to 22.3 % and improved comfort levels by 21.8 % to 28.5 % in the evaluated cities. The paper significantly contributes to developing a data-driven, generalisable, and interpretable framework, which can usher how to optimise heat transfer using deep learning to make smart city infrastructure resilient and comfortable. It also provides a novel solution to addressing the problems posed by energy efficiency and climate change in Indian cities. Policymakers and urban planners can utilise these key policy recommendations suggested in the paper to design new, liveable and self-sustaining urban environments in India.

This study investigates the impact of introducing horizontal barriers within the internal cavity of flat plate solar collectors on their thermal efficiency. The primary objective is to enhance thermal performance by reducing convective heat loss. An experimental test bench was constructed to evaluate five solar collectors under controlled conditions. One collector was unmodified as a reference, while the other four had 1 to 4 horizontal barriers inserted between the absorber plate and glass cover. Each collector’s efficiency was assessed by measuring inlet and outlet water temperatures, incident solar radiation, ambient temperature, and water flow rate. Efficiency versus heat loss parameter curves were generated, and correction factors were applied to account for material and sensor differences. The collector with four barriers demonstrated the highest overall thermal efficiency, achieving an efficiency improvement of up to 12 % compared to the reference collector. Specifically, the efficiency of the reference collector was around 70 %, while the collector with four barriers reached an efficiency of approximately 82 %. Introducing two barriers resulted in a 9 % increase in efficiency, bringing it to about 79 %. Conversely, the collector with three barriers showed a slight decrease in efficiency to 68 %. The barriers effectively reduced internal convective heat loss, enhancing the collector’s ability to harness incident solar radiation. Inserting horizontal barriers within the internal cavity of flat plate solar collectors significantly improves thermal efficiency by reducing convective heat loss. The optimal configuration, based on this study, involves using four barriers. This method presents a straightforward yet effective approach to enhancing solar collector performance. Future research should focus on refining barrier design and placement for different collector sizes and geometries, potentially supporting broader adoption of solar thermal energy systems and contributing to sustainable energy solutions.

Solar greenhouses play a crucial role in winter crop cultivation in the cold regions of China. However, adverse weather conditions such as low temperatures can negatively affect their production. Therefore, improving the greenhouse thermal environment and energy utilisation is crucial for optimising greenhouse productivity. One effective method of storing energy is phase change technology. In this study, melt blending was used to prepare composite phase change materials (CPCMs), with methyl palmitate and hexadecanol as raw materials. In addition, ceramsite was encapsulated with a styrene-acrylic emulsion to form a shape composite phase change material (SCPCM). The results showed that the latent heat of phase change of the CPCMs was 221 J/g, with an initial phase change temperature of 23.48 ℃. The encapsulation of the SCPCM with a styrene-acrylic emulsion significantly reduced leakage. Phase-change ceramsite concrete slabs were developed by integrating the SCPCM into concrete. These slabs were used to construct phase-change and non-phase-change greenhouses. A temperature-testing system was installed in the greenhouses to examine the temperature variations and distributions under typical sunny and cloudy conditions. Results revealed that compared with the control greenhouse, the phase-change greenhouse exhibited a decrease of 3.0 ℃ in the maximum indoor temperature during sunny days and an increase of 3.2 ℃ in the minimum indoor temperature at night. This study highlights the effective temperature control capabilities of phase-change ceramsite concrete slabs for improving energy utilisation and provides valuable theoretical and technical insights for the future utilisation and widespread adoption of phase-change greenhouses.

Defrosting can have a detrimental impact on the functioning of regularly used refrigeration systems. The primary objective of this study is to enhance the cooling efficiency by resolving the defrost process, which impacts the cooling performance due to the heat received from the system. A new solar PVT-assisted system, which includes a cold chamber, was created and tested for this specific purpose. Furthermore, a sophisticated automation scenario has been devised to function in five distinct modes, ensuring the successful execution of the defrost process. Two experiments, Experiment 1 and Experiment 2, were conducted. The average coefficient of performance (COP) and exergy values obtained were 2.29 and 2.25, and 25.74 % and 24.45 %, respectively. The maximum temperature change measured in the cold room during defrosting was 2 °C. In Experiment 1, the PVT collector produced a total energy of 2.85 kWh; Experiment 2 generated 2.79 kWh. Consequently, the defrosting procedure was effectively executed by directing hot air into the chilly chamber using the proposed sustainable method. This system is highly recommended because of its innovative defrosting mechanism, which guarantees optimal solar energy utilization.

In deep excavation projects in confined strata, due to the high water content and high pressure head of the strata, problems such as excessive horizontal displacement of the retaining structure and sudden surge at the bottom of the pit often occur during the excavation process. To solve these problems, it is usually necessary to carry out dewatering construction. However, precipitation construction can cause serious damage to groundwater resources and the surrounding environment. Therefore, in order to protect groundwater resources and the environment, it is necessary to carry out recharge construction after precipitation construction. This article is based on the coupling analysis of stress field and seepage field in foundation pit dewatering. By studying the interaction between pumping wells and buildings in foundation pit engineering, the idea of optimizing the design of foundation pit recharge is proposed. Based on the coupling analysis results of the stress field and seepage field in the foundation pit dewatering, the reasonable position and water volume of the pumping well can be determined to achieve the effect of foundation pit dewatering. At the same time, based on the decrease in groundwater level of the building, the start time and amount of reinjection water can be determined to avoid wasting water resources and increasing the burden on the pumping well due to premature reinjection. By optimizing the design of reasonable foundation pit recharge, water level changes in the project can be better controlled, settlement problems can be avoided, and the safety and efficiency of the project can be improved.

Sugarcane bagasse was used as energy resources. Thermogravimetric analysis was performed at varying heating rates of 10, 20, 30, and 40 °C/min, within the temperature range of 25 to 900 °C. Using the iso-conversional models like Flynn–Wall–Ozawa (FWO), Friedman, Kissinger–Akahira–Sunose (KAS), and Starink, kinetics and thermodynamics were examined, and the Coats–Redfern (CR) model-fitting technique was used to identify the reaction mechanism. The pre-exponential factors were ascertained by applying the Coats–Refern method. According to KAS, FOW, Starink, and Friedman techniques, the average activation energy (Ea) values were found to be 323.46, 168.89, 162.52, and 174.70 kJ/mol, respectively. Thermodynamic characteristics indicate, sugarcane bagasse is a potential feedstock. The pyrolysis reaction was spontaneous, generating sufficient quantity of energy. This research can offer a theoretical foundation for thermochemical conversion of sugarcane bagasse and applications.

Addressing the rising energy demand while minimizing environmental impacts is imperative in today’s energy landscape. This challenge necessitates the development of innovative, high-efficiency, and environmentally-friendly energy systems. This study investigates a hybrid static power generation system combining alkali metal thermal electric converters (AMTEC) and thermoelectric generators (TEG). A detailed parametric analysis is conducted through a comprehensive analytical model that integrates thermodynamics and electrochemistry. The results reveal that the synergistic integration of AMTEC and TEG enhances power generation by 67.1 % and improves efficiency by 27.1 % compared to standalone AMTEC systems. Consequently, the proposed system can achieve a maximum output power of 11.2 kW and an efficiency of 38.9 %. Additionally, the system demonstrates a 10 % load-following capability, highlighting its potential to meet fluctuating demand. Ultimately, the proposed system offers a scalable and effective solution for direct heat-to-electricity conversion.

This study investigates the dynamic optical properties of saline solutions, specifically transmissivity, absorptivity, and reflectivity, and their impact on the performance of solar stills. This research addresses the critical challenge of enhancing freshwater production through solar desalination, which is vital in water-scarce regions. Utilizing a validated mathematical model, the study examines how variations in saline depths (ranging from 5 mm to 40 mm), nanofluids, chemical additives, and dyes influence the optical properties and efficiency of solar stills. The results show that a depth of 20 mm emerges as optimal, providing a balance between high transmissivity, absorptivity, and low reflectivity, also a higher saline absorptivity, ranging from 0.014 to 0.021, significantly boosts solar still performance, while transmissivity, ranging from 0.26 to 0.95, affects instantaneous efficiency. The study reveals that the production of distilled water decreases from 6.77 to 4.87 L/m² as the refractive index increases from 1.2 to 2.6, while higher extinction coefficients enhance production, reaching up to 6.96 L/m² at 300 m⁻¹. These findings demonstrate the importance of optimizing saline optical properties to improve solar still efficiency. The novelty of this work lies in its comprehensive analysis of the dynamic nature of saline optical properties and their practical application in enhancing solar desalination technology, going beyond previous efforts that assumed constant optical properties. This advanced understanding significantly contributes to the development of more efficient and effective solar desalination systems.