Thermal Science and Engineering Progress最新文献

With the wide application of renewable energy, solar energy as a clean and sustainable energy gradually received attention. In the visual communication design of the museum, how to effectively use solar energy and improve the comfort and energy efficiency of the exhibition space has become a research hotspot. In this study, a light sensor was installed in the museum to monitor the changes of indoor and outdoor light intensity and temperature in real time. Combined with AI algorithms, the collected data is analyzed to optimize the collection and distribution of solar thermal energy. At the same time, the corresponding visual communication system is designed to guide visitors to make effective use of the museum space. The research shows that the solar thermal energy utilization system based on the light sensor can achieve high thermal energy efficiency, keep the indoor temperature within the comfortable range, and reduce the use frequency of traditional air conditioning. The AI navigation system effectively guides visitors to the exhibition in a more efficient way, enhancing their satisfaction and interactive experience. The combination of light sensor and AI navigation technology can effectively improve the utilization efficiency of solar heat energy in the visual communication design of the museum, optimize the environmental quality, and promote the sustainable development of the museum to achieve more efficient resource utilization and environmental protection.

The lack of research on the boiling heat transfer coefficient on billet surfaces during the high-pressure fan-shaped water descaling process significantly affects the cooling, quality, and rolling efficiency of the billet surface. This paper utilizes the Eulerian multiphase flow model in Fluent 19.0 software to simulate the boiling heat transfer behavior of multiple high-pressure fan-shaped water jets impinging the surface of high-temperature steel billets during descaling. The study highlights the correlation between the boiling heat transfer coefficient and three key parameters: the Reynolds number, dimensionless target distance, and dimensionless temperature. The simulation’s accuracy was validated by comparing the simulation results against experimental data. Findings indicate that the boiling heat transfer coefficients were respectively higher in the stagnation area, the lower side of the overlap zone, and at the edges of the flow strands on the billet surface, reaching up to approximately 6000 W·m⁻²·K⁻¹. Additionally, the heat transfer coefficients were higher in the downstream region compared to the upstream area. The boiling heat transfer coefficient increased by 13.7 % and 9.38 % as the Reynolds number increased from 278,031 to 340,486 and as the initial temperature increased from 1373.15 K to 1573.15 K, respectively. On the other hand, the boiling heat transfer coefficient decreased by 19.0 % when reducing the target distance from 20 de to 54 de. Finally, a function was established to describe the boiling heat transfer coefficient based on the Reynolds number, dimensionless target distance, and dimensionless temperature.

Hydrothermal carbonization (HTC) is a low-energy thermochemical process that converts wet biomass into a carbon-rich solid, commonly called hydrochar, for use in a variety of areas, such as soil amendment, biofuels or to produce carbon-based materials. The purpose of this paper is to increase knowledge for the economic valorization of municipal wet waste, considered as a raw material to obtain high value-added products through an HTC process and an additional chemical activation procedure. In the first part of the work, a 4.5-liter batch reactor was designed, built, and used in the HTC experimental campaign by varying the main process parameters, namely reaction time, amount and type of organic waste (e.g. vegetables, fruits, bread, pasta), water concentration, temperature and pressure. In addition, some experiments were conducted by applying the steam explosion technique at the end of the HTC process. The HTC results showed that in biomass with high water content, increasing residence time decreases the hydrochar yield. Considering a dry heterogeneous waste with high carbon content, the yields at the end of the process are much higher. In the second part of this work, the hydrochar samples were treated with a high-temperature activation process based on the use of KOH, obtaining activated carbon. Particularly, the best results were achieved by using high KOH: hydrochar ratios, resulting in high-quality activated carbons with good porosity and a high surface area of 2890 m²/g. Finally, an energy analysis was carried out to evaluate how to make the whole process cost-effective.

Harnessing the cold energy inherent in LNG transportation processes can significantly mitigate energy wastage. Employing an innovative incremental analysis methodology, this study scrutinizes six LNG cold energy power generation systems, featuring a newly proposed parallel and cascade combined cycle (PAC) system. A novel approach that setting the minimum pressure within the systems higher than atmospheric levels has been adopted, for the optimal working fluid selection. The net power output (W_net) of the direct expansion (DC) system registers at −129.51 kW, while both the Single-Stage Organic Rankine Cycle (SORC) and Combined Cycle (CC) systems yield W_net of 2868.46 kW and 3081.46 kW with R32 as working fluid. Despite the lower available exergy extraction of the working fluid, the CC system outperforms due to its superior efficiency in converting pressure exergy into power output. Sensitivity analysis suggests the optimal T_con in CC is limited by the normal boiling point temperature (NBPT) of working fluid, while that in SORC remains unrestricted. The maximum W_net of two-stage Parallel Combined Cycle (PCC) and Cascade Combined Cycle (CCC) can reach 3291.65 kW and 4268.78 with the optimal working fluid combinations R32 + propane, and ethane + propane. The reason W_net of CCC outperforms is the cascade utilization of LNG cold exergy enables the working fluid in its second stage obtains significantly 9.49 times higher amount of exergy compared to PCC. Through sensitivity analysis, while T_con1 mostly predominates the performance of PCC, both T_con1 and T_con2 exert substantial influence on CCC. For the three-stage PAC, its W_net can reach the highest 4700.82 kW with ethane + propane + propane. It is because the PAC not only utilizes LNG’s cold exergy in a cascaded manner, but also obtains the exergy from working fluid. According to economic analysis, the PAC system exhibits an advantage with the highest annul total net income (ATNI). And the CC emerges as a cost-effective choice if the irreversible losses and W_net are not considered. According to innovatively explores about the impact of direct expansion and changes in NG outlet pressure on working fluid selection and economic feasibility, it shows the optimal combinations remain the same, and the systems incorporating a direct expansion component with lower NG outlet pressure demonstrate a more economically advantageous solution.

This study proposes a new passive thermal-control device utilizing phase-change materials (PCMs) that require minimal active thermal support, such as heaters, to achieve a high-performance and high-reliability power supply for nanosatellites and other space applications. This study evaluated two different PCMs as candidate materials for the device and compares their performances as thermal control devices. One was a solid–solid PCM based on vanadium dioxide doped with tungsten (VWO₂), and the other was a microencapsulated PCM containing n-paraffin (NPH-MPCM). For integration into nanosatellites, it is essential to form a PCM as solid blocks. This report adopted a solidification method using epoxy resin (EP) as the binder and determined the optimal block composition for each PCM. The thermal-insulation properties of both PCM blocks in vacuum and low-temperature environments were evaluated and found to be almost equivalent. Considering that the latent heat of VWO₂ is only approximately one-fifth that of NPH-MPCM, the practical application of VWO₂ as a PCM was demonstrated. Furthermore, VWO₂ exhibits a phase-change temperature hysteresis of 4 °C, which is significantly smaller than the 23 °C of NPH-MPCM. This characteristic is expected to help maintain a more constant temperature for power supplies in earth-orbiting micro/nanosatellites. Moreover, lithium-ion battery cells were incorporated into both VWO₂-based and NPH-MPCM-based PCM blocks, and their charge–discharge behaviors were evaluated. Only the VWO₂-based PCM block could maintain appropriate temperatures to ensure stable charge–discharge operation. Vacuum resistance results suggested that the VWO₂-based PCM block is well-suited as a temperature-stabilizing device for electric power supplies in nanosatellites.

Laser cutting is an extremely precise and versatile industrial technique that utilizes a focused laser beam to accomplish precise and accurate material cutting or engraving. Because of its efficiency and adaptability, laser cutting has become an essential component of modern production and design. The transient thermal and stress distribution of laser cutting of a sheet is introduced numerically in this study. Temperature, equivalent elastic strain, and equivalent stresses at different workpiece materials (structural steel, titanium alloy, and aluminum alloy) are investigated. Three different laser beams (500 W, 1000 W, and 1500 W) were used in this study. The modeling applies a heat source based on a Gaussian distribution to predict heat flow with an accurate temperature distribution field. The numerical model is validated with experimental data, and the error percentage is consistent and reasonable. The results showed that titanium could attain higher temperatures for the material of the workpiece under the same working conditions as both stainless steel and aluminum alloy. In comparison to stainless steel, the temperature increase ratios for titanium and aluminum are 121 % and 113.5 %, respectively. Aluminum expands rapidly, structural steel endures stresses, and titanium withstands high temperatures effectively. In comparison to 500 W, the temperature rise ratios for laser beams of 1000 W and 1500 W are 174 % and 237 %, respectively. These results highlight how critical it is to select the ideal laser power dependent on the properties of the material, adding to a more sophisticated knowledge for increased accuracy and effectiveness in laser cutting procedures.

This research investigates the dynamic behavior and impact of various factors on the hydraulic, thermal, and exergetic characteristics of a solar-based thermoelectric device using a pin–fin heatsink cooled by supercritical CO₂. A comprehensive numerical model analyzes the heat dissipation and performance of the power generator, integrating a thermoelectric generator and a pin–fin heatsink with various pin shapes. Key geometric and operational parameters, such as the height of PN (P-type and N-type semiconductor) legs of the TEG, the number of thermocouples, operating pressure, Reynolds number, and CO₂ temperature, are examined for a comprehensive performance assessment. The study highlights the superior performance of CO₂ coolant over traditional water-cooling system. Near the critical temperature of CO₂, enhanced heat transfer significantly boosts power output, conversion efficiency, and exergetic efficiency. For example, at 8 MPa, the TEG’s (thermoelectric generator) power output increases from 1.31 mW at 295 K to 2.35 mW at 310 K. Comparisons reveal that while water coolant lowers the cold side temperature more effectively, it results in reduced power output due to decreased temperature differentials and increased pressure loss. Conversely, CO₂ coolant maintains higher cold side temperatures while having advantages in power output. At 315 K, the cold side temperature with water is 315.7 K compared to 346.7 K with CO₂. Increasing the number of thermocouples from 18 to 32 for a leg height of 1 mm leads to an approximate 102.3 % increase in voltage. Raising the PN leg height from 1 mm to 2 mm for an NTC of 50 results in a nearly 99.8 % increase in voltage. Lozenge-shaped fin produces a peak power output of 2.73 mW, while square fin generates 2.62 mW. This research underscores CO₂’s potential as a high-performance coolant in solar thermoelectric applications, offering insights into optimizing system design for maximum efficiency.

Thermoelectric generator (TEG) is a promising energy-converting device that produces electricity from the temperature difference between a heat source and a heat sink. Enhancing the heat transfer between the TEG and the heat source or heat sink can improve the TEG performance. This study proposes a novel automobile exhaust TEG. The novelty originates from the fact that the proposed TEG uses magnetized Ferro-fluid flow as coolant to enhance cooling rate. Computational fluid dynamics (CFD) approach, through C++ coding in the OpenFOAM open-source software package, is used to assess the system’s performance. The results indicate that employing the magnetized Ferro-fluid flow can favorably reduce the cold side temperature of the TEG module, leading to a 5.5 % voltage rise. It is also shown that to achieve the same voltage enhancement without the use of the proposed magnetized Ferro-fluid flow, a tough task of a 470 % rise in the cold side mass flow rate is required. A parametric study reveals that the effectiveness of using the magnetized Ferro-fluid flow decreases with the exhaust temperature but is almost independent of the exhaust mass flow rate. This study also introduces the best location for the magnetic sources.

The solidification of phase-change materials (PCMs) is a key process that occurs commonly in materials science and metallurgy, such as in the casting of alloys and energy management systems. There is a lot of literature in this area that assumes the PCMs are in close contact with the heat source or sink. However, a non-freezing wall frequently encloses them in practical situations. This work presents a phase change problem that describes the solidification of a semi-infinite PCM with thermal resistance. We assume that time-dependent heat flux drives the solidification process. The PCM first convert into mush and then into solid, which leads to a three-region problem. The current study accounts for both conduction as well as convection heat transfer mechanisms. Unfortunately, the exact solution to such problems with time-dependent flux-type boundary conditions may not be possible. Thus, there is considerable interest in deriving the analytical solution. The space–time transformation yields the analytical solution to the problem. A numerical example of $\mathrm{Al}-\mathrm{Cu}$ alloy with $5\text{\%}\mathrm{Cu}$ is presented to demonstrate the current study. Thermal resistance shows a pronounced impact on the temperature field. Lower thermal resistance offers faster solidification rate. It is found that as the heat transfer constant increases, the rate of propagation of solid–mush and mush–solid interfaces gets enhanced. In addition, the growth of thermal resistance is of linear nature, with variation in the value of $Q$. The solidified region has higher concentration than the mush region. The current study is applicable to both eutectic systems and solid solution alloys.

High heat flux density may lead to a decline in the performance of highly integrated electronic components, which presents a major challenge to thermal management strategies. This work developed ionic wind heat sinks with parallel-fin channels for cooling high-power chips. The study examined the effects of intake air velocity, number of electrodes, and discharge spacing on the distribution of ionic wind flow and the improved heat transfer performance of the ionic wind heat sink. The findings suggest that the ionic wind heat sink with wire electrodes perpendicular to the fin channels can withstand higher operating voltages and generate more reliable corona discharges. The improved heat transfer capabilities are achieved with reduced inlet air velocity. The heat transfer enhancement factor (HTEF) of the ionic wind heat sink decreases as the discharge spacing increases, leading to a reduction in the peak value of the body force. The heat transfer capacity declines as the number of wire electrodes increases, because marginal effects lessen disruption to the thermal boundary layer. An effective airflow is achieved when wire electrodes are positioned upstream of the heat sink and run parallel to the fins, ensuring a steady and efficient cooling process. The design effectively disrupts the thermal boundary layer, reducing momentum loss in the flow and increasing the HTEF value by 21.2%. This improvement significantly enhances the heat dissipation capacity. The structurally optimized heat sink demonstrates excellent overall performance and is a viable option for improving heat dissipation in electronic devices.