Search Results (117)

Photovoltaic–thermal (PVT) technology has attracted considerable attention for its ability to significantly improve solar energy conversion efficiency by simultaneously providing electricity and heat during the day. PVT technology serves a purpose in condensers and subcoolers for passive cooling in refrigeration systems at night. In our previous work, we proposed a switchable film-insulated photovoltaic–thermal–passive cooling (PVT-PC) module to address the structural incompatibility between diurnal and nocturnal modes. However, the performance of the proposed module strongly depends on two key design parameters: the structural height and the vacuum level of the air cushion. In this study, a numerical model of the proposed module is developed to examine the impact of design and meteorological parameters on its all-day performance. The results show that diurnal performance remains stable across different structural heights, while nocturnal passive cooling power shows strong dependence on vacuum level and structural height, achieving up to 103.73 W/m² at 10 mm height and 1500 Pa vacuum, which is comparable to unglazed PVT modules. Convective heat transfer enhancement, induced by changes in air cushion shape, is identified as the primary contributor to improved nocturnal cooling performance. Wind speed has minimal impact on electrical output but significantly enhances thermal efficiency and nocturnal convective cooling power, with a passive cooling power increase of up to 31.61%. In contrast, higher sky temperatures degrade nocturnal cooling performance due to diminished radiative exchange, despite improving diurnal thermal efficiency. These findings provide fundamental insights for optimizing the structural design and operational strategies of PVT-PC systems under varying environmental conditions. Full article

The shortage of freshwater resources has become the core bottleneck of global sustainable development. Traditional freshwater harvesting technologies are restricted by geographical conditions and environmental limitations, making them increasingly difficult to satisfy the growing water demand. In this study, based on the synergistic coupling mechanism of photothermal conversion and radiative cooling, a solar auto-tracking assisted selective solar absorber and radiative cooling all-weather freshwater harvesting device was innovatively developed. The prepared selective solar absorber achieved a high absorptivity of 0.91 in the solar spectrum (0.3–2.5 μm) and maintained a low emissivity of 0.12 in the mid-infrared range (2.5–20 μm), significantly enhancing the photothermal conversion efficiency. The radiative cooling film demonstrated an average cooling effect of 7.62 °C during typical daytime hours (12:00–13:00) and 7.03 °C at night (22:00–23:00), providing a stable low-temperature environment for water vapor condensation. The experimental results showed that the experimental group equipped with the solar auto-tracking system collected 0.79 kg m⁻² of freshwater in 24 h, representing a 23.4% increase compared to the control group without the solar auto-tracking system. By combining theoretical analysis with experimental validation, this study presents technical and economic advantages for emergency water and island freshwater supply, offering an innovative solution to mitigate the global freshwater crisis. Full article

Film cooling, a vital method for controlling surface temperatures in components subjected to intense heat, strives to enhance efficiency through innovative technological advancements. Over the last several decades, considerable advancements have been made in film cooling technologies for applications such as liquid rocket engines, combustion chambers, nozzle sections, gas turbine components, and hypersonic vehicles, all of which operate under extreme temperatures. This review presents an in-depth investigation of film cooling, its applications, and its key mechanisms and performance characteristics. The review also explores design optimization for combustion chamber components and examines the role of gaseous film cooling in nozzle systems, supported by experimental and numerical validation. Gas turbine cooling relies on integrated methods, including internal and external cooling, material selection, and coolant treatment to prevent overheating. Notably, the cross-flow jet in blade cooling improves heat transfer and reduces thermal fatigue. Film cooling is an indispensable technique for addressing the challenges of high-speed and hypersonic flight, aided by cutting-edge injection methods and advanced transpiration coolants. Special attention is given to factors influencing film cooling performance, as well as state-of-the-art developments in the field. The challenges related to film cooling are reviewed and presented, along with the difficulties in resolving them. Suggestions for addressing these problems in future research are also provided. Full article

As photonic integrated circuits (PICs) gain prominence in quantum communication and quantum computation, the development of efficient and stable cryogenic packaging technologies becomes paramount. This paper presents a robust and scalable cryogenic packaging method for thin-film lithium niobate (TFLN) photonic chips. The packaged fiber-to-chip interface shows a coupling efficiency of 15.7% ± 0.3%, with minimal variation of ±0.5% as the temperature cools down from 295 K to 1.5 K. Furthermore, the packaged chip exhibits outstanding stability over multiple thermal cycling, highlighting its potential for practical applications in cryogenic environments. Full article

Mesh adaptation techniques can significantly impact Computational Fluid Dynamics by improving solution accuracy and reducing computational costs. In this review, we begin by defining the concept of mesh adaptation, its core components and the terminology commonly used in the community. We then categorise and evaluate the main adaptation strategies, focusing both on error estimation and mesh modification techniques. In particular, we analyse the two most prominent families of error estimation: feature-based techniques, which target regions of high physical gradients and goal-oriented adjoint methods, which aim to reduce the error in a specific integral quantity of interest. Feature-based methods are advantageous due to their reduced computational cost: they do not require adjoint solvers, and they have a natural ability to introduce anisotropy. A substantial portion of the literature relies on second-order derivatives of scalar flow quantities to construct sensors that can be equidistributed to minimise discretisation error. However, when used carelessly, these methods can lead to over-refinement, and they are generally outperformed by adjoint-based techniques when improving specific target quantities. Goal-oriented methods typically achieve higher accuracy in fewer adaptation steps with coarser meshes. It will be seen that various approaches have been developed to incorporate anisotropy into adjoint-based adaptation, including hybrid error sensors that combine feature-based and goal-oriented indicators, sequential strategies and adjoint weighting of fluxes. After years of limited progress, recent work has demonstrated promising results, including certifiable solutions and applications to increasingly complex cases such as transonic compressor blades and film-cooled turbines. Despite these advances, several critical challenges remain: efficient parallelisation, robust geometry integration, application to unsteady flows and deployment in high-order discretisation frameworks. Finally, examples of the potential role of artificial intelligence in guiding or accelerating mesh adaptation are also discussed. Full article

Film cooling can continuously cover a layer of low-temperature gas film on the surface of hot-end components, thereby achieving the effect of isolating high-temperature gas, and can achieve a temperature drop of 600 K. As an advanced and efficient cooling technique, film cooling plays a crucial role in the process of turbine power and efficiency increase, with the key factor influencing its cooling performance being the configuration and arrangement of the film holes. This paper summarizes the design and arrangement of film hole configurations and discusses the potential directions for enhancing film cooling performance. Through analysis, the optimization of film cooling performance is mainly approached from two aspects: first, optimizing the hole configuration, which includes the study of shaped holes, enhancing the cooling performance of cylindrical holes using auxiliary structures, and forming a “reverse kidney-shaped vortex” structure by using a single combined film hole; second, optimizing the arrangement of the cooling holes on the turbine surface to achieve a more uniform and efficient distribution of the cooling film. Future development trends are primarily reflected in the following aspects: designing new, easily manufacturable, high-efficiency film hole configurations and further expanding their stable operating range is an important development direction. It is essential to validate the reverse heat transfer method, assess its applicable range, and, when experimental conditions exceed the applicable range, use related theories to correct its predictive performance. This is key to overcoming the bottleneck in film cooling prediction. It is critical to develop a film hole arrangement guideline that is suitable for various types of film holes and components with temperature differences at the thermal end, to fill the gap in future film cooling optimization design technologies. This study aims to provide new ideas for the optimal design of the cooling system and further improve the power and efficiency of gas turbines. Full article

In the casting and stamping process of automobile, ship, aerospace, and other fields, improving the atomization quality of the spray release agent can effectively solve the problems of difficult film removal, low efficiency, and poor surface finish, and greatly improve the efficiency of production and manufacturing. The geometric model of the external mixing nozzle was constructed, and the calculation domain and grid were divided. The atomization flow field velocity, liquid film thickness, particle distribution, and cooling amount were calculated using fluid simulation software. Finally, an experimental platform was set up for verification. With the increase in the distance between the iron plate and the nozzle, the velocity of the flow field decreases from the nozzle exit to the periphery, and the frequency distribution of D_60–70 increases gradually. With the increase in the pressure ratio (K), the particle velocity increases gradually, the liquid film thickness increases first, and then gently decreases, and the D_60–70 frequency distribution decreases. The influence of gas pressure on atomized particle velocity and liquid film thickness is greater than that of liquid phase pressure, and the ion velocity reaches the peak value when K = 2. When K = 1.5, the average thickness increment of absolute liquid film is small, the atomized particle diameter changes the least, the frequency distribution of D₆₅ particles is approximately the same, and the atomization effect is the most stable. When the spraying time is 1 s, the K value is larger, and the smaller the temperature drop will be. In 2–4 s, the change in K value has little influence on the cooling amount. Full article

To address the challenge of heat transfer enhancement in the condensation of steam with non-condensable gases on a vertical wall under natural convection conditions, an improved boundary layer model with coupled multi-physics field was proposed in this paper, and traditional theoretical limitations were broken through by innovations. The particle swarm optimization algorithm was first introduced into the solution of the condensation boundary layer, and the convergence difficulty in the laminar–turbulent transition region under infinite boundary conditions was overcome. A coupled momentum–energy–mass equation system that simultaneously considered temperature–concentration dual-driven gravity terms and liquid film drag–suction dual effects was established, and higher computational efficiency and accuracy were achieved. A new mechanism where the concentration boundary layer dominated heat transfer resistance under the coupled action of the Prandtl number (Pr) and Schmidt number (Sc) was revealed. Experimental validation demonstrated that a prediction error of less than 5% was exhibited by the model under typical operating conditions of passive containment cooling systems (pressures of 1.5–4.5 atm and subcooling temperatures of 14–36 °C), and a theoretical tool for high-precision condensation heat transfer design was provided. Full article

As global demand for energy-efficient cooling technologies grows, optimizing window air conditioners (WACs) is crucial. This study integrates computational fluid dynamics (CFD) and experimental fluid dynamics (EFD) to analyze condensate transport induced by the slinger ring in a WAC system. To investigate condensate behavior, the WAC domain is divided into six regions based on the slinger ring’s rotational direction and impact. In the initial impact zone, large liquid structures adhere to the slinger ring before breaking into ligaments. In the upward transport region, condensate films rise along the wall due to centrifugal forces, forming short ligaments. In the rebound region, condensate impacts the top surface and transitions into droplets. In the accumulation zone, droplet coalescence occurs in a confined space, leading to localized mass buildup. In the dispersion region, condensate spreads widely due to increased rotational speed. In the splash zone, splashing and wave-like structures form near the reservoir surface. A newly identified mechanism of condensate mass discharge shows that mass ejection is concentrated in four key regions near the condenser coils. These findings offer insights into optimizing a slinger ring design for improved condensate dispersion. Future research should explore airflow variations and alternative slinger ring configurations to enhance WAC performance. Full article

Radiative cooling is a passive cooling strategy that dissipates heat externally through the atmospheric window (8–13 μm). This study presents a radiative cooling film with a simple and cost-effective fabrication process. The film was fabricated by mixing SiO₂ hollow microspheres with a UV-curable resin, employing a photopolymerization-induced phase separation method. The resulting gradient refractive index structure enhanced thermal radiation emissivity. At an optimal silica-to-resin mass ratio of 1:1.5 and a film thickness of 1.1 mm, the film achieved a solar reflectivity of 85% and an emissivity of 91% within the atmospheric window. Outdoor experiments conducted in both summer and winter demonstrated stable cooling performance. Under a solar irradiance of 796.9 W/m² (summer), the film reduced surface temperature by 10 °C compared to ambient air and 20 °C compared to an uncoated glass substrate, achieving a radiative cooling power of 76.7 W/m². In winter (solar irradiance of 588.8 W/m²), the film maintained a significant cooling effect, though with reduced efficiency due to lower solar exposure. Furthermore, long-term stability tests over six months showed that the film retained high solar reflectivity and infrared emissivity, indicating good durability. Overall, the developed radiative cooling films demonstrate excellent optical properties, structural stability, and cooling efficiency, making it a promising candidate for real-world radiative cooling applications. Further studies on environmental resilience and optimization under diverse climatic conditions are necessary for broader deployment. Full article

This paper presents a numerical study investigating the coupled effects of periodic incoming wake and pulsating jets on the film cooling efficiency of a flat wall. The sweeping frequency of the wake is maintained at a constant 10 Hz, while the blowing ratio (M) varies from 0.3 to 1. By adjusting the initial position of the rod, different phase lags are generated to assess the interaction between the incoming wake and the pulsating jet concerning film cooling efficiency. The results reveal that coupling the wake-affected surface with the low-blowing-ratio phase of the pulsating jet can effectively enhance film cooling efficiency at lower blowing ratios. Conversely, at higher blowing ratios, aligning the low-pressure phase of the pulsating jet at the film hole with the high-blowing-ratio jet pulsation results in an improved film cooling effect. Notably, when the phase lag (ψ) is set to zero, the cooling efficiency of the pulsating film reaches its maximum across all blowing ratios, indicating an optimal coupling strategy. Full article

The hydrocarbon liquid rocket engine working environment is harsh; the thrust chamber needs to withstand high temperatures and a high-pressure working environment, and the thrust chamber wall material is difficult to bear, so it is necessary to design the cooling structure to reduce the gas damage to the chamber wall. Liquid film cooling is a common cooling method for hydrocarbon rocket engines, and numerical simulation is an important method for studying liquid film cooling. Most of the liquid film cooling numerical simulation is for a fixed model. This paper proposes a liquid film cooling numerical calculation method for a variable-configuration hydrocarbon liquid rocket engine, based on the secondary development of Fluent software (ANSYS Fluent 2022) to form a high-energy hydrocarbon liquid rocket engine design software, which can be realized on the Qt platform. The visualization interface can be for different engine injection port locations, numbers, angles, mass flow rates, and other parameters, to calculate and improve design efficiency and reduce operating difficulty. Full article

As the inlet temperature of the gas turbine exceeds the high temperature limit of the blade materials, efficient leading edge cooling technologies are crucial for the further development of gas turbines. Therefore, this paper reviews the research progress on external cooling technology, internal cooling technology, and composite cooling technology for gas turbine rotating blade leading edge cooling. It focuses on the impact of the geometric shape, arrangement, and flow parameters of film cooling holes on external cooling performance, the influence of jet hole design, configuration, crossflow, ribs on internal cooling efficiency, and the characteristics and influencing factors of composite cooling technologies are also discussed. Among the most promising composite cooling techniques, the impingement jet film composite cooling technology and swirl film composite cooling technology stand out. For impingement jet film composite cooling technology, this paper explores the effects of blowing ratio, nozzle parameters, jet hole characteristics, and flow field parameters on the overall cooling performance of the rotating blade leading edge. Impingement jet film composite cooling technology has been shown to significantly improve the cooling performance of the leading edge compared to traditional single cooling techniques. For applications requiring large area cooling or maintaining film integrity, swirl film composite cooling technology not only enhances heat transfer efficiency but also improves the uniformity of heat transfer. The design of swirl nozzles, coolant flow rate, Reynolds number, and jet temperature all have significant effects on the heat transfer efficiency of swirl film composite cooling. To further advance the development of gas turbine rotating blade leading edge cooling technologies, it is recommended to focus on the study of film composite cooling techniques, particularly investigating the effects of various parameters of impingement, swirl on composite cooling performance. Full article

Inorganic materials used in passive radiative cooling have achieved a commendable level of performance through synthesis, yet they lack sustainability and environmental friendliness as they do not incorporate recycling. This study developed a novel passive radiative cooling (PRC) film utilizing calcium carbonate extracted from discarded oyster shells (D-CaCO₃) and polyurethane (PU) as the matrix. This sustainable approach leverages the unique properties of CaCO₃, such as high solar reflectance and strong infrared emissivity, to achieve significant cooling effects. The PU/D-CaCO₃ film absorbs only 22% of total solar light and exhibits a high emissivity of 95% in the atmospheric window, achieving temperatures up to 7 °C lower than the surrounding environment under 650 W/m² solar irradiance. Furthermore, field tests were conducted to verify the implementation of our optical strategy by analyzing the optical properties and FDTD simulations. Consequently, the PU/D-CaCO3 film outperformed conventional white paint and pure PU, demonstrating a maximum temperature difference of 7 °C. Additionally, the passive radiative cooling efficiency of the film was verified through theoretical calculations. The oyster-shell-derived CaCO₃ utilizes waste and contributes to carbon sequestration, aligning with sustainable and eco-friendly goals. This research demonstrates the potential of using marine-derived materials in passive cooling technologies, offering a path to reduce energy consumption and greenhouse gas emissions in cooling applications. The findings highlight the commercial viability and environmental benefits of PU/D-CaCO₃ films, marking significant progress in passive radiative cooling. Full article

The high-pressure die-casting process is growing since it is a cost-effective solution in the production of lightweight parts for a variety of industries. Nevertheless, the harsh working conditions of the die lead to premature failing and poor quality of the produced parts. Lubricants are applied to cooling the die surface and create a protective film to minimize die wear. However, the high temperature of the die during the casting production makes it difficult for the lubricant to reach the die surface due to the Leidenfrost effect. In this study, the effectiveness of newly developed ester-based lubricants designed to address Leidenfrost phenomenon in high-pressure die-casting is evaluated at laboratory and pilot plant scale. The new lubricants are based on the same ester solution; however, one of them includes a specially formulated anti-Leidenfrost additive to optimize performance at the temperature ranges typically encountered in industrial aluminum high-pressure die-casting processes. The results show a correlation between lubricant heat-transfer capability and aluminum adhesion. Additionally, a pilot plant methodology for testing newly formulated lubricants has been established while the experimental methodology developed for assessing heat-transfer capability is validated as a rapid and cost-effective approach for evaluating lubrication alternatives for high-pressure die-casting applications. Finally, the efficiency of environmentally friendly ester-based lubricants for high-temperature applications has been demonstrated. Full article