Bag breakup is a typical breakup mode of the Supercooled Large Droplet (SLD) in the field of aircraft icing. The deformation and breakage processes of a water droplet in continuous airflow is studied by combining experimental and numerical simulation methods. A regime map is drawn to give the physical boundary of the bag breakup mode. The deformation ratio, velocity of the initial droplet and size distribution of the secondary droplets are analyzed, and the causes of droplet morphology evolution in each stage of the bag breakup mode are explained. The results show that the range of gaseous Reynolds number and Weber number corresponding to the bag breakage mode are 3100∼4250 and 12∼18, respectively. At the disk moment, the horizontal deformation ratio of the droplet is about 0.4, and it varies slightly with the increase of gaseous Weber number. While, the vertical deformation ratio of the droplet increases gently with the increasing gaseous Weber number. When the gaseous Weber number is 13.4, the droplet breaks in the bag breakup mode. The dimensionless size distribution of the secondary droplets ranges from 0 to 0.28, showing a unimodal distribution, and the peak value appears when the dimensionless size of the secondary droplet is 0.024. This study plays a crucial role in improving the physical model of SLD bag breakup and advancing the simulation accuracy of SLD icing.

With the increasing integration of renewable energy, the inherent uncertainty of energy sources and loads, coupled with the nonlinear coupling characteristics of multi-energy systems, poses significant challenges to the operation and management of distributed energy systems. This paper accounts for the nonlinear characteristics of electricity-heat transmission and conversion processes by incorporating a heat current model and a column-and-constraint generation algorithm, proposing a two-stage robust optimization model and a bilevel iterative optimization algorithm. Compared to a simplified robust optimization model that neglects nonlinear characteristics, the proposed approach reduces operating costs by 3.2%. Furthermore, the results demonstrate that in actual system operation, the proposed algorithm effectively mitigates the infeasibility risk of robust scheduling strategies caused by model simplifications, thereby verifying its economic efficiency and robustness. 

Synthetic lubricating oil is widely used in various types of refrigeration and heat pump equipment, and its thermophysical properties are the basic data for analyzing thermodynamic energy efficiency, heat transfer performance and pressure drop along the way, which is of great significance for evaluating and optimizing the system structure. In this paper, a set of low-temperature and high-pressure pendant drop surface tension experimental measurement system was developed, and the liquid phase density and surface tension of basic lubricating oils (POE, PVE and PAG) were studied by using vibrating tube density meter and pendant drop surface tension experimental system, and the measured temperature range was 243.15∼363.15 K, and the extended uncertainty of liquid phase density and surface tension measurement was within 0.2% and 0.1 mN·m⁻¹, respectively. The experimental results show that the liquid phase density and surface tension of the base lubricating oil decrease with the increase of temperature, and the absolute average deviation between the calculated value and the experimental value of the correlation equation is less than 0.04% and 0.5%, respectively.

To investigate the operating characteristics of bifacial photovoltaic (BPV) module in a specific region, an optical model integrating direct solar radiation and sky-scattered radiation was proposed, a thermal model of coupled environment was constructed, and an electrical model based on discrete method was introduced. The effects of ground reflectivity (R) and solar incidence angle (θ) on the performance of BPV module operating in Shapingba District, Chongqing (29◦33′9.08′′N, 106◦27′36.60′′E) were investigated by using the coupled optical-thermal-electricalenvironmental method and compared with the results based on average temperature electrical model. The results indicate that instantaneous electrical efficiency (η_el) decreases with the increase of R, while instantaneous electrical power (P) of BPV module is the opposite. When tilt angle of module exceeds local latitude, η_el increases and P decreases with the increase of θ. Conversely, when the tilt angle is less than local latitude, η_el decreases and P increases with increasing θ. The temperature uniformity of module improves as R and θ increase. The maximum relative deviations of P and η_el calculated by discrete method and average temperature method are 1.64% and 1.66%, respectively.

As a natural refrigerant, CO₂ exhibits excellent environmental performance and low production costs, making it an ideal replacement for high-GWP refrigerants. To enhance system efficiency, vapor injection technology, characterized by its simple structure and reliable operation, has been widely employed in CO₂ heat pump systems. However, these systems still face significant challenges in practical applications due to inherent issues such as high operating pressures and substantial throttling losses. To address these challenges, this study incorporates three low-pressure refrigerants into the CO₂ heat pump system to improve operational efficiency and reduce system pressure. The research findings demonstrate that the CO₂/R161 system surpasses traditional CO₂ heat pump systems in terms of energy efficiency. The CO₂/R161 system achieves up to a 17.6% increase in efficiency under various thermal demand conditions and a maximum pressure reduction of 33.7% at an outlet water temperature of 85°C, compared to conventional CO₂ heat pump systems.