Over the past few years, the combination of solar power with refrigeration technology has matured, providing a promising solution for sustainable cooling. However, a key challenge remains, namely the inherent intermittency of solar energy. Due to its uneven temporal distribution, it is difficult to ensure continuous 24 h operation when relying solely on solar energy. To address this issue, thermal energy storage technology has emerged as a viable solution. This paper presents a comprehensive systematic review of phase-change material (PCM) applications in solar refrigeration systems. It systematically categorizes solar energy conversion methodologies and refrigeration system configurations while elucidating the fundamental operational principles of each solar refrigeration system. A detailed examination of system components is provided, encompassing photovoltaic panels, condensers, evaporators, solar collectors, absorbers, and generators. The analysis further investigates PCM integration strategies with these components, evaluating integration effectiveness and criteria for PCM selection. The critical physical parameters of PCMs are comparatively analyzed, including phase transition temperature, latent heat capacity, specific heat, density, and thermal conductivity. Through conducting a critical analysis of existing studies, this review comprehensively evaluates current research progress within PCM integration techniques, methodological classification frameworks, performance enhancement approaches, and system-level implementation within solar refrigeration systems. The investigation concludes by presenting strategic recommendations for future research priorities based on a comprehensive systematic evaluation of technological challenges and knowledge gaps within the domain.

The dynamic characteristics of dual droplet successive oblique impact on a thin liquid film are numerically studied by using the coupled level set and volume-of-fluid model. This three-dimensional model effectively predicts the evolution of crown and crater, which is validated qualitatively and quantitatively by comparing with experimental observations. Some interesting interface features during the collision and coalescence of crowns are revealed in the present simulations, such as the gas cavity, liquid crest, and air gap. In addition, the crater contour takes on different phases with time in the case of dual droplets impact. The evolution characteristics of crater contours in front view and side view have been summarized within a certain time period. Furthermore, the variations of the maximum crater radius in upstream, downstream, and lateral directions as time are quantitatively analyzed. It is found that in the circumferential direction of the crater, the radial kinetic energy of the liquid decreases gradually from the upstream to the downstream direction. This research establishes a foundation for industrial and agricultural applications involving droplet impact.

Compared with film condensation, dropwise condensation based on droplet growth can significantly improve the condensing equipment’s water collection and thermal efficiency in the vapor condensate system. Therefore, as a critical behavior affecting the evolution of dropwise condensation, research on droplet growth is of great significance to further understanding the evolutionary characteristics and heat transfer mechanism of dropwise condensation. In this paper, a model for simulating the entire evolution process of dropwise condensation is improved and constructed, and the evolution process of dropwise condensation with different condensation nucleus densities on the vertical wall is simulated based on certain assumptions. Moreover, parameters such as evolution rate and size contribution are proposed to measure droplet growth’s influence on the evolution process of dropwise condensation. In the simulation, the Cassie model was used to describe the condensation growth of droplets. The neighbor finding algorithm and conservation law are coupled to simulate the coalescence growth process of droplets. Through the comparison of the theoretical model and experimental results, it is indicated that the simulation method in this paper is highly reliable. The simulation results demonstrate that more than 95% of the maximum droplet size of dropwise condensation is derived from coalescence growth, and its growth rate can characterize the evolution rate of dropwise condensation. The evolution rate reveals a linear growth trend with the increase of condensate nucleus density, and the average heat flux shows an increasing trend followed by a decreasing trend, reaching the peak, q_average = 30.5 kW·m⁻², at the N_S = 5 × 10⁹ m⁻². The surfaces with a high coalescence frequency can increase the contribution of the coalescence growth to the maximum droplet size more effectively and, conversely, the contribution of condensation growth is weakened, which is less than 1% at the N_S = 7.5 × 10⁹ m⁻².

The impact of droplets on liquid films is a fundamental phenomenon in fluid dynamics, with significant implications across various scientific and engineering applications. While much research has focused on normal droplet impacts, where the droplet strikes the liquid surface perpendicularly, the dynamics of oblique droplet impacts remain less understood. This study aims to explore the complex interactions governing oblique droplet impacts on the liquid film. Based on superhydrophobic coating technology, this study proposes a novel experimental method for achieving oblique droplet impacts. Compared to existing methods, this approach offers good experimental repeatability. The experimental setup developed is centered around a droplet generation unit capable of stably producing oblique droplets, with the evolution of the ship's prow-like liquid crown captured using high-speed imaging technology. The effects of the Weber number, impact angle, and liquid film thickness on the evolution and characteristic parameters of the liquid crown were investigated. The model for predicting the variation of the dimensionless liquid crown radius was validated. Additionally, a splashing discrimination method based on the normal K number was introduced, and an empirical correlation for the splashing threshold was established using the soft-margin support vector machine. The findings of this study could pave the way for innovative solutions in industries where precise fluid control is paramount and lay the groundwork for future explorations into more intricate multiphase flow phenomena.

During solar cell operation, most light energy converts to heat, raising the battery temperature and reducing photoelectric conversion efficiency. Thus, lowering the temperature of solar cells is essential. Nanofluids, with their superior heat transfer capabilities, present a potential solution to this issue. This study investigates the mechanism of enhanced heat transfer by nanofluids in two-dimensional rectangular microchannels using the two-phase lattice Boltzmann method. The results indicate a 3.53% to 22.40% increase in nanofluid heat transfer, with 0.67% to 6.24% attributed to nanoparticle–fluid interactions. As volume fraction (φ) increases and particle radius (R) decreases, the heat transfer capability of the nanofluid improves, while the frictional resistance is almost unaffected. Therefore, the performance evaluation criterion (PEC) of the nanofluid increases, reaching a maximum value of 1.225 at φ = 3% and R = 10 nm. This paper quantitatively analyzes the interaction forces and thermal physical parameters of nanofluids, providing insights into their heat transfer mechanisms. Additionally, the economic feasibility of nanofluids is examined, facilitating their practical application, particularly in solar cell cooling.