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.

Spray cooling is an effective heat transfer technique capable of handling high heat fluxes and temperatures. The study of droplet impact offers a simplified approach to understanding the fundamentals of spray cooling and elucidates the effects of droplet diameter and velocity. Experiments on a single-droplet impact on a thin liquid film with boiling bubbles are carried out in this study. Two-phase interface evolution is observed using high-speed video, and the heater surface temperature variation at the impact point following an impact is recorded and analyzed, which can be divided into the response stage, the recovery stage, the steady stage, and the slow recovery stage. Furthermore, a cooling factor based on the change in heater surface temperature is introduced to evaluate the cooling effect of droplet impact. Results show that the steady stage plays a significant role in the heater surface cooling process. Moreover, the maximum cooling factor increases appreciably with increasing droplet diameter and impact velocity.

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.

The flow and heat transfer characteristics of a droplet obliquely impact on a stationary liquid film is numerically studied by using a coupled level set and volume of fluid method (CLSVOF). The effects of impact angle, Weber number, and film thickness are analyzed. As compared with the normal impact, the flow features and surface heat flux distribution for oblique impact are asymmetric and where the secondary droplets only can be observed on one side. Corresponding mechanisms have also been interpreted. The maximum value of the local surface heat flux decreases and moves to the right with the increase in impact angle, while the minimum local surface heat flux on both sides increases as the impact angle increases. With a greater Weber number or a thinner film thickness, the maximum local surface heat flux is higher, while the minimum local surface heat flux on both sides appears to be an opposite trend. In addition, the impact angle has little effect on the average surface heat flux.

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.