In this study, a solar single/double-effect switching LiBr-H₂O absorption refrigeration system was investigated to make full use of solar energy and give full play to the advantages of solar refrigeration systems. A corresponding thermodynamic dynamic mathematical model was developed. The operation characteristics of the system operating continuously for one week were analyzed. In order to highlight the advantages of the solar single/double-effect switching absorption refrigeration system, it was compared with other forms of solar refrigeration systems and compression refrigeration systems. The practical application potential of the single/double-effect switching LiBr-H₂O absorption refrigeration system was evaluated from the perspective of economy and environmental effect. The results showed that the system could achieve the switching operation between single-effect mode and double-effect mode under weather conditions of high solar radiation intensity, and the daily cooling efficiency on such days was relatively high. After an auxiliary heater was added, the primary energy savings of the solar single/double-effect switching LiBr-H₂O absorption refrigeration system were 25–52%, depending on the area of the collector and the volume of the storage tank. The solar fraction of the system was about 71.99% for continuous operation during the whole refrigeration season. However, the initial investment cost of the system equipment accounted for 89.66% of the total cost. Compared with the traditional compression refrigeration system, the initial investment cost of the solar single/double-effect switching LiBr-H₂O absorption refrigeration system was higher, but it had a better environmental protection effect.

The flow boiling heat transfer characteristics of zeotropic mixture R290/R601a in a horizontal mini-channel with an inner diameter of 2 mm were experimentally studied. The experiments were conducted at saturation pressure from 1 to 1.5 MPa, mass flux from 100 to 500 kg/(m²·s), heat flux from 20 to 30 kW/m², and vapor quality from 0 to 1. The effects of mass fraction, mass flux, saturation pressure, heat flux, and vapor quality on the flow boiling heat transfer coefficient in a mini-channel were analyzed. The experimental results show that the boiling heat transfer coefficient initially decreases and then increases with a decrease in the R290 mass fraction. The boiling heat transfer coefficient increases with the increase in mass flux and heat flux and decreases with the increase in saturation pressure. In addition, due to the dry-out phenomenon, the boiling heat transfer coefficient first increases and then decreases with the increase in vapor quality. The experimental data were compared and evaluated with existing correlations. Finally, a new prediction correlation for the boiling heat transfer coefficient is proposed, and the mean absolute relative deviation is 13.7%. This work provides key data for the development of green refrigeration technology, which is helpful in promoting the application of low-GWP natural refrigerants in new refrigeration systems. It also offers experimental guidance for the energy efficiency optimization of the ORC system and the structural design improvement of the compact heat exchanger.

The present study aims to numerically investigate the impact of inclination angle on the boiling heat transfer and pressure drop in rectangular micro-channel tubes with a large length-diameter ratio. The volume of fluid approach was utilized to model the two-phase flow in micro-channels using the CFD method. The effects of different inclination angles, aspect ratio and Reynolds number on heat transfer and pressure drop characteristics are analyzed by simulation. According to the latent heat percentage and saturation temperature differential, the mass transfer factor was calculated using the Lee model, which describes the mass and energy transfer throughout the boiling process. The convective heat transfer coefficients of the walls of structures at angles ranging from 0? to 90? (aspect ratios of 1.271, 1.017 and 0.763, respectively) were analyzed. It was found that with the decrease of aspect ratios, the convective heat transfer coefficients decreased by 16.64% and 11.56%, respectively. In order to keep the evaporator outlet superheat within 5?C, the inlet Reynolds number should not be lower than 3000. The study offers insightful information for designing and refining micro-channel evaporators in refrigeration systems, particularly for horizontal freezers with specific inclination angle arrangements.

Effective thermal management of electronic modules is crucial to the reliable operation of variable frequency air conditioners. For this reason, two types of plate-finned heat sinks of electronic modules were selected. The experiments utilized ceramic heating plates to simulate chip heating, conducted in an enthalpy difference laboratory with controlled environments. Four installation cases were analyzed to evaluate the impact of heat sink orientation, airflow direction, and structural layout. The results showed that when multiple chips were arranged on the same heat dissipation substrate, the heat dissipation process of the chips would be coupled with each other, and the rational layout of the chips played an important role in heat dissipation. In the case of cooling air impacting the jet, the heat dissipation performance of the heat sink was significantly improved, and the heat transfer coefficient of the heat sink was as high as 316.5 W·m⁻²·°C⁻¹, representing a 6.9% improvement over conventional designs (case I: 296.1 W·m⁻²·°C⁻¹). The maximum temperature of the chips could be reduced by 11.1%, which is 10.1 °C lower. This study will provide a reference for the optimization design of the heat sink of the electric control module in inverter air conditioners.

As the increasingly serious impact of CFC and HFC on the environment, research on zeotropic mixtures plays an indispensable role in many industries. Especially, the study of zeotropic mixtures is essential for optimizing liquefied natural gas system design. As primary constituents of natural gas, methane (R50), and ethane (R170) are equally vital in mixed-refrigerant Joule-Thomson cycles. This work experimentally examines flow condensation heat transfer for R50/R170 blends in horizontal smooth tubes across wide-ranging conditions. A non-equilibrium film theory-based analytical model was proposed to examine heat and mass transfer during binary zeotropic mixture condensation, incorporating vapor-liquid interfacial mass transfer resistances. Rigorous examination quantified impacts of mass flux, saturation pressure, heat flux, and vapor quality on temperature and concentration gradients. The results revealed substantial heat transfer degradation from temperature/mass fraction gradients, exhibiting strong dependency on volatile component concentration and mixture vapor quality. Model predictions demonstrated good agreement with measured condensation heat transfer coefficients for binary refrigerants.