A CO₂ data center cooling and heating system integrated with dedicated mechanical subcooling and dual-temperature evaporation technology (DMS-DE) is proposed to realize green and efficient cooling for data centers and improve comprehensive energy efficiency. A thermodynamic and carbon emission performance system model was established and compared with the basic CO₂ system (Base) and a single evaporating-temperature CO₂ system with dedicated mechanical subcooling (DMS-SE). The results demonstrated that the DMS-DE system had the maximum coefficient of performance (COP), optimal subcooling degree, and discharge pressure. Therefore, adopting the DMS-DE can significantly increase the system COP and exergy efficiency. Compared with Base and DMS-SE, COP increased by 14.1% and 9.0%, and the exergy efficiency increased by 13.24% and 4.31%, respectively. The life cycle carbon emissions of the DMS-DE system were reduced by 16.1% and 9.3% compared with Base and DMS-SE, respectively. This study can provide a technical reference for the highly efficient and clean operation of combined heating and cooling utilization for data center scenarios.

Microencapsulation technology based on sodium alginate hydrogels can be used to optimize freezing and rewarming procedures and to reduce cryo-damage to cells and tissues. This study first observed the morphology of oocytes of sodium alginate hydrogels at different volume fractions (0.5%, 1.0%, 1.5%, and 2.0%) to determine the safe concentration for their encapsulation. Second, the crystallization temperature and crystallization behavior of sodium alginate hydrogels with different volume fractions were systematically investigated using cryo-microscopy, and the morphology and crystallization of oocytes were compared when they were cooled down/retempered in the base solution (cryoprotectant solution). Finally, the freezing effects of the sodium alginate antifreeze hydrogel-encapsulated oocytes prepared by solvent replacement and physical mixing were compared. The results revealed that oocytes maintained their overall morphology and volume better in sodium alginate gels at volume fractions of 0.5% and 1.0%. Furthermore, oocytes in both the 1.0% sodium alginate group and the cryoprotectant solution group of 12.5% DMSO + 12.5% EG + 0.5 mol/L trehalose did not produce intracellular ice during the cooling process. Additionally, compared with the physical mixture, oocytes in the hydrogel solvent replacement group did not produce intracellular ice during the cooling process, and the cells retained their normal morphology after rewarming.

The application of latent thermal energy storage with heat pumps has been extensively studied in recent years. The combination of phase change heat storage and a heat pump can improve the performance of the heat pump and the utilization of renewable energy; however, further cost reduction and efficiency increase are required. Therefore, this study reviews the progress of heat pumps coupled with solid-liquid phase change materials and summarizes the applicable conditions and characterization methods for phase change materials applied to heat pumps. The optimization approaches for the performance of the heat pump system are summarized, including the selection and improvement of phase change materials, the optimal setting of the heat exchanger, and the dynamic optimization control strategy of the system. The outstanding performance of heat pumps with cascade heat storage in improving the supply-side comfort and utilization rate of renewable energy indicates the broad prospect of cascade heat storage being applied to heat pump energy storage systems. Herein, mixed, non-eutectic phase change materials are proposed as alternative materials for cascade heat storage. Notably, summarizing and developing new methods for adjusting the thermophysical properties of phase change materials for energy storage is necessary for adapting the selection and improvement of phase change materials to the optimization of the thermodynamic cycle of cascade heat storage devices and further improving the heating decarbonization ability of latent heat storage heat pumps.

Heat pump technology is an energy-saving solution that could potentially combat global warming and reduce carbon emissions. Industrial heat pumps recover waste heat from the heating process to heat water or air, thereby reducing electricity consumption and carbon emissions. Industrial heat pumps are energy-saving, environmentally friendly, and provide stable heating. They have been widely used at all stages of production and life. This study analyzes the compressor types and characteristics of domestic and international high-temperature heat pumps (HTHP) that recover industrial waste heat and analyzes their application and technical status with a focus on twin-screw and centrifugal compressors. Twin-screw heat pump compressors should adopt an open structure when the evaporation temperature is high, and high-speed and oil-free design can be used when the condensation temperature is high. In addition, centrifugal heat pump compressors should prioritize highly efficient impellers, high-temperature-resistant motors, and oil-free lubricated bearings. Screw steam compressors need to solve the problems of rotor thermal deformation and shaft seal, and target for large temperature lifts.

A compressor outlet tube is a transmission component of sound power, and its sound power loss directly affects the performance of pulse tube cryocoolers. Flexible bellows can adjust the relative positions of compressors and cold fingers in applications compared with traditional rigid smooth tubes. This study analyzed the flow characteristics of two types of connected pipes by simulation, and the influence of different types of connected pipes on the performance of the entire machine was verified experimentally to determine the influence of flexible bellows on the cryocooler. The simulation results demonstrated that mixed flow appears at the ripple of the bellows, resulting in greater resistance loss, when compared with a rigid smooth pipe. Under the same inlet parameters, the outlet mass flow and pressure amplitude were lower, and the sound power loss was greater. The experimental results demonstrated that the input power required by the bellows was higher when the cooling capacity was the same. When the cooling temperature was 37.5 K and the cooling capacity was 0.5 Wthe input power of bellows and smooth tubes was 119 W and 112 W, respectively; when the cooling capacity was 3.0 W, the input power of bellows and smooth tubes was 279 W and 259 W, respectively.

The air-source heat pump capillary radiant floor heating system directly heats the floor using a refrigerant as the heat transfer fluid, which employs a simple system and promotes good heat transfer. This study developed an experimental device for capillary floor radiant heating with an air-source heat pump, and a heating experiment with parallel capillary floor radiant terminal was conducted at different outdoor ambient temperatures. The experimental results demonstrate that a longer time is required for the temperature of the capillary floor radiation terminal to reach steady as the outdoor temperature decreases. When the outdoor temperature was -5 ℃, the required time was 120 min. The temperature difference between the discharge inlet end and the condenser outlet end on the same capillary wall was large. The temperature difference on the capillary wall reached 6.40 ℃, while that on the surface of the 20 mm-thick cement floor reached 4.20 ℃. Conversely, the vertical temperature difference from the capillary wall to the cement floor surface was small, not exceeding 0.40 ℃, and the vertical heat transfer effect of the floor was good. The temperature difference at the same position of different capillaries was within 0.80 ℃, and the temperature uniformity was good. When the outdoor temperature was -5 ℃, the heating coefficient of performance of the unit reached 4.61 with good heating performance.

Drying of Lentinus edodes is an effective method to prevent problems such as rotting and browning. During the drying process, the loading density has a significant impact on system performance and drying quality. Based on a newly designed quasi-two-stage enhanced vapor injection heat pump closed drying system, the effects of different loading densities of Lentinus edodes on moisture ratio, drying rate, coefficient of performance of the system (COP_sys), specific moisture extraction rate (SMER), drying capacity per unit energy consumption, and rehydration ratio were experimentally investigated. The results showed that when the drying air supply temperature was 55 ℃ and the circulating air volume was 580 m³/h, the drying rate of Lentinus edodes decreased gradually with the loading density in the drying chamber, from 1.5 kg/m² to 3.0 kg/m². Meanwhile, the average COP_sys, average SMER, drying capacity per unit energy consumption, and rehydration ratio increased first and then decreased. When the loading density was 2.4 kg/m², the average SMER, drying capacity per unit energy consumption, and rehydration ratio reached the maximum values of 0.320 kg/(kW·h), 0.391 kg/(kW·h), and 3.6, respectively. When the loading density was 2.4 kg/m², the average COP_sys reached its maximum of 4.22.

This study employed a validated computational fluid dynamics (CFD) model to investigate the influences of the mixer length and diffuser angle on the ejector pressure-recovery performance. The results demonstrated that an optimal combination of mixer length and diffuser angle exists at which the ejector has the highest performance. The effects of these two geometrical parameters on the ejector performance were highly consistent. When the mixer length was sufficiently long, the mixing was sufficient, and the mixed flow was not subjected to separation during pressure recovery. Under these circumstances, the effect of the diffuser angle on the ejector performance was relatively trivial, varying between 0.5° and 3°. However, when the mixer length was short, the flow was prone to turbulent losses near the diffuser wall. In this case, the effect of the diffuser angle was significant. In addition, the optimal geometries were affected by the operating conditions. The optimal mixer length increased as the nozzle inlet pressure and temperature decreased, whereas the optimal diffuser angle decreased. Under the conditions and nozzle configuration investigated in this study, the optimal mixer length was approximately 38 mm and the optimal diffuser cone half angle was between 1° and 1.5°.

Circulating water is used as the working medium in water-based chillers. Salt ions, such as calcium in circulating water, may precipitate during long-term operation, resulting in the attenuation of heat transfer performance. The application of small-diameter tubes in heat exchangers may lead to more prominent fouling problems. This study developed an accelerated fouling method to evaluate water fouling risk. The most typical operating conditions for water-based chillers were selected as the experimental conditions. The test samples included small diameter (5 mm) smooth tubes, with 7 mm smooth tubes selected for the control experiment. The experimental conditions include a circulating water inlet temperature of 60 ℃, a flow rate of 1 m/s, a foulant mass concentration of 800 mg/L, and a test time of 0-400 h. The results revealed that the total fouling mass was 39.5% higher and required fouling time was 17.6% shorter when comparing the 5 mm and 7 mm smooth tubes; the small diameter tubes had a larger total fouling mass and higher fouling rate. The heat transfer coefficients of the 5 mm and 7 mm tubes after fouling decreased by 12.5% and 9.7%, respectively, and the pressure drops increased by 50.6% and 10.4%, respectively, demonstrating a more severe heat transfer performance deterioration of small diameter tubes after fouling. The microscopic observation results of the fouling layer morphology demonstrated that the fouling layer in 5 mm tubes is a form of compact lamellar scaling, which is more difficult to remove compared with the 7 mm tube; therefore, the fouling risk should be considered when promoting the application of small diameter tubes in chillers.

The low-carbon transformation of data centers is highly significant for achieving carbon peaking and carbon neutrality. This study compared and analyzed the overall situation of data centers in China. Three variables—energy efficiency improvement rate, proportion of non-fossil energy—and negative emission technology intensity were introduced based on the CO₂ emission and intensity targets of China in key years, and the total CO₂ emissions of the data centers were projected via scenario analysis. The results demonstrated that the power consumption of the data centers increased gradually; the carbon emissions first increased and then decreased, and the power usage effectiveness (PUE) of the data centers decreased gradually. The carbon peak time of the three scenarios is 2030, and the expected times to achieve carbon neutrality are 2059, 2057, and 2055 in the three scenarios. In light of the goal to achieve carbon neutrality by 2060, the data center industry should further improve the energy efficiency utilization rate, increase the proportion of non-fossil energy, strengthen the technological innovation of carbon capture and storage, and enhance the level of carbon sinks.