Microchannel cooling, with its high heat transfer efficiency, low thermal resistance, and light weight advantages, is one of the most effective technologies for solving the problem of heat dissipation with high heat flux; however, it faces the issue of increased pressure drop. The microchannel structure determines the thermal-hydraulic performance. This study describes the research progress on single-phase liquid-cooled microchannel heat sinks in terms of domestic and international structural design to address this problem. Among them, single-phase heat dissipation structures are divided into variable cross-sectionals, flow disruption, pin-fin, double-layered, bionic, and hybrid-reinforced structures. The advantages and disadvantages of the heat transfer coefficient, pressure drop, comprehensive performance, and temperature uniformity were analyzed based on the principle of enhancing heat transfer in various structures. A cost analysis of the commonly used matrix materials and processing methods for microchannel heat sinks was conducted. Finally, we provided the prospect and development direction of microchannel heat sinks from an application perspective. The application of composite structures, integration of simulation and experimentation, advances in material science and processing technology, and the nexus of disciplines are noted as the focus of future structural research.

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 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.

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.

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.

The two-phase flow pattern of hydrocarbon working fluids on the shell side of a helically baffled heat exchanger for liquefied natural gas determines its heat transfer performance. This study tested the two-phase flow patterns of propane and ethane/propane mixtures on the shell side of a helically baffled heat exchanger using a visualization experimental method. The test results demonstrated that with the increase in vapor quality, the experimental observations sequentially included stratified flow, stratified-spray flow, and spray flow; as the mass flux of propane increased from 20 kg/(m²·s) to 40 kg/(m²·s), the transition vapor quality from stratified flow to stratified-spray flow decreased from 0.7 to 0.3, while the transition vapor quality from stratified-spray flow to spray flow decreased from approximately 1 to 0.7; when the proportion of ethane increased from 0 to 50%, the transition vapor quality from stratified flow to stratified-spray flow increased from 0.30-0.45 to 0.43-0.55, while the transition vapor quality from stratified-spray flow to spray flow increased from 0.69-0.85 to 0.83-close to 1. The existing flow pattern map for water-air mixtures was inadequate for predicting the flow patterns of hydrocarbon working fluids. A new set of flow pattern transition criteria was established with prediction deviations of approximately 6.5%, 5.5%, and 4.2% for the experimental stratified flow, stratified-spray flow, and spray flow, respectively.

An energy-saving optimization operation strategy based on maintaining the high-energy-efficiency operation of chillers is proposed to address the prevalent issue of increased energy consumption in the application of cold-storage technology for economic optimization in the current air-conditioning industry. This strategy involves the storage and release of cooling using small cold-storage tanks to actively control the load ratio of the water chiller, thus ensuring that the unit operates efficiently for an extended period to achieve energy savings. A physical model of the air-conditioning system is established and simulated using operational data from the central air-conditioning system of a hospital. Performance curves of the water chiller under different environmental conditions are obtained to accurately depict the high-efficiency operational states of the unit at each moment. On a typical day with a peak cooling load of 9 979 kW, using an active chilled-water storage system, as compared with using the conventional chiller operation strategy without active storage, can reduce 2 777 kW·h of daily electricity consumption, which constitutes 6.0% of the daily electricity usage of the central air-conditioning system. Over the entire cooling season, this approach can save 2.35% of the total electricity consumption of the central air-conditioning system and 4.45% of the electricity consumption of the chiller.

The refrigeration systems in high- and low-temperature test chambers face challenges of high energy consumption and low efficiency. This study developed an enhanced vapor injection system in a test chamber and conducted experiments using R448A and R404A refrigerants to improve the system efficiency and ensure its alignment with low-carbon environmental goals. The impact of refrigerant charge amounts and compressor frequencies on system performance was analyzed. The results demonstrated that the cooling capacity and coefficient of performance (COP) of the R404A and R448A systems initially increased and then decreased with increasing refrigerant charge amounts. The R448A system demonstrated an 11.3% higher maximum cooling capacity and a 10.4% higher COP than the R404A system. In addition, the compressor power consumption of the R448A system was lower than that of the R404A system. At a refrigerant charge amount of 2.0 kg, the R448A system consumed 7.5% less power than the R404A system. The refrigeration capacity of the R448A system exhibited a 7.7% higher increase compared with that of the R404A system, whereas the compressor power consumption increase was 1.9% lower than that of the R404A system.

Motor cooling is critical for ensuring the high reliability of linear compressors. This study established a linear oscillating motor loss model based on experimental operating parameters and temperatures. The trends of the copper loss, iron core loss, and eddy current loss of the motor with temperature were analyzed, coupled with a three-dimensional flow field model of the linear compressor to analyze the temperature distribution characteristics of the motor coils and permanent magnets under different operating conditions. The research results demonstrated that, for every 0.2 g/s increase in mass flow rate, the motor temperature can be reduced by 4-20 ℃, and the variance of temperature distribution decreases by 0.5-1.2 under the same intake temperature. Furthermore, for every 5 ℃ decrease in intake temperature, the motor temperature decreases by 4-6 ℃ under the same mass flow rate. The maximum temperature difference of the permanent magnet was 7.3 ℃ at a mass flow rate of 0.6 g/s and 6.9 ℃ at a mass flow rate of 1.4 g/s. The optimized intake structure reduced the variance of motor temperature distribution by 5.521, the highest temperature decreased by 4.1 ℃, and the maximum temperature difference decreased by 4.55 ℃.

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°.