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.

HP-1 is an eco-friendly hydrofluoroolefin (HFO) refrigerant with favorable thermodynamic and environmental properties. The critical parameters and saturated vapor pressure of HP-1 are similar to those of R245fa, with HP-1 serving as a potential replacement for R245fa, which has a high global warming potential (GWP) in high-temperature heat pumps. The flammability, solubility, and material compatibility of HP-1 were mainly determined experimentally, with the results demonstrating that HP-1 has a flammability range of 9.75%-16.1%, exhibiting excellent solubility with MK220 lubricating oil at elevated temperatures, and good compatibility with materials used in high-temperature heat pump systems. When HP-1 is applied to high-temperature heat pump units, the condensing temperature of the unit can reach up to 125 ℃ when the evaporating temperature ranges between 50 ℃ and 70 ℃, with a heating capacity of 99.27-153.14 kW and a coefficient of performance (COP) of 2.25-4.85.

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.

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.

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.

In an occupied enclosure space formed by multiple opposing jet outlets, understanding vortex structures is crucial in controlling the spread of viruses and pollutants. In this study, a scaled model of an occupied enclosed space with opposing jet flows was constructed by incorporating a heated floor as a heat source to create thermal plumes under cooling conditions. A particle image velocimetry (PIV) system was employed to measure the flow field under isothermal and cooling conditions. The identification performance of different vortex identification algorithms was compared by studying the turbulent characteristics of the flow field from the perspective of the vortex. The Liutex vortex identification method was applied to analyze the vortex motion within one oscillation period, revealing distinct strengths in counterclockwise and clockwise directions, with maximum intensities of 50 s^-1 and 110 s^-1, respectively. The study concluded that the motion, merging, and annihilation of vortices influenced the flow field structure with a jet oscillation period of approximately 3.67 s. Owing to the trapping effect of vortices on pollutants, areas of pollutant accumulation can be represented using relative frenquency distribution maps of vortex cores. Despite the unsteady flow field, the vortex distribution remained relatively stable. Specifically, on the left side of the CS4 cross-section, the vortex core appeared at the same point up to 21 times. Under cooling conditions, pollutants are confined to smaller regions, which aids in containing the spread of pollutants.

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 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.

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 ℃.