Propane (R290) is a potential refrigerant substitute for household air conditioners. However, its flammability limits its application. In this study, the flammability limits of R290, 2,3,3,3-tetrafluoropropene (R1234yf), trans-1,3,3,3-tetrafluoropropene (R1234ze(E)), R1234ze(E)/R290, and R1234yf/R290 were determined according to the ASHRAE 34-2022 standard. The effects of R1234yf and R1234ze(E) on the flammability of R290 were analyzed, and the inhibiting abilities of R1234yf, R1234ze(E), R32, R13I1, and R134a on the flammability of R290 were compared. In addition, the refrigeration cycle performance of R290 mixtures with different compositions was simulated. The results showed that both R1234yf and R1234ze(E) exhibited limited flame inhibition capabilities for R290. When the mass fractions of R1234yf and R1234ze(E) reached 80%, the lower flammability limit of the mixture increased by approximately 1.0%. The experimental data were correlated using the Le Chatelier model, which resulted in an average absolute deviation of 0.57% between the calculated and experimental results. Compared with R290, the energy efficiency ratio of the two refrigerants and R290 mixture decreased by less than 1%, and the volumetric cooling capacity increased by less than 0.4%. The flame inhibition effect of the refrigerant on R290 decreased in the following order: R13I1>R134a>R32>R1234ze(E)/R1234yf.

With continuous economic development, the world faces a growing freshwater shortage and energy scarcity crisis. Reducing energy consumption in handling heat and moisture loads in air-conditioning systems and solving the global water crises have become urgent priorities. The dynamic adsorption and desorption properties of adsorbents significantly affect the heat and moisture transfer characteristics of adsorptive atmospheric water-harvesting systems and dehumidifying heat-exchanger air-conditioning systems. In this study, the dynamic adsorption and desorption properties of thermosensitive composites doped with different thermally conductive nanomaterials, such as nano-copper powder, nano-silver powder and nanographene, were investigated, and the theoretical daily water production capacity of the optimal materials was analyzed. The results show that the thermosensitive materials doped with graphene nanopowder have good adsorption/desorption kinetics. Their equilibrium adsorption capacity reaches 2.51 g/g, which is 1.46 times higher than the undoped thermally conductive materials. The desorption within 60 min is 1.17 times higher than undoped thermally conductive materials. In addition, with a cycle time of 3 h and an adsorption-to-desorption time ratio of 2∶1, the thermosensitive material doped with nanographene can achieve a theoretical daily water volume of 7.02 g/(g·d), which is 21% higher than that of the undoped material.

To further study the influence of heat exchanger structures on system performance and overall power consumption in transcritical CO₂ heat pump air conditioning systems for high-speed trains to improve performance and reduce power consumption, this study builds a numerical simulation model based on the AMEsim simulation platform. The simulation results show that, in the high-speed train heat pump air conditioning system, the influence of the gas cooler structure on system performance is greater than that of the evaporator structure. In terms of the selection of heat exchanger structure, the optimal structure is that during refrigeration, the outdoor heat exchanger adopts the countercurrent arrangement and the indoor heat exchanger adopts the concurrent arrangement (vice versa for heating). At the rated cooling condition of 35 ℃ ambient temperature, the COP is increased by 20.38% compared to the concurrent arrangement in outdoor heat exchangers, and at a rated heating condition of 7 ℃ ambient temperature, the COP is increased by 68.04% compared to the concurrent arrangement of indoor heat exchangers. Considering both the degree of backflow and fan power consumption, in the "fully heat exchange state", system COP increases with backflow degree, while system COP decreases with backflow degree when the air flow rate is insufficient.

Ground-source heat pump (GSHP) systems using composite energy geostructures can efficiently transfer heat to soil and provide a high coefficient of performance (COP) for both cooling and heating, which has broad application prospects for energy saving in buildings. However, groundwater seepage in the soil can significantly affect the heat-transfer performance of a composite energy geostructure, thereby affecting the overall system performance. Therefore, this study establishes a numerical model of composite energy geo-structures considering groundwater seepage and investigates their synergistic heat transfer mechanism of composite energy geo-structures during summer. The results indicate that the heat transfer of composite energy geostructures is 60% higher than that of single energy piles under seepage conditions owing to the synergistic heat transfer of the energy pile and borehole. Groundwater seepage contributes to heat transfer in composite energy geostructures. When the seepage velocity reaches 60 m/a, heat transfer capacity increases by 1.39 compared to non-seepage conditions, while the temperature rise of the structure itself decreases by 25.32%. Under seepage, the upstream energy geostructures exhibit greater heat transfer with the soil than those downstream. The thermal influence area of the energy geostructures significantly reduced upstream and expanded downstream. This study guides the rational application of composite energy geostructures in regions with seepage.

Microchannel heat exchangers, including a bionic secondary branch (MHE-BS), complete vein bionic branch (MHE-CVB), and incomplete vein bionic branch (MHE-IVB), were designed based on the straight secondary branch (MHE-SS) inspired by the leaf vein structure of Parashorea chinensis. ANSYS FLUENT software was utilized to simulate the flow and temperature characteristics of 20 ℃ cooling water entering these heat exchanger structures under a constant heat flux of 50 kW/m² at different inlet Reynolds numbers (Re=660.07, 990.10 and 1 320.13). The research findings indicate that multistage bionic channel structure can significantly enhance the overall heat transfer performance of the heat exchanger, with MHE-CVB showing more than a 35% reduction in inlet and outlet pressure drop compared to MHE-SS under different working conditions. In addition, it showed an decrease in surface temperature by over 2 ℃ and a strengthening factor for comprehensive heat transfer performance exceeding 1.2.

Unnecessary or delayed defrosting results in increased energy consumption, reduced stability, and increased failure rates in refrigeration and heat pump units. Accurately identifying the frost status and timely defrosting are important for improving the performance of refrigeration and heat pumps. Frost status identification methods based on digital and intelligent technologies have shown significant potential. However, existing technologies have significantly reduced accuracy in complex real-world conditions and require urgent improvement. In this paper, we proposed an intelligent recognition method based on the texture features of evaporator surface images. We used a gray-level co-occurrence matrix to extract texture features and combine them with the extreme learning machine optimized by the sparrow algorithm for classification. This is expected to mitigate the impact of external conditions, such as shooting angles and light intensity, thereby achieving strong adaptability. An experimental setup was established to collect 4 125 images of the evaporator in three different frost states under complex working conditions, and the proposed method was validated and compared. The results showed that the accuracy of the method in identifying different conditions can reach 95%, which is significantly higher than that of existing methods by 5-35%. Furthermore, this method has high stability and low cost thereby demonstrating great potential for practical applications.

To address the low thermal storage performance of solid-liquid phase change composites caused by the encapsulation composite effect, composite-shaped phase change materials based on paraffin (PA)/hydrogenated styrene-butadiene block copolymer (SEBS) were prepared using the melt-blending method. A porous mesh structure was designed to optimize the thermal storage performance of the materials through the modulation of process parameters. First, the optimal mass ratio of SEBS-encapsulated PA was determined to be 2∶8; at this ratio, the 80% PA/20% SEBS composite material was well-shaped, and the mass retention rate was maintained above 99%. Furthermore, the results of the orthogonal experiments showed that the process parameters significantly affected the encapsulation and thermal storage properties of the materials, and the extreme difference in the enthalpy of phase change of the nine groups of 80% PA/20% SEBS samples was as high as 28 J/g. Among them, the enthalpy of phase change was increased by 8% when the melting temperature was increased from 150 ℃ to 200 ℃. The results of the orthogonal experiments also showed that the phase change enthalpy of the 80% PA/20% SEBS composites increased by 8%. The optimized PA/SEBS melt blending process parameters were finally determined as: blending time of 2 h, temperature of 200 ℃, stirring rate of 100 r/min, and direct cooling to room temperature. Under this preparation process, the phase transition enthalpy of the composites reached 161.2 J/g with 99.3% crystallinity.

With global warming and the rapid growth of the ski industry, the demand for artificial snowmaking technology and improved snow quality has increased, both of which are closely linked to the atomization characteristics of snowmaking nozzles. In this study, the influences of different nozzle interferences and gas-liquid mass mixing ratios (g_glr) on the droplet size distribution and collision mechanism in a spray field were investigated. The nozzle spacing (d) represents the degree of interference between the nozzles, whereas g_glr signifies the varying degrees of mixing disturbance under identical nozzles. The velocity and size distribution of the droplets in the spray field were measured using a laser particle size measuring instrument and a high-speed camera, whereas the fragmentation and collision of the droplets in the spray field were analyzed based on the Weber number (We). The results indicated that the axial velocity of double nozzles exceeded that of single nozzles at varying spacing intervals. Specifically, when the nozzle spacing was 10 cm and 15 cm, the peak axial velocities were recorded as 5.6 m/s and 5.5 m/s, respectively. The droplet size underwent a non-monotonic variation with the axial distance because of the competition between fragmentation and coalescence, which initially decreased before increasing. The interaction between the spray fields of the two nozzles enhanced the droplet collision, resulting in a higher We number than the individual nozzles. Analysis of the flow field of double nozzles under different arrangement conditions revealed that a higher level of uniformity in particle size distribution was observed when g_glr=0.10 and d=15 cm.

Evaporation of functional nanoparticle-containing droplets on solid surfaces plays a key role in applications such as air conditioning, refrigeration, and electronic cooling. In this study, we experimentally investigated the evaporation behavior and particle deposition of nanofluid droplets on solid surfaces. The deposition patterns were photographed, and microscopic characterizations were performed. The results show that the droplets always evaporate in the mode of constant contact radius. Changes in substrate temperature and droplet volume have little influence on the evaporation mode and morphology of the droplets, and the contact angle changes linearly with time. The surfactant can significantly regulate the kinetic behavior of droplet spreading. The addition of only 0.25% of surfactant sodium dodecyl sulfate (SDS) increases the droplet spreading radius from 0.71 mm to 1.12 mm, decreases the initial contact angle from 83° to 54°, and increases the area of spreading by 89%. The substrate temperature and droplet volume significantly affect the deposition patterns after droplet evaporation. The higher the substrate temperature, the larger the droplet volume and the more obvious the coffee-ring pattern formed after evaporation. SDS significantly increases the coffee ring width, which reaches 230 μm when the mass fraction of SDS reaches 1.00%, and the particles have been widely distributed throughout the entire evaporation area, suggesting that the coffee ring effect has been effectively suppressed. By introducing the Ma number, the influence of the Marangoni effect, guided by temperature, volume, and mass fraction changes, on the internal flow of droplets and the mechanism of coffee-ring formation are explained.

Slurries containing a large number of suspended particles, such as ice slurries, have a strong correlation between internal flow patterns and resistance characteristics. The study of its flow characteristics is of great significance for ensuring safety, energy saving, and the prevention of blockages in slurry transportation systems. To ensure safe and energy-efficient operation of the slurry transport system and prevent blockages, this study experimentally investigated the flow characteristics of slurry in pipelines and its critical Reynolds number (Re_c). The focus is on analyzing the flow behavior of the slurry in the transition region, as well as the effects of the ice packing factor (IPF), particle size, and pipe diameter on the slurry flow properties. The results show that the Re_c increases with an increase in the IPF, while the Re_c decreases with an increase in the pipe diameter and particle size. The flow regime transition of the slurry occurred within the Reynolds number (Re) range of approximately 1 700-2 600. In the transition region, the resistance coefficient of the slurry first increases and then decreases as the Re increases.