While prior reviews have addressed single temperature ranges or isolated applications, this work provides the first unified cross-sectoral benchmarking framework spanning the full cryogenic-to-comfort spectrum (-160°C to +35°C) with charging strategies utilizing off-peak electricity, renewable sources, and waste cold recovery, integrated with techno-economic analysis. This review introduces a PCM Selection Index (PSI) with domain-specific criteria weighting across six sectors, and quantifies the conductivity energy-density trade-off (10-50x enhancement at 15-25% latent heat penalty) that governs all composite designs, the first framework of its kind to make this trade-off explicit and comparable across application domains. Analysis of 294 sources exposes a 15-35% laboratory-to-field performance gap for mature applications and identifies cycling durability beyond 10,000 cycles as the critical unvalidated barrier for building deployment, findings that reframe durability, not material discovery, as the field's principal bottleneck. Across field-validated deployments, PCM-CTES delivers domain-specific performance gains, 15-30% for HVAC load-shifting, up to 56% for envelope integration, 71-91% operating cost reduction in cold-chain transport, and 8-15°C peak temperature reduction in electronics cooling, though no single PCM class performs optimally across domains, underscoring the need for the domain-differentiated selection framework developed here. Future priorities include accelerated-aging protocol standardization with Arrhenius-based lifetime modeling, comprehensive lifecycle assessment, and grid-interactive demand-responsive systems that monetize peak-shaving via time-of-use tariffs.

Icing of engineering equipment is widely occurring in cold and humid environments, and ice thickness is a critical parameter for determining when to activate or deactivate de-icing operations. Thermal-based ice detection methods offer numerous advantages, such as low cost and compact size. However, their application is limited by their inability to measure ice thickness. To fill this technical gap, a novel thermal pulse ice thickness detection method is proposed in this study. Through experimental analysis of the transient temperature response of uniform ice layers of varying thicknesses under thermal pulses of varying power and duration, and by incorporating changes in parameters such as ambient temperature and airflow velocity, a mathematical model relating thermal pulses to ice thickness was established, and the mapping relationship between thermal response characteristics and ice thickness was determined. The results show that this method enables high-precision detection of uniform ice thickness, with an average error of 10.11% for ice thicknesses ranging from 0 to 14 mm at −10 °C. By optimizing the model based on the coupling of the peak measured temperature and the time of its occurrence, the average error can be further reduced to 7.31% for ice thicknesses ranging from 0 to 7 mm. The results of this study provide valuable references and insights for enriching dynamic icing parameters detection methods, developing low-cost, high-precision, and highly efficient anti-icing and de-icing technologies, and enhancing the adaptability of engineering equipment to cold and humid environments.

Water droplets on cold surfaces lead to ice/frost formation, causing equipment failure. Micro/nano-structured surfaces attract widespread attention due to their excellent anti-icing/de-icing performances and it is essential to study the icing of water droplets on them. This study focuses on the icing characteristics of micropillar-encapsulated sessile water droplets through combining experiments and simulations. The effects of micropillar radius, height, and droplet volume on the freezing front, freezing tip morphology, freezing time, and temperature field are systematically investigated. The results show that the presence of micropillars accelerates water droplet freezing. Three freezing tip morphologies are observed: A singular tip on the top (S-Tip), a singular tip on the top and an annular tip on the side (SA-Tip), and an annular tip on the side (A-Tip). A-Tip dominates at smaller micropillar radii and S-Tip prevails at smaller micropillar heights, while increasing both radius and height promotes a transition to SA-Tip. The three freezing tip morphologies are caused by two heat transfer pathways from the top and side surfaces of the micropillar to the droplet, corresponding to three effective heat transfer distances or freezing heights. A quantitative model is established to correlate freezing tip morphology with micropillar geometry, revealing that the boundaries between morphologies scale approximately linearly with the square of micropillar radius and height. Furthermore, based on heat transfer analysis, a predictive correlation for freezing time under different freezing tip morphologies is developed with a deviation of <25%. The findings provide guidance for optimizing micro/nano-structured surfaces in anti-icing/de-icing applications.

Aerothermal loads during hypersonic flight vary dramatically along trajectories, posing severe challenges to the design of Thermal Protection Systems (TPS). While Phase Change Material (PCM) integration has been proven effective for thermal buffering, most existing studies are limited to constant or singular operating conditions. To enhance thermal control during complex missions while maintaining structural compactness, a numerical model based on the enthalpy-porosity method is developed to investigate the performance of a multilayer PCMintegrated TPS. The transient heat transfer characteristics and phase change behaviors are analyzed by considering the effects of maximum Mach number, maximum flight altitude, and PCM thickness. The results indicate that the inner wall temperature can be significantly lowered by increasing the PCM thickness. Specifically, for a flight mission at a maximum altitude of 20 km and a Mach number of 4, increasing the PCM thickness reduces the maximum inner wall temperature by 324 degrees C. The results show that the inner wall temperature escalates sharply with increasing Mach number but decreases with rising flight altitude, identifying low-altitude, high-velocity conditions as the most significant challenge to TPS design. Furthermore, to address the critical need for efficient tools that can balance thermal safety with extreme weight constraints, a simplified theoretical model is creatively proposed for predicting the optimal PCM thickness in this study. It enables the rapid optimization of both TPS structural weight and temperature control performance. Validation results indicate that the maximum relative deviation in predicting the PCM melting thickness is under 11%. This work provides an efficient theoretical method and design reference for the thermal management and weight optimization of hypersonic vehicles.

​Against the backdrop of intensifying global energy supply-demand imbalances, enhancing energy utilization efficiency has become a critical challenge. As a phase change material with high energy storage density, ice slurry holds significant application value in HVAC systems. To fully leverage the heat transfer and flow advantages of ice slurry, this research adopts the Euler-Euler two-fluid model to conduct a numerical investigation of the flow and heat transfer characteristics of ice slurry within twisted flat tubes. The analysis focuses on the effects of the straight section length (W) and the twist pitch length (P) of the twisted flat tube cross-section on flow patterns, resistance characteristics, heat transfer performance, and the ice particle phase change process. Results indicated that a helical secondary flow forms within the twisted flat tube, with its intensity increasing as both W and P decrease. The average friction factor (f) decreases with increasing flow velocity (u), increases with rising W and ice slurry volume fraction (α), and decreases with increasing P. The average nusselt number (Nu) increases with rising W and u, decreases with increasing P, and shows a decreasing trend with increasing α. The concentration of ice particulates exhibits a monotonic decline along the streamwise path. Higher W values and lower P values promote the melting of ice particles. The temperature field exhibits an S-shaped distribution across the cross-section, reducing P significantly improves the temperature uniformity. Finally, empirical correlations for f and average Nu are established, with prediction deviations controlled within ±10% and ±5%, respectively. This study provides theoretical support for the structural optimization of twisted flat tube heat exchangers and the efficient application of ice slurry in thermal energy storage configurations.

The quality of the ice surface is crucial for speed skating performance and safety. The layered ice making method is widely used in speed skating rinks to create a smooth and consistent ice surface. However, the relationship between water injection temperature and ice surface properties in this method remains unclear. This study used a layered ice making method to experimentally investigate the effect of water injection temperature on key ice surface characteristics, including ice temperature, transparency, and hardness. A series of experiments were conducted under controlled conditions, with water injection temperatures ranging from 10 degrees C to 90 degrees C. The results indicate that the water injection temperature has a significant impact on the characteristics of the ice surface. A higher water injection temperature usually results in a slower freezing rate, and the ice surface has higher hardness and transparency, which is ideal for speed skating. When the water injection temperature increased from 10 degrees C to 70 degrees C, the transparency of the ice increased by 43.2 %, the average drop hardness increased by 21.1 %, but the total ice making time also increased by 31.2 %. This study provides experimental guidance for optimizing the layered ice making scheme of professional ice rinks, and emphasizes the importance of temperature control in achieving high-quality ice surfaces.

Global energy demand is growing continuously, and emission reduction pressures in the construction industry have become increasingly pronounced. Ice storage, a latent heat storage technology with high energy storage density, is characterized by energy regulation capabilities and low-carbon advantages. It has emerged as a key solution in refrigeration fields, especially construction. This study systematically reviews the principles and research progress of two major technical systems, static ice storage and dynamic ice storage. Static ice storage focuses on encapsulated ice storage and ice-on-coil storage, while dynamic ice storage centers on ice slurry storage. The optimization methods of static ice storage mainly include two aspects, structural design and additives. Research on dynamic ice storage covers production and optimization, as well as flow and heat transfer characteristics, focusing on parameters such as pressure drop, rheological properties, and heat transfer coefficient. Existing research has achieved certain optimization results. For example, static ice storage can shorten the solidification time of PCM by at least 20% through appropriate methods, and the new preparation methods of ice slurry cold storage technology can make the cooling capacity reach 4 times that of traditional methods. This study summarizes the development status, existing challenges, and application potential of the two types of technologies, providing references and insights for the future research directions of ice storage technology.

CO2 laser-based non-contact rapid de-icing is promising for polar engineering. However, existing research is constrained by ideal isothermal conditions, lacking quantitative insight into melting dynamics and energy efficiency under realistic polar longitudinal temperature gradients. Distinct from traditional isothermal tests, we constructed an experimental system simulating the longitudinal temperature gradient of polar ice, investigating the laser-ice interaction mechanism within a non-uniform thermal field for the first time. We proposed three evolutionary stages covering explosion hole forming, radial expanding, and rapid deepening, elucidating the hole-forming process driven by laser energy density under the synergistic effect of melt flow and vapor recoil. Analysis indicates that the gravitational detachment of the water film is critical for triggering the transition from radial expansion to deep penetration, while the high-power-induced vaporization shielding effect constitutes a bottleneck for energy efficiency. Quantitative results show that the temperature gradient reduces the melting rate by 13.5% similar to 29.4% compared to the existing isothermal conditions. While increasing laser power boosts melting rate by 123.79% but decreases energy efficiency non-monotonically from 70.86% to 64.21%. These finding reveals a trade-off mechanism between melting rate and energy efficiency, providing a key basis for optimizing polar de-icing equipment that balances high speed and low energy consumption.

Rectangular microchannel printed circuit heat exchangers (RM-PCHEs) exhibit excellent flow and heat transfer characteristics. However, within the operating range of low-temperature recuperator for the supercritical carbon dioxide (SCO2) Brayton recompression cycle, their performance data remain scant for hot-side inlet temperatures ranging from 373.8 K to 423.4 K. To address this gap, this study conducted experimental research on the flow and heat transfer characteristics of an RM-PCHE using SCO2 as the working fluid, based on a comprehensive performance test system for heat exchangers. The results showed that the heat transfer performance of test sample was most significantly influenced by SCO2 inlet temperature, with a 4.3 % increase in Qave and a 1.3 % decrease in UA for every 1 % increase in Thot,i, and a 3.6 % increase in epsilon for every 1 % increase in Tcold,i. Besides, the test sample was most greatly influenced by mass flow rate, with a 1.5 % decrease in Delta Phot for every 1 % decrease in mhot, and a 1.7 % in Delta Pcold for every 1 % decrease in mcold. Finally, test sample demonstrated enhanced thermal hydraulic performance, achieving maximum UA and epsilon values of 414.8 W & sdot;K-1 and 0.92, respectively, while the maximum pressure drops on hot-and cold-side were 42.0 kPa and 13.9 kPa, respectively.

The motionless wind turbine with opposing paired airfoils offers a compact and noiseless alternative to conventional wind energy systems, but its performance remains well below the Betz limit, limiting urban deployment potential. To address this gap, this study conducts a dual-parameter optimization of angle of attack (0–16°) and inter-foil spacing (0.4c–1.0c) for S1210 airfoils, focusing on maximizing suction while minimizing flow asymmetry/separation a critical trade-off unexplored in the prior literature. This study optimizes the aerodynamic efficiency of an S1210 airfoil pair through an integrated approach that combines numerical with experimental analysis. The numerical results show that a reduced spacing of 0.4c amplifies suction but causes premature flow separation and instability, whereas larger spacings of 1.0c produce more stable flow. The optimal configuration is found at an angle of attack of 12° with a spacing of 1.0c, which attains the highest average suction pressure with minimal flow disturbances. Experimental validation with a prototype confirms computational fluid dynamics (CFDs) predictions: a 12° angle of attack yields the highest duct velocity, corresponding to a peak coefficient of performance (COP) of 0.31. The study also identifies that the key design balance to achieve stronger suction requires closer spacing or higher angles, but this comes at the cost of increased flow instability and separation. Conversely, wider spacing improves stability but reduces peak suction. The system’s improved efficiency stems from enhanced venturi effects and controlled flow asymmetry, making the design suitable for scalable urban deployment.

Heating pipelines encounter high resistance and energy loss during fluid transport. Existing low-resistance optimization mainly focuses on individual pipe components, and the applicability of traditional guide vane arrangement or shape optimization strategies to closely coupled pipe configurations remains unclear. This study investigates the resistance formation mechanism of S-elbows in building water systems through full-scale experiments and numerical simulations, and proposes a low-resistance S-elbow with double guide vanes (SE-GV). The resistance reduction threshold and applicability of the low-resistance S-elbow design were analyzed under various Reynolds numbers, nominal diameters, curvature ratios, and coupling distances. Compared with the discrete adjoint method, the SE-GV structure achieved better resistance reduction, with resistance reduction rates (RRRs) of 34.0%-38.0% over Reynolds numbers from 1.0 & times; 105 to 6.0 & times; 105. At various nominal diameters and curvature ratios, the RRR of SE-GV ranged from 0% to 34.2%. With increasing coupling distance, the RRR value gradually decreases, ranging from 34.2% to 13.3%. The geometric parameters of the SE-GV structure and equations for the double GVs are provided for different nominal diameters. Inserting double GVs effectively reduces the flow recirculation region and flow separation intensity while disrupting the original secondary-flow vortex structure, thereby weakening vortex intensity and energy dissipation. Energy-saving studies demonstrate confirm that the SE-GV design is a practical life-cycle energy reduction strategy with high return on investment. This work provides insights for designing building piping components with low resistance and energy consumption.

Frost accumulation severely restricts the safe and efficient operation of equipment. Frost layers fundamentally comprise crystals growing on frozen droplets; thus, clarifying these early-stage characteristics is crucial for revealing macroscale frosting mechanisms. This study investigates the effects of wind velocity, cold surface temperature, and droplet volume on crystal growth characteristics on a single frozen droplet under forced convection. Results indicate that compared to natural convection, forced convection yields shorter maximum crystal heights but significantly larger mean radial lengths (e.g., 2.78 mm at 1.62 m/s versus 2.25 mm at 0 m/s) and equivalent radii. Lower temperatures promote all growth parameters, while droplet volume primarily influences local surface temperature and leeward water vapor transport. Crucially, forced airflow not only accelerates vapor transport but promotes the reverse melting of tip frost crystals, fundamentally reshaping the morphology. Fractal analysis quantifies this evolution. The fractal dimension decreases with increasing wind velocity, from similar to 1.25 under natural convection to 1.05-1.10 at 2.95 m/s, reflecting a smoother profile induced by enhanced reverse melting. Finally, based on the fractal dimension, a symmetric growth mode under natural convection and a distinct asymmetric growth mode under forced convection are proposed. The findings provide droplet-scale theoretical support for modifying macroscale frost layer porosity and density prediction models.

Air cooling remains the most common thermal management method for data centers, although liquid cooling is gaining popularity for high power density servers and racks. Air-cooling data centers are heavily influenced by cooling methods and rack power density. This research compares the performance of room- and row-based air-cooling systems based on a real data center under varying rack power densities (2-32 kW/rack). Return Temperature Index (RTI) and Server Overheating Parameter (SOP) are employed to identify the optimal cooling strategies for different power densities and quantify the thermal dissipation limits of different air-cooling systems. The row-based cooling system is recommended under the index of average outlet temperature of the cabinets. The row-based cooling system is the preferred option under the Return Temperature Index (RTI). It is recommended to select the configuration by power density according to different scenarios under the Server Overheating Index (SOP): In the case of < 8 kW/rack, room-based cooling systems should be preferred as their SOP are lower and the temperature distribution is uniform with strong thermal stability. Under >= 8 kW/rack, row-based cooling systems are recommended. The maximum heat dissipation capacity of row-based air-cooling system is 7.4% higher than that of room-based air-cooling systems. These findings suggest that air-cooling systems should be flexibly configured based on actual power density to achieve an optimal balance between energy efficiency and system reliability for data centers.

Saline droplet impact on solid surfaces is widespread in nature and industry, yet existing research lacks systematic analysis over a wide salinity range. Herein, we investigate the dynamic characteristics of saline droplets (0-26 wt. %) impacting flat aluminum plates at different velocities (0.5-2.5 m/s) through experiments and theoretical analysis. The impact process is quantified by the spreading factor, height factor, characteristic times, and post-impact oscillation parameters. A higher impact velocity enhances inertial spreading, thus increasing the maximum spreading factor and reducing the minimum height factor. Increasing salinity suppresses spreading mainly by increasing viscosity, decreases the maximum spreading factor, and only weakly affects the spreading/retraction rates and the final equilibrium spreading factor. The post-impact oscillation cycle time increases with salinity, whereas the damping coefficient is positively correlated with salinity but nearly independent of impact velocity. A scaling law for the oscillation cycle time and a modified model for the maximum spreading factor and its corresponding time are established by accounting for salinity-dependent density, viscosity, surface tension, and dissipation pathways. The revised spreading model predicts the data over the whole salinity range at room temperature, with relative deviations of about -6% to 16%. The energy analysis shows that the increase in salinity mainly affects the droplet impact process through enhancing viscous dissipation. This study deepens the understanding of salinity's influence on droplet impact dynamics and provides references for related engineering applications.

Frost formation is a common phase-change phenomenon and a nonlinear complex physical process involving heat and mass transfer. Previous studies have focused on the frosting and defrosting characteristics of cold surfaces at horizontal and vertical angles, indicating that the inclination angle significantly impacts the dynamic characteristics of frosting and defrosting. Since heat exchangers are often used at inclined angles in practical applications, an experimental platform for frosting and defrosting with an adjustable inclination angle ranging from 0 to 180° was constructed to investigate the frosting characteristics and defrosting process of surfaces with different wettability at various inclination angles. Four distinct surfaces with different wettability were prepared, namely hydrophilic, bare aluminum, hydrophobic, and superhydrophobic surfaces. The experimental results show that the surface inclination angle affects frosting: as the inclination angle increases, the droplet size on each type of surface decreases (mean radius drops from 0.06 mm to 0.05 mm between 0° and 60°), the growth rate of droplets slows down, and the freezing time of droplets is advanced (by about 20 min on the superhydrophobic surface). Similarly, the surface inclination angle also influences the defrosting process of each surface: the larger the surface inclination angle, the stronger the surface’s ability to drain water during defrosting, resulting in a lower water retention rate—superhydrophobic specimens retain <10 % water at ≥30° and dry within 10 s under 40 °C, 9 m s⁻¹ hot-air forced defrost.

Icing is a widespread phenomenon that adversely impacts industrial operations and daily life. Icing presents significant risks to an individual's safety and efficiency. This study reviewed ice nucleation and nature-inspired anti-icing methods, offering valuable insights into the calculation of Gibbs free energy and the critical nucleation radius. A range of anti-icing techniques is examined, encompassing thermal, mechanical, ultrasonic, microwave, superhydrophobic, and slippery liquid-infused porous surface technologies. This investigation explores anti-icing methods inspired by nature, including self-removing condensation, reducing the duration of solid-liquid interactions, directing condensate jumping, preventing ice formation through antifreeze proteins, inhibiting ice nucleation with alcohol, and employing self-lubricating surfaces. Even with the shift in surface characteristics from hydrophilic to superhydrophobic, the critical radius for nucleation was consistently measured around 3.87 nm in all cases. The approach employing superhydrophobic magnetically responsive blade arrays achieved a droplet contact time of 2.9 ms and an energy transfer efficiency of nearly 95 %, surpassing the effectiveness of traditional bouncing droplet methods. The design of texture and materials plays a vital role in improving antiicing characteristics. The integration of nanoparticles with hybrid composites has significantly enhanced selflubricating materials, achieving an impressive 97.8 % reduction in wear rate, while the friction coefficient values have decreased to 0.12 across a wide range of temperatures. Durable and environmentally resilient coatings, energy-independent active mechanisms, and standardized benchmarking protocols will be essential for advancing the next generation of anti-icing technologies.

Uniform frosting on the surface of finned heat exchangers in low temperature and high humidity environments can help alleviate the performance degradation of air source heat pumps. Traditional research has mostly focused on system defrosting strategies and optimization of surface wettability of fins, without paying attention to the study of uniform frosting on individual fins. This study proposes a new strategy aimed at inducing uniform frosting on fins by designing convex structures on the surface of the fins. Through systematic experimental observation, the influence of convex structures with different geometric shapes on the full cycle process of condensation and frost growth was studied. The research results indicate that due to the influence of edge effects and center temperature, droplets and frost on the surface of fins without convex structures are distributed in a W-shaped pattern along the airflow direction. At 60 minutes, the non-uniformity of condensate droplet coverage and frost thickness was 11.3% and 0.023 mm, respectively. The effect of inducing condensation and frosting was significant after adding the protruding structure, but it would block the leeward airflow and suppress condensation and frosting. The non-uniformity of droplet coverage of the vertical linear convex structure fins was reduced by 25.0%. After adding the edge convex structure, the gap is less likely to enter humid air, and the non-uniformity of frosting increases by 26.2%. This study can provide important theoretical basis and innovative technological path for the design and management of surface convex structures during frosting process.

Although spraying antifreeze solution onto cold surface has been proven effective for frost inhibition, the freezing characteristics of alcohol-based antifreeze binary droplet are not fully understood. Therefore, visualization experiments were carried out to achieve the freezing processes of ethylene glycol and glycerol solution droplets on cold surface under varying conditions. Experimental results demonstrate that alcohol-based droplet exhibits prolonged freezing duration and reduced deformation. The formation of an annular dry zone surrounding the droplet inhibits frost crystal propagation, increasing propagation time by 3 to 6.2 times. Unlike the freezing of water droplet, the freezing mechanism of alcohol-based droplet is attributed to ice crystals on the cold surface initiating nucleation upon contact with the droplet. The solution membrane formed on the freezing droplet surface rises along the ice crystals inducing localized melting, which results in the ice crystals sparse and the freezing droplet forming a circular table-shaped morphology. Furthermore, an empirical correlation for predicting dry zone length is proposed, with a relative error within +/- 25%. These findings contribute to understanding the freezing mechanisms of alcohol-based binary droplet and provide foundation for optimizing antifrosting strategies by using alcohol solution.