Bed-type latent heat storage (LHS) systems employing phase change materials (PCMs) offer a viable strategy to mitigate the mismatch between intermittent thermal energy supply and continuous demand. However, their practical application is often constrained by inadequate thermal transport efficiency due to suboptimal structural configurations. Here, inspired by the structure and function of the pea stem, this study proposes a novel bionic pea-stem bed-type (BPSBT) LHS system. The proposed system shortens the heat transfer path between the heat transfer fluid and the PCMs, and its melting/solidification behavior, as well as thermal cycling performance, are evaluated through numerical simulations. Compared to a conventional spherical-capsule packed-bed system, the BPSBT system significantly reduces melting/solidification time, while improving specific power density, thermal energy efficiency, exergy storage efficiency, and entransy storage efficiency during both charging and discharging processes. Over a complete storage-release cycle, the BPSBT system achieves a 52% reduction in total cycle time and a 60% increase in thermal cycle efficiency relative to the conventional counterparts. This work presents a simple yet effective biomimetic approach for designing advanced LHS systems that combine both rapid charging/discharging rates with high thermodynamic efficiency.

Droplet impact is ubiquitous in numerous applications and plays an important role in fields such as anti-icing, pesticide spraying, and inkjet printing. With the advancement of high-speed imaging and surface fabrication technologies, an increasing variety of multifunctional surfaces have been developed and utilized, deepening our understanding of the dynamic characteristics and energy changes during droplet impact. This paper first introduces the basic parameters of droplet impact, including the maximum spreading coefficient, contact time, and a list of relevant dimensionless numbers. Next, the kinetic and dynamic characteristics of droplet impact on single-functional and multifunctional surfaces are discussed. Multifunctional surfaces, typically possessing two or more different functionalities, exhibit unique motion phenomena such as lateral migration, self-splitting, and self-rotation due to their anisotropy during droplet impact. This paper categorizes these multifunctional surfaces based on their topological and chemical characteristics, including surfaces with micro-physical structural adjustments, macro-special shaped multifunctional surfaces, and externally coupled multifunctional surfaces. The kinetic and dynamic behaviors of droplet impact on these surfaces are described in detail, providing theoretical models and practical applications. This work aims to provide theoretical support and technical guidance for the optimized design of multifunctional surfaces and their applications across various fields through a comprehensive exploration of droplet impact dynamics.

When aircraft passes through clouds or vehicles travel in rainy weather, droplets impact these transportation surfaces at high velocities, forming liquid films that impair driver visibility and threaten operational safety. However, existing studies have predominantly focused on low-speed droplet impact. To better understand the motion characteristics and influencing factors of droplets during high-speed impacts, this paper investigates the dynamic behavior of droplets impacting solid surfaces at high velocities. An innovative velocity generation device was developed by modifying a split Hopkinson pressure bar.By integrating ultrasonic levitation technology with dual-view high-speed photography, the entire process from droplet impact to stabilization was dynamically captured. The study explores the influence of solid surface wettability on high-speed droplet impact. Experimental results reveal that during high-speed impact, the retraction rate of the droplet spreading factor is significantly lower than the spreading rate. The maximum spreading factor scales with the Weber number (We) according to We0.23, which is consistent with the Clanet model, exhibiting an absolute relative error ≤10%. Furthermore, the number of fingers increases as a power-law function of the We, while the maximum finger length exhibits a nonlinear trend of initial increase followed by decrease. It was also found that solid surface wettability significantly affects droplet dynamic behavior and promotes finger branching. This research provides critical theoretical support and experimental evidence for optimizing inkjet printing resolution and designing anti-icing coatings.

Bubbles, while highly responsive, exhibit negligible viscosity, causing surface tension to dominate and drive them to collapse into spheres. To overcome this limitation, we present an embedded 3D printing approach that leverages wettability-contrast substrates and a hydrophobic capillary to template and draw bubble columns within freezing water. Pre-patterned hydrophilic and hydrophobic regions establish the initial bubble size, while synchronized gas injection through the capillary maintains the columnar shape during ice growth. By judiciously controlling the capillary pressure and motion, we achieve fully tunable bubble structures: single column with the diameter graded or oscillated from tens to hundreds micrometers, and inclined, curved, coiled or even connected multiple columns. Rapid solidification immobilizes the bubbles and suppresses Rayleigh-Plateau instabilities, enabling stable cylindrical bubbles growth down to ∼50 μm diameter with length-to-diameter ratios over 100 within 200 s. Detailed analysis of the freezing front and interfacial forces elucidates the mechanism by which the advancing ice front “locks in” the column geometry and controls tilt angles. This cost-effective, high-throughput gas-based approach produces high-resolution 3D bubble templates with programmable geometries, offering new avenues for the development of ice-templated materials, microfluidic devices, and soft-matter engineering.

Enhancing the vaporization efficiency of evaporators is crucial for improved energy management and heat transfer enhancement. To explore efficient evaporation methods, this study proposes a novel technique that actively introduces microbubble clusters to intensify the vaporization of the working fluid. Experiments were conducted using a microbubble generator fabricated from microporous titanium foam mesh. The effects of key parameters, including operation mode (continuous heating/no heating), average pore size of the titanium foam (2, 5, 10 μm), and gas flow rate (1-15 NL/min), on the evaporation performance (vapor output, liquid temperature drop) were quantitatively investigated. The associated bubble dynamics were analyzed via high-speed visualization. The results indicated that under the no-heating condition, the introduction of microbubble clusters with an average pore size of 10 μm and a flow rate of 15 NL/min led to a temperature drop of 30 ℃, while the corresponding vapor output increased by 38 times compared to the case without bubbles. Under the continuous heating mode, microbubbles with the same parameters caused a temperature decrease of approximately 15 ℃ and enhanced the vapor output by a factor of 1.7. Mechanistic studies reveal that the microbubble clusters substantially increase the vapor-liquid phase change interface area. The agitation caused by the rising bubbles and the alteration of vapor partial pressure due to the presence of non-condensable gas collectively accelerate the vaporization process at the interface, thereby enhancing the evaporation efficiency. This method requires no external fields or surface modifications, offering a simple and effective new approach for enhanced evaporation.

Latent heat thermal storage (LHTS) systems utilizing phase change materials (PCMs) face a significant challenge of poor thermal transport efficiency. Topology optimization (TO) has emerged as a promising technique to address this challenge. This paper presents a comprehensive review of TO applications in LHTS devices, including shell-tube LHTS units, PCM-based heat sinks, and skeleton materials, with a critical evaluation of their research progress and persistent challenges. The review outlines the fundamental steps and mathematical definition of the TO process, while demonstrating the efficacy in enhancing thermal storage/management performance. For shell-tube LHTS units, TO has primarily been applied to optimize fin structures, leading to marked enhancements in thermal storage performance, evidenced by reduced melting time and accelerated thermal storage rate, through increased heat-exchange surface areas between PCMs and heat transfer fluids. Similarly, in PCM-based heat sinks, TO-derived bifurcation structures have enabled the optimization of heat transfer networks, resulting in superior thermal management, including lower heat-source temperatures and faster heat-absorption efficiency, through self-organized heat transport pathways. Moreover, TO designs of skeleton materials have greatly enhanced the effective thermal conductivity of composite PCMs, leading to accelerated thermal storage/release rates of devices. However, current research mainly focuses on 2D steady-state simulations. Future efforts should develop transient-state optimization to maximize LHTS performance under dynamic interface evolution and time-varying operating conditions.

Water-repellent properties of superhydrophobic surfaces make them promising for anti-icing and deicing applications. Through experimental visualization of frozen sessile droplets undergoing melting on superhydrophobic surfaces, we identify a melting mode with the unmelted ice layer deposited at the bottom of the melting droplet, even though the density of ice is lower than that of water. In the deposited mode of the melting process, the time required for the frozen droplet to melt completely is much shorter than that in the floating mode. Force analysis shows that the melted fluid flows along the gas-liquid interface toward the top of the melting droplet, thereby exerting force and then suppressing the upward movement of the unmelted ice layer. Moreover, the flow within the liquid film formed between the unmelted ice layer and the heating wall is dominated by the viscous force, which has a lubrication effect and maintains the deposition of the unmelted ice layer. High heating temperature, large contact angle, and low particle concentration are helpful for the occurrence of the deposited mode.

Energy storage batteries require strict thermal management due to temperature sensitivity, operating optimally within a narrow thermal range. Simultaneously, control rooms demand stable and comfortable ambient conditions for staff staying long-term. Conventional temperature control systems typically employ isolated solutions, resulting in functional fragmentation and inefficient resource utilization. To address these challenges, this study proposes and implements an integrated R290 secondary loop heat pump air-conditioning system designed to simultaneously manage the thermal environments of both energy storage batteries and control rooms. By adopting a secondary-loop coupling architecture, all thermal regulation is achieved indirectly via indirect heat transfer with a circulating ethylene glycol-based coolant, eliminating the risk of direct refrigerant (R290) exposure in occupied spaces and enhancing safety. The system supports multiple operational modes, enabling flexible and efficient dual-zone climate control. The heating performance-evaluated in terms of heat exchange capacity and coefficient of performance (COP)-is analyzed under varying ambient temperatures and compressor speeds. Additionally, the frosting behavior of the outdoor heat exchanger and its impact on heat transfer and system performance are examined. Results showed heat output ranged from 3.01 to 4.27 kW, and COP varied between 1.9 and 2.8. Ambient temperature (more dominant than compressor speed) and speed both affected performance: higher speed/warmer temperatures improved heat transfer efficiency; low temperatures accelerated frosting (e.g., -5 circle C reduced heat output by 19.67% and COP by 31.13%, vs. 13.72% and 12.40% at 5 circle C). These findings provide critical insights for optimizing heat transfer design and operation of integrated thermal management systems in energy storage facilities.

Fingerprint recognition technology plays a critical role in modern security and information protection.Traditional 2D fingerprint recognition methods are still limited due to an imbalance between growing security demands and inefficiency of encoding detailed information.Although various 3D fingerprint technologies have been introduced recently,their practical applications are restricted by complex sampling procedures and bulky equipment.This paper proposes a new 3D fingerprint fragments reconstruction method based on the condensation of microdroplet clusters,resulting in efficiently extracting detailed structural information from fingerprint patterns.By identifying the unique topological features of fingerprint valleys,a micrometer-scale vapor transport model is developed.A differential approach is used to divide the microdroplet clusters formed when a finger is pressed on a cold surface into discrete units.In each unit,the diffusion distance and mass transfer in the condensation process are calculated.Nonlinear regression techniques are then utilized to reconstruct the 3D fingerprint fragments.Furthermore,the experimental validation shows excellent consistency with premeasured fingerprint data,with a reconstruction error of less than 9.3％.It has made a significant improvement in capturing high-density fingerprint data in a short period of time,completing the data acquisition in less than 1 second.Compared with ultrasound imaging techniques,this method significantly shortens the acquisition time,which typically involve complex procedures.Additionally,it offers a more efficient alternative to deep learning methods,which require extensive data training and computational processes.This 3D fingerprint reconstruction method provides an efficient,low-cost and easy-to-operate solution.It holds the potential to significantly enhance personal identification and information protection systems,contributing to the advancement of 3D fingerprint recognition technology in practical applications.

Deep cryogenic temperatures were widely applied in various fields such as biomedicine, aerospace, and fundamental physics research. The Auto-cascade Refrigeration Cycle was one of the primary methods for achieving temperature requirements ranging from-40 degrees C to-180 degrees C. However, with the implementation of environmental agreements, the use of refrigerants with lower Global Warming Potential had become a trend in refrigeration system development. To investigate the impact of low-GWP mixed refrigerants on ARC system performance, this paper focused on a typical three-stage self-refrigerating cascade system, selected R600a, R1150, and R50 as refrigerants, analyzed the impact of Hydrocarbons(HCs) mixed refrigerant ratios on evaporation temperature, system refrigeration capacity, COP, and other ARC performance, and compared the characteristics with the ARC system using R600a/R23/R14 mixed refrigerants. The results showed that the mixed refrigerants R600a/R1150/R50 had an optimal mass fraction in the ARC; that is, when the ratio of R600a, R1150, and R50 was 73/15/12, the evaporation temperature was lowest at-125.3 degrees C, and the COP was relatively high at 0.15. The change in the mass fraction of R50 has a greater impact on ARC. A 9 % increase in mass fraction results in a 17 % increase in ARC cooling capacity, but only an 9 % decrease in COP to 2.5 %. The discharge temperature of HCS systems is 15 % higher than that of R600a/R23/R14 systems, but the GWP of HCs is 99.6 % lower than that of the latter. The use of HCs reduces set-up costs(SET) by more than 90 % and reduces carbon emissions by more than 47 %.

This study presents a strategy for enhancing the performance of steam generators through introducing air microbubble clusters into hot liquid media. Unlike existing surface-evaporation constrained steam generation methods, this work leverages buoyant air microbubbles to absorb steam during their upward motion, thereby expanding the gas-liquid interfacial area within the whole fluid domain. Experimental findings demonstrate that introducing air microbubble clusters significantly increases steam output. Under adiabatic conditions, steam generation exhibits a remarkable increase of 3900%, alongside a seven-fold faster temperature drop compared to bubble-free scenarios. This substantial enhancement is attributed to intensified heat and mass transfer resulting from the dynamic growth of air microbubbles. Parametric studies reveal that several operational factors, such as initial water temperature, air flow rate, and water level, influence bubble residence time, interfacial area, and thermal uniformity, yielding differences on the in-vessel liquid temperature drop and steam output. Notably, this system completely eliminates fouling by distributing the evaporation process away from heating surfaces, thereby reducing the reliance on water pre-purification. This research underscores the potential of bubblemediated volumetric evaporation as a sustainable solution for steam generation in applications such as desalination and waste heat recovery, offering a pragmatic approach to enhancing efficiency and mitigating fouling.

Electrical and electronic devices are producing a higher density of heat along with their elevated performance to meet the booming needs of industrials and human activities, and in response, more effective cooling technologies are always in demand. Liquid immersion is one of the most popular cooling methods developed due to its thermal efficiency and operational feasibility. However, conventional single-phase immersion cooling exhibits relatively lower thermal efficiency and heat capacity, and dual-phase immersion cooling occurs only when the heating surface temperature exceeds the liquid boiling point, constraining the selection of suitable coolants. This work presents a cooling method using guest noncondensable gas (NCG) microbubbles to enhance heat transfer in immersion cooling. Direct experimental results show that the heat transfer rate increases drastically, and surface superheating is suppressed or even eliminated. NCG microbubbles can disturb the thermal boundary layer, serve as evaporation/boiling nuclei, and collide with existing bubbles to facilitate their departure. This cooling method performs better at a large degree of pool subcooling, while the effect of bubble size is relatively minor. The fundamental understanding of bubble dynamics upon impinging onto the heating surface in subcooled liquid has promising applications in thermal management systems, such as microelectronic chips, nuclear reactors, steam generators, and among others.

Freezing of multicomponent droplets and thin films is ubiquitous in natural environments and engineered settings.Previous studies on multicomponent droplets,including Marangoni-driven self-lifting droplets and soap-bubble freezing,have identified the roles of interfacial flow and solute redistribution,often exhibiting a snow-globe effect of migrating ice particles.Curvature and field-of-view constraints in droplet systems hinder continuous observation of a single object.Here,utilizing the comparability of interfacial heat and mass transfer between droplets and films,we employ a flat isopropanol-water binary film on a cooled substrate to achieve high-resolution,time-resolved in-situ microscopy observation of individual separated ice flakes within a supercooling(ΔT)range of the substrate.Experiments show that with the increase of ΔT,the external shape of ice flakes evolves from hexagonal pyramid to dodecagonal pyramid and ultimately to a nearly-conical form,accompanied by the decrease of transparency.We quantify morphological evolution by using a shape factor βand qualitatively distinguish crystal-structure differences by combining bright-field and dark-field microscopy.A minimal model that couples solute and thermal diffusion with Marangoni stress rationalizes the observations:solute-concentration gradients primarily drive structural evolution,while the competition between advection and diffusion governs anisotropic growth.These results provide mechanistic insight into interfacial freezing dynamics of multi-component liquid films and establish flat-film microscopy as a platform for single-flake kinetics.

Based on the rapid advancements in nanomaterials and nanotechnology, the Nanofluidic Reverse Electrodialysis (NRED) has attracted significant attention as an innovative and promising energy conversion strategy for extracting sustainable and clean energy from the salinity gradient energy. However, the scarcity of research investigating the intricate multi-factor coupling effects on the energy conversion performance, especially the trade-offs between ion selectivity and mass transfer in nanochannels, of NRED poses a great challenge to achieving breakthroughs in energy conversion processes. This numerical study innovatively investigates the multi-factor coupling effect of three critical operational factors, including the nanochannel configuration, the temperature field, and the concentration difference, on the energy conversion processes of NRED. In this work, a dimensionless amplitude parameter s is introduced to emulate the randomly varied wall configuration of nanochannels that inherently occur in practical applications, thereby enhancing the realism and applicability of our analysis. Numerical results reveal that the application of a temperature gradient, which is oriented in opposition to the concentration gradient, enhances the ion transportation and selectivity simultaneously, leading to an enhancement in both output power and energy conversion efficiency. Additionally, the increased fluctuation of the nanochannel wall from s = 0 to s = 0.08 improves ion selectivity yet raises ion transport resistance, resulting in an enhancement in output power and energy conversion efficiency but a slight reduction in current. Furthermore, with increasing the concentration ratio CH/CL from 10 to 1000, either within a fixed temperature field or at a constant dimensionless amplitude, the maximum power consistently attains its optimal value at a concentration ratio of 100 but the cation transfer number experiences a monotonic decrease across this entire range of concentration ratios. Finally, upon modifying the operational parameters from the baseline condition of s = 0, CH/CL =10, and Delta T = 0 K to the targeted condition of s = 0.08, CH/CL = 50, and Delta T = 25 K, there is a concerted improvement observed in the open-circuit potential, short-circuit current, and maximum power, with respective increments of 8.86%, 204.97%, and 232.01%, but a reduction in cation transfer number with a notable decrease of 15.37%.

The exploration of performance and prediction of environmentally friendly refrigerant physical properties represents a critical endeavor. Equilibrium molecular dynamics simulations were employed to investigate the density and transport properties of propane and ethane at ultra-low temperatures under evaporative pressure conditions. The results of the density simulation of the evaporation conditions of the blends proved the validity of the simulation method. Under identical temperature and pressure conditions, increasing the proportion of R170 in the refrigerant blends leads to a density decrease while the temperature range in which the gas-liquid phase transition occurs is lower. The analysis of simulated results pertaining to viscosity, thermal conductivity, and self-diffusion coefficient reveals heightened deviation levels within the phase transition temperature zone. This increase in deviation attributed to intensified molecular activity. In terms of uncovering the physical mechanism of gas-liquid phase transition, the work illustrates the macroscopic phenomenon of the intensified existing disorder during phase transitions at the molecular level. Molecular dynamics simulations analyzing the thermophysical properties of refrigerant blends from a microscopic point of view can deepen the comprehension of the thermal optimization of refrigeration processes.

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In the context of low temperatures, the outdoor evaporator surface in an electric vehicle's heat pump air conditioning system tends to accumulate frost unevenly. This uneven frosting occurs due to the varying heat exchange capacity of the refrigerant's two phases within the evaporator. Any reduction in the heat exchanger's capacity would lead to a negative impact on system performance. To address these challenges, this study introduces a gas-liquid separator placed in front of the outdoor evaporator. The aim was to enhance both the outdoor evaporator's performance and the overall system efficiency while investigating frost formation and heat distribution in the outdoor evaporator within a heat pump air conditioning system. The research outcomes demonstrate that the gas-liquid separator can effectively enhance evaporating pressure by regulating the opening degree of the gas-phase bypass valve. Optimal performance is achieved with the gas-phase branch bypass valve set between 20% and 30%, ensuring a stable operational condition and higher evaporating pressure. Moreover, the incorporation of a gas-liquid separator could lead to significant improvements in system performance, with increases of 6.9% in heat capacity and 7.4% in COP observed. Additionally, this enhancement extends to the outlet air temperature, showing improvements ranging from 3.6% to 11.2%.