Phase Change Research Articles

A Periodic Horizontal Shell-And-Tube Structure as an Efficient Latent Heat Thermal Energy Storage Unit

Thermal energy storage systems utilising phase change materials offer significantly higher energy densities compared to traditional solutions, and are therefore attracting growing interest in both research and application fields. However, the further development of this technology requires effective methods to enhance thermal efficiency. We propose a horizontal periodic shell-and-tube structure as an efficient latent heat thermal energy storage unit. This research aims to analyse heat transfer not only between the tube containing the heat transfer fluid and the phase change material but also between adjacent shell-and-tube units. The results obtained for a single cell within the periodic structure are compared with those of reference single shell-and-tube units with insulated adiabatic and highly conductive shells. The enthalpy–porosity approach, combined with the Boussinesq approximation, is applied to address the heat transfer challenges encountered during melting and solidification. The periodic horizontal shell-and-tube structure proves to be an efficient latent heat thermal energy storage unit with short melting and solidification times. In contrast, the non-periodic case with neglected conduction in the shell increases the melting and solidification times by 213.8% and 21%, respectively. The shortest melting and solidification times were recorded for the case with a periodic horizontal shell-and-tube structure and shell aspect ratios of 0.44 and 1, respectively.

Numerical Analysis of the Thermal Performance of a Hybrid Heat Sink Comprised of Perforated Foam Fins Embedded Within a Phase Change Material

ABSTRACTThis study presented a numerical model to evaluate a novel design of a hybrid heat sink incorporating perforated foam fins (PFFs) instead of solid fins (SFs) within a phase change material (PCM). This innovation is designed to enhance thermal performance in electronic cooling applications. The base of the heat sink was subjected to constant heat fluxes of 2, 3, and 4 kW/m2. The effect of the perforation location (top, center, and bottom) within the foam fin and foam porosities (0.85, 0.90, and 0.95) were investigated. The results showed that the hybrid PFF design demonstrably improved thermal efficiency compared to the SF configuration. This innovative approach offered three benefits: a significant reduction in overall heat sink weight, an augmentation of the thermal conductivity of PCM, and the intermixed molten PCM between the fins passages through perforations. The PFF heat sink extended the operational time by 6%–8% for the range of heat fluxes at SPT of 70°C and led to a 24.5% increase in PCM volume, compared to the SF configuration. Complete melting of the PCM in the PFF heat sink is observed at 29 min for the highest heat flux of 4 kW/m2, while the melting rates are 25% and 62% for the applied heat flux of 2 and 3 kW/m2. Perforation location within the foam fin (top, center, and bottom) achieved equivalent heat transfer capabilities, enabling design flexibility for perforation location. The PFF with a porosity of 0.85 demonstrated superior thermal performance.

Rotating Bending Fatigue of Laser Powder Bed Fused 316L Stainless Steel at Various Stress Levels: Microstructural Evaluation and Predictive Modeling

ABSTRACTThis research studies the effect of variable stress levels on the rotating bending fatigue (RBF) tests of 316L stainless steel fabricated by the laser powder bed fusion (LPBF) method. The mechanical properties and fatigue behavior were evaluated to ascertain the correlation between the applied stress levels and microstructural changes that occurred during the fatigue experiments. These relationships were further investigated using a classical model developed on the Python platform. The microstructural analysis demonstrated that the face‐centered cubic structure was maintained throughout the application of stresses, varying from 255 to 402 MPa along with no phase changes. Nevertheless, the density of shear lines on the surface was substantially influenced by variations in stress levels as demonstrated by high‐stress areas in Kernel average misorientation maps. At lower stress levels, the model analysis exhibited a higher degree of reliability, with R2 values of 96.25% at lower stress rather than 89.30% at higher stress.

Design and Simulation of Flat Plate Collector With a Tube Rotation and Phase Change Materials Sn3N4‐LiNO3‐KNO3/Boron‐Arsenide for Enhanced Efficiency

ABSTRACTSolar thermal energy is crucial in our transition to renewable energy sources. Recent studies have focused on enhancing the efficiency of solar collectors by minimizing thermal energy loss during absorption. A promising approach involves an innovative design that integrates phase change materials (PCMs) and rotating tubes to capture thermal energy more effectively. Advanced nitride‐based salt hydrates, with boron‐arsenide additives, enhance thermal performance of the collector. In a flat plate collector using composite PCMs, radiative heat loss decreases from 250 to 210 W (a 6% reduction) with tube rotation, while convective heat loss drops from 225 to 195 W (a 4% decrease). The decomposition rate of the novel PCMs is low, measuring only 0.5% at a maximum temperature of 850°C, with a specific heat capacity of up to 4.50 W/m K. This unique blend, including the Sn₃N₄‐LiNO₃‐KNO₃/boron arsenide mixture, enhances thermal conductivity by 30%, significantly improving thermal absorption rates. The exergy efficiency achieved with the Nano‐enhanced phase change materials (NEPCM) and tube rotation reaches an impressive 90%. With tube rotation at 3 rad/min, the flat plate collector's efficiency improves by 22%, reaching an overall efficiency of 90% at a fluid flow rate of 25 kg/h. Simulations using Anaconda Jupyter Notebook and Python validate the effectiveness of both tube rotation and NEPCM in enhancing collector efficiency.

Point-of-Care Diagnostics Using Self-heating Elements from Smart Food Packaging: Moving Towards Instrument-Free Nucleic Acid-Based Detection.

Compromising between accuracy and rapidity is an important issue in analytics and diagnostics, often preventing timely and appropriate reactions to disease. This issue is particularly critical for infectious diseases, where reliable and rapid diagnosis is crucial for effective treatment and easier containment, thereby reducing economic and societal impacts. Diagnostic technologies are vital in disease modeling, tracking, treatment decision making, and epidemic containment. At the point-of-care level in modern healthcare, accurate diagnostics, especially those involving genetic-level analysis and nucleic acid amplification techniques, are still needed. However, implementing these techniques in remote or non-laboratory settings poses challenges because of the need for trained personnel and specialized equipment, as all nucleic acid-based diagnostic techniques, such as polymerase chain reaction and isothermal nucleic acid amplification, require temperature cycling or elevated and stabilized temperatures. However, in smart food packaging, there are approved and commercially available methods that use temperature regulation to enable autonomous heat generation without external sources, such as chemical heaters with phase change materials. These approaches could be applied in diagnostics, facilitating point-of-care, electricity-free molecular diagnostics, especially with nucleic acid-based detection methods such as isothermal nucleic acid amplification. In this review, we explore the potential interplay between self-heating elements, isothermal nucleic acid amplification techniques, and phase change materials. This paves the way for the development of truly portable, electricity-free, point-of-care diagnostic tools, particularly advantageous for on-site detection in resource-limited remote settings and for home use.

Controlling Temporally and Spatially Homogeneous Temperature Distribution of Paper Substrates by Biogenic Phase Change Hybrid Material Coatings

AbstractHere the performance of phase change material (PCM)‐coated paper made from unbleached kraft pulp is introduced. The applied PCM consists of a mixture of ethylene glycol distearate (EGDS), a well‐known PCM wax material, and a fully substituted cellulose stearoyl ester (CSE). Transfer of the PCM material onto/into paper is achieved by spray as well as blade coating of EGDS + CSE mixture. It is shown that the kind of coating method used does not interfere with observed PCM properties. The significantly higher melt viscosity of the EGDS + CSE blends ensures that the EGDS wax is not bleeding out of the paper, which avoids the use of further encapsulation processes. The PCM behavior, as observed by thermal load measurements, and the thermal buffering of the coated paper is a function of the applied mass of the PCM material applied. The thermal retention exhibited a quasi‐isothermal behavior at ≈65 °C with EGDS + CSE coatings. These effects can offset fluctuations in temperature, and the PCM papers can be employed to achieve a more uniform temperature setting. PCM‐modified papers are therefore interesting candidates for paper‐based packaging or for use in paper‐based sensors, where overheating can strongly affect reliability of results.

Strongly enhanced shift current at exciton resonances in a noncentrosymmetric wide-gap semiconductor

Excitons are fundamental quasiparticles that are ubiquitous in photoexcited semiconductors and insulators. Despite causing a sharp and strong photoabsorption near the interband absorption edge, charge-neutral excitons do not yield photocurrent in conventional photovoltaic processes unless dissociated into free charge carriers. Here, we experimentally demonstrate that excitons can directly contribute to photocurrent generation through a nonlinear light−matter interaction in a noncentrosymmetric semiconductor CuI. Epitaxial thin films of CuI exhibit a substantial enhancement of photocurrent at exciton resonance energies even below the bandgap. From the light polarization dependence, this photocurrent is identified to be shift current, a nonlinear photocurrent driven by the change in the geometric Berry phase of electron wave functions upon the optical transition. The shift current at the exciton resonance is much larger than that induced above the band gap by free electron−hole excitation, and their signs are opposite. First-principles calculations elucidate that the sign and magnitude of the exciton shift current are strongly dependent on the strain in the thin film. The present study reveals the crucial role of excitons in enhancing the shift current magnitude and its strain sensitivity, and will open an unprecedented route for efficient manipulation of nonlinear optical effects.

SPL13 controls a root apical meristem phase change by triggering oriented cell divisions.

Oriented cell divisions are crucial for determining the overall morphology and size of plants, but what controls the onset and duration of this process remains largely unknown. Here, we identified a small molecule that activates root apical meristem (RAM) expression of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE13 (SPL13) a known player in the shoot's juvenile-to-adult transition. This expression leads to oriented cell divisions in the RAM through SHORT ROOT (SHR) and cell cycle regulators. We further show that the RAM has distinct juvenile and adult phases typed by morphological and molecular characteristics and that SPL factors are crucially required for this transition in Arabidopsis and rice (Oryza sativa). In summary, we provide molecular insights into the age-dependent morphological changes occurring in the RAM during phase change.

Nonuniform Temperature Compensation in Ultrasonic Guided Wave Pipeline Health Monitoring Using Local Phase Matching

Faced with a complex working environment, pipelines are prone to nonuniform temperature variations, which cause nonuniform phase changes in the guided wave signals during structural health monitoring, thereby increasing the difficulty of monitoring. To address this, a simulation model is established in this paper to analyze the effects of temperature on material parameters and the variation patterns of guided wave signals. A nonuniform temperature compensation method based on local phase matching is proposed. The algorithm first uses cosine similarity to find the locally best-matched signal segments between the monitoring signal and the baseline signal. Then, an indicator is introduced to quantify the differences between these best-matched signal segments, with the maximum difference considered to be the damage index. Three heating experiments on pipelines with nonuniform temperature fields ranging from 24 °C to 80 °C demonstrate that the proposed method can effectively overcome the resulting phase deviations while achieving high detection accuracy and a reduction false positives. Additionally, the method shows high resolution in detecting defects in both temperature-varying and non-temperature-varying regions.

Optimization of Thermal Management for the Environmental Worthiness Design of Aviation Equipment Using Phase Change Materials

A phase change materials (PCM)-based heat sink is an effective way to cool intermittent high-power electronic devices in aerospace applications such as airborne electronics and aircraft external carry. Optimizing the heat sink is significant in designing a compact and efficient system. This paper proposes an optimization procedure for the PCM/expanded graphite (EG)-based heat sink to minimize the temperature of the heat source. The numerical model is built to estimate the thermal response, and a surrogate model is fitted using the Kriging model. An optimization algorithm is constructed to predict the optimum parameters of the heat sink, and the effects of heat sink volume, heat flux, and working time on the optimal parameters of the heat sink are investigated. This shows that the numerical results agree well with the experimental data, and the proposed optimization method effectively obtains the optimal EG mass fraction and the geometric dimensions of the PCM enclosure. The optimal EG mass fraction increases with the rise in heat sink volume and decreases with the increase in heat flux and working time. The optimal ratio of the height to the length of the heat sink is 0.43. This study provides practical guidance for the optimal design of a PCM/EG-based heat sink.

Spatio-temporal variations of the heat fluxes at the ice-ocean interface in the Bohai Sea

Thermodynamic process between the ice and the ocean plays a critical role in the evolution of sea-ice growth and melting in marginal seas. At the ice-ocean interface, the oceanic heat flux and the conductive heat flux transmitted through the ice layer jointly determine the latent heat flux driving the phase change (i.e., ice freezing/melting). In this study, the determination of two important thermal parameters in the ice module of the HAMSOM ice-ocean coupled model, namely the mixed layer thickness and the heat exchange coefficient at the ice-ocean interface, has been adjusted to improve the model performance. Spatio-temporal variations of heat fluxes at the ice-ocean interface in the Bohai Sea are investigated, based on the validated sea ice simulation in the 2011/2012 ice season. The relationships between the interfacial heat fluxes and oceanic and atmospheric conditioning factors are identified. We found that the surface conductive heat flux through ice shows short-term fluctuations corresponding to the atmospheric conditions, the magnitude of these fluctuations decreases with depth in the ice layer, likely due to reduced influence from atmospheric conditions at greater depths. Atmospheric conditions are the key controlling factors of the conductive heat flux through ice, while the oceanic heat flux is mainly controlled by the oceanic conditions (i.e., mixed layer temperature). Spatially, the value of the oceanic heat flux is larger in the marginal ice zone with relatively thin ice than in the inner ice zone with relatively thick ice. In the Bohai Sea, when ice is growing, heat within the ice layer is transferred upward from the ice base, and the heat is losing at the ice-ocean interface. This heat loss in the inner ice zone is obviously greater than that in the marginal ice zone. Whereas when ice is melting, the opposite is true.

Substrate induced composition change during Ge2Sb2Te5 atomic layer deposition and study of initial reactions on SiO2 surface

Ge2Sb2Te5 (GST) is a well-known phase change material used in nonvolatile memory devices, photonics, and nonvolatile displays. This study investigates the impact of precursor sequence during atomic layer deposition (ALD) of GST from GeCl2.C4H8O2, SbCl3, and Te[(CH3)3Si]2 on Si/SiO2 substrates, focusing on growth per cycle, morphology, and composition along with initial precursor reactions on the substrate. We found that while thick layers approach stoichiometric Ge2Sb2Te5, a Ge-rich interfacial layer is initially formed, regardless of the binary ALD sequence used to start the deposition (GeTe vs Sb2Te3). Starting the ALD process with the GeTe-Sb2Te3 sequence results in a higher Ge content near the GST/SiO2 interface compared to the Sb2Te3-GeTe sequence. To understand these phenomena, we examine the initial precursor reactions on the SiO2 substrate by total reflection x-ray fluorescence spectrometry. The analysis reveals that SbCl3 exhibits lower reactivity with the SiO2 substrate than GeCl2.C4H8O2, and not all Ge adspecies react with the Te[(CH3)3Si]2 precursors. Additionally, the impact of the initial SiO2 surface on deposition extends over several ALD cycles, as the SiO2 surface only gradually gets covered by GST due to island growth. These processes contribute to the formation of a Ge-rich GST layer at the interface, irrespective of the precursor pulse sequence. These insights from the study may contribute to optimizing the initial deposition stages of GST and other ternary ALD processes to enable better composition control and enhanced device performance.

Three-Dimensional CFD Analysis of a Hot Water Storage Tank with Various Inlet/Outlet Configurations

This study presents a comprehensive 3D numerical analysis of thermal stratification, fluid dynamics, and heat transfer efficiency across six hot water storage tank configurations, identified as Tank-1 through Tank-6. The objective is to determine the most effective design for achieving uniform temperature distribution, stable stratification, and efficient heat retention in sensible heat storage systems, with potential for integration with phase change materials (PCMs). Using COMSOL Multiphysics 5.6, simulations were conducted to evaluate key performance indicators, including the Richardson number, capacity ratio, and exergy efficiency. Among the tanks, Tank-1 demonstrated the highest efficiency, with a capacity ratio of 84.6% and an exergy efficiency of 72.5%, while Tank-3, which achieved a capacity ratio of 70.2% and exergy efficiency of 50.5%, was identified as the most practical for real-world applications due to its balanced heat distribution and feasibility for PCM integration. Calculated dimensionless numbers (Reynolds number: 635, Prandtl number: 4.5, and Peclet number: 2858) indicated laminar flow and dominant convective heat transfer across all the configurations. These findings provide valuable insights into the design of efficient thermal storage systems, with Tank-3’s configuration offering a practical balance of thermal performance and operational feasibility. Future work will explore the inclusion of PCM containers within Tank-3, as well as applications for heat pump and solar water heaters, and high-temperature heat storage with various working fluids.

Theoretical Design of Smart Bionic Skins with Self-Adaptive Temperature Regulation.

Thermal management presents a significant challenge in electric design, particularly in densely packed electronic systems. This study proposes a theoretical model for radiative bionic skin that emulates human skin, enabling the self-adaptive modulation of the thermal exhaustion rate to maintain homeostasis for objects covered by the skin in fluctuating thermal environments. The proposed artificial skin consists of phase change material (VO2) nanoparticles embedded in a low-loss matrix situated on a metallic substrate with a minimal thickness of several micrometers. The findings from our theoretical analyses indicate that substantial alterations in thermal radiation power around the phase transition temperature of 340 K enable a silicone substrate to sustain a relatively stable temperature, with variations confined to ±6 K, despite external heat fluxes ranging from 150 to 450 W/m2. Furthermore, to improve the spectral resemblance to natural skin, a plasmonic surface composed of self-assembled silver nanocubes is incorporated, allowing for modifications to the visible light properties of the bionic skin while maintaining its infrared characteristics. This theoretical investigation offers a cost-effective and conformal approach to the design of ultra-compact, fully passive, and versatile thermal management solutions for robotic systems and related technologies.

Enhanced Readout Reliability in Phase Change Memory with a Dual-Sensing-Margin Offset-Compensated Sense Amplifier

Phase change memory (PCM) is considered one of the most promising candidates for next-generation non-volatile memory, owing to its scalability, durability, and cost-effectiveness. However, with the shrinking of device sizes and the reduction in supply voltages, achieving high-speed and reliable readouts in PCM has become increasingly challenging due to process variations. To address this, the dual-sensing-margin offset-compensated sense amplifier (DSOC-SA) is proposed. The DSOC-SA achieves the highest sensing margin, and the lowest read energy consumption compared to traditional sense amplifiers by utilizing a dual-sensing-margin structure, offset compensation, and strong positive feedback. Simulation results demonstrate that, compared to differential sense amplifier and offset-canceling current-sampling sense amplifier, DSOC-SA achieves a 5.6× and 1.6× improvement in sensing speed, respectively, while reducing power consumption by 87.1% and 51.2%.

Analysis of the Properties and Thermal Behavior of Low-Temperature Phase Change Materials (PCMs) That Can Be Applied in Heating and Ventilation Systems.

This article analyses the use of low-temperature PCMs in devices supplementing a room ventilation system to prevent the overcooling effect. In this study, the phase change is numerically simulated in an axisymmetric system consisting of two tubes. One is filled with RT11HC with an initial temperature of 0 °C, while air with an inlet temperature of 20 °C flows through the other, heating the PCM and causing it to melt. Calculations are performed using commercial software with the apparent heat method for a system of given dimensions. Spatial distributions of the system temperature and liquid volume fraction at different time moments (from 0 to 120 min) are determined. It is found that the results depended mainly on the method of determining the latent heat. For the beginning of the charging process (t < 40 min), the values of the liquid phase fraction determined by the H and S methods are similar, while the one determined by the G method is definitely higher (even three times at t = 10 min). In turn, the outlet air temperature determined by the S method is lower than that determined by the other methods. The size and shape of the mesh have no significant effect on the results.

Dual-Phase Singularity at a Single Incident Angle with Spectral Tunability in Tamm Cavities.

The phase singularity, a sudden phase change occurring at the reflection zero is widely explored using various nanophotonic systems such as metamaterials and thin film cavities. Typically, these systems exhibit a single reflection zero with a phase singularity at a specific incident angle, particularly at larger angles of incidence (>50 degrees). However, achieving multiple phase singularities at a single incident angle remains a formidable challenge. Here, the existence of a dual-phase singularity is experimentally demonstrated at a lower incident angle using a tunable Tamm plasmon polariton (TPP) cavity that consists of gold-coated ultralow-loss phase change material Sb2S3-based distributed Bragg reflector. It can excite narrowband TPP resonances from normal incidence to a wide angle of incidence for both s- and p-polarizations of light. Notably, this TPP cavity shows dual-phase singularity at lower angles of incidence since the excited TPP for s- and p-polarizations exhibits zero reflection at slightly different wavelengths for the same incident angle. A TPP cavity-based scalable hydrogen sensor is proposed and shows that the dual-phase singularity can further improve the sensitivity of singular phase-based sensing approaches. Moreover, spectrally tunable dual-phase singularity is experimentally demonstrated at a lower incident angle using a metal-free Tamm cavity.

Epicardial Lead Performance Trends in Pediatric and Congenital Heart Disease.

Background: Epicardial pacing systems, rather than transvenous systems, are utilized in pediatric patients who are too small to undergo transvenous access and/or have complex congenital heart disease (CHD) anatomically precluding a transvenous system. Longitudinal performance studies indicate that epicardial leads have higher failure rates when compared with transvenous leads but there are limited data on lead measurement changes in the acute phase after implantation. The objective of this study was to assess epicardial lead performance in the acute postimplant period and at one-year follow-up. Methods: This is a retrospective single center study of children and adult patients with CHD undergoing epicardial bipolar pacing lead and generator implantation between January 2012 and June 2022. We empirically selected 2 V as a critical lead threshold. Results: There were 256 leads implanted in 127 patients (mean age 6.1 ± 9.8 years), including 201/256 (79%) leads in patients with CHD. At the time of implant, 47/256 leads (18%) had a lead threshold of ≥2 V. Of those, 42 of 47 (89%) had recorded threshold values on postoperative day 1 (POD1) and 37 of 42 (88%) had decreased to a more acceptable threshold that was <2 V. For patients with an implant threshold of ≥2 V; impedance >1000 ohms, presence of CHD, perioperative or acute postop status, and location of the lead (atrial vs ventricular) did not significantly impact the odds of having a persistently high threshold (≥2 V) on POD1. Conclusion: Epicardial pacing lead thresholds generally improve in the immediate postop period and in our experience most leads with a high implant threshold improved to <2 V by POD1.

Enhancing thermal performance of phase change materials in building envelopes

AbstractPhase change material in conjunction with a passive latent heat thermal energy storage approach is a potentially effective way to solve the growing concerns about building energy usage. This research examines the thermal performance of building envelopes in Miskolc, Hungary. The factors impacting the thermal performance of phase change material integrated into the building envelope were assessed. The findings indicate that the enthalpy and melting temperature of the phase change material significantly impact the effectiveness of phase change material-based walls. It was determined the optimal location of the phase change material layer is possible. This determination is intricately related to the thermal properties of the phase change material and the prevailing environmental conditions.

Picosecond Operation of Optoelectronic Hybrid Phase Change Memory Based on Si‐Doped Sb Films

AbstractPhase‐change random access memory is anticipated to break the bottleneck of the “storage wall” due to its advantages in simultaneous data storage and in‐memory computing. However, operation speed constrains its application scenarios. Antimony (Sb) thin film has ultrafast phase change speeds, low power consumption, and a straightforward chemical composition. In this study, silicon (Si) doping is employed to enhance the stability of pure Sb while achieving both ultrafast operational speeds and superior thermal stability concurrently. By utilizing optoelectronic hybrid phase change memory, the SET and RESET operation speeds can reach as fast as 26 and 13 ps, respectively, when using Si‐doped Sb films. The absence of the Si─Sb bond results in simple cubic nuclei within the amorphous film, which is posited as the structural basis for the high operational speed. These novel insights into ultrafast speed and phase mechanisms are poised to have valuable evidence for future high‐speed memory designs.