Degree Of Supercooling Research Articles

The microscopic contact morphology of ice crystal on substrate and its effect on heterogeneous nucleation/icing

As one of the long-standing crucial theoretical assumptions of the heterogeneous nucleation and substrate icing theory, the tiny shape of an ice tip on the substrate commands further detailed experimental observation. In this paper, the morphology and growth processes of ice on different near-thermal insulation surfaces at a low supercooling degree were observed by microscope. Experimental results show that the contact angles of the dendritic ice tip on the substrates are all obtuse under a lower supercooling degree, and decrease with temperature as a Sigmoid function. Moreover, the analysis of ice growth on different substrates reveals that the surface property can affect substrate icing by altering the ice tip; that is, as the ice contact angle increases, the radius will increase and the influence of the thermal conduction of substrate on the ice tip will decrease, ultimately leading to a slower growth rate. Significantly, heterogeneous nucleation experiments illustrate that the obtained ice contact angle is close to the ice nucleus contact angle. Consequently, compared with previous theories, the temperature-dependent ice contact angle could be used to accurately predict the nucleation rate and ice growth.

Experimental study of solid-liquid phase change in the presence of supercooling and natural convection

This study experimentally investigates the supercooling and natural convection behavior in three PCM, namely pure octadecane (organic), a eutectic PCM, and sodium acetate trihydrate (inorganic). The aim is to explore the effect of different factors on the degree of supercooling and on the natural convection, and to provide data for numerical simulation models. Results show that the type of PCM, the temperature of the cooling fluid, and mechanical shocks have a direct effect on the degree of supercooling. The supercooled PCM shows a high sensitivity to any changes in the applied conditions. The thermal insulation of the unheated PCM boundaries has a major effect on the solidification and melting dynamics and topology, particularly regarding the solid-liquid interface. The cross-sectional temperature profiles, the inclination of the solid-liquid interface, and the melting rate show that regardless of the PCM, natural convection plays a significant role during heating but not during cooling.

Thermal energy storage properties of carbon nanotubes/sodium acetate trihydrate/sodium monohydrogen phosphate dodecahydrate composite phase-change materials as promising heat storage materials

A novel hydrated salt composite phase change material was prepared. Firstly, the phase transition process of sodium acetate trihydrate (SAT)/ sodium monohydrogen phosphate dodecahydrate (DSP) eutectic salt was studied. And the optimization effect of hydrophilic carbon nanotubes (HCNTs) on the thermal properties of eutectic salt was analyzed. The results showed that the cycle stability of the eutectic salt was the best when the mass ratio of SAT/DSP was 9:1 and the degree of supercooling was 2.5 ℃. With increasing HCNTs mass fraction, the thermal conductivity of the composite showed a linear increase, reaching the highest value of 1.29 W/(m K), which was 182.89% higher than that without HCNTs. The heat storage density exhibited a linear decrease, with a maximum decrease of 5.59%. Finally, the cyclic stability of the HCNTs/SAT/DSP composites was tested, and the results showed that after 200 solid–liquid cycles, each group of materials showed good cycle stability for phase change heat storage system. In this study, the problems of supercooling and phase separation of sodium acetate trihydrate were solved. And its thermal conductivity was significantly strengthened, the results of this study provide a reference for the collaborative adjustment of phase-change materials and thermal storage system components.

Thermal performance of cold thermal energy storage system with fin and fin–foam structures

The heat transfer performance of most cold thermal energy storage (CTES) devices is limited by the low thermal conductivity of phase change materials (PCMs) and the increase in the thickness of PCMs. A comparative work was performed to explore the heat transfer performance of CTES systems with a fin structure (Fin-CTES) and a fin–foam structure (Fin–foam-CTES). The heat transfer performance, temperature distribution, and thermal effectiveness of Fin-CTES and Fin–foam-CTES at different inlet temperatures and volume flow rates of heat transfer fluid were investigated and compared. Results demonstrated that the overall heat transfer performance of Fin–foam-CTES is better than that of Fin-CTES. However, compared with the PCM in Fin-CTES, that in Fin–foam-CTES has a greater degree of supercooling, reaching 4.35 °C at the maximum. In the discharging (melting) process, Fin-CTES and Fin–foam-CTES have almost similar heat transfer effectiveness, in which the maximum difference is only 0.0107. That is, the enhanced heat transfer effect of the natural convection of the liquid PCM and the metal foam is basically the same during the discharging process.

Investigation on the evolution of ice particles and ice slurry flow characteristics during subcooling release

For the subcooling method ice slurry generator, the characteristics of ice slurry during subcooling release have a significant impact on the efficiency and stability of the system. An object of this paper is to investigate the evolution and distribution of ice particles in supercooled water and the flow characteristics of ice slurry during subcooling release in horizontal straight pipe, based on computational fluid dynamics (CFD). Moreover, the population balance model (PBM) is adopted to research the growth, agglomeration and breakage of ice particles. The effects of velocity, subcooling degree and ice volume fraction at the inlet are investigated. In terms of pressure and velocity, the average error between numerical simulations and experimental results is approximately 10%. The results indicated that the evolution of ice particle diameters is significantly affected by the degree of subcooling, which contribute to the growth of ice particles. For each 1 K increase in supercooling degree, the particle diameter will increase by 50 µm. The temperature trend of water from the supercooled state to the phase equilibrium state is consistent with the evolution of ice particles. Besides, the ice volume fraction along the vertical axis at the outlet can be divided into low-concentration, high-concentration, and stable regions, which is significantly affected by the degree of supercooling. Close to the wall, the ice volume fraction drops sharply due to collisions between the wall and the particles. The velocity of the ice slurry is symmetrically distributed along the vertical axis.

Glutaric acid/expanded graphite composites as highly efficient shape-stabilized phase change materials at medium-temperature

Interest in phase change materials (PCMs) in the medium-temperature range has recently gained significant attention due to their economic benefits and environmental sustainability. This study focuses on investigating the thermal properties of glutaric acid/expanded graphite shape-stabilized phase change materials (GA/EG SSPCMs) prepared by varying GA contents. The morphology, porosity, crystal structure, and chemical and thermal reliability of the prepared SSPCMs were characterized using a range of instrumental analyses. Given a high porosity, EG porous network can confine and stabilize up to 85 wt% GA without leakage, while maintaining the excellent crystallinity of the PCM, due to the capillary and surface tension forces. The SSPCMs exhibited high latent heat storage capacities of up to 167 J/g and crystallization fraction of up to 96.8 %. Interestingly, the SSPCMs effectively suppressed the supercooling degree of GA to below 5 °C, making them ideal for practical applications due to the shifts in both the melting and solidification temperatures. The SSPCMs also showed a significant enhancement in thermal conductivity and heat charge/discharge rates compared to the pure GA. Finally, the thermal reliability and stability of the 85 wt% GA/EG SSPCM were confirmed after 300 accelerated thermal cycle tests, making them a promising candidate for long-term applications in medium-temperature thermal energy storage.

Analysis of the thermal characteristics of the paraffin wax/high-density polyethylene (HDPE) composite as a form-stable phase change material (FSPCM) for thermal energy storage

The present work is specifically focused on the form stability of paraffin as a phase change material (PCM) through the addition of high-density polyethylene (HDPE). The aim of adding HDPE is to obtain a stable form of paraffin during the phase transition. Moreover, improving the performance of PCM leads to an advanced operation of the latent heat storage unit with an excellent charging duration and response time. The study uses HDPE at a ratio of 5 wt %, 10 wt % and 15 wt %. The results indicate significant differences between the form-stable PCM (FSPCM) and pure paraffin. For instance, the supercooling degree is decreased with the addition of HDPE, where paraffin has a supercooling degree of 8.01 °C while FSPCM with 15 wt % HDPE has a supercooling degree of 3.73 °C. The latent heat of fusion by adding 10 wt % and 15 wt % HDPE is slightly decreased by 1.85 %, which is much lower compared to adding 5 wt % HDPE, which reduces the latent heat of fusion by about 6.02 %. Adding HDPE leads to a faster charging process and a better response time during the discharging process. The charging rate is increased significantly by adding 15 wt % HDPE with a substantial increment of around 40 % with an average charging rate of 2.39 °C/min. The heat release during the discharging process is increased for FSPCM with 5 wt % HDPE where the temperature drops by more than 70 °C within 20 minutes. The findings indicate that adding HDPE contributed positively to reducing the supercooling degree and providing a steady phase transition. Thus, the heat exchange process of paraffin is more favorable, which improves the performance of the latent heat storage unit. Furthermore, the operation can be improved significantly by providing a faster charging and discharging process

Polymorphism of d-Mannitol in Zeolite-Added d-Mannitol-Based Phase Change Materials and Its Effect on Supercooling Degree

Polymorphism of d-Mannitol in Zeolite-Added d-Mannitol-Based Phase Change Materials and Its Effect on Supercooling Degree

Optimization of super water-retention phase change gels for cold energy storage in cold chain transportation

A eutectic hydrated salt (EHS) formed by disodium hydrogen phosphate dodecahydrate (DHPD) and sodium carbonate decahydrate (SCD) was used as the cold energy storage functional medium, and then the nucleating agent sodium pyrophosphate decahydrate (SPD), the phase change temperature regulators ammonium sulfate (N) and potassium sulfate (K) were added to prepare a sample DSSNK5, and by adding superabsorbent polymer (SAP), a phase change gel DSSNK5-SAP was finally obtained. The results show that the phase change temperature of DSSNK5-SAP is 7.71 °C, and its latent heat value is 122.1 J g−1, which remains unchanged after 50 cycles. Compared with pure DHPD, the supercooling degree of DSSNK5-SAP is reduced to 3 °C, and the thermal conductivity is 1.5 times that of DHPD. In addition, the crystal structure and chemical compatibility of DSSNK5-SAP were analyzed, and the regulation mechanism of auxiliaries and SAP on the phase change behavior of EHS was described. The cold energy storage/release and transient response performance of DSSNK5-SAP were tested, and the application experiment of fruit preservation was also carried out. As a result, DSSNK5-SAP can make the fruit have a good fresh-keeping effect, which proves its considerable application potential in cold chain transportation. It reduces the cost of cold chain transportation from the root and contributes to the stable development of the city and society.

Effect of Ni and Mo on microstructure and mechanical properties of grey cast iron

ABSTRACT Alloying elements (Ni, Mo) were added to grey cast iron, and the effect of Ni, Mo on microstructure and mechanical properties were analysed in this study. When Ni was added alone, the precipitation of graphite was inhibited at the early stage of solidification, and part of graphite was formed between the dendrites, resulted in an uneven distribution of graphite. Ni played a role of solution strengthening and reduced the pearlite interlammer spacing, improved the mechanical properties. The addition of Mo refined the austenite dendrites and made the carbon unevenly distributed, which led to the abnormal growth of graphite. Mo increased the eutectoid supercooling degree, reduced the pearlite interlammer spacing and improved tensile strength. When Ni and Mo were added together, the elements beneficial to strength (Mo, Sn) were not uniformly distributed, and the influence on graphite size and pearlite interlammer spacing was not obvious, resulted in poor mechanical properties.

Experimental Investigation of Graphene Nanoplatelets Enhanced Low Temperature Ternary Eutectic Salt Hydrate Phase Change Material

A sustainable approach to ensuring the thermal regulation of space is reliable with phase change materials (PCMs) operating at 15–25 °C. Henceforth, there is a need of a search of binary and ternary eutectic PCMs operating at desirable phase transition temperatures of 15–25 °C, high energy storage enthalpy (180–220 J/g), improved thermal conductivity and better absorptivity of solar energy. In this current research, we developed a ternary eutectic inorganic salt hydrate PCM intended for a low-temperature thermal regulation system. Based on the eutectic melting point theory, the phase transition temperature and proportion of sodium carbonate decahydrate (SCD), sodium phosphate dibasic dodecahydrate (SPDD) and sodium sulphate decahydrate (SSD) were determined. As per the calculated proportion, ternary eutectic PCM was experimentally prepared. Furthermore, to enhance the thermal property, graphene nanoplatelets (GNP) were dispersed at weight concentrations of 0.4%, 0.7% and 1.0%. The prepared nanoparticle-dispersed PCMs were characterized using an optical microscope, Fourier transform infrared (FT-IR) spectroscopy and a thermal conductivity meter, and a differential scanning calorimeter (DSC) was used to evaluate the morphology, chemical stability and thermal properties. The results showed increases in thermal conductivity and optical absorbance by 71.5% and 106.5%, respectively, with GNP at 1.0% weight concentration. Similarly, the degree of supercooling and transmissibility was reduced by 43.5% and 76.2% correspondingly. The prepared composite PCM is expected to contribute towards cooling, with an intention to contribute towards sustainable development.

Phase change temperature adjustment of CH3COONa·3H2O to fabricate composite phase change material for radiant floor heating

Hydrated salts phase change materials (PCMs) have a great potential for use in floor radiant heating considering outstanding cost competitiveness and remarkable energy storage density. However, their inappropriate phase change temperatures and the limited methods for temperature adjustment have hindered their widespread applications. Herein, using the formation of non-eutectic mixture to realize phase change temperature adjustment, a novel composite PCM used in the floor radiant heating was developed based on sodium acetate trihydrate (SAT) as main PCM, glycine as temperature modifier and Na2HPO4·12H2O as nucleating agent. The temperature regulation mechanism was discussed and properties of the composite PCM were investigated. The results showed that glycine could regulate melting temperature of SAT from 48.34 to 58.38 °C, ascribing to the formation of hydrogen bond between them. Thereinto, the mixture containing 12% glycine melted at 48.62 °C with enthalpy of 258.5 J g−1, making it applicable to the floor radiant heating. With the addition of 0.5% Na2HPO4·12H2O, the crystallization behavior of the composite PCM was promoted with a low supercooling degree (3.62 °C). The composite PCM presented a melting temperature of 47.55 °C with enthalpy of 256.5 J g−1, good thermal stability and reliability, indicating that the material can be promisingly engineered into the floor radiant heating.

Synthesis of shape stabilized phase change material with high thermal conductivity via in situ N-doped carbon derived from chitin

Stearic acid (SA) is recognized as a promising phase change material (PCM). Nevertheless, poor thermal conductivity and leakage are great challenges for SA in practical application. To this end, the shape stabilized PCM (CTX/SA) with high thermal conductivity is fabricated by impregnating SA into the in situ N-doped carbon (CTX) derived from chitin (CH). The thermal storage performance of CTX/SA is investigated to acquire the optimal carbonization temperature for CTX. Meanwhile, characterizations of FTIR, XRD, SEM, and N2 isothermal adsorption-desorption are conducted to reveal the influence of CTX on thermal storage performance. The synthesized CT800/SA exhibits high thermal conductivity of 0.461 W/(m·K) and thermal storage efficiency of 92.84 % with a low supercooling degree of 1.06 °C. CT800/SA also has desirable thermal stability and reliability even after 200 repeated thermal cycles. Moreover, the photothermal conversion of CT800/SA is 74.12 %.

Does freezing induce self-assembly of polymers? A molecular dynamics study.

This work investigates the freezing-induced self-assembly (FISA) of polyvinyl alcohol (PVA) and PVA-like polymers using molecular dynamics simulations. In particular, the effect of the degree of supercooling, degree of polymerization, polymer type, and initial local concentration on the FISA was studied. It was found that the preeminent factor responsible for FISA is not the diffusion of the polymers away from the nucleating ice front, but the increase in the polymer's local concentration upon freezing of the solvent (water). At a higher degree of supercooling, the polymers are engulfed by the growing ice front, impeding their diffusion into the supercooled solution and finally inhibiting their self-assembly. Conversely, at a relatively lower degree of supercooling, the rate of diffusion of the polymers into the supercooled solution is higher, which increases their local concentration and results in FISA. FISA was also observed to depend on the polymer-solvent interactions. Strongly favorable solute-solvent interactions hinder the self-assembly, whereas unfavorable solute-solvent interactions promote the self-assembly. The polymer and aggregate morphology were investigated using the radius of gyration, end-to-end distance, and asphericity analysis. This study brings molecular insights into the quintessential factors governing self-assembly via freezing of the solvent, which is a novel self-assembly technique especially suitable for biomedical applications.

Preparation, thermal storage properties and application of sodium acetate trihydrate/expanded graphite composite phase change materials.

The development of energy storage technology is beneficial for the efficient use of energy and sustainable development. As an effectual approach for storing and transporting thermal energy, latent heat storage using phase change materials (PCMs) has attracted tremendous attention. However, low thermal conductivity, poor stability, and leakages are considerable challenges to the widespread application of solid-liquid PCMs. Composite phase change materials (CPCMs) were prepared by combining expanded graphite (EG) and sodium acetate trihydrate (CH3COONa·3H2O, SAT). EG as a supporting material plays a crucial part in both enhancing the thermal conductivity and preventing the melted PCMs from leakage. The chemical structure, micromorphology, thermal stability, thermal conductivity, phase change behavior and heat storage performance of SAT/EG CPCMs have been extensively investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermal conductivity analysis, differential scanning calorimetry (DSC), and cycling stability measurement. The results of SEM indicate that EG with a loose and porous layered structure has a good molding effect and can adsorb SAT well. XRD and FTIR results show that only a simple physical combination between EG and SAT exists, and no new substances have been produced. Compared with pure SAT, thermal conductivity and supercooling tests show that the supercooling degree of the CPCMs was decreased and the thermal conductivity was increased by 205.1%. In addition, the addition of 2 wt% of disodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O, DHPD) as a nucleating agent and 0.5 wt% of gelatin as a thickening agent to SAT could reduce the supercooling degree and inhibit the phase separation well. Based on SAT/EG-8% CPCMs, an oven with phase change energy storage was designed and the heat storage/release performance of the oven was investigated under different operating conditions.

Self-assembly of MXene-decorated stearic acid/ionic liquid phase change material emulsion for effective photo-thermal conversion and storage

As a typical latent functionally thermal fluid with large energy storage capacity and good liquidity, phase change material emulsion (PCME) plays a broad and important role in solar energy utilization. However, the high-temperature instability and supercooling problems of PCME limit its practical application. The ionic liquid (IL)-based PCME allows for the possibility of being used as a heat transfer fluid (HTF) under more extreme temperature conditions. In this work, stearic acid (SA)/IL PCME, prepared by one-step self-assembly of MXene nanosheets at the SA/IL interface, can effectively absorb and convert solar energy into thermal energy. Furthermore, MXene-decorated SA/IL PCMEs have good high-temperature stability, little supercooling degree (0.9–3.1 °C), and large energy storage capacity. The maximum apparent specific heat capacity and average absorbance of the MXene-decorated SA/IL PCME are 4.5 and 303.1 times higher than those of IL, respectively. Under 2 sun irradiation, the 0.05–20 wt% MXene-decorated SA/IL PCME achieves high photo-thermal conversion efficiencies (91.3% at 68.9 °C, 39.4% at 115.1 °C) due to its large energy storage capacity and excellent optical absorption property. The simple interfacial self-assembly provides a promising strategy to prepare high-performance SA/IL PCME used as a novel HTF for medium-temperature solar energy utilization systems.

A novel metal-organic framework aerogel based hydrated salt composite phase change material for enhanced solar thermal utilization

In recent years, metal-organic frameworks (MOFs) have been regarded as ideal carriers for phase change materials (PCMs) due to their outstanding properties and attractive structures. In this work, a novel shape-stabilized SAT/Fe-EA aerogel composite PCM is prepared by impregnating sodium acetate trihydrate (SAT) into MOF aerogel with iron as the metal ion and ellagic acid (EA) as the organic ligand. The three-dimensional network structure of Fe-EA aerogel and Fe-EA guarantee sufficient supporting space, excellent light-to-thermal effect and efficient heat transfer rate, leading to an ultra-high heat storage density (245.6 J/g) and excellent light-to-thermal conversion performance (the light-to-thermal conversion efficiency is up to 94.5 %). Besides, benefit from the abundant pore structure and hydrophilic surface of Fe-EA aerogel obtained via freeze-drying, which could provide a large number of heterogeneous nucleation sites for SAT, the supercooling degree of SAT is decreased to as low as 2.07–2.63 °C. Notably, the supercooling degree shows no significant change after 200 cycles, and the SAT/Fe-EA aerogel composite PCM still maintains a high heat storage density of 214.9 J/g, exhibiting a superior thermal reliability. Consequently, the SAT/Fe-EA aerogel composite PCM could be a promising candidate for solar thermal storage systems.

Spontaneous oscillatory growth of ice crystals in supercooled water under a microgravity environment: Theoretical hypothesis on the effect of antifreeze glycoprotein

In a crystal growth experiment conducted on the Japanese Experiment Module “Kibo” aboard the International Space Station, an unknown phenomenon, i.e., spontaneous oscillation of the growth rate of ice-crystal basal faces in supercooled water containing antifreeze glycoprotein (AFGP), was observed. In this study, we modeled growth-inhibiting and growth-promoting effects of the AFGP adsorbed on the ice-crystal basal face and discussed the mechanism of the spontaneous oscillatory growth. The normal growth rate of the basal face depends on the amount of AFGP adsorbed on the basal face. Simultaneously, the amount of adsorbed AFGP is controlled by the crystal growth, because the higher the growth rate, the more frequently the crystal surface is renewed. The normal growth rate and the amount of adsorbed AFGP can be determined as a steady state that satisfies the interdependence between these quantities. By formulating the interdependence and finding the steady state, we demonstrated the appearance of two different stable steady states in a certain range of supercooling (bistability). This is theoretical proof of a crystal growth hysteresis, in which the trace of the growth rate varies with when the degree of supercooling is increased or decreased. We also clarified that the spontaneous oscillation of the growth rate is triggered by the release of the latent heat of crystallization. Our findings herein provide novel possibilities for the effect of AFGP on ice-crystal growth.

Fast Solidification of Pure Gallium at Room Temperature and its Micromechanical Properties

AbstractWith excellent electrical conductivity, fluidity, rheological property, and biocompatibility, gallium has been intensively studied in the fields of flexible electronics and devices, thermal management, and soft robotics. However, the large degree of supercooling of gallium presents a large limitation for phase transition‐related applications such as the very low temperature required for solidification, the impurities, and side effects brought in by nucleating agents. In this study, solidification process of liquid gallium by using solid gallium as a nucleating agent is discovered to be fast and facile at room temperature compared with other agent materials including copper, iron, and nickel. Quantificationally, solidified gallium as a nucleating agent, can effectively reduce the supercooling degree from about 66.3 to 14.8 °C. The freezing velocity can reach to 200 mm3 min−1. The possible mechanism is reducing the energy barrier via adding nucleation site, allowing rapid solidification at room temperature accompanying heat dissipation. Moreover, micromechanical properties are compared between raw solid Ga and the solidified Ga induced by Ga agent, which suggests a slight decrease in mechanical strength at room temperature with the nucleating agent. It will be beneficial to understand the phase change and also provide guidance for the application of gallium regarding its mechanical properties.

METHOD OF REDUCE SUPERCOOLING PHENOMENON OF PHASE CHANGE MATERIAL

In this research, the author proposed a supercooling phenomenon reduction PCM that suppresses the decrease in latent heat by installing a PCM with a small supercooling degree on the heat transfer surface side of the PCM with a large supercooling degree. As a result, it was shown that the supercooling phenomenon reduction PCM can reduce the supercooling degree by forming and growing solidified crystals even when the temperature is higher than the supercooling release temperature. Furthermore, the calculation results for predicting the cooling and heating characteristics of the supercooling phenomenon reduction PCM were in good agreement with the experimental values.