Melting Time Research Articles

Efficiently all-weather anti-icing and de-icing coatings enabled by polyaniline microcapsules encapsulated phase change materials

Photothermal superhydrophobic coatings are one of the most promising anti-icing/de-icing materials. However, the intermittence of light energy limits the application of photothermal energy conversion technologies when continuous de-icing is required. Herein, an innovative solution for the integration of photothermal effect and phase change thermal storage was proposed. In this work, an efficient anti-icing/de-icing coating was successfully fabricated based on multifunctional polyaniline microcapsule encapsulating butyl stearate (BS). Benefiting from the heat storage capacity of BS in the microcapsule, the coating could achieve all-weather anti-icing capability. Under the condition of −20 °C, the freezing time of water droplets on the coating with only 10 wt% microcapsules was delayed by about 12.6 times compared to the blank coating. At the same time, under simulated dark conditions, the freezing time of water droplets could be delayed by about 14.1 times. Moreover, owing to the thermal conductivity and high solar energy exploitation, polyaniline endowed the coating with outstanding photothermal de-icing performance, presenting the superiority of outdoor applications. Under NIR (200 mW/cm2) illumination, the melting time of water droplets was reduced to 18 s, which was nearly 10 times faster than that on the blank coating. Moreover, the polyaniline microcapsules also possessed outstanding anticorrosion property, which was particularly attractive for mental coating applications. The combined properties of this all-weather anti-icing and de-icing coating could render it a promising contender for challenging outdoor applications.

High-power fiber laser incident beam absorptivity variation of molten pool surfaces during their solid-liquid-gas state evolution

The thermal and ablation effects of lasers are widely used in laser additive manufacturing, laser welding, laser cleaning, and laser cladding technologies. Absorptivity is the core index of laser beam-thermal energy conversion efficiency. This paper analyzed the irradiated material's absorption behavior during the solid-liquid-gas evolution of laser-ablated metal surfaces by comparing the temperature fields and the corresponding weld cross-sections for different laser action periods, considering the fusion and vaporization latent heats. The solid-liquid-gas state evolution of high-power fiber laser-irradiated metal surfaces occurs during several milliseconds, with a short solid-phase existence period, since fusion or melting time is much shorter than the vaporization time. As the solid-liquid-gas state evolves, the average absorptivity and the share of thermal conduction energy loss decrease with the laser action time, while the fusion energy loss gradually increases. The solid-phase surface of the metal in laser processing absorbs significantly more incident laser energy than the liquid-phase one. The longer the solid-phase occurrence period of the metal surface during the laser action, the greater its average absorptivity of the incident laser. By increasing the laser spot area and scanning rate, the solid-phase period of the laser-irradiated metal surface can be increased, improving its incident laser absorptivity.

Enhancing the melting rate of RT42 paraffin wax in a square cell with varied copper fin lengths and orientations: A numerical simulation

Latent thermal energy storage units are especially preferred in renewable thermal energy systems for their significant capacity to store heat. Nevertheless, the phase change materials in these units have low thermal conductivity, prompting researchers to tackle this problem using several methods, such as incorporating fins. This numerical study contributes to improving the charging rate of a square cell (50 × 50 mm) used paraffin wax RT42 as phase change material by adding 4 copper fins inside, 1 mm thick and of different lengths. The fins were positioned on the left wall, where a constant-temperature heat flux was applied, while the other walls were thermally insulated. Four configurations of the cell were examined: without fins, with 10 mm length fins, with 20 mm length fins, and with 30 mm length fins, respectively. The results demonstrated that the presence of fins significantly improved the charging rate of the square cell. Compared to the baseline configuration without fins, the time required for the paraffin wax RT42 to completely melt was reduced by 22.22 %, 33.33 %, and 55.56 % with fins of 10 mm, 20 mm, and 30 mm lengths, respectively. Configuration four was also compared with a setup where similar fins were positioned on the bottom wall while maintaining the heat flux on the left wall. It was observed that the total melting time doubled compared to configuration four, suggesting that the optimal placement for the heat flux is on the wall where the fins are located. The study contributes to enhancing and developing the charge rates of square and rectangular PCM cells such as these used for cooling PV panels.

Partitions influence on rectangular latent heat thermal energy storage unit performance during melting and solidification

The growing use of renewable energy sources demands efficient storage solutions due to their variability. Thermal energy storage systems utilising phase change materials are emerging as viable options to address this challenge. This study evaluates the impact of various partition types on phase change duration in thermal energy storage systems. The well-known and validated enthalpy-porosity algorithm implemented in the Fluent 2021R2 software was used. The shortest melting time was observed in the case with four vertical tubes and three horizontal partitions, which was 82 % shorter than in the reference case. The highest change in specific enthalpy of phase change material (252.5 kJ/kg) during melting was also noted for this system. The shortest solidification time was observed for the case with four tubes and two diagonal partitions, which was 72 % shorter than in the reference case. The greatest increase in the specific enthalpy of phase change material (240.4 kJ/kg) during the solidification process was also observed in this system. In conclusion, due to the thermal conductivity of the partitions, the temperature distribution throughout the domain becomes more homogeonous, thus contributing to more uniform heat flux extraction and supply throughout the process.

Effectiveness of a PCM-based heat sink with partially filled metal foam for thermal management of electronics

Electronics often experience overheating, which occurs when insufficient or improper cooling causes temperatures to rise quickly, potentially leading to component failure. Recently, a passive technique utilizing phase change material (PCM)-based heat sinks is suitable for modern electronic cooling. However, due to its low thermal conductivity, Aluminum (Al) foam as a thermal conductivity enhancer (TCE) is used. In this study, a partial filling approach is employed, involving a heat sink designed to cool a protruding electronic component (EC) attached to a metal fin. The enthalpy-porosity method and the thermal equilibrium model are applied. Results show that the efficiency of the heat sink is improved by increasing the filling ratio of the Al foam, thereby reducing the EC temperature by 15.85 °C, shortness the melting time by more than 1000 s, and the overall effective conductivity enhanced by 25 times compared to the case without Al foam. In addition, the optimal partial filling ratio is determined to be 2/3, due to the considerable savings of 33.33 % in material cost and overall heat sink weight. The findings suggest that partial filling is a strategy that can be employed to achieve a more comprehensive performance in thermal management using PCM-based heat sinks.

Modifying the performance kinetics in the shell-and-multi tube latent heat storage system via dedicated finned tubes for building applications

Phase change materials (PCMs) offer significant potential for building energy management, but are limited by poor heat transfer rates. This study investigates charging/discharging performance optimization of a shell-and-multi-tube heat storage system using high-enthalpy PCM (RT70HC) with differentiated fin configurations. The key novelty of the work lies in its thorough examination of geometric mutations within this system, specifically targeting building energy applications. A validated numerical model simulated charging and discharging processes, comparing finned and plain tube designs. Key performance metrics analyzed here include melting times, heat storage rates, phase transition velocities, and temperature profiles. Results reveal the finned tube design enables a 268 % higher heat storage rate (1421 W vs 387 W) and 74.5 % faster melting time (196 min vs 770 min) compared to the plain tube. Detailed analysis of the 10-h charging process exposes intricate thermal stratification patterns. The inclusion of dedicated discharging finned tubes significantly enhances heat distribution. During the 20-h discharge, heat transfer rates decrease from 2000 W to 100 W, providing crucial insights into solidification dynamics. These quantified findings highlight the potential of optimized finned tube arrays to substantially improve thermal performance of shell-and-multi-tube heat storage systems for building energy applications.

Optimization of Methodologies to Study Freeze/Thaw Processes in Drug Substance Bottles.

Biological drug substance (DS) is often frozen to enhance storage stability, prolong shelf life, and increase flexibility during manufacturing. However, the freezing and thawing (F/T) of bulk DS at the manufacturing scale can impact product quality as a result of various critical conditions, including cryo-concentration during freezing, which are influenced, among other things, by product-independent process parameters (e.g., container type, fill level, F/T equipment, and protocols). In this article, we report the optimization of two major methodologies to study product-independent process parameters in DS bottles at the manufacturing scale, namely the recording of temperature profiles and liquid sampling after thawing to quantify the concentration gradients in the solution. We report experimentally justified measuring positions for temperature recordings, especially for the selection of the last point to freeze position, and highlight the implementation of camera-assisted inspection to determine the last point to thaw and the actual thawing time. In particular, we provide, for the first time, a detailed description of the technical implementation of these two measuring set-ups. Based on the reported case studies, we recommend choosing relevant measuring positions as a result of initial equipment characterization, resulting in a resource-conscious study set-up.

Self-growing bionic leaf-vein fins for high-power-density and high-efficiency latent heat thermal energy storage

Latent heat storage (LHS) has found extensive applications across various fields. However, large-scale deployment is still restricted due to the worse thermal charging performance of traditional LHS systems. In this research, the self-growing fins of the tube-shell LHS system are designed via the bionic topology optimized method to improve thermal storage performances, inspired by the structures and functions of leaf veins. Notably, the system installed with topology-optimized self-growing fins (T-FIN) demonstrates the shortest melting time, largest specific power density (SPD), and highest efficiency simultaneously. At the inlet conditions of 0.5 L min−1 and 358.15 K, the thermal charging time decreases by 46.4 % and 57.1 % compared with the systems equipped with traditional long-fins (L-FIN) and short-fins (S-FIN), while increasing the SPD by 80.6 % and 125.7 %, respectively. Moreover, the efficiency of exergy and entransy storage is 2.49 and 2.42 times, respectively, as large as those of the S-FIN. The intrinsic mechanism is attributed to enhanced synergy between the liquid-PCM temperature field and the flow field. Furthermore, outer tube shapes are optimized by the Genetic Algorithm for the first time, leading to a further decrease in charging time by 21.57 % compared with its original counterpart. These findings provide a valuable idea for designing efficient bionic LHS systems.

ELISA-based detection of fresh and frozen-thawed lamb meat: a promising analytical approach for meat authentication.

Fresh/chilled meat differs in quality from frozen-thawed meat, and consumers prefer fresh meat over frozen-thawed meat. Differentiating between the two types of meat is an important part of the meat quality control system. This study aimed to develop an ELISA based on cytoplasmic antioxidant enzyme superoxide dismutase (SOD) as a biomarker. IgGs were raised in experimental animals and purified using immunoaffinity chromatography. The assay was optimized with guinea pig anti-SOD pAb as the capture antibody and rabbit anti-SOD pAb as the detection antibody. The assay showed excellent performance for differentiation, as the ROC area under the curve values were >0.9. A sensitivity of 95.8% and specificity of 95.0% were observed at a positive percentage (PP%) criterion value of 52.752. Sandwich ELISA results showed a significant difference between the chilled and repeatedly frozen-thawed lamb samples. Lamb meat stored for five days in a chiller showed a PP% value below the threshold PP% value, indicating that the assay can differentiate meat until 5 days of chiller storage. In addition, a thawing time of more than 18 h at 4 ± 1 °C is required to differentiate between both types of lamb meat with a size of 500 g. The developed ELISA can be applied at various points in the meat value chain to differentiate fresh meat from frozen-thawed meat.

Effect of melting time and temperature on radiation shielding and mechanical parameters of barium borate glass

Effect of melting time and temperature on radiation shielding and mechanical parameters of barium borate glass

Improving Reliability of Immunological Assays by Defining Minimal Criteria for Cell Fitness.

Human PBMC-based assays are often used as biomarkers for the diagnosis and prognosis of disease, as well as for the prediction and tracking of response to biological therapeutics. However, the development and use of PBMC-based biomarker assays is often limited by poor reproducibility. Complex immunological assays can be further complicated by variation in cell handling before analysis, especially when using cryopreserved cells. Variation in postthaw viability is further increased if PBMC isolation and cryopreservation are done more than a few hours after collection. There is currently a lack of evidence-based standards for the minimal PBMC viability or "fitness" required to ensure the integrity and reproducibility of immune cell-based assays. In this study, we use an "induced fail" approach to examine the effect of thawed human PBMC fitness on four flow cytometry-based assays. We found that cell permeability-based viability stains at the time of thawing did not accurately quantify cell fitness, whereas a combined measurement of metabolic activity and early apoptosis markers did. Investigation of the impact of different types and levels of damage on PBMC-based assays revealed that only when cells were >60-70% live and apoptosis negative did biomarker values cease to be determined by cell fitness rather than the inherent biology of the cells. These data show that, to reproducibly measure immunological biomarkers using cryopreserved PBMCs, minimal acceptable standards for cell fitness should be incorporated into the assay protocol.

Improving Wastewater Heat Recovery Using Phase Change Material Heat Exchangers: A Numerical Study of Thermal Performance

ABSTRACTIndustrial processes often generate substantial amounts of wastewater with significant thermal energy content, which is typically discarded as waste. A promising approach to increase energy efficiency and advance sustainable resource management is waste water heat recovery. Utilizing a phase change material (PCM) to extract waste heat from wastewater and transfer it to cold water is an innovative method that separates the demand and supply of heat, while also integrating storage and transmission within a single heat exchanger (HE). A 3D numerical model of PCM‐based HE is developed and simulated. The thermal behavior of PCM and preheating of cold water are investigated in this study. In order to increase the thermal conductivity of the PCM, fins are strategically positioned. Around 71.13% of melting time is reduced by adding fins. Further, the 10° orientation of the fins is also numerically observed and it is found that it helps to improve natural circulation of molten PCM. Thus, melting time is reduced by 34% compared to the vertical fin. A 3.5°C–4.5°C temperature rise in cold water is obtained with the inclined fin, which is 14.28% higher than the vertical fin model.

A 3.3‐Million‐Year Record of Antarctic Iceberg Rafted Debris and Ice Sheet Evolution Quantified by Machine Learning

AbstractOver the last 3.3 million years, the Antarctic Ice Sheet (AIS) has undergone phases of ice sheet growth and decay, impacting sea level and climate globally. Presently, the largely marine‐terminating AIS loses mass primarily by iceberg calving and basal melt of ice shelves. Quantifying past rates and timing of AIS melt is vital to understanding future cryosphere and sea level changes. One proxy for past ice sheet instabilities is iceberg rafted debris (IRD) fluxes. However, traditional methods of IRD quantification are labor‐intensive. Here, we present a new method of identifying IRD grains in sediment core X‐ray images using a convolutional neural network machine learning algorithm. We present a 3.3‐million‐year record of AIS IRD melt events using sediment cores from International Ocean Discovery Program Sites U1536, U1537, and U1538 in the Southern Ocean's “Iceberg Alley.” We identify two increases in the IRD fluxes throughout this period, at ∼1.8 and 0.43 Ma. We propose that after 1.8 Ma, the AIS expanded and transitioned from a primarily terrestrial‐terminating to a primarily marine‐terminating ice sheet. Therefore, after 1.8 Ma, glacial terminations and AIS iceberg discharge are associated with variations in global ice volume, presumably through the mechanism of sea level and, therefore, grounding line change. The second AIS regime change occurs during the Mid‐Brunhes Event (∼0.43 Ma). After this time, there are heightened and continuous IRD fluxes at each glacial termination, indicating increased AIS size and instability after this time.

Design optimization of finned multi-tube PCM heat exchanger for enhancing EV energy performance

This study presents an optimized design of a finned multi-tube phase change material-based thermal energy storage system for electric vehicle thermal management, addressing the challenge of low battery efficiency in cold climates. While finned multi-tube designs are recognized for their thermal advantages, their application in electric vehicles has been underexplored. Previous research often overlooks the full operational cycle of electric vehicles, including charging (melting), discharging (solidification), and driving conditions. This work bridges the gap by optimizing the thermal energy storage design using a multi-objective genetic algorithm to enhance both thermal efficiency and energy density. The optimized design reduces melting and solidification times by 68.6% and 60.3%, respectively, and increases energy density by 4.9% compared to the initial design. The study further integrates the optimized thermal energy storage system into an electric vehicle thermal management strategy, analyzing its performance under real-life driving cycles in various ambient temperatures. This integration reduces total energy consumption by 20.6% compared to a baseline system. These findings offer a novel approach to improving the driving range of electric vehicles in cold climates by minimizing power demand on electric batteries for cabin heating.

Numerical investigation of performance enhancement in a PCM-based thermal energy storage system using stair-shaped fins and nanoparticles

This study numerically investigates the melting performance enhancement of phase change material (PCM) in a latent heat thermal energy storage (LHTES) unit using a novel stair-shaped fin and nano-enhanced PCM. Different fin configurations are designed and their thermal performance is compared to traditional straight fins, while the total mass of fins is kept constant. Nano-enhanced PCM is prepared by the inclusion of CuO nanoparticles into RT82 as PCM. The simulation results reveal that the stair-shaped fins can notably enhance the efficiency of phase change compared to the traditional straight fins. The configuration with more extended fin close to the lower zone of the latent heat thermal energy storage unit had the best thermal performance. The full PCM melting time for the most efficient stair-shaped fin configuration is reduced by 52% compared to the straight fins. The combined impacts of the most effective stair-shaped fin design and nanoparticles on the phase change melting performance are evaluated. The inclusion of nanoparticles with volume concentrations of 2% and 5% into the pure PCM leads to 61% and 65% reduction in charge rate, respectively, as compared to the straight fin with pure PCM.

A Study of Asymmetric Hyperbolic Heat Storage Unit

ABSTRACTDue to the advantages of high energy density and constant temperature, phase change energy storage technology has attracted much attention in energy saving and efficient utilization of energy. In this paper, Fluent software is used to simulate and analyze the heat storage characteristics of six new thermal storage units: corrugated tube, hyperbolic‐shape, non‐hyperbolic‐shape, symmetric frustum‐shape, non‐frustum‐shape, and bow‐shape. The results show that the melting rate of the non‐hyperbolic‐shape phase change unit is significantly higher than that of the circular tube, the heat storage time is shortened by 22.52%, and Ra* reaches 0.0086. Second, the effects of the radius difference (δ) between the inlet and outlet of the non‐hyperbolic‐shape phase change unit and the asymmetric position (s) on the heat storage process are studied. The results show that when δ increases from 2 to 10 mm, the melting time of phase change material (PCM) is shortened by 22.89%, that is, the average heat transfer rate between PCM and heat transfer fluid increases with the increase of δ. On the other hand, the average heat storage rate of the heat storage unit decreases first and then increases with the increase of s. When δ = 10 mm, s = 35 mm is the best working condition, the average heat storage rate of the non‐hyperbolic‐shape thermal storage unit reaches 34.3 J/s. This study can provide new ideas and references for the optimization design of latent heat storage units and the progress of experiments.

Progressive melting of surface water and unequal discharge of different DOM components profoundly perturb soil biochemical cycling

Freeze-thaw (FT) events profoundly perturb the biochemical processes of soil and water in mid- and high-latitude regions, especially the riparian zones that are often recognized as the hotspots of soil-water interactions and thus one of the most sensitive ecosystems to future climate change. However, it remains largely unknown how the heterogeneously composed and progressively discharged meltwater affect the biochemical cycling of the neighbor soil. In this study, stream water from a valley in the Chinese Loess Plateau was frozen at –10°C for 12 hours, and the meltwater (at +10°C) progressively discharged at three stages (T1 ∼ T3) was respectively added to rewet the soil collected from the same stream bed (Soil+T1 ∼ Soil+T3). Our results show that: (1) Approximately 65% of the total dissolved organic carbon and 53% of the total NO3--N were preferentially discharged at the first stage T1, with enrichment ratios of 1.60 ∼ 1.94. (2) The dissolved organic matter discharged at T1 was noticeably more biodegradable with significantly lower SUVA254 but higher HIX, and also predominated with humic-like, dissolved microbial metabolite-like, and fulvic acid-like components. (3) After added to the soil, the meltwater discharged at T1 (e.g., Soil+T1) significantly accelerated the mineralization of soil organic carbon with 2.4 ∼ 8.07-folded k factor after fitted into the first-order kinetics equation, triggering 125 ∼ 152% more total CO2 emissions. Adding T1 also promoted significantly more accumulation of soil microbial biomass carbon after 15 days of incubation, especially on the FT soil. Overall, the preferential discharge of the nutrient-enriched meltwater with more biodegradable DOM components at the initial melting stage significantly promoted the microbial growth and respiratory activities in the recipient soil, and triggered sizable CO2 emission pulses. This reveals a common but long-ignored phenomenon in cold riparian zones, where progressive freeze-thaw can partition and thus shift the DOM compositions in stream water over melting time, and in turn profoundly perturb the biochemical cycles of the neighbor soil body.

Numerical study on the combined application of multiple phase change materials and gradient metal foam in thermal energy storage device

Latent heat thermal energy storage (LHTES) offers significant energy-saving benefits, but its application is limited due to the low thermal conductivity of phase change material (PCM). To address this issue, this article studied the combined application of metal foam structures with different porosity gradients and multiple PCMs with different melting points through numerical simulation to accelerate the melting of PCM and enhance system efficiency. The results showed that the application of multiple PCMs improved the heat transfer performance of the system, reducing the complete melting time by 9.18% compared to using a single PCM with uniform metal foam. Based on the multi-PCM storage system with an average porosity of 0.90, this article designed metal foam structures with one-dimensional and two-dimensional porosity gradients and explored their impacts. The results indicated that in the structure with a one-dimensional porosity gradient along the heat flow direction, the positive gradient decreased thermal resistance, further reducing the complete melting time by 6.18%, while the negative gradient increased it by 19.78%. However, the temperature non-uniformity was lowest with the negative gradient and highest with the positive gradient. The optimal two-dimensional porosity gradient multi-PCM storage model not only reduced thermal resistance but also effectively solved the issue of uneven melting, reducing the complete melting time by 17.96% and increasing the energy storage efficiency by 20.16% compared to the single PCM system with uniform porosity. Furthermore, the article conducted a dimensionless analysis of the optimal structure and different gradient structures, establishing formulas for the liquid fraction concerning modified Fourier number, modified Stefan number, and modified Rayleigh number.

A shell-tube latent heat thermal energy storage: Influence of metal foam inserts in both shell and tube sides

Enhancing heat transfer in latent heat thermal energy storage systems is of utmost importance to facilitate the efficient absorption and release of thermal energy. The primary objective of the current study is to investigate the influence of a metal foam layer on heat transfer enhancement in both the heat transfer fluid side and the shell side. The research explores the incorporation of a fixed 30 % foam layer, which can either extend along the tube wall or penetrate deeper into the shell, moving away from the heat transfer fluid tube. A local thermal non-equilibrium two-temperature heat equation model is utilized to mathematically model the interactions within the metal foam embedded in the heat transfer fluid tube and the phase change material domain. The governing equations are solved using the finite element method. The results indicate that adjustments to the inlet pressure and the metal foam shape parameter (FL) can significantly reduce the melting time, with a variation of approximately 40 %. Specifically, at a constant inlet pressure of 750 Pa, the energy storage power at a 90 % charging increases from 32.2 W (FL = 0.75) to 48.7 W (FL = 1.37). A modification of FL shape parameter increased the power output by 34 %.

Thermal effect of the anisotropic metal foam on the melting performance of phase change material: A pore-scale study

Recently, metal foams have been attractive in reinforcing the heat storage process of phase change materials (PCMs) beneficial from their high thermal conductivity, interconnected structure, and large specific surface. Nevertheless, the melting of PCM is not uniform caused by convective heat transfer, so it cannot be sufficiently accelerated by a traditional isotropic metal foam. In this study, we numerically investigated the melting performance of PCM in isotropic and anisotropic metal foams. Results illustrated that the X-anisotropic structure can more efficiently enhance the melting performance as compared to the isotropic original metal foam, but the Z-anisotropic structure suppresses it. Moreover, the X-anisotropy-0.5 shows the fastest melting, its complete melting time is significantly reduced by 7.99 % compared with the original model, and its heat storage power is 8.68 % higher than the original one. Instead, the Z-anisotropic models prolong the complete melting time by 11.10 % ˗ 28.55 %. It is owing that the anisotropic structure would promote the heat transfer along one direction but suppress its vertical direction. This article provides a feasible routine to accelerate the melting of metal foam-based PCMs, thus improving the heat storage power of the latent heat thermal energy storage system.