Phase Change Time Research Articles

Effect of Macrocapsule Geometry on PCM Performance for Thermal Regulation in Buildings

The integration of phase-change materials (PCMs) into thermal energy storage systems offers significant potential for reducing energy consumption and improving thermal comfort, crucial issues for achieving sustainable building stocks. Nevertheless, the performance of PCM-based systems is strongly influenced by the container geometry. Among the various forms of incorporating PCMs into building applications, macroencapsulation is the most versatile and is, therefore, widely used. Herewith, this paper analyzes the impact of macrocapsule geometry on PCM thermal performance. Thermal properties of the material were first tested using Differential Scanning Calorimetry at five heating/cooling rates to evaluate its influence on phase-change temperatures and enthalpy. Then, an experimental setup evaluated four macrocapsule geometries on the enclosed PCM behavior during charging and discharging processes. The PCM characterization revealed that the slowest-tested rate minimized the supercooling effect. Analysis across different macrocapsule geometries showed that sectioning the contact surface improved heat transfer efficiency by fully mobilizing the PCM and reducing phase-change times. Conversely, double-layered geometry designs hindered heat transfer, presenting challenges in completing PCM charging and discharging. These findings suggest that optimizing its performance is a necessary direction for further research, which may include adjusting the PCM operating temperature range across layers or redesigning the geometry to misalign contact surfaces.

Characterization of droplet freezing on superhydrophobic surfaces with different microstructures

Superhydrophobic surfaces with microstructures have garnered significant attention for anti-icing applications due to their lower cost and higher efficiency. In this paper, we designed and prepared surfaces with differently spaced groove microstructures on aluminum substrates using femtosecond laser technology combined with low-surface-energy coatings. In addition, droplet freezing times and freezing processes were investigated to study the anti-icing properties of different surfaces. The results demonstrated that the sample surfaces exhibit excellent superhydrophobicity. At the cold surface temperature of −15 °C, the freezing time of droplets on the surface with a spacing of 100 μm is 707.9 s, which is far more than that of other sample surfaces. Additionally, groove spacing has a more pronounced effect on the rate of change in height compared to the diameter before and after droplet freezing. During the freezing process, the freezing front initiates from the cold surface and grows upward in a convex shape. As the growth of the freezing front at the edge accelerates, it eventually becomes concave, and this phenomenon occurs earlier at lower temperatures. Freezing is considered complete when the freezing tip appears. As the temperature decreases, both the droplet supercooling time and phase change time shorten. This paper is anticipated to provide a reference for the design of efficient anti-icing materials.

Performance Characterisation of Thermal Energy Storage Containing a Phase Change Material (PCM) Sphere with Low Conductivity Fins: Simulation-Based Analysis

This paper presents the outcomes of a simulation study aimed at investigating the thermal performance of modified phase change material (PCM) structures within a sphere with integrated fins. The escalating global warming crisis and its associated weather anomalies necessitate urgent measures to mitigate its impacts. Numerous research endeavours have been undertaken to address this issue, including the utilization of thermal energy storage systems (TES) augmented with PCM. PCM can be incorporated into building walls to counteract rising temperatures. However, inadequate heat transfer caused by poor thermal conductivity has been a persistent challenge in these systems. The addition of high conductivity fins has found to improve the overall performance of TES. Yet, this study proposes the addition of low conductivity fins to study for the effect of shape factor to its performance. The research evaluates the phase change of 2-fins and 4-fins with varying thicknesses within the PCM structure. A comprehensive simulation framework is employed to analyse the thermal behaviour of the PCM-enhanced sphere without considering ambient temperature nor PCM properties, but fin dimensions and configurations. The simulation results reveal that the inclusion of fins significantly improves heat transfer within the system by cutting a minimum of 20% in phase change time and could promote the phase change process to happen earlier by a maximum of 38% in starting time. By optimizing the fin configuration and thickness, the overall thermal conductivity of the PCM-based TES can be enhanced. These findings contribute to the development of efficient thermal energy storage systems, offering potential solutions to combat global warming and promote sustainable thermal management.

Thermal Performance Analysis of Aluminum Alloy Phase Change Panels for Regions with Hot Summers and Warm Winters

Utilizing phase change materials (PCMs) in passive energy-saving wall panels to regulate indoor temperatures during hot seasons can improve people’s thermal comfort and reduce the energy consumption of air conditioning systems. This study is based on the hot summer and warm winter climatic characteristics of Hainan. According to local meteorological data and residents’ living habits, a suitable phase change temperature of approximately 28 °C was determined. A composite PCM of paraffin and stearic acid n-butyl ester was prepared and tested for thermal performance. Encased in an aluminum box with non-penetrating aluminum rods to enhance heat transfer, the phase change panel was applied to the inner side of exterior walls. Thermal tests demonstrated that increasing the mass ratio of stearic acid n-butyl ester to paraffin lowers the melting point and latent heat. At a 3:7 mass ratio, the melting point of the composite PCM was 28.30 °C, and the latent heat was 128.26 J/g. The 20 mm thick panel maintained a stable phase change process, with unheated surface temperatures between 28 °C and 29 °C for up to 180 min. Compared to panels without aluminum rods, those with rods exhibited a 20% longer phase change time, extended heat transfer paths, and reduced liquid-phase convective heat transfer rates, demonstrating improved PCM utilization. Therefore, the phase change panel with non-penetrating aluminum rods exhibits excellent insulation and temperature control properties.

Heat transfer investigation of nano – Encapsulated phase change materials (NEPCMs) in a thermal energy storage device

Phase change natural convection heat transport and flow features of a variety and new types of hybrid nanoliquids, suspension of Nano – encapsulated phase change materials (NEPCMs), within a square cavity is inspected theoretically in this analysis. The capsules are arranged with a shell and a PCM as a core. The shell of this NEPCM prevents the phase change material from the direct interaction of hot fluid and from the leakage. The heat capacity of the suspension contains latent heat generated at the time of phase change. The modeled equations are numerically scrutinized with Finite element method. Variable thermal conductivity parameter 1≤Nc≤5, variable viscosity parameter 1≤Nv≤5, radiation number 0.5≥R≥0.1, Rayleigh parameter 102≤Ra≤103, volume fraction of NEPCMs1%≤ϕ≤5% and fusion temperature (0.2≤θf≤1.0) impact on the patterns of heat capacity ratio, isotherms and velocity lines are examined in detail. The results indicates that, as the volume fraction values of NEPCMs amplifies from 1% to 5% the rates of heat transfer of the nanoliquid magnifies 42% compared to the host fluid. Non – dimensional rates of heat transport magnifies with growing (Ste) values.

Experimental validation of a design model for latent thermal energy storage extended with sensible heat

Latent thermal energy storage can be a key technology for a green energy transition by matching fluctuating heat demand and supply. In order to implement a storage system, it needs to be designed which requires estimating the outlet temperature of a system for a given geometry and time history of the heat transfer fluid’s mass flow rate and inlet temperature. Currently, design methods are either overly simplistic, focusing solely on e.g. the phase change time or requiring the solution of partial differential equations which can be computationally expensive. The present paper proposes a novel approach where a latent thermal energy storage system is decomposed into a heat transfer fluid vessel, a sensible storage system and a storage system with only latent heat. Computationally inexpensive models are available for all three of these sub heat exchangers. A heat exchanger model is obtained by connecting the sub heat exchangers in parallel. This novel approach is used to model an industrial scale shell and tube latent thermal energy storage heat exchanger. The predicted outlet temperature is compared to the measured outlet temperature and the design model obtains good agreement.

Thermal performance of polymer gyroid heat exchangers combined with phase change materials as a latent heat thermal energy storage system: An experimental investigation

Latent heat thermal energy storage (LHTES) systems utilizing phase-change materials (PCMs) in conjunction with heat exchangers (HXs) have been widely investigated for efficient thermal energy utilization. This study experimentally evaluated the heat transfer performance and pressure loss of a PCM-based gyroid HX fabricated using a polymer 3D printer. Initially, the study compared the phase change time, heat storage and release characteristics, and pressure drop of the gyroid HX with those of a conventional shell-and-tube HX (S&T HX). The results demonstrate that the gyroid HX achieved up to 20 % shorter thermal charge and discharge times than the S&T HX, which is attributed to a higher heat transfer rate. Additionally, the measured pressure drop of the gyroid HX was up to 44 % lower than that of the S&T HX. Consequently, considering both the heat transfer rate and pressure drop, the gyroid HX showed an average improvement of 57 % and 31 % in the overall enhancement factor during charging and discharging, respectively, compared to the S&T HX. Further, metal gyroid HXs fabricated from steel and aluminum using metal 3D printing were experimentally compared with the polymer gyroid HX. Despite the polymer thermal conductivity being only 1/90 and 1/790 that of steel and aluminum, respectively, the heat transfer rate per unit mass of the polymer gyroid HX was 1.7 times that of the steel gyroid HX and approximately half that of the aluminum gyroid HX. This finding suggests that the polymer gyroid HX is suitable for LHTES applications where lightweight characteristics are crucial.

Dual-sided melting of a one-dimensional composite wall comprising two distinct phase change material (PCM) layers

Past literature on theoretical modeling of solid-liquid phase change heat transfer mostly addresses a single phase change material (PCM), whereas, a series combination of two or more PCMs is often used in practical applications. This work presents an approximate analytical model for the melting/freezing of a one-dimensional composite of two PCMs being heated/cooled from both ends. It is shown that up to three phase change fronts may simultaneously exist in this problem. In addition to direct melting/freezing from the respective walls, it is shown that each PCM may also melt/freeze due to heat transfer through the other PCM. Using a quasi-stationary assumption, temperature field during the multi-stage phase change process is approximated by solving a multilayer transient thermal conduction problem using eigenfunction expansion. Good agreement with numerical simulations, and with the Stefan solution for a special case is demonstrated. The impact of key non-dimensional parameters on performance metrics including total time for phase change is determined. A quantitative prediction of conditions leading to the thermodynamically favorable situation of simultaneous completion of phase change of two commonly used PCMs is carried out. This work improves the theoretical understanding of phase change in composite PCMs, leading to optimization of practical thermal systems.

Natural variation in CYCLIC NUCLEOTIDE-GATED ION CHANNEL 4 reveals a novel role of calcium signaling in vegetative phase change in Arabidopsis.

The timing of vegetative phase change (VPC) in plants is regulated by a temporal decline in the expression of miR156. Both exogenous cues and endogenous factors, such as temperature, light, sugar, nutrients, and epigenetic regulators, have been shown to affect VPC by altering miR156 expression. However, the genetic basis of natural variation in VPC remains largely unexplored. Here, we conducted a genome-wide association study on the variation of the timing of VPC in Arabidopsis. We identified CYCLIC NUCLEOTIDE-GATED ION CHANNEL 4 (CNGC4) as a significant locus associated with the diversity of VPC. Mutations in CNGC4 delayed VPC, accompanied by an increased expression level of miR156 and a corresponding decrease in SQUAMOSA PROMOTER BINDING-LIKE (SPL) gene expression. Furthermore, mutations in CNGC2 and CATION EXCHANGER 1/3 (CAX1/3) also led to a delay in VPC. Polymorphisms in the CNGC4 promoter contribute to the natural variation in CNGC4 expression and the diversity of VPC. Specifically, the early CNGC4 variant promotes VPC and enhances plant adaptation to local environments. In summary, our findings offer genetic insights into the natural variation in VPC in Arabidopsis, and reveal a previously unidentified role of calcium signaling in the regulation of VPC.

Optimisation of a hybrid latent heat storage unit based on phase change time and exergy efficiency

Optimisation of a hybrid latent heat storage unit based on phase change time and exergy efficiency

Efficient Power Conversion Using a PV-PCM-TE System Based on a Long Time Delay Phase Change With Concentrating Heat

Based on the characteristics of phase change concentrated heat, this paper proposes a photovoltaic/phase change/thermoelectric (PV-PCM-TE) self-supply system with sidewall integrated TE. In the system, an intelligent control circuit for phase change time is designed to intelligently switch the TE working mode using real-time temperature tracking. Therefore, the phase change time of the phase change material (PCM) is delayed with enhanced heat absorption and storage capacity, resulting in greater suppression of the PV temperature rise. Based on the constant temperature difference during the delayed phase change, more electrical power output can be obtained with integrated multistage thermoelectric generators (TEG) in the sidewall of the PCM container. With the supplementary TEG energy injected into the PV battery, a complete self-powered design is constructed, leading to improved system energy efficiency. Experimental results show that compared with the PV-PCM-TEG system, the PCM phase change time of the proposed system is extended by 15 min, where the peak PV temperature after suppression is only 68.5 °C, which is 8 °C lower than that of the conventional PV-TEG-PCM system. The conversion efficiency of the entire system reached 30.26%, an improvement of 43.15%. The proposed self-powered PV-PCM-TE power conversion system with a long-time delay and high efficiency can operate during both day and night, providing a green scheme for intelligent low-power electrical systems.

Melting and solidification analysis of paraffin phase change material in a circular space, molecular dynamics simulation

The increasing use of renewable energy sources has led to more studies in the field of eliminating the weaknesses of these sources. The use of energy storage systems is one of these things that increase the sustainability of renewable resources and reduce the share of fossil fuel resources in daily energy consumption. One of the most important things in heat storage systems is the use of suitable phase change materials (PCM). In this research, the behavior of paraffin, as a well-known PCM, is investigated on a molecular scale. For this purpose, an annular space has been selected as a nanochannel and the behavior of this material inside it has been investigated in different states. First, the thermal performance of this PCM is investigated. Then, the effect of its temperature on index parameters such as viscosity, heat flux, thermal conductivity, charge time, discharge time, and phase change time are evaluated. The research results show that increasing initial temperature (from 300 K to 350 K) improves the performance of PCM (the duration of charging and discharging are increased from 1.78 and 2.15 ns to 1.41 and 2.24 ns, respectively.). In addition, increasing the speed of the material also reduces the charging and discharging time to 1.65 and 2.09 ns, respectively. Increasing the diameter ratios also changes the indicator times to 2.18 and 2.03 ns, respectively.

Identification of the Teopod1, Teopod2, and Early Phase Change genes in maize.

Teopod1 (Tp1), Teopod2 (Tp2), and Early phase change (Epc) have profound effects on the timing of vegetative phase change in maize. Gain-of-function mutations in Tp1 and Tp2 delay all known phase-specific vegetative traits, whereas loss-of-function mutations in Epc accelerate vegetative phase change and cause shoot abortion in some genetic backgrounds. Here, we show that Tp1 and Tp2 likely represent cis-acting mutations that cause the overexpression of Zma-miR156j and Zma-miR156h, respectively. Epc is the maize ortholog of HASTY, an Arabidopsis gene that stabilizes miRNAs and promotes their intercellular movement. Consistent with its pleiotropic phenotype and epistatic interaction with Tp1 and Tp2, epc reduces the levels of miR156 and several other miRNAs.

Novel four-port RF phase change switches based on GeTe thin film

An indirect-heated phase-change switch (PCS) using germanium telluride (GeTe) has been fabricated using thermal actuation driven by thin film heater on the model. Switches require a low ON-state resistance and a high OFF-state resistance with OFF/ON resistance ratio of 105. The finite element analysis simulation is applied to simulate the temperature of individual node GeTe with different microwave heating pulses. Finally, in order to reduce the phase-change time and increase the switching speed of indirectly heated switching structures, a new four-port indirectly heated phase change switching structure is proposed. In this paper, the heat dissipation of the switch is increased by etching deep grooves on the back of the switch. This structure obviously reduces the phase change time compared to conventional indirectly heated phase change switches the time between ON-state and OFF-state is reduced by more than 19% and the total process is reduced by more than 47%. The GeTe PCSs with etched grooves not only significantly increases the switching speed, but also reduces the risk of recrystallization of the phase change material.

The application of magnesium nitrate hexahydrate/hybrid carbon material phase change composites in solar thermal storage

AbstractBackgroundIn this study, a series of phase change composites were developed. Phase change materials (PCMs) are substances with a high heat of fusion, thereby possessing great potential for solar thermal storage. However, their disadvantages, such as low thermal conductivity, phase separation, and supercooling, limit their further applications.ObjectiveIn this study, magnesium nitrate hexahydrate (MNH) was used as the phase change material, and different proportions of photothermal materials were added to improve the thermally conductive property and solar thermal storage efficiency of MNH.MethodsThis study used magnesium nitrate hexahydrate (MNH) as the substrate. In addition, different proportions of photothermal materials (carbon nanotubes, nano‐graphite, graphene, and partially reduced graphene oxide) were added to promote the efficiency of thermal energy storage. Additionally, a fixed ratio of carboxy methyl cellulose (CMC) was added. The phase change temperature and enthalpy change of the phase change material samples were explored and analyzed by differential scanning calorimeter (DSC). In addition, the thermophysical properties, photothermal storage performance, and thermal reliability analysis of the samples were investigated.ResultsThe results showed that the PCM composites prepared with nano‐graphite have higher latent heat and longer time of phase change. However, the composites prepared with carbon nanotubes (CNTs) have lower latent heat and a shorter time of phase change. Therefore, the partially reduced graphite oxide (PRGO)‐containing composites can retain the latent heat storage capacity of nano‐graphite and decrease the time of phase change, thereby improving the photothermal storage efficiency. The results reveal that the solar thermal storage efficiency of the composite with both CNTs and PRGO could reach up to 0.716.ConclusionsMCGOT‐1 and MCGOT‐2 have high latent heat values, and the phase transition time is short. Therefore, the thermal energy storage efficiency can be as high as 0.716. In addition, compared with related literature, the photothermal storage efficiency of MCGOT‐2 increased by about 2 times. Therefore, the environmentally friendly composites developed in this study have a high potential to be used in solar energy storage and energy‐saving systems.

Effect of fin configuration and orientation of latent heat storage system on the melting and solidification performance

Phase change materials (PCMs) are used to store thermal energy. They possess high specific energy at nearly constant temperatures. The usage of the PCMs is limited due to their very low thermal conductivity, which results in poor heat transfer. To overcome this problem usage of fins is a potential technique. In the current analysis, the surface area of the heat transfer fluid (HTF) tube is increased by radial (R-type), spiral (S-type), and longitudinal (L-type) fins. A 3D numerical analysis of melting and solidification is carried out on R-type, S-type, and L-type shell and tube (S&T) PCM heat exchanger (HX) by considering the inclination effects. Lauric acid is used as PCM. Phase change time, energy ratio, and exergy efficiency are considered to analyze the performance of HXs. MOORA analysis is carried out to select the best HX. It is observed that R-type HX at the vertical position has shown better performance among the selected HXs. Among the considered geometries, the maximum average exergy efficiency is obtained for 45° inclination with R-type HX and minimum for horizontally positioned L-type HX during both melting and solidification. The charging time of the vertically positioned HX, when compared to 45o oriented HX with R type, S type, and L type HX is observed to decrease by 47.5%, 45.7%, and 23%, respectively.

Divergent selection for timing of vegetative phase change

AbstractVegetative phase change is a key trait in plant development and marks the transition from juvenile to adult growth phases. In maize (Zea mays L.), juvenile plants and plants with a late phase change can be identified by the increased production of tillers, aerial roots, and distinctive epicuticular wax. Resistance to agronomically significant pathogens can also differ between juvenile and adult plants. Using last leaf with juvenile wax as the target of selection, the maize population Minnesota 11 underwent 16 cycles of divergent selection. The objectives of this research were to identify emergent trends for each trait and to determine the magnitude and direction of phenotypic changes over long‐term selection compared to the source population. Phenotypic data on plant architecture traits, ear traits, and common rust resistance were collected in 2020 and 2021 by concurrently growing plants from selection cycles representing both directions of selection. Last leaf with juvenile wax, the direct target of selection increased to leaf 17.8 in the late phase change population and decreased to leaf 5 in the early phase change population from leaf 9 in the source population. Late vegetative phase change was positively correlated with increased common rust infection and plant height, and negatively correlated with ear size traits. This study shows that the observed phenotypic changes follow patterns of genetic variation consistent with divergent selection, but with possible effects of inbreeding.

ZmSPL13 and ZmSPL29 act together to promote vegetative and reproductive transition in maize.

Flowering time is a key agronomic trait determining environmental adaptation and yield potential of crops. The regulatory mechanisms of flowering in maize still remain rudimentary. In this study, we combine expressional, genetic, and molecular studies to identify two homologous SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factors ZmSPL13 and ZmSPL29 as positive regulators of juvenile-to-adult vegetative transition and floral transition in maize. We show that both ZmSPL13 and ZmSPL29 are preferentially expressed in leaf phloem, vegetative and reproductive meristem. We show that vegetative phase change and flowering time are moderately delayed in the Zmspl13 and Zmspl29 single knockout mutants and more significantly delayed in the Zmspl13/29 double mutants. Consistently, the ZmSPL29 overexpression plants display precocious vegetative phase transition and floral transition, thus early flowering. We demonstrate that ZmSPL13 and ZmSPL29 directly upregulate the expression of ZmMIR172C and ZCN8 in the leaf, and of ZMM3 and ZMM4 in the shoot apical meristem, to induce juvenile-to-adult vegetative transition and floral transition. These findings establish a consecutive signaling cascade of the maize aging pathway by linking the miR156-SPL and the miR172-Gl15 regulatory modules and provide new targets for genetic improvement of flowering time in maize cultivars.

Numerical investigation of microcapsules of phase change materials with au nanoparticles: The effect of radius and the atomic ratio of Au nanoparticles on the thermal storage efficiency of the simulated structure

The addition of nanoparticles (NPs) can change the thermophysical properties of materials. Hence, adding NPs to phase change materials (PCMs) can accelerate phase transition processes. Moreover, the NPs concentration changes can change the structures' dynamic and thermal properties. Thus, it is crucial to survey how the volume fraction (size and atomic ratio) of NPs affects the PCM's thermal behavior. In the current work, molecular dynamics (MD) simulation was used to examine the thermal behavior of PCM microcapsules containing gold NPs. These microcapsules were taken into consideration together with aminoacetaldehyde (C2H5NO) and bromohexadecane (BrC16) as PCM, and the effect of gold nanoparticle radius and atomic ratio on simulated structure's thermal behavior was investigated. The findings demonstrate that charging and discharging periods were shortened by increasing the radius and atomic ratio of gold NPs in the atomic microcapsule structure. The heat flux (HF), and thermal conductivity (TC), on the other hand, are increased by increasing the radius of NPs from 3 to 6 nm, reaching 299.43 W/m2 and 1.42 W/mK, respectively. Moreover, by increasing the atomic ratio of NPs from 0.01 to 0.05, HF and TC values increased to 300.08 W/m2 and 1.45 W/mK, respectively. Furthermore, increasing the radius and atomic ratio of gold NPs in the microcapsule structure increased viscosity and phase change time. The methods offered in this study might be used as a viable mechanism in application domains to improve the thermal efficiency of this structure.

Investigating the effect of different base fluids in atomic and thermal behaviors of different nano-refrigerants using molecular dynamics simulation

Nano-refrigerants, which are the suspensions of nano-sized particles in a base fluid, were applied in many devices and systems to enhance thermal conductivity and improve heat transfer performance. This work studied the thermal and atomic behavior of two kinds of nano-refrigerants located inside an aluminum nanochannel for 5 ns. The molecular dynamics (simulation method simulated Nano-refrigerants, including R-134a and R-407A as base fluids and copper as nanoparticles. The density, velocity, and temperature profiles were studied to investigate the atomic behavior of the simulated sample. The thermal behavior of structures was studied by examining the phase transition rate, phase change time, thermal conductivity, and heat flux. The results show that R-407A base fluid showed better thermal behavior. The results show that in Cu/R-407A, the phase-changed particle reached 31% in 5 ns, and phase change time was estimated to be 3.91 ns. In contrast, in Cu/R-134a, the samples' phase changed particle and phase change time reached 26% and 4.06 ns. Moreover, the study of heat flux shows that nano-refrigerant with R-407A base fluid had more HF (1028 W/m2) than R-134a (654 W/m2). The results show that the thermal conductivity of R-407A and R-134a nano-refrigerant converged to 0.0975 and 0.0098 W/mK, respectively.