Phase Change Research Articles

Thermal performance analysis of a Trombe wall with the multi-row channel PCM wallboard

A novel Trombe wall with the multi-row channel phase change material wallboard (MCPCM-TW) is proposed to enhance the solar energy utilization. The structure contains the glazing, the heat-absorbing layer and several built-in channels, either aligned vertically or horizontally, located in the phase change thermal storage layer. The thermal performance of the Trombe walls, which consist of the multi-row vertical channel phase change material wallboard (V-MCPCM-TW) and the multi-row horizontal channel phase change material wallboard (H-MCPCM-TW), were investigated numerically in the present research. Meanwhile, the Trombe wall incorporating phase change thermal storage layer without built-in channels also studied in the paper. The results indicate that, the multi-row channel phase change material wallboard effectively enhances the heat storage and release of the phase change thermal storage layer, thereby extending the duration of ventilation and increasing the cumulative heat supply of the rooms equipped with the novel Trombe wall. Specifically, the V-MCPCM-TW has a higher maximum liquid volume fraction during the heat storage phase. Compared with the Trombe wall incorporating phase change thermal storage layer without built-in channels, the V-MCPCM-TW has a 16% increase in maximum liquid volume fraction and a 15.5% increase in cumulative heat supply within a certain period.

Phase Change Thermal Interface Materials with Interface Adaptability and Self-Healing Properties

Thermal stress resulting from excessive temperatures is a major cause of electronic device failure. In this work, with easy installation and good interface adaptability, Phase Change Thermal Interface Materials (PCTIMs) which possess high thermal conductivity were prepared. By incorporating phase change material stearic acid (SA) into the thermal interface material, the instantaneous heat absorption during the solid-liquid phase transition of SA effectively alleviates the problem of instantaneous high heat flux impacting electronic devices. Additionally, the solid-liquid transition reduces the modulus of TIMs, thereby minimizing the contact thermal resistance between the heat source and the heat sink during mechanical installation. To further enhance performance, the thermal interface material utilizes a dynamically cross-linked polyolefin elastomer (POE) with borate bonds, which effectively restricts the flow of SA even at its phase change point due to the three-dimensional cross-linked framework. By constructing a thermal conductive network using carbon fibers and aluminum nitride of different dimensions, the thermal conductivity of the thermal interface material reached 1.82 W∙m−1K−1 with a filler content of only 30 vol% . At 70°C, with a force of 50 N applied to a sample area of 400 mm², the contact thermal resistance was only 2.39×10−4K∙m2W−1. Furthermore, the PCTIMs exhibits excellent self-healing ability under thermal conditions, assuring the permanent encapsulation of small electronic devices.

Membrane-cryogenic hybrid CO2 capture—A review

The membrane-cryogenic hybrid process is a promising CO2 capture process, which combines the advantages of membrane and cryogenic, such as high efficiency (up to 98 % CO2 captured) and low energy consumption (specific energy consumption around 1.7 MJ/kg CO2 avoided). Through pretreatment by membranes, CO2 concentration can be increased, which makes it possible to separate CO2 via phase change in the cryogenic unit. This work reviews the current status of the development of membrane-cryogenic hybrid processes. The synergy between membrane and cryogenic separation is summarized to identify the bottleneck of such processes and provide insights for process improvement. It was found that cold temperatures would be beneficial to reduce CO2 activation energy and then improve CO2 selectivity of membranes. To further improve the CO2 separation performance, the potential intensification methods of the membrane-cryogenic hybrid process including cold-membrane synthesis, process optimization via heat integration are discussed and envisioned.

Spray pyrolysis derived V2O5 thin films as an alternative electrochromic layer for electrochromic devices

In this study, vanadium oxide films were produced in the vanadium pentoxide (V2O5) films phase as an alternative electrochromic layer for electrochromic devices by ultrasonic spray pyrolysis technique at 300 °C. The V2O5 films were subjected to heat treatment at different temperatures (400-450-500 °C) and the ellipsometric, structural, morphological, optical and electrical properties of the films were investigated. The optical parameters of the V2O5 films were calculated by different theoretical methods and compared with the ellipsometric results. The average thickness and refractive index values are 172 nm and 2.29, respectively. The V2O5 films showed high optical absorbance in the visible region and band gap energy values ranged from 2.10 to 2.44 eV. The resistivity and roughness of the films decreased. The average roughness was determined to be 45 nm on average. These results suggest that V2O5 phase films, whose physical properties are improved by annealing without phase change, can be considered as promising electrochromic layers for electrochromic devices applications.

Boosting electricity generation associated with Saudi Arabi buildings using PCM and PV cells on walls and roof leading to a sustainable building

In Saudi Arabia, where the majority of regions receive a minimum incident shortwave solar energy exceeding 4 kWh/(m2.year), there is a high potential for electricity generation and simultaneously, a challenge in building cooling. In this study, by adding photovoltaic (PV) on the roof and wall, as well as using phase change material (PCM) inside the walls, electricity production and energy consumption of Saudi residential buildings were investigated. Taking into account the effects of radiation on vertical and horizontal envelopes as well as phase change in PCM, the energy equation was solved using DesignBuilder to specify hourly energy consumption and electricity generation. When installing PV cells at the optimal tilt, incoming radiation to the cells increases. However, creating shadows on subsequent rows of cells diminishes the effective PV surface area. Surprisingly, calculations revealed that if PV cells are installed at zero angle, owing to installing more PV cells, up to 31% extra electricity is produced than when installed at the optimal tilt. As a side effect, the cooling load decreases by 5.1% due to reduced radiation intensity on the roof. The orientation of the walls significantly impacts both phase change material (PCM) and PV-associated electricity generation. Placing PCM on the east wall optimizes its performance, while walls containing PV panels perform best when facing south. To further enhance cooling and reduce electricity demand, phase change material was incorporated into both the roof and wall, resulting in a 2% reduction in overall electricity demand. Notably, in eight major populated areas across Saudi Arabia, under the constraint of the constant PV cell area, installing PV cells on the roof proves three times more advantageous than placing them on the walls.

Controlling the heating wall temperature during melting via electric field

Thermal energy storage technology utilizing phase change materials (PCMs) is extensively applied in thermal management and energy storage. The inclination angle (θ) plays a critical factor in the phase change melting processes in practical implementations. However, the precise experimental velocity fields of liquid PCM and the impact of active regulation technology on the heating wall temperature at various angles remain unclear. Herein, a transparent melting experiment platform was established to measure velocity, and adjust θ and manipulate input electric voltage. Results from Particle Image Velocimetry indicated that the installation angle significantly impacts natural convection in the convection-dominated melting regime. The liquid fraction decreased from 73.5 % (when θ = 90°) to 54.4 % (when θ = 150°) due to reduced thermal energy absorption, as input energy was stored as sensible heat on the copper wall. The electrohydrodynamic (EHD) effect mitigated thermal resistance between the heater and the melt front, increasing melt thickness. EHD flow exhibited limited ability to regulate heating wall temperature under strong natural convection, with a 6.5 % decrease observed under +20 kV conditions. As natural convection rates decreased, the decrease rate of heating wall temperature increased to 10.7 %. The EHD effect demonstrated a heightened capability in enhancing heat transfer melting with increasing θ, leading to an increase in temperature difference from 3.3 °C to 5.3 °C under the +15 kV input voltage. These findings suggest that the electric field is an efficacious method for controlling the heating wall temperature at different inclination angles during the melting process.

Metallic wood-based phase change material with superior anisotropic thermal conductivity and energy storage capacity

In this study, metallic wood-based phase change material (MWM) with high performance anisotropic thermal conductivity and energy storage capacity was developed by impregnating wood with myristic acid, and subsequent introducing low melting point alloy (LMA) into the wood through a facile alternating high and low temperature heat treatment. The heat-driven LMA was rapidly squeezed into the cell lumens of the wood so as to effectively inhibit the leakage of the internal myristic acid during melting. Benefited with the well-aligned and hierarchical porous structure, the filled LMA formed a continuous heat transfer network along the highly oriented transport tissue of wood, which could greatly reduce the interfacial thermal resistance and promote heat transfer. Compared with untreated wood, the thermal conductivity of MWM in longitudinal and radial directions were improved by more than 67 % and 75 %, respectively. In addition, it exhibited superior energy storage capability, with the latent heat of 90.23 J/g and 86.42 J/g during melting and solidification. The thermal stability and anti-leakage performance were satisfied. The phase change temperatures, enthalpies and chemical structure of MWM remained unchanged after 100 thermal cycles, demonstrating outstanding cycling reliability. With excellent energy storage performance and favourable thermal conductivity, the prepared MWM shows a promising application in energy saving buildings and solid wood floors.

Performance analysis of a low concentrated photovoltaic system thermal management by hybrid phase change materials

With the widespread use of cells, the significance of thermal management is increasingly emphasized in academic research. The issue of decreasing photoelectric conversion efficiency due to overheated cells in photovoltaics has garnered attention. Thermal management technology utilizing phase change materials (PCM) has the potential to enhance the overall efficiency of solar energy utilization. However, the PCM has poor thermal conductivity, which makes attaching it directly to the back of the solar cell ineffective. The heat trapped in PCM is also difficult to discharge. To solve this problem, a new low-power concentrating photovoltaic system with integrated PCM and comprehensive utilization of photoelectricity and photothermal is proposed (LCPV-PCM). It is verified with the reference. The effects of Porous metal materials (PMMs), PCMs filling sequence, and collector tube diameter on the cooling effect are studied. The results indicate a clear temperature equalization effect of PMMs, leading to a 4.08 % increase in electrical efficiency when filling PCM with lower phase change temperature. The temperature of the collector tube with a diameter of 2.5 mm can be reduced by 21.9 K, increasing electrical efficiency by 9 %. The results are of significance in exploring the application of PCM in cell thermal management.

Enhancement of battery thermal management effect by a novel MOF based composite phase change material

The introduction of phase change materials (PCMs) into battery thermal management systems (BTMS) can effectively enhance the cooling performance, safety and practical thermal management applications of lithium-ion batteries (LIBs). However, further study is needed to address the low heat conductivity and rapid phase change leakage of PCMs. This study proposed a metal–organic framework based shape-stabilized composite PCM (MOF/expanded graphite (EG) /multi-walled carbon nanotube (MWCNT) /paraffin wax (PW)) to construe battery cooling system, and its effect of battery thermal management is experimentally tested under various conditions. The results show the CPCM reveals a superior thermal management effect under varying ambient temperatures and discharge multipliers and outperforms natural convection. Even in the harsh environment of 40 °C and 3 C, the maximum temperature (Tmax) and Tmax difference (ΔTmax) of the CPCM-cooled module are 61.38 and 2.67 °C, which are 22 and 9 °C below the natural air-cooled module. Remarkably, the ΔTmax of the CPCM-cooled battery module in discharge decreases with the temperature rise at the discharge rate of 3 C, which is the exact opposite to the case of the air-cooled module. Moreover, the ΔTmax of CPCM-cooled module is 1.69, 1.84, 2.67 °C, all below the safe 5 °C at high temperatures (40 °C) as the discharge rate increases. The designed MOF-CPCM cooling system can effectively improve the temperature uniformity and thermal safety of the battery in harsh environments. Therefore, this novel MOF-based CPCM shows great promise in BTM.

Wood-based phase change energy storage composite material with reversible thermochromic properties

With the continuous increase in global energy demand and environmental challenges, the efficient utilization and storage of energy have become critical areas of scientific research. This study presents the preparation and performance assessment of a wood-based phase change composite (TPW) with reversible thermochromic properties. Thermogravimetric analysis (TG) confirmed thermal stability across 26 °C to 270 °C, while differential scanning calorimetry (DSC) demonstrated that TPW has good thermal cycling performance, and suitable phase change temperature at about 34 °C. Thermal insulation tests showed that TPW can reduce heat exchange between inside and outside environment, maintaining the internal temperature for longer time. Below the transition temperature, the material displays a bluish-purple color, transitioning to light yellow upon heating, with a notable color difference (ΔE⁎) increase from 3.46 to 67.89. Since the phase transition temperature close to human body temperature, enhances TPW’s compatibility for applications in home decor, temperature indicators, and anti-counterfeit labeling. This research contributes novel insights and foundational data for advancing wood-based functional materials in sustainable applications.

Sustainable polyurethane biocomposite foams by improved microstructure, acoustic characteristics, thermoregulation performance and reduced CO2 emission through phase change material integration

In this research, phase change material (PCM) comprised of energy storage biocomposite materials were improved with raw materials obtained from renewable resources. Modified raw material was synthesized by epoxy castor oil (ECO). After mixing the obtained modified castor oil (MCO) and polyether polyol, PCM of capric acid (CA) was supplemented. To initiate the chemical reaction, a certain amount of methylene diphenyl diisocyanate (MDI) was added to the mixture to provide cross-linking. The physical and chemical properties of the resulting biocomposite foams (BCF) were characterized. According to the results obtained, mixing MCO into polyether raw material increased the number of closed pores in BCF resulting in more CA stored in BCF cells produced. The use of MCO in BCF materials increased the CA integration ratio to 68 wt%. The melting enthalpy value of the novel BCF-PCM composites has been determined as 121.43 J/g. In a warm environment, the PCM additive creates a temperature difference exceeding 6 °C, while in a cold environment, it provides a cooling effect close to 6 °C. A more than 50 % improvement in thermal conductivity was achieved with 68 wt% PCM addition compared to pure BCF. The addition of PCM caused a reduction in tensile stress and strain values to an acceptable level. BCFs with PCM additives exhibit a sound absorption coefficient of 0.9 in narrow frequency ranges, whereas, in broad frequency ranges, this value was more than 0.7. In cold weather conditions, employing BCF-PCM material instead of traditional EPS material with a thickness of 0.1 m has led to at least a 30 % drop in CO2 emissions, no matter the type of fuel used for heating. When opting for BCF-PCM materials, the necessary heat demand was approximately 33 % less compared to using the same thickness of EPS in cold climates.

Surfactant Effects in Functionalized Multiwall Carbon Nanotube-Filled Phase Change Materials

Energy storage using phase change materials (PCM) is an efficient way to harness thermal energy from solar energy due to its higher storage density, particularly for medium-temperature applications. However, the PCMs have lower thermal conductivity; owing to this, the thermal performance and heat transfer rate are inadequate. To address this challenge, the current work explores the integration of carbon-based nanoparticles into the PCM to enhance thermal conductivity and overall performance. In the present study, a novel functionalized multi-walled carbon nanotube (FMWCNT) dispersed in organic PCM in different weight fractions (0.1, 0.3, 0.5, 0.7 and 1.0%) with and without surfactant is investigated. A two-step technique was employed to prepare nano enhanced phase change material (NePCM), with subsequent assessment of its thermophysical properties. Findings reveal a remarkable enhancement in thermal conductivity, with a staggering 150.7% at 1.0 wt.% FMWCNT without surfactant and a substantial 110.2% improvement in the presence of surfactant. Furthermore, the Ultraviolet-visible spectrum (UV-Vis) demonstrates an 84.56% reduction in transmittance compared to pure organic PCM. Furthermore, the prepared NePCM are thermally stable up to 405°C and no chemical reaction takes place. Importantly, the best optimal nanocomposites chemical and thermal properties were evaluated for 500 heating and cooling cycles to ensure reliability. Remarkably, the inclusion of surfactant on FMWCNT enhanced PCM has minimal impact on thermophysical properties.

Investigating the thermal performance of a pipe-encapsulated movable PCM wall and its impact on reducing indoor heat gain during summer

The utilization of phase change materials (PCM) in building envelopes is considered to be an effective technology for reducing energy consumption during building operations. In this study, a novel approach is presented for integrating PCM into walls by encapsulating it using pipes, allowing for its mobility through the use of compressed air. Four experimentally validated thermal models, pipe-encapsulated movable PCM (PEM-PCM) wall (Model 1), wall with PCM fixed to the exterior (Model 2), wall with PCM fixed to the interior (Model 3), and wall without PCM (Model 4), were proposed to compare their energy efficiency in summer. Different upper threshold limits (Ttr,up) and lower threshold limits (Ttr,low) were employed to explore the impact of various threshold combinations control strategies on the thermal performance of the wall. The results show that the most effective operating scheme is Ttr,up of 27 °C and Ttr,low of 25 °C. In terms of long-term operation, cumulative summer indoor heat gain of Model 1 is 10.65 %, 10.85 % and 11.4% lower than that of Model 2,3 and 4. Notably, September demonstrates the greatest potential for energy savings, with Model 1 reducing the monthly cumulative indoor heat gain by 54.12% compared to Model 4.

Analysis and prediction of battery temperature in thermal management system coupled SiC foam-composite phase change material and air

Lithium-ion batteries crucially rely on an effective battery thermal management system (BTMS) to sustain their temperatures within an optimal range, thereby maximizing operational efficiency. Incorporating bio-based composite phase change material (CPCM) into BTMS enhances efficiency and sustainability. This study commences by blending lauric acid and myristic acid in a 7: 3 mass ratio to synthesize a bio-based CPCM, following which the thermophysical properties of this CPCM are tested. Subsequently, the CPCM is integrated into a SiC foam and coupled with air to develop a novel BTMS. Then the effects of air velocity and initial temperature on the temperature of the battery pack are analyzed. Finally, the RIME-Convolutional Neural Network (CNN)- Self-Attention (SA)- Gated Recurrent Unit (GRU) model is established to predict the temperature of the battery in this BTMS. The results indicate that the latent heat of the CPCM is 97.98 J/g, melting at 35 °C upon heating. The incorporation of SiC foam-CPCM effectively reduces battery temperatures. When the air velocity is set at 3 m/s, the battery temperature remains below 40 °C during a discharge rate of 2C. Notably, the CPCM melts at higher initial temperatures, effectively mitigating the temperature rise in the battery pack. The RIME-CNN-SA-GRU model exhibits remarkable accuracy, with a maximum prediction error of 0.56 °C and a RMSE of 0.23, precisely capturing the trend of a sharp temperature rise at the end of discharge. This study presents an efficient solution for lithium-ion battery thermal management and temperature prediction.

Energy and exergy analysis and performance optimization of buildings integrated with transpired solar collectors and phase change materials

Transpired solar collectors (TSCs) are one of the cost-effective air heating technologies that can be easily installed on building facades to provide heated fresh air to condition indoor space. The economics of TSCs can be further enhanced by integrating with phase change materials (PCMs). This study presents the performance investigation and optimization of a building-integrated TSC and PCM system (TSC-PCM). The interactions between PCM thermal properties, their locations in the building envelope, and TSC design parameters were investigated. Based on the modeling of the TSC-PCM by using energy balance and enhanced enthalpy method, a series of orthogonal tests, which varied PCM type, thickness, and location within building envelopes, and TSC suction flow rate were conducted. Multivariate testing, through the Taguchi method, was then applied to identify the optimal design combination. The results showed that the suction flow rate of the TSC-PCM on the external wall showed the highest influence on enhancing indoor thermal performance (up to 77.6%), followed by PCM location on the external wall (up to 9.2%). The optimized TSC-PCM system improved the thermal comfort increase index (TCI) to 3.7 and achieved a maximum thermal efficiency of 401.8%, with an exergy improvement of 26.9% in comparison with the use of the TSC-only. The optimized TSC-PCM system increased the average indoor room temperature to 18.8 oC, which was 6.8% and 18.2% higher than the use of the TSC-only and a baseline without using PCM and TSC, respectively.

Investigation of enhanced PCM heat sink design under extreme thermal conditions for high-heat-generating electronic devices

In this study, a novel enhanced phase change material (PCM) heat sink design is proposed to improve energy efficiency and maintain quiet operation under extreme thermal conditions for high-heat-generating electronic devices. To overcome the thermal conductivity and heat transfer limitations of the PCM heat sinks, fins, metal foams, and nanoparticles were integrated. A simulation model for the PCM heat sink was developed based on experiments. The thermal performances of different PCM heat sinks were comprehensively evaluated and compared through an in-depth analysis of their thermal behaviors. Consequently, at the heat flux of 20 kW·m−2, a proposed nano-enhanced PCM heat sink with fins and metal foams reduces the surface temperature of high-heat-generating electronic devices by 40.0 K during pre-heating process and maintains a minimum temperature of 54.47°C, decreasing the temperature by 41.4 K during melting process compared to the PCM heat sink without thermal conductivity enhancers. Furthermore, the proposed PCM heat sink exhibited the longest critical duration, approximately 26 times longer than that of a PCM heat sink without thermal conductivity enhancers. Additionally, within the critical temperature range, employing a PCM with a suitable melting temperature and metal foam parameters is advantageous for the thermal management of high-heat-generating electronic devices.

Investigation of the influence of the air layer on the phase change material melting process inside a hemicylindrical enclosure: A numerical approach

The rapid growth in energy consumption and the associated difficulties have made thermal energy storage processes using phase change materials (PCMs) a prominent subject of study and development in the last century. The exceptional thermo-dynamic characteristics of this material enable it to accumulate substantial quantities of heat within very limited spaces. The present work involved a numerical investigation of the impact of the air layer on the melting time of paraffin wax RT42 (PCM) within an enclosure with a hemicylinder shape. The enthalpy-porosity relationship is analyzed numerically using ANSYS/FLUENT 16 software. The study included three distinct scenarios that examined the thermal and mass characteristics of paraffin wax within a hemicylindrical enclosure, with the curving wall of the enclosure being thermally insulated. The initial scenario lacked any air layer on the heated vertical wall, whereas the subsequent scenario had an air layer measuring 1 mm thick on the same wall. The third scenario contained an air layer measuring 2 mm within the same wall. The findings indicated that including a 1 mm thick air layer would result in a 125% extended complete melting time of paraffin wax. Similarly, including a 2 mm thick air layer would lead to a 225% rise in the complete melting time of paraffin wax. The presented outcome demonstrates the impact of ambient air on thermal storage units during the charging procedure.

The Impact of Tube Arrangement in Latent Heat Thermal Energy Storage on the Melting Rate of Phase Change Material

The Impact of Tube Arrangement in Latent Heat Thermal Energy Storage on the Melting Rate of Phase Change Material

Investigation of the Arrangement of Aluminum Fins on the Thermal Behavior of Lauric Acid as a Phase Change Material in a Two-pipe Heat Exchanger by CFD Simulation

BackgroundPhase change material (PCM) thermal storage systems store more thermal energy per unit volume than sensible heat storage systems. PCMs offer a potential solution to reduce energy consumption in various thermal engineering applications. This study aimed to examine how fin arrangement affected the thermal efficiency and melting time of PCMs. MethodsA two-dimensional numerical analysis of the melting process of lauric acid in a heat exchanger featuring two pipelines and fins was conducted using CFD simulation. In most previous investigations, the heat transfer fluid was a single-phase liquid. An enthalpy-porosity technique was used to model the solid and liquid phases of PCM. The governing equations were solved using the commercial software ANSYS Fluent 2021, and the pressure and velocity equations were coupled using the SIMPLE algorithm. Significant FindingsThe best model among the 13 tested was Model 5, which featured 6 fins and a consistent angle of 60 degrees. For Model 5, the melting time was 1818.3 seconds. Due to sensible heating, the fin's temperature (Temp) rose gradually from 300 K to 318 K. Temp then gradually increased as the PCM melted in the phase transition zone between 316.5 K and 321.2 K. Once the phase transition was complete, the PCM's Temp steadily rose from 324 K to 340 K. In Model 5, the inner wall Temp and the maximum Temp of the PCM were closest, at 327.34 K and 333.55 K, respectively. The thermal shock between the PCM and the ambient Temp caused a peak heat flux at the beginning of the PCM loading process.

Transient heat transfer characteristics of cooling fluid loop with latent heat storage unit

In the realm of electronic cooling, it is of significance to efficiently manage the transient heat load. In this context, an innovative strategy is introduced by integrating a cooling fluid loop with a latent heat storage (LHS) unit. The effects of strategic positioning of LHS units on the dynamic temperature under varying conditions, such as heat load intensities, filling rates of phase change materials (PCMs), heating durations, and coolant flow rates, are examined and analyzed. The results indicate that the introduction of LHS unit can significantly alleviate the temperature fluctuation of microchannel heat sink (MHS) under instantaneous heat load. When the LHS unit is located upstream and downstream of the cooler, the maximum temperature of the MHS surface is reduced by 10 °C and 42 °C, respectively. The heat load determines the dynamic temperature characteristics of LHS units, and PCM performs best at precise melting states. When the heat storage of LHS unit matches the heat generated by the heating surface, further increasing the PCM filling rate has no positive effect, and extending the heating time is not conducive to cooling MHS. Additionally, increasing flow rate of working fluid has a limit effect on thermal enhancement of fluid loop with LHS.