Phase Change Emulsion Research Articles

Development of highly stable low supercooling paraffin nano phase change emulsions for thermal management systems

Current research on thermal management systems focuses on aspects such as structural optimization of liquid cooling channels, with less research on the development of cooling media. Phase change emulsions, as latent heat functional fluids with significant potential, enhance heat transfer efficiency and temperature control in thermal management systems. However, the issues of significant supercooling and poor stability have hindered the further development of phase change emulsions. In this study, a highly stable, low-supercooling paraffin nano emulsion was successfully prepared by ultrasonication using SDBS, Span80, and Tween80 as composite surfactants and titanium dioxide nanoparticles as nucleating agents. It was found that the emulsion maintained excellent stability for 180 days of static stability and 200 thermal cycles without significant stratification. Subsequently, thermophysical property tests showed that the emulsion had a latent heat of phase transition of 45.48 J·g−1, and maintained good electrical insulating properties. The successful dispersion of 0.9 wt% titanium dioxide nanoparticles in the presence of SDBS resulted in a 77 % reduction in supercooling and a 20.5 % increase in thermal conductivity. Meanwhile, no instability was observed in the emulsion over 90 days of static stability test and 200 thermal cycles. The titanium dioxide-modified paraffin nano emulsions are characterized by high energy storage density, low supercooling, excellent stability, high thermal conductivity, and good electrical insulating properties, which give them significant potential as a cooling medium in thermal management systems.

Evaluation of Energy Density in Hexadecane Phase Change Emulsions in Comparison to Water

The development of energy-dense, thermomechanically stable, and low-viscous phase change emulsions (PCMEs) is proposed as an alternative thermal energy storage solution for building air conditioning. A set of oil-in-water (O/W) nanoemulsions with hexadecane concentration varied between 10, 20, 25, 30, 35, and 40 wt. % is prepared and characterized with respect to their physical, thermal, and rheological properties. The storage characteristics are evaluated in terms of storage density, phase transition behaviour, supercooling, and dynamic viscosity. A systematic comparison in terms of energy density between the PCMEs and water is carried out at different temperature conditions. For this purpose, the storage break-even temperature TBE is proposed as a novel parameter to determine suitable operating temperature ranges and cycling conditions. The cycle stability is evaluated by rheological measurements, applying thermomechanical loads to the samples for a high number of cycles. According to the results, the energy density of the PCMEs is always higher than that of water, when the minimum temperature used for the cycling is below the storage break-even temperature. The emulsion with 30 wt. % hexadecane fraction is considered particularly promising, thanks to its high stability when exposed to thermomechanical stress, relatively low viscosity between 10 and 22 mPa s (0–30°C), and a storage density of 98 MJ/m3 within a cycling temperature range of 12 K.

Functional Soft Materials with Resistance to Liquid Leakage for Thermal Energy Storage

AbstractFunctional soft materials have great potential commercial applications in thermal energy storage, which are required to have a long life, good flexibility, and resistance to liquid leakage. Herein, a composite hydrogel with thermal storage properties is prepared through coupling molecular self‐assembly and in situ polymerization. Hydrophobic stearic acid (SA), as a thermal storage phase change material (PCM), is dispersed in polyacrylamide (PAM) hydrogel network in the form of oil–water emulsion (O/W). The PAM polymer network with good flexibility physically limits high‐frequency collision between SA PCM droplets. This unique design avoids demulsification in phase change emulsion so that the as‐prepared hydrogel composite can resist liquid leakage. The PAM hydrogel network plays the role of heterogeneous nucleation, resulting in the super‐cooling of SA emulsion at only 0.3 °C. On the other hand, SA PCM droplets in as‐prepared soft material do not directly contact with liquid water, so melting/crystallization process is independent of water. As a result, the soft material exhibits a thermal storage density of up to 99.3 J g−1. The present study is an important step toward designing soft energy storage materials.

Studying the photothermal activation of polydopamine-shelled, phase-change emulsion droplets into microbubbles using small- and ultra-small-angle neutron scattering

Polydopamine-shelled perfluorocarbon (PDA/PFC) emulsion droplets are promising candidates for medical imaging and drug delivery applications. This study investigates their phase transition into microbubbles under near-infrared (NIR) illumination in situ using small- and ultra-small-angle neutron scattering (SANS and USANS) and contrast variation techniques. Supported by optical microscopy, thermogravimetric analysis, and ultrasound imaging, SANS and USANS results reveal rapid phase transition rates upon NIR illumination, dependent on PFC content and droplet size distribution. Specifically, perfluoropentane droplets rapidly transform into bubbles upon NIR irradiation, whereas perfluorohexane droplets exhibit greater resistance to phase change (bulk boiling points = 30 °C and 60 °C, respectively). Furthermore, smaller emulsion droplets with unimodal distribution resist NIR-triggered phase changes better than their bimodal counterparts. This observation is attributable to the lower boiling points of large emulsion droplets (lower Laplace pressure than smaller droplets) and the faster photothermal heating rates due to their thicker polydopamine shells. The insights gained from these techniques are crucial for designing phase-change emulsions activated by NIR for photothermal therapies and controlled drug delivery.

Development of highly stable n-Heptadecane/water-based phase change emulsion with mixed surfactant for thermal management applications

Phase change material (PCM) emulsions have grown in popularity due to their versatility and various thermal management applications. Therefore, new PCM materials and emulsion compositions have been investigated to enhance their functionality and widen their range of applications. In the present work, PCM emulsion was formulated using n-heptadecane as a dispersed phase, DI-water as base fluid, and sodium dodecyl sulfate and Brij30 as surfactant. The effect of mixed surfactants on the stability and other thermophysical properties of the PCM emulsions were investigated. The emulsions with mixed surfactants show excellent stability when compared to single surfactants. The average droplet size of the PCM emulsion was 102.8 nm with a phase change temperature and latent heat of fusion of 18.9 °C and 14.17 Jg−1, respectively, for 10 wt% PCM concentration. The thermal conductivity was decreased by about 16.4 %, and the viscosity increased by nearly 128 % when compared with DI-water for the 10 wt% dispersed phase emulsion with mixed surfactants. The gravimetric and structural studies confirm the stability of dispersed phase and base fluid in the presence of surfactant. Overall, it can be concluded that the PCM emulsion with mixed surfactant can be a potential heat transfer medium with improved heat storage and transportation capacity.

Development of a pipeless, cascade phase change power battery thermal management system

To solve the problems of pipe weight and phase change material (PCM) utilization in the PCM coupled liquid cooling system, a novel pipeless cascade shape-stabilized phase change material coupled phase change emulsion (PCE) cascaded with the shape-stabilized PCM BTMs was proposed. Firstly, a pipeless shape-stabilized PCM channel with high thermal conductivity was prepared. Compared with pure PCM, its thermal conductivity was increased by about 45 times, and it had excellent leakage prevention ability. Then the cooling performance of the shape-stabilized PCM channel BTMs was compared to the metal channel BTMs, and the cooling performance of the PCE/shape-stabilized PCM channel BTMs was compared to the performance of the water/shape-stabilized PCM channel BTMs. It turns out that the shape-stabilized PCM channel coupled PCE BTMs have both good temperature control performance and excellent temperature uniformity. And the thermal management performance of pipeless cascaded shape-stabilized PCM and the cascade between shape-stabilized PCM and PCE in BTMs was studied. Compared with BTMs without cascade phase change, the maximum temperature and maximum temperature difference are reduced by 1.7 °C and 0.5 °C, respectively. What's more, compared to the PCE cascaded with the shape-stabilized PCM, the cascaded shape-stabilized PCM channel has a greater influence on the performance of the BTMs. Finally, compared with other existing BTMs, this work has strong competitiveness in reducing the maximum temperature and the maximum temperature difference of the battery module.

An Antimicrobial, Environmental Protection, and High‐Efficiency Solar Steam Generator Based on Carbonized Sawdust

Solar‐powered desalination technology offers a promising solution to the global scarcity of freshwater resources. Recently, researchers have become interested in solar‐powered steam generators utilizing biomass materials. Herein, wood waste (sawdust) is recycled and subjected to high‐temperature treatment to obtain carbonized sawdust (CSd), which is sprayed onto the surface of a sponge to assemble a sponge‐based light absorber. The impact of sawdust carbonization temperature on water evaporation performance is examined, and it is found that a sponge‐based light absorber with a sawdust carbonization temperature of 600 °C exhibits a photothermal conversion efficiency of 87.7% while maintaining low‐energy consumption. Incorporating metal Ag into the light absorber improves water evaporation performance (photothermal conversion efficiency of 92.3%) and provides antibacterial properties. This photothermal evaporator maintains 89% photothermal conversion efficiency after 24 h of operation under 1 sun irradiation in 3.5 wt% NaCl solution. The antibacterial, efficient solar steam generator is expected for practical seawater desalination.

Thermal performance of cold plate based on phase change emulsion for Li-ion battery

A battery thermal management system (BTMS) is responsible for the safety performance of lithium-ion batteries. In this paper, different cooling methods based on phase change emulsion (PCE) containing 10 wt% to 40 wt% paraffin were investigated and compared with a water-cooling system. The three-dimensional thermal simulation results showed that the cooling performance of the mini-channel configuration was better than the baffle plate, fin cooling and jacket cooling methods. Based on the optimized structure of the mini-channel cold plate, the operation conditions for cooling Li-ion batteries were determined to keep the maximum temperature limit of 313 K and maximum temperature difference of 5 K at various discharge rates. There was advantage for the PCE cooling in reducing the pump energy consumption for high discharging rates compared with water cooling. The pump power declined by 24% and 36% for 2.0C discharging when applying the PCE with 25 wt% and 40 wt% paraffin as the coolant, respectively. The cooling with the PCE containing 25 wt% paraffin had 16% less energy consumption for 3.0C discharging.

Thermal Storage: From Low‐to‐High‐Temperature Systems

Different technologies of cold and heat storages are developed at Fraunhofer ISE. Herein, an overview of ongoing research for sensible and latent thermal energy storages is provided. Phase change emulsions are developed supported by molecular dynamic simulations. A narrow temperature range of the phase change is crucial for the applicability. By the simulations, a nucleation additive is identified that reduces supercooling by up to 9 K. The long‐term stability of phase change material is investigated by degradation experiments. Thermal cycling and ageing of materials at elevated temperature are applied. The change of melting enthalpy and characteristic temperatures are evaluated. Among erythritol, adipic acid, and myristic acid, the smallest degradation is observed for the latter. For sensible storage, the reduction of thermal oil by low‐cost filler materials and their compatibility is investigated at elevated temperature. It can be concluded that the materials are compatible up to 320 °C. At the component level, different macroencapsulations and immersed heat exchangers are tested for phase change materials. The investigated configurations achieve similar values of thermal power during (dis‐)charge. Compared to water as storage medium, the capacity increases by a factor of 2.2 and 4.1 for the macroencapsulation and the immersed heat exchanger, respectively.

Experimental investigations into thermal performance of phase change emulsion in a fin-and-tube heat exchanger

AbstractPhase change emulsions (PCMEs) are always identified as potential working fluids that could be used to reduce circulating pump energy consumption in chill water air conditioning systems. But how PCME behaves in a fin-and-tube heat exchanger is still unclear, which limited the application of such material. The paper focused on experimental studies of performance of a novel PCME, named as PCE-10, in a fin-and-tube heat exchanger. The research analyzed heat transfer and flow behavior in fin-and-tube heat exchangers and the experimental results are compared with numerical studies published. Both studies showed that PCE-10 had its advantages as a cold storage medium, as PCE-10 did help to improve the heat transfer rate of heat exchanger by factor of 1.1–1.3 at the same flow rate compared with water.

A coupled power battery cooling system based on phase change material and its influencing factors

With the improvement of electric vehicle technology and requirements, power battery thermal management systems should not only have excellent temperature control ability but also meet the development requirements of compactness and lightweight. To achieve this goal, a pipeless cooling system coupled with shape-stabilized phase change material (SSPCM) channel and phase change emulsion (PCE) was proposed. In this study, the thermal performance of cooling systems based on metal channel and SSPCM channel were compared, and the thermal properties of the PCE/SSPCM channel system and the Water/SSPCM channel system were compared. Based on the above, the key factors affecting the PCE/SSPCM channel battery thermal management system were analyzed. Finally, the effects of these factors were studied together by an orthogonal simulation. The results show that the maximum temperature and the maximum temperature difference of the SSPCM channel system were 16.8 °C and 3.3 °C lower than the metal channel system, respectively. And the PCE/SSPCM channel system surpasses the Water/SSPCM channel system when the PCE undergoes phase change at low inlet velocity. The orthogonal simulation results show that under the optimal parameters, the battery thermal management system can maintain the temperature and temperature difference of the battery module below 54.8 °C and 4.8 °C in 7 C charge–discharge cycles, which can meet the thermal management requirement of power battery under high-rate charge and discharge.

Oil-in-Oil emulsions of stearic acid dispersed in silicone oil with enhanced energy storage capability for heat transfer fluids

Non-aqueous phase change emulsions are very unknown and promising multifunctional fluids consisting of phase change materials dispersed in carrier fluids, both being oily phases. The oil-in-oil phase change emulsions allow the possibility of using the same medium for latent heat storage and transport under more extreme pressure and temperature conditions. In this paper, stable emulsions composed of stearic acid with a melting point of 68–71 °C dispersed in silicone oil have been developed. Stearic acid-in-silicone oil emulsion samples with different phase concentrations were evaluated by analysing their thermophysical properties, viscous and viscoelastic behaviour and microstructure. Emulsion properties below the melting point of the phase change material were greatly influenced by the concentration of the disperse phase. Thus, as the temperature lowered, a well-developed three-dimensional network of stearic acid crystalline structures interconnected with each other was formed. Furthermore, emulsion physicochemical and thermal stabilities were examined and proved under several mechanical–thermal cycles, withstanding more than 100 cycles in the calorimeter. The results indicate that stearic acid-in-silicone oil emulsions are an attractive candidate for energy storage applications with a phase change enthalpy in emulsions with the 10 wt% of phase change material of 22.32 J/g. • Phase change emulsions PCME are obtained by dispersing stearic acid-in-silicone oil. • PCME present a great potential application as thermal energy storage fluids. • PCME resist heating-cooling cycles and remain microstructurally stable. • Structural/rheological changes are related to the crystallization of the steric acid. • Microstructure is highly susceptible to shear, which is positive for the application.

Next-Generation Colloidal Materials for Ultrasound Imaging Applications.

Ultrasound has important applications, predominantly in the field of diagnostic imaging. Presently, colloidal systems such as microbubbles, phase-change emulsion droplets and particle systems with acoustic properties and multiresponsiveness are being developed to address typical issues faced when using commercial ultrasound contrast agents, and to extend the utility of such systems to targeted drug delivery and multimodal imaging. Current technologies and increasing research data on the chemistry, physics and materials science of new colloidal systems are also leading to the development of more complex, novel and application-specific colloidal assemblies with ultrasound contrast enhancement and other properties, which could be beneficial for multiple biomedical applications, especially imaging-guided treatments. In this article, we review recent developments in new colloids with applications that use ultrasound contrast enhancement. This work also highlights the emergence of colloidal materials fabricated from or modified with biologically derived and bio-inspired materials, particularly in the form of biopolymers and biomembranes. Challenges, limitations, potential developments and future directions of these next-generation colloidal systems are also presented and discussed.

Preparation and characterization of phase change microcapsule emulsion for thermal energy storage and transportation

A method of water phase separation is adopted to prepare phase change emulsion samples, and a self-designed multi-stage gravity flow heat exchange system is then used to measure fluid flow and heat transfer performance. Under the conditions of different flow velocities and initial temperatures, flow and heat transfer performance of the emulsion is tested. Results show that phase change capsule in emulsion sample has a uniform core-shell structure, and core material is completely encapsulated by a uniform thickness of the shell. Thermal conductivity of emulsion is generally higher than 0.53 W·m-1·K-1, indicating that the emulsion itself has excellent thermal conductivity. The maximum encapsulation ratio and encapsulation efficiency of the capsule reached 80.7% and 80.8%, respectively, and thermal decomposition temperature of the capsule reached 300 °C, which indicated that the synthesized emulsion has potential excellent heat storage and release performance. When flow velocities are 0.35 m·s−1 and 0.65 m·s−1, heat transfer coefficients of phase change capsule emulsion are 1231.5 W·m-2·K-1 and 2020.5 W·m-2·K-1, respectively, which are more than 55% of the heat transfer coefficient of deionized water in same flow state.

Shape-stabilized phase change material with internal coolant channel coupled with phase change emulsion for power battery thermal management

With the rapid development of new energy vehicles, fast charging and fast discharging are gradually popularized, which puts forward higher requirements for power battery thermal management. In this paper, a novel power battery thermal management system with emulsion as coolant and shape-stabilized phase change material (SSPCM) as its channel is designed and heat transfer performance was experimentally studied. The cooling performance of water, emulsion and graphene oxide emulsion (GO emulsion) were compared. The results show that GO emulsion with high thermal conductivity not only shows better temperature uniformity than water, but also exhibits maximum temperature control ability than pure emulsion. Furthermore, to verify the heat storage effect of SSPCM, thermal performance of the novel system is compared with metal (aluminium) channel system. The SSPCM cooling system can greatly improve temperature uniformity compared with metal cooling system at high charge–discharge rate. Based on the above comparative analysis, the SSPCM cooling system with GO emulsion cooling presents optimal cooling performance of batteries. Finally, to reduce pump consumption, the cooling strategies of different start-up times for GO emulsion are studied. The results show that compared with continuous cooling, starting GO emulsion cooling when the maximum temperature of power battery reaches 42 ℃ can improve latent heat utilization of emulsion and reduce the power consumption with few temperature rise (0.2 ℃).

Investigation on the influence of dispersion mass transfer on the thermal characteristics of phase change emulsion

This paper aims to investigate the influence of dispersion mass transfer on thermal properties of n-hexadecane phase change emulsion in terms of thermal diffusivity, thermal conductivity and heat storage capacity. The microscopic evidence has been revealed, and a self-designed interface dispersion mass transfer measuring device is established to confirm with micro-formation. It is worth noting that dispersion mass transfer could enhance part of thermal properties and heat storage performance of the emulsion. In a certain range, the larger the intensity of dispersion mass transfer is, the greater the amount of deionized water homogenized by phase change materials will become. Dispersion mass transfer will weaken thermal diffusivity of phase change emulsion, the weakening ratio is about 57.1%–66.5%. In addition, dispersion mass transfer will significantly enhance thermal conductivity and heat storage performance of the emulsion, and enhancement ratio are above 11.52% and 11.56%, respectively. Although difference in the types of emulsifiers will cause small fluctuations in research results, it does not affect the influence trend of dispersion mass transfer on thermo-physical properties. Based on the finding of mass transfer, it may be quite prospective for future phase change emulsion preparation. • The influence of dispersion mass transfer on thermal properties shows that it is meaningful to discuss dispersion mass transfer. • Dispersion mass transfer process will decrease thermal diffusivity, and the weakening ratio reached 57.1%–66.5%. • Dispersion mass transfer has a strengthening effect on heat storage performance and thermal conductivity, and the enhancement ratio is higher than 11.5%.

Effect of Thermal History and Hydrocarbon Core Size on Perfluorocarbon Endoskeletal Droplet Vaporization.

Vaporizable hydrocarbon-in-fluorocarbon endoskeletal droplets are a unique category of phase-change emulsions with interesting physical and thermodynamic features. Here, we show microfluidic fabrication of various morphologies, such as solid-in-liquid, liquid-in-solid, and Janus-type, of complex solid n-C20H42 or n-C21H44 and liquid n-C5F12 droplets. Furthermore, we investigated the vaporization behavior of these endoskeletal droplets, focusing on the effects of heat treatment and core size. Comparison of vaporization and differential scanning calorimetry results indicated that vaporization occurs prior to melting of the bulk hydrocarbon phase for C20H42/C5F10 droplets and near the rotator phase for C21H44/C5F10 droplets. We found that heat treatment of the droplets increased the fraction of droplets that vaporized and also increased the vaporization temperature of the droplets, although the effect was temporary. Furthermore, we found that changing the relative size of the solid hydrocarbon core compared to the surrounding liquid shell increased the vaporization temperature and the vaporizing fraction. Taken together, these data support the hypothesis that surface melting behavior exhibited by the linear alkane may trigger the fluorocarbon vaporization event. These results may aid in the understanding of the interfacial thermodynamics and transport and the engineering of novel vaporizable endoskeletal droplets for biomedical imaging and other applications.

Towards idealized thermal stratification in a novel phase change emulsion storage tank

Energy storage density and charging/discharging speed are crucial performance indices for an energy storage unit. Phase change materials (PCMs) have been perceived to improve the energy storage density in thermal energy storage, but the relatively low charging/discharging speeds have been a bottleneck to their application. In building cooling storage applications using ice, the energy efficiency is compromised as the working temperature of ice storage is far below that required for air dehumidification and building cooling, which ranges between 7 and 17 °C. In this study, both experimental and numerical studies were carried out to demonstrate a novel stratified storage tank of PCM-in-water nano-emulsion for cold storage in building radiant cooling applications. A 20 wt% PCM-in-water nano-emulsion was utilized as both the storage medium and heat transfer fluid. The experimental results showed that the cooling capacity of a cooling panel was increased by 60% with phase change emulsion circulating in the loop. The effective energy storage capacity of the stratified storage tank was 1.6–1.7 times that of water in a wide range of discharging flow rates/speeds. Validated with the experimental data, the numerical simulation showed that installing baffle plates in the storage tank could effectively reduce the fluid mixing and significantly increase the effective energy storage capacity, especially at high discharging flow rates/speeds. In comparison with other PCM thermal energy storage designs, the stratified storage tank of PCM-in-water nano-emulsion has the advantage of a lower temperature difference between the cooling source and the demand, and thus raising the overall system energy efficiency.

Shape-Stabilized Phase Change Material with Internal Coolant Channel Coupled with Phase Change Emulsion for Power Battery Thermal Management

Shape-Stabilized Phase Change Material with Internal Coolant Channel Coupled with Phase Change Emulsion for Power Battery Thermal Management

Role of crystallinity on the thermal and viscous behaviour of polyethylene glycol-in-silicone oil (o/o) phase change emulsions

Stable polyethylene glycol-in-silicone oil phase change emulsions were successfully prepared with a selected silicone surfactant. These oil-in-oil (o/o) emulsions have been scarcely examined up, despite the highly remarkable properties of both phases for energy recovery applications and cosmetic/pharmaceutical compositions. The objective of the present work was to study the effect of composition (surfactant and disperse phase concentrations) and the post-processing conditions (further agitation at the processing temperature for 24 h) on the final features of the emulsion. For this purpose, optical morphology, thermo-physical and the rheological behaviour of the emulsions and binary blends of their compounds were measured and analysed. Special attention has been paid to structural changes and crystallinity modifications of the emulsion disperse phase. The observed miscibility of the silicone surfactant and silicone chains with the disperse phase reduces its crystallinity degree and modifies in the crystallization mechanism of the polyethylene glycol, from heterogeneous to homogeneous nucleation. Interestingly, the change in the disperse phase crystallinity remarkably modifies final thermal and rheological properties of the emulsion.