Enthalpy Loss Research Articles

Alkali alkanoate ionic liquids for thermal energy storage at mid-to-high temperature: Synthesis and thermal–physical characterization

Thermal energy storage is gaining much attention and experiencing a renascence in last years. In this sense, storing thermal energy in form of latent heat is of special interest due higher energy density, lower energy losses and higher energy efficiency. To store thermal energy as latent heat the presence of a phase change material (PCM) is needed and its performance the key for its implementation in a thermal energy storage (TES) system and the temperature at which the phase change takes place, low (<150 °C) or high (>150 °C) temperature, will condition the application of a given PCM. In this context, the development of PCM materials to store latent heat at mid-to-high temperature in between 150 °C and 350 °C is of special interest e.g., in the field of concentrated solar power or heat recovery. There are already some solid–liquid phase change materials working in this range of temperature e.g., sugar alcohols, aromatic organic compound, inorganic salts, or blend of inorganic salts but all of them present different drawbacks, such as vapor pressure, degradation, low thermal conductivity, corrosion, etc. In consequence, there is a need to explore new PCM materials in this range of temperature applications. In this context, ionic liquids could play a key role in the development of novel PCMs due to their intrinsic properties. Indeed, ILs are gaining increased attention in the field of thermal energy storage in the last years but mainly in the low temperature range (<150 °C) remaining their application in the mid-to-high temperature range in between 150 °C and 350 °C underestimated. In this work, we prepared six different alkali alkanoate ionic liquids, namely [Na][MeOC2], [K][MeOC2], [Na][MeOC3], [K][MeOC3], [Na][MeOC4] and, [K][MeOC4] by direct reaction between the desired methyl methoxycarboxylate ester with NaOH or KOH. The prepared ionic liquids were structurally characterized, and their thermal–physical properties evaluated. Five of them but [K][MeOC3] showed good enthalpy values ranging from 119 J/g to 197 J/g and four of them [Na][MeOC2], [K][MeOC2], [Na][MeOC4] and, [K][MeOC4] have showed excellent thermal stability above 380 °C. In addition, these four ionic liquids have successfully passed the cyclability test showing no significant enthalpy losses (between 0 % minimum and 7 % maximum) after 50 heating/cooling cycles compiling with the cycling category F of the RAL-GZ 896 (Quality Association PCM). All in all, these prepared ionic liquids surpass sugar alcohols in terms of cyclability and thermal stability and are comparable with the inorganic salts e.g. NaNO3 employed in the studied range of mid-to-high temperature (150–350 °C).

Surfactant hydrophilic modification of expanded graphite to fabricate water-based composite phase change material with high latent heat for cold energy storage

Glycine water-based (GW) phase change material (PCM) is considered a promising candidate for cold energy storage due to its lower cost and high latent heat. However, low thermal conductivity hinders its practical application. Adding high thermal conductive fillers can effectively enhance the thermal conductivity of PCM, but it also leads to a decrease in enthalpy. Thus, the study employed a non-covalent functionalization method to modify the thermal conductivity filler of expanded graphite (EG) using the surfactant Triton X-100 (TX-100) in this study. The hydrophilic groups in TX-100 facilitated the formation of hydrogen bonds between modified expanded graphite (MEG) and GW PCM, thereby inhibiting the enthalpy loss of GW/MEG materials. The prepared GW/MEG composites containing 2 to 8 wt% of MEG exhibited thermal conductivities ranging from 0.88 to 1.28 W/(m·K), representing an increase of 46.47 % ∼ 113.35 %. Simultaneously, the melting temperature ranged from −5.35 to −5.65 °C, with a high melting latent heat of 284.6 to 264.5 J/g. After 100 thermal cycles, only minor fluctuations in melting temperature (−1.62 % ∼ +2.20 %) and latent heat (−2.18 % ∼ −4.66 %) were observed. Furthermore, the application of GW/MEG2 in cold storage of strawberries resulted in a significant reduction in pre-cooling time by 56.60 % compared to that of ice storage. The GW/MEG2 materials allow strawberries to be refrigerated for up to 17.86 h within the temperature range of 1.54 ∼ 3.39 °C. This study provides an effective solution for short-distance transportation of perishable food within cold chain logistics system.

Power engineering of the tangential supply device of the microturbine of the thermal control system of a promising spacecraft

This paper presents an overview of the current technical problem related to two-phase spacecraft thermal control systems and possible technical applications of thermal energy recovery in the organic Rankine cycle as an integral part of thermal management systems. The design solution involves the integration of a steam microturbine behind an evaporator radiator. The microturbine is a tangential supply device and a radially centripetal impeller of low speed nst40. In this area, there is no reliable data on the design and energy of both the supply device and the impeller. The energy (loss of enthalpy) of the supply device mainly determines the transport of the swirling flow to the impeller and, as a result, the circumferential operation on the turbine. A prototype of a radial microturbine has been developed and presented in order to evaluate the design of the flow part of both the supply device and the impeller. As a result of the analysis, the main determining hydrodynamic areas necessary for hydrodynamic analysis and mathematical elaboration of the flow calculation algorithm with an assessment of energy losses are identified: the flow of a swirling flow of a radial-annular slit; axial-annular slit and tangential supply device. The first two algorithms assume computational modeling, the model of energy losses in a tangential supply device is not amenable to analytical modeling because it includes a sequence (or compatibility) of flows under boundary conditions defined as “local resistances”: the sudden expansion, reversal of the flow, together with a section of radially circumferential flow, the mutual influence of these boundary conditions assumes only an expe rimental assessment of energy losses in a tangential supply device through the loss coefficient of local resistance in the range of changes in geometric and operating parameters. As a result of experimental studies, a database has been proposed on the loss coefficient of tangential microturbine supply devices in the field of the practical range of the existence of operating and design parameters.

Characterization of centrifugal compressors operating in FRIB’s sub-atmospheric compression system

Helium cryogenic systems operating below the normal boiling point (of 4.22 K) are required for many modern high-energy particle accelerators to achieve the necessary performance criteria. Temperatures below the normal boiling point are established by lowering saturation pressure below atmospheric conditions using vacuum equipment. FRIB operates a multi-stage string of cryogenic compressors (or ‘cold-compressors’) to achieve the sub-atmospheric pressures required (30 mbar) for the accelerator operating conditions of approximately 2 K. Housed within a vacuum insulated vessel (i.e., the sub-atmospheric cold box), the cold-compressor system re-pressurizes the helium from approximately 30 mbar to above atmospheric pressure condition before injecting the flow back into the helium refrigerator. Despite the implementation of cold-compressors in several existing large-scale cryogenic systems, openly available literature is insufficient to provide the information necessary for a general characterization of the performance and stability for these cold compressors. A one dimensional steady-state model to predict the performance of cryogenic centrifugal compressors has been developed. This model enables performance prediction by using optimally selected enthalpy loss correlations and basic impeller and diffuser geometrical data. The present work provides an initial comparison of the estimated performance of the individual and string of cryogenic centrifugal compressors to the operational / test data. With appropriate validation, the model is anticipated to allow assessment and prediction of optimal operational envelops that ensure stable and efficient operation at different operating conditions.

Synergistic enhancement of photothermal energy storage capacity of polyethylene glycol by polydopamine and nano-copper particles

Phase change materials (PCMs) are a crucial focus of research in the field of photothermal energy storage. However, due to their inherently low photothermal conversion efficiency, traditional PCMs absorb solar energy scarcely. The photothermal conversion ability of PCMs are usually enhanced by incorporating photothermal conversion nanoparticles. Polydopamine (PDA) is widely used in various fields due to its excellent photothermal conversion and adhesion performance. We dispersed PDA into PEG containing CuNPs to test the effect of PDA on thermal properties of cPCMs. Our team has conducted experiments to test the thermal characteristics and photothermal conversion ability of cPCMs. Results demonstrated that the addition of PDA mitigated the enthalpy loss caused by integrating CuNPs. The enthalpy of melting of cPCMs with addition of polydopamine is greater than that without polydopamine for the composites with different mass fractions. The addition of PDA in cPCMs enhanced their photothermal conversion capacity, resulting in higher temperatures being achieved within the same exposure time compared to samples without PDA. Therefore, the cPCMs with dispersed polydopamine can store higher energy. Meanwhile, PDA also improved the overall thermal conductivity of the material. Our work provided a new method to utilize the photothermal properties of polydopamine. Meanwhile, it can reduce the cost of photothermal energy storage PCMs and further improve the potential of PCM energy storage.

Phase change materials encapsulated in a novel hybrid carbon skeleton for high-efficiency solar-thermal conversion and energy storage

Phase change materials (PCMs) with high energy density and stationary transition temperature are now considered promising solar energy storage mediums. However, their intrinsic poor light absorption, thermal conductivity and stability severely impede their potential applications. In this study, a novel carbonized hybrid aerogel (CHA) structure was firstly constructed by incorporating MXene and carbon nanofibers (CNFs) into a continuous phase polyamic acid salt (PAAS) aqueous solution, followed by directional freezing, vacuum drying, imidization, and carbonization processes. Finally, the composite PCMs (CPCMs) were fabricated by vacuum impregnation of PCMs into the CHAs. The CPCM, of which CHA consists of 20 wt% MXene and 10 wt% CNF@PDA, demonstrates high solar-thermal conversion efficiency (>91 %), improved thermal conductivity of 0.40 W·m−1·K−1, great thermal stability (enthalpy loss < 0.19 % after 100 cycling tests with no obvious leakage). The introduction of MXene and CNFs endows PCM with broader light absorption spectrum range. The skeleton matrix embedded with bonded MXene sheets and CNFs provides more thermal pathways, light absorption sites and carrying capacity, improves the thermal conductivity, solar-thermal conversion property and stability of PCM. In addition, CPCM also exhibits outstanding EMI SE (95 dB). The multifunctional and high-performance CPCMs shows potential to realize the effective capture and utilization of solar energy. This work provides a new strategy to construct stable and multifunctional hybrid carbon skeleton for high-efficiency solar-thermal conversion and energy storage.

Photo-curable bio-based comb/bottle brush epoxy resin/beeswax/copper foam phase change materials with high enthalpy value, high conductivity, and multifunctional properties

At present, the demand for green energy has reached a new height in history, and thermal energy storage technology has been widely used to reduce energy consumption. It is still a challenge to develop bio-based polymeric form-stable phase change materials (FSPCMs) with high enthalpy value and thermal conductivity (TC), short curing time, and multifunctional properties. This work not only exploited a series of adjustable and photo-curable comb/bottle brush bio-based epoxy resin/beeswax (bw) FSPCMs with the above superiorities, but also revealed the effects of cross-linking density on the energy storage capacity and encapsulation rate of the FSPCMs. As a result, the optimal system can encapsulate the maximum amount of bw (60 wt%) and obtain the highest enthalpy value (142.1 J/g) with only 0.5% enthalpy loss. Through further introducing the optimal curing system into the copper (Cu) foam, the electromagnetic interference shielding property, TC, tensile strength, and photo-thermal conversion efficiency of the final composite (modified by Cu of 95% porosity) can reach 110 dB, 2.387 W m−1K−1, 2.81 MPa, and 80%, respectively, and the enthalpy value (84.2 J/g) is still satisfactory. This study can provide theoretical guidance for the structural design of reliable fast photo-curable bio-based polymeric FSPCMs with excellent phase change performances and multifunctional properties.

Experimental evaluation of the performance and power output enhancement of a divergent solar chimney power plant by increasing the chimney height

Solar energy is an attractive renewable energy option for countries located in the tropical region. Harvesting this energy using simple yet innovative technologies such as solar chimney power plants (SCPP) will help the developing countries in meeting their sustainable development goals. In an SCPP, air is heated under a greenhouse collector and the hot air is passed to a chimney, where it drives a turbine while rising up. Research efforts have been directed in the past at improving the performance and power output of an SCPP by varying its geometric parameters. The chimney height of a previously optimized solar chimney power plant, having a divergent chimney, was increased from 4 to 6 m and then to 8 m in this first experimental work of this kind. The temperature variations inside the collector, along the chimney height, the velocity at the turbine section, the power available and the output power of an air turbine, estimated by applying mechanical load, are compared for the three chimney heights. The temperature rise of the air inside the collector was the highest for the 4 m tall SCPP and reduced as the chimney height was increased to 6 and 8 m due to the lower time of stay of air in the collector for greater chimney heights. Along the height of the divergent chimney, the temperature dropped with the maximum drop occurring for the 8 m tall SCPP indicating a lower enthalpy loss at the chimney exit. The air velocity at the turbine section was found to increase with chimney height for given solar insolation/time of the day due to the higher driving force which is the buoyancy effect produced by the hot air. The maximum turbine output power for the 8 m tall SCPP increased by 252% compared to the 4 m tall SCPP indicating that significant improvement in the power output can be achieved by increasing the height of a divergent chimney SCPP. An average power of about 40 kW will be available for a chimney height of 100 m which will be extremely beneficial for the sustainable development of small islands.

CH3COONa·3H2O/flaky modified vermiculite composite phase change materials enhanced phase change behavior and thermal storage through curing lotus root starch modification

With the establishment of the basic policy of environmentally-friendly and resource-saving society, the energy storage technology using phase change materials (PCMs) as the medium has developed unprecedentedly. Hydrated salt PCMs plays a vital role due to its large latent heat density, wide range of phase transition temperature, and high thermal conductivity. However, the problems of low enthalpy, poor thermal stability and phase separation are critical drawbacks of composite phase change materials (CPCMs), which limited the extensive use in fields of energy storage. In this work, the flaky vermiculite (MEVM) was fabricated by the acid treatment and alkali leaching, and the cured lotus root starch (CLRS) was embedded and used to enhance the water holding capability of hydrated salts. A series of sodium acetate trihydrate (SAT)-CLRS/MEVM was prepared, and the form-stable composite phase change materials (SAT fs-CPCMs) were obtained. Results showed that the encapsulation capacity of SAT fs-CPCM with 2 wt% CLRS was 71.3 %, and the thermal enthalpy reached 180.1 J/g, which was 43.7 % higher than that of SAT/MEVM. The contact angle of the sample with H2O was 22.24°, which represented hydrophilicity. SAT fs-CPCM also had good thermal stability and thermal reliability. After 200 thermal cycles, the enthalpy loss of the SAT fs-CPCM was only 5.2 %, and the 200th enthalpy value was 173.72 J/g. In addition, Calculations indicated that there were hydrogen bonds and van der Waals weak interaction between SAT and CLRS. This work provides a new perspective for the improvement of the thermal properties of hydrated salt and offers a promising approach for the applications of PCMs in cost-effective energy storage.

Synthesis and hygrothermal aging of polycarbonates containing a bisphenol fluorene moiety.

This study aims to synthesize a specific type of polycarbonate with high refractive index, low birefringence, and resistance to hygrothermal aging by copolymerizing 2,2'-bis(2-hydroxyethoxy)-1,1'-binaphthyl (BNE) with 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (BPEF). Comparative analysis revealed that the copolymer synthesized from BNE and BPEF demonstrated superior hydrolytic stability relative to the bisphenol A-based polycarbonate. This augmented stability can be attributed to the monomers' higher pKa values, rendering acidic substances less capable of dissociating and thereby mitigating ester hydrolysis under hygrothermal conditions. Furthermore, the investigation probed into the phenomenon of physical aging in copolymerized polycarbonate when exposed to hygrothermal environments. It was discerned that the enthalpy loss, observable under both dry and hygrothermal conditions, could be linearly correlated with the difference between the aging temperature and the glass transition temperature (Tg), signifying a close correlation between the magnitude of physical aging and Tg. A lower Tg in the copolymerized polycarbonate led to more pronounced physical aging within the same timeframe, resulting in an augmentation of tensile strength and modulus, while higher Tg effectively mitigated the physical aging phenomenon.

Adjustable comb/bottlebrush fast UV-curable epoxy-based form-stable phase change materials with high encapsulation rates and ultralow enthalpy loss

The design strategy of reliable epoxy-based FSPCMs with fast UV-curable performance or self-healing behavior.

Design and development of a stable supercritical CO2 centrifugal compressor

Introducing supercritical carbon dioxide (s-CO2) as a working fluid can enhance the power generation of Brayton cycles. However, various challenges are involved in designing, and developing a stable s-CO2 centrifugal compressor on a reasonably sized s-CO2 Brayton cycle. This article presents a 1-D design and development procedure for s-CO2 centrifugal compressors suitable for Brayton power cycles. The 1-D compressor design approach employs the Widom region, AMC, and internal and external loss models to optimize the compressor design. The 1-D design code is validated with CFD simulation and experimental data from Sandia. Further, a new stable compressor for a 10 MWe s-CO2 Brayton cycle is designed, proposed, and discussed in this paper. Based on the 1-D design code and the CFD results, the newly designed compressor exhibits an improved operational range. Additionally, a loss analysis of the designed s-CO2 compressor revealed that internal losses accounted for 75.8% of the total enthalpy loss. The compressor's internal flow behavior at choke is investigated by utilizing a novel analogy between the impeller at choke and a converging–diverging nozzle. The CFD results showed that condensation is inevitable in an s-CO2 centrifugal compressor operation; however, condensation does not significantly affect compressor performance near the design point.

Thermodynamic investigation of the secondary flow inside centrifugal compressor for compressed air energy storage based on local dissipation

Centrifugal compressors are critical components of compressed air energy storage (CAES) systems and are of great interest to understanding internal secondary flows and their resulting energy losses. While previous studies have primarily described these secondary flows using empirical correlation equations, this paper conducts numerical simulations of a high-loading centrifugal compressor after performing an experimental validation. The changes in the secondary flow structure in the impeller are analyzed for different operating conditions using a specific identification method based on the simulation results. The local dissipation coefficient is used as a weighting to analyze the enthalpy losses due to different sources during the impeller's thermodynamic process. The variations of the loss proportions from different sources with the dimensionless operating parameters (flow coefficient, impeller machine Mach number, and loading coefficient) are discussed. The reasons for the trends of different loss types correlate with the flow structure, and three different loss regions in the whole operation range are distinguished. The energy loss inside an optimized impeller is compared with the baseline, and the results demonstrate that different losses can be controlled by adjusting the secondary flow structure within the impeller. This study provides a reference for enhancing the understanding of thermodynamic processes within a centrifugal impeller and aims to further the development of advanced centrifugal compressors.

Harvesting CO2 reaction enthalpy from amine scrubbing

Amine-based CO2 capture technology suffers high energy consumption, of which the exergy loss of CO2 absorption enthalpy is a significant contributor to the process irreversibility. Recovery and utilisation of CO2 absorption enthalpy is therefore of paramount significance to advance amine technology towards low capture cost. The present study proposed a reaction enthalpy harvesting amine process (REHA) with the purpose to directly utilise the CO2 absorption enthalpy for building heating. In the REHA process, we redefine the operational conditions of CO2 capture process with dual targets of high capture performance as well as high enthalpy recovery. It is revealed that using the benchmark mono-ethanolamine (MEA) absorbent 1.62 GJ/tonne CO2 could be harvested though process modification and multiple heat extraction, enabling a high energy recovery efficiency of 82%, whilst maintaining 90% absorption efficiency and low heat requirement of 2.6 GJ/tonne CO2. Integration of REHA with CO2 capture process enables an appreciable cost of CO2 avoided decreased from $63.5/tonne to $54/tonne CO2 (16% reduction) at a heat price of $7/GJ and 5-months heat supply. The economic viability of REHA process is anticipated to be further promoted with the rise of heating price and increasing demand of space heating.

Low-cost and highly thermally conductive silver modified mica-paraffin multifunctional composite phase change materials for photo-thermal conversion and electrical insulation

To improve the utilization efficiency of renewable energy and adaptability of composite materials, a new mineral-based composite phase change material (Ag-Mica/CNF/PW) was designed and prepared by chemically modifying natural mica, attaching silver nanoparticles to the mica surface as functionalized support material, and using paraffin wax as the phase change functional medium. As expected, the thermal conductivity of the composite phase change material (CPCMs) increased significantly to 0.9 W/m k, which was 330.1% higher relative to pure paraffin. With the addition of silver-modified mica, the volume resistivity of CPCMs reached 11.9 × 1012 Ω cm. The relative enthalpy efficiency achieved 104.8%, and the photothermal conversion efficiency reached 91.3%, proving that the silver-modified mica-based CPCM was successful and feasible. The heat resistance index of CPCMs was 137.2 °C, and the enthalpy loss rate after 50 cycles was only 0.7 %, indicating that CPCMs have excellent thermal stability. The designed CPCMs are a promising candidate for developing thermal storage and building thermal management, electrical insulation and solar energy conversion.

Characterization by differential scanning calorimetry of thermal storage properties of organic PCMs with operating temperature of 150 °C

The involvement of Phase Change Materials (PCMs) in energy storage systems leads to more sustainable and efficient use of energy. Medium operating temperature (melting point 100–400 °C) find various applications in industrial waste heat recovery and hybrid compressed air - thermal energy storage systems. However, there is still a lack of detailed knowledge in terms of their thermal storage properties that hinders them from being more integrated in industry. In this study, thermal properties such as melting point, enthalpy and heat capacity of three medium temperature PCMs were characterized using Differential Scanning Calorimetry (DSC). The enthalpy-temperature graph for each PCM is presented that contains key information on sensible and latent heat contribution in the total energy storage. The selected organic PCMs are adipic acid with two different purities 99%, 99.5%, and its chemical equivalent PureTemp151® with a melting point of (150.5 ± 0.5 °C) and a latent heat of (230 ± 10 J/g). Furthermore, the effect of heating rate and sample mass in DSC procedures on transition temperatures and enthalpy were evaluated. Finally, thermal performance of PCMs was quantified through 150 cycles of melting and solidification. The tested PCMs show a significant storage capacity and good thermal stability with less than 10 % enthalpy loss.

Exhaust heat harvesting of automotive engine using thermoelectric generation technology

Exhaust heat recovery from internal combustion engines is growing interest to reduce fuel consumption, increase the efficiency and consequently, reduce the environmental pollution and global warming. Thermoelectric generator (TEG) is a promising technology to harvest engine exhaust heat by directly converting it into electrical power via the Seebeck effect. In this work, commercial Bi2Te3 (SP1848-27145 SA) thermoelectric modules (TEMs) were used for recovering exhaust heat from gasoline engines and convert it directly into electricity. Two types of setups were constructed using copper and steel materials, where both setups consist of triangular channels. The first setup was constructed entirely from copper material to work as a heat exchanger from exhaust heat to the TEMs’ hot surface. The second setup was constructed with a portion of copper at the installation area of TEMs and the rest of the portion was constructed with steel material to investigate the best performance from these two TEG systems. Six TEG modules which are electrically series connected were installed on the outer surfaces of each copper made and steel made setup. The maximum power output from copper made TEG was found to be 2.96 W for an exhaust temperature of 297 °C and at 126 °C temperature difference between the hot and cold sides. Whereas steel made TEG provided the maximum power output of 2.0 W for an exhaust temperature of 305 °C and at a 107 °C temperature difference between hot and cold sides. Therefore, the copper made TEG setup provided 48% higher power output than the steel made TEG setup. The higher power output of copper made TEG lowers the expelled exhaust temperature to the environment, which results in the decrease of entropy loss. Furthermore, since there is no effect of engine operating pressure on enthalpy loss, therefore, the engine can operate at higher operating pressure which means the contribution of the reduction of fuel cost, fuel consumption and environmental pollution parallelly. Between exhaust gas temperature ranges 297 °C to 300 °C, the highest conversion efficiency was found 4.65 % and 4.63% for steel made TEG setup and copper made TEG setup, respectively.

Yin-Yang heat flow rate converter: Based on Guar Gum composite phase change materials with controllable thermal conductivity

Solid-liquid phase change materials (PCMs) have broad potential but suffer from leakage problems and unreasonable thermal conductivity, resulting in low utilization efficiency. In this study, using Guar Gum (GG) as large frame and graphene oxide (GO) or SiO2 aerogel microchip as small frame, thermal conductivity strengthening PCMs (GG-C-PEG) and thermal conductivity weakening PCMs (GG-I-PEG) were prepared after loading polyethylene glycol (PEG). In-depth characterizations turned out that the phase change enthalpy retention was close to 100% of PEG. In particular, the composites achieved 0.94 W/(m·K) of enhanced thermal conductivity and exhibited a reduced thermal conductivity of 0.11 W/(m·K). Simultaneously, the mass of the PCMs remained above 94.08% when heated at 80 °C for 45 min and the loss of melting enthalpy was less than 6.11% after 100 cycles, indicating outstanding stability in shape and performance during the heating–cooling cycles. To further utilize of solar energy, GG-C-PEG exhibited great photothermal conversion efficiency reaching 83.67%. Moreover, inspired by Tai Chi culture, a novel device that could control the heat flow rate from minimum to maximum by utilizing different thermal conductivity properties of the two types of PCMs was designed, taking composite PCMs further into practical scenarios.

Ultrafast microwave heated form-stable thermal package providing operating temperature for PEO all-solid-state batteries

All-solid-state batteries (ASSBs) have been regarded as satisfying future energy storage devices owing to the advantages of notably high energy density and outstanding safety. However, their attainable energy density, especially in poly(ethylene oxide) (PEO)-based ASSBs, is limited by low operating ambient temperature due to sluggish lithium-ion transport of solid electrolyte. Herein, a functional anti-leakage skeleton (alumina ceramic and boron nitride) with efficient graphene-modified phase change material (GPCM) and microwave thermal energy storage system is proposed for providing the operating temperature of ASSBs. The composite, prepared by alumina ceramic fiber, boron nitride, and GPCM, presenting excellent thermal properties such as great enhancement of thermal conductivity (64.6%) and low enthalpy loss (11.27%). The superior thermal effect is confirmed by experiments and simulations of microwave absorption. Through microwave irradiating the ASSBs wrapped with the composite, ASSBs can realize cold-starting in 1 min from room temperature in a fast, safe and low-power heating pathway. Significantly, the combination of multi-scale characteristics in graphene increases the thermal energy generated by the composite during microwave processing. Furthermore, the composite material (GPBC), used as portable auxiliary heating equipment, enables the ASSB to exhibit 92% capacity of those ASSBs placed in 55 °C ovens at 1C. This work provides a distinctive route to achieve efficient and extensive applications of ASSBs through external preheating.

A comparative study of mean-line models based on enthalpy loss and analysis of a cavity-structured radial turbine for solar hybrid microturbine applications

Lightweight components are essential for the future of the energy and aerospace fields. This paper presents an innovative radial turbine design that utilizes a cavity structure on the rotor for solar hybrid microturbines. The performance of the cavity-structured radial turbine is studied using mean-line models, computational fluid dynamics (CFD), and finite element analysis (FEA) simulations. The radial turbine is compared using air and supercritical carbon dioxide (sCO2) as the working fluid. The mean-line models based on enthalpy losses from recent literature are validated using commercial code Rital and CFD results. The impact of the isentropic velocity ratio (νs) and absolute flow angle at the rotor inlet (α1) on the optimum design for the rotor radial turbine is also demonstrated. A comparative loss enthalpy breakdown on the rotor is examined, such as incidence loss, passage loss, trailing edge loss, clearance loss, exit loss, and windage loss. The results show that the recent mean-line models based on enthalpy losses can accurately estimate the stage efficiency for both air and sCO2 turbines. By comparing the simulation results obtained from 3D-CFD and mean-line models, the efficiency prediction deviation is within an acceptable range of tolerance for both turbines when comparing the results obtained from 3D-CFD and mean-line models. The FE analysis reveals that the maximum stress decreased significantly for the air and sCO2 turbine after the rotor blade was added using the cavity structure inside. The maximum stress value on the rotor with the cavity structure design is still below the yield strength of the material limits. Furthermore, after the variations of the cavity structure design were added to the rotor blade of both turbines, the results were promising when the dangerous resonance at below 4EO (Engine Order) was minimized. The results of this study provide a promising direction for the development of high-efficiency and lightweight turbines in the energy and aerospace fields.