Thermal Energy Storage Medium Research Articles

Performance of an Isobaric Hybrid Compressed Air Energy Storage System at Minimum Entropy Generation

Abstract Efficient, large-scale, and cost-effective energy storage systems provide a means of managing the inherent intermittency of renewable energy sources and drastically increasing their utilization. Compressed air energy storage (CAES) and its derivative architectures have received much attention as a viable solution; however, optimization objectives for these systems have not been thoroughly investigated in the literature. A hybrid thermal and compressed air energy storage (HT-CAES) system is investigated that mitigates the shortcomings of the otherwise attractive conventional CAES systems and its derivatives—shortcomings such as strict geological locations, low energy densities, and the production of greenhouse gas emissions. The HT-CAES system allows a portion of the available energy to operate a compressor and the remainder to be converted and stored in the form of heat through joule/resistive heating in a high-temperature, sensible, thermal energy storage medium. Internally reversible and irreversible HT-CAES system assumptions were investigated, in addition to regenerative and non-regenerative design configurations. Several system optimization criteria were examined—including maximum energy efficiency, maximum exergy efficiency, maximum work output, and minimum entropy generation—with a focus on whether the latter may lead to conclusive design guidelines in a real system. It is shown that an HT-CAES system designed based on a minimum entropy generation objective may operate at a lower energy and exergy efficiency as well as lower output power than otherwise achievable. Furthermore, optimization objective equivalence is shown to be limited to certain design conditions.

Ceramic encapsulated metal phase change material for high temperature thermal energy storage

Thermal energy storage (TES) is a broad-based technology for reducing CO2 emissions and advancing concentrating solar, fossil, and nuclear power through improvements in efficiency and economics. Phase change materials (PCMs) are of interest as TES media because of their ability to store large amounts of heat in relatively small volumes. The volume expansion during a phase change, typically between a solid and liquid, can cause breakage of protective coatings. This effort reports on the fabrication of a ceramic encapsulated metal (CEM) high temperature TES technology using a rotary calcining furnace and a fluidized bed chemical vapor deposition coating technique. Aluminum beads were chosen as the PCM because Al has a high melting point (660 °C), low cost, high heat of fusion, and an ability to form a thin, strong alumina layer capable of supporting the Al melt for subsequent processing. Quite remarkably, this study shows that 1 mm diameter Al can be fluidized up to at least 1500 °C in an appropriate atmosphere while maintaining a spheroid geometry. This allowed for producing a first of a kind CEM whereby Al particles were encapsulated in pyro-carbon (PyC) and high purity, dense chemical vapor deposited SiC. The CEM with a PyC only coating was exposed to thermal cycling to test the performance with a differential scanning calorimeter; the melting point and latent heat were measured to be 648.4 ± 2.8 °C and 293.3 ± 6.2 J/g respectively. It was demonstrated that the CEM design is possible to produce, laying the foundation for manufacturing of high temperature, tunable, TES media.

Synthesis and characterization of phase change material integrated with aluminium waste as the thermal energy storage medium

In this paper, an investigation of a new innovation of heat storage properties of thermal conductivity enhancement via a newly formulated composite consists of paraffin wax incorporated with waste aluminum can from solid municipal waste as the potential PCM composite was studied. The samples composite was synthesized at different percentage of waste aluminum powder mass loading ranging from 0wt% until 100wt% into the paraffin wax and characterized. From differential scanning calorimetry (DSC) analysis, the rate of heat flow has been has found to be increased as more mass loading of waste aluminum was added. However, the latent heat during melting and freezing of DSC data has reduced. This is due to the high amount filler which has reduced the amount of PCM, whereby latent heat is only absorbed/released by the PCM; not the filler/additive. Besides that, the thermal stability has improved strongly when waste filler is added rather than lone paraffin PCM. The density of waste composite PCM materials has also be found to be higher and thus, has increased the heat flow between the materials and improves the energy storage process. From the addition of filler, the smooth surface of lone paraffin has improved as the surface area has becoming to be rougher and shinier, thus resulted with higher contact surface area. Therefore, the new formulated waste PCM composite of paraffin wax incorporated with aluminum waste ranging from 60wt% and above could become a promising material for TES medium.

Charcoal characterization and application is solar evaporator for seawater desalination

Solar desalination is the most attractive and simple technique for desalination process but suffers low thermal efficiency. The objective of this research is to study the effect of charcoal in seawater desalination for clean water production. The experiment was conducted in a basin type solar evaporator by using seawater with charcoal to seawater mass ratio variation of 1:50 to 1:500. The investigation was carried out for eight hours in sunny daylight. The water qualities including pH, conductivity, total dissolve solid (TDS), chemical oxygen demand (COD) and turbidity of the seawater and amount of evaporated water were determined. The spent and fresh charcoals were also characterized by using Nitrogen Adsorption (BET), X Ray Detector (XRD) and Scanning Electromagnetic Microscope (SEM). It is found that the addition of charcoal in the water leads to20 % increment of water temperature. Charcoal’s exposed area to the energy source significantly affects the temperature raise. The best charcoal to water mass ratio was achieved at 1:100 to produce 16.8% evaporated water. Charcoal was stable in seawater because minimum changes of pore size and pore volume were observed. In conclusion, charcoal is a potential salt adsorbent and medium for solar thermal energy storage for seawater solar desalination process.

Cyclic mechanical stability of thermal energy storage media

Closing the gap between supply and demand of energy is one of the biggest challenges of our era. In this aspect, thermal energy storage via borehole thermal energy storage (BTES) and sensible heat storage systems has recently emerged as a practical and encouraging alternative in satisfying the energy requirements of household and industrial applications. The majority of these heat energy storage systems are designed as part of the foundation or sub-structure of buildings with load bearing capabilities, hence their mechanical stability should be carefully studied prior to the design and operation phases of the heat storage system. In this study, the cyclic mechanical performance of a commercial cement-based porous heat storage material is analyzed under different amplitudes of cyclic loading and medium temperatures using a recently developed cyclic thermo-mechanical triaxial device. The results show a significant dependence of the cyclic mechanical behavior of the material, such as in the form of cyclic axial and accumulated plastic strains, on the different thermo-mechanical loading schemes.

Thermal conductivity enhancement of sodium thiosulfate pentahydrate by adding carbon nano-tubes/graphite nano-particles

Abstract Phase change materials are great thermal energy storage medium, while their low thermal conductivity presents the main obstacle for their potential applications. Improvement of the thermal conductivity and specific heat of Sodium Thiosulfate Pentahydrate as a base phase change material with joining Carbon Nano tubes CNT and Graphite Nano particles GNP as Nano-fillers was investigated in this work. CNT and GNP Nano-fillers added in a mass fraction of 1, 3, 5 and 7% in Sodium Thiosulfate Pentahydrate. Thermal conductivity and specific heat were measured by Hot Disk Thermal Constants Analyzer Instrument. Results have shown that increasing the mass fraction of Nano-fillers increases the composite's thermal conductivity. Thermal conductivity of the composite containing: 7% GNP was 2.944 W/m.k with 155.33% enhancement, in the other hand, thermal conductivity of the composite containing: 7% CNT was 4.031 W/m.k with 249.61% enhancement. Moreover, the charging/discharging rates have been enhanced by adding Nano-fillers to Sodium Thiosulfate Pentahydrate.

Analytic Modeling of Heat Transfer to Vertical Dense Granular Flows

Abstract The high packing fractions of dense granular flows make them an attractive option as a heat transfer fluid or thermal energy storage medium for high temperature applications. Previous works studying the heat transfer to dense flows have identified an increased thermal resistance adjacent to the heated surface as a limiting factor in the heat transfer to a discrete particle flow. While models exist to estimate the heat transfer to dense flows, no physics-based model describing the heat transfer in the near-wall layer is found; this is the focus of the present study. Discrete element method (DEM) simulations were used to examine the near-wall flow characteristics, identifying how parameters such as the near-wall packing fraction and number of particle-wall contacts may affect the heat transfer from the wall. A correlation to describe the effective thermal conductivity (ETC) of the wall-adjacent layer (with thickness of a particle radius) was derived based on parallel thermal resistances representing the heat transfer to particles in contact with the wall, particles not in contact with the wall, and void spaces. Empirical correlations based on DEM results were developed to estimate the near-wall packing fraction and number of particle-wall contacts. The contribution from radiation was also incorporated using a simple enclosure analysis. The ETC correlation was validated by incorporating it into dense flow models for chute flows and cylindrical flows and comparing with the experimental data for each.

Crystal Growth Observation of Tetrabutylphosphonium Acetate (TBPAce) Hydrate Suitable as Thermal Energy Storage Medium

Crystal Growth Observation of Tetrabutylphosphonium Acetate (TBPAce) Hydrate Suitable as Thermal Energy Storage Medium

Design and Evaluation of Solar Powered Dryer System with Integrated Thermal Energy Storage

Drying of food products in open air under sun is the most common and easiest way of drying. However, it cannot assure the hygiene of the dried product because of the involvement of wind-borne dust, rain, insects, rodents and birds. This will affects the quality of the product and hence may have contrary economic effects on domestics and global markets. Some of the problems associated with open-air sun drying can be solved through the use of a cabinet type or indirect type solar dryer. The major drawback of all these types of conventional solar dryers is that they cannot be used in cloudy weather or during night time. By incorporating Thermal Energy Storage (TES) we can make use of the dryer throughout the day or at least during late evenings. Water is one of the best sensible TES medium within its operating range. Solar water heater is a device used to collect solar energy and heat up water without any electrical or fossil fuel aid. So the idea of this project is to incorporate solar dryer with solar water heater so that the dryer can be used even at late evenings or in cloudy weather, and also it can be used as water heater for hot water consumption.

MXene aerogel-based phase change materials toward solar energy conversion

Two-dimensional transition-metal carbides/carbonitrides (MXenes) have demonstrated wide application prospect in energy conversion and storage, mostly in the form of electrochemical energy storage. Compared with the conversion between chemical energy and electrical energy, an energy conversion process initiated by solar energy and driven by the physical change of energy materials will be a sustainable and environmentally friendly strategy. Therefore, a high-performance MXene aerogel-based phase change material for solar energy conversion and thermal energy storage is constructed. MXene nanosheets with an extinction coefficient of 25.67 L/(g.cm) at 808 nm demonstrate excellent light absorption performance, which can spontaneously convert the solar energy into thermal energy. The polyethylene glycol (PEG) possessing high affinity with MXene acts the medium for thermal energy storage and release in the process of fusion and solidification. The MXene@PEG aerogels are lightweight, with a density about 30 mg/cm3. The MXene skeleton is introduced as supporting materials to keep the shape of MXene@PEG aerogel stable during the phase change process. The MXene nanosheets improve the thermal stability of PEG, the thermal decomposition temperatures can be increased by 40 °C. The actual fusion and solidification enthalpies of MXene@PEG aerogels can reach 167.72 and 141.51 J/g, respectively. The photothermal storage efficiency of MXene@PEG aerogels reaches a relatively high value of 92.5%. This work provides a new type of scaffold for lightweight and shape-stable photothermal carrier and paves the way for the application of non-graphene 2D materials toward solar energy utilization.

Design and performance evaluation of solar - LPG hybrid dryer for drying of shrimps

The study was aimed at design and development of an energy efficient solar dryer suitable for continuous drying operation. In this dryer, water was used as a thermal energy storage and heat transfer medium, and air as an intermediate fluid. The major parts of the dryer were flat-plate solar water collector, water storage tank, drying chamber, heat exchanger, and liquefied petroleum gas (LPG) water heater. The dryer was designed to work mostly on solar energy during peak sunshine hours and LPG water heater as auxiliary heat source during low sunshine hours. The performance of the developed solar-LPG hybrid dryer was evaluated using shrimps (Metapenaeus dobsoni). The moisture content of fresh shrimp was reduced from 76.71% (w.b) to 15.38% (w.b) within 6 h of drying. The drying rate curve showed that shrimp drying occurred under falling-rate drying period. Results revealed that the water was capable of capturing maximum heat energy during peak sunshine hours. The maximum collector outlet temperature of 73.5 °C was obtained during drying. Overall, solar system supplied 73.93% of heat energy and LPG water heater assisted rest of the energy requirement due to lower incident solar radiation during start and end of drying. The maximum collector and drying efficiency obtained for shrimp drying were 42.37% and 37.09%, respectively.

Techno-economic analysis of using three Fresnel solar fields coupled to a thermal power plant for different cost of natural gas

In this paper, the effect of using three solar fields in a solar thermal power plant has been evaluated. Two separate solar direct steam generations are used to provide a portion of the energy required by the high-pressure turbine and low-pressure turbine. The third solar field is used for molten salt energy storage. If the energy stored during the daytime is not enough, the fossil fuel boiler will provide the rest of the energy needed. Given the current price of natural gas, the use of solar energy is not cost-effective, regardless of environmental issues, government incentives or external costs, such as health costs. Furthermore, the use of solar energy for the power plant was unable to make a significant reduction in electricity cost, regardless the 3.5$/MMBTU natural gas price. However, considering the complexity of the solar system, the use of solar energy for the price of the current natural gas is not recommended. By increasing the price of natural gas, the use of solar energy is more economically feasible.The results of the study show that the use of three solar fields (two separate solar fields to produce superheated steam for a high-pressure turbine and low-pressure turbine and a solar field for energy storage using molten salt as thermal energy storage medium) rather than one solar field reduces electricity consumption by 1.83%–13.78% for the price of 9 $/MMBtu natural gas. Although each of the first and second solar fields produce different energy quantities, and therefore, require different field areas, the field coefficient of the field is the same for both solar fields.

Review of solid particle materials for heat transfer fluid and thermal energy storage in solar thermal power plants

AbstractCurrent concentrated solar power (CSP) plants that operate at the highest temperature use molten salts as both heat transfer fluid (HTF) and thermal energy storage (TES) medium. Molten salts can reach up to 565°C before becoming chemically unstable and highly corrosive. This is one of the higher weaknesses of the technology. Solid particles have been proposed to overcome current working temperature limits, since the particle media can be stable for temperatures close to 1000°C. This work presents a review of solid particles candidates to be used as HTF and TES in CSP plants in open receivers. In addition, the interactions between solid particles with major system components are described in this review, for example, with TES system or heat exchanger. The parameters and properties of solid particles are identified from the material science point of view explaining their nature and the relation to the power plant efficiency and lifetime durability. Finally, future development is proposed; such as material selection according to each specific design, materials characterization, or durability test.

Experimental Study on Temperature Distribution and Heat Losses of a Molten Salt Heat Storage Tank

Two-tank molten salt heat storage systems are considered to be the most mature thermal storage technology in solar thermal power plants. As the key part of the system, the thermal performance of molten salt tanks is of great importance. An experimental thermal storage system with a new type of molten salt as a thermal energy storage medium has been built to investigate the temperature distribution of molten salt inside the tank during the cooling process from 550 °C to 180 °C. The temperature distribution of the salt was obtained, which reveals that temperature stratification appears at the bottom of the tank within the height of 200 mm. The position, with the maximum temperature difference of 16.1 °C, is at the lower edges of the molten salt storage tank. The temperature distribution was also measured to deepen our understanding of the insulation foundation, which shows that the maximum temperature appears at the middle upper part of the foundation and decreases radially. The heat losses of the molten salt tank were calculated by the classical equation, from which it was found that the heat loss decreases from 3.65 kWh to 1.82 kWh as the temperature of the molten salt drops from 550 °C to 310 °C. The effect of temperature stratification on the heat losses of the tank’s bottom was also analyzed.

Graphene oxide Pickering phase change material emulsions with high thermal conductivity and photo-thermal performance for thermal energy management

In this study, novel graphene oxide Pickering phase change material emulsions (GO Pickering PCMEs) containing 10 wt% of paraffin were prepared. GO was utilized as a Pickering stabilizer. The formation of GO Pickering PCMEs was successfully clarified via designing a contrast experiment. The effects of different GO concentrations on the morphology, rheological behavior, stability, thermal conductivity and thermo-physical properties of GO Pickering PCMEs are explored. The result shows that the optimal GO concentration is 0.2 wt%. In addition, the thermal conductivity of GO Pickering PCMEs with 0.2 wt% GO is 0.645 W m−1 K−1, reaching an increased percentage as high as 109.42% in comparison with that without GO. The addition of GO improves the efficiency of photo-thermal conversion performance of GO Pickering PCMEs. Owing to the high thermal conductivity and photo-thermal conversion performance of GO Pickering PCMEs, it can be expected that GO Pickering PCMEs possess great potential for heat transfer fluids and thermal energy storage media.

Material selection and properties for adsorption heat storage: perspectivity of TMPS series mesoporous silica nano-materials

Six samples from the TMPS family of mesoporous silica nano-materials from Taiyo Kagaku Co., Ltd. were studied for their potential as a medium for the adsorption thermal energy storage. Selected specimens are distinguished by their pore size from 1.9 to 4.1 nm and aluminium doping. As the adsorbate for the adsorption pair was selected water with the most advantageous properties of high latent heat and safe chemical properties. The tested materials doped with aluminium show high affinity towards the selected adsorbate and high uptakes. The theoretical storage energy density of the materials spans from 700 to 1700 kJ kg−1 based on the adsorption heat. The storage capacity depends mostly on the pore volume and partially on the pore size. The theoretical estimation shows the temperature gain of the adsorption potential as high as $$\varDelta T= 23\,^{\circ }\text {C}$$ for the material TMPS-1.5A with the smallest pore diameter and aluminium doping and as low as $$\varDelta T= 6\,^{\circ }\text {C}$$ for the TMPS-4R with the biggest pore diameter and without aluminium doping.

Fatty Amines As a New Family of Organic Phase Change Materials with Exceptionally High Energy Density at Ambient Temperature

The development of phase change materials (PCMs) with high energy density is of great importance for thermal or solar energy storage. In this work, we report for the first time the exploitation of fatty amines (FAs) as a new category of organic PCMs. FAs with carbon number in the range of 12-36 have extremely high latent heat (230-437 kJ kg-1), which is far higher than most of organic PCMs reported to date. The phase transition temperature of these FAs were measured to be in the range of 27.4-71.6 °C with very low supercooling degree (<10 °C). Taking advantages of these inherent feature, FAs may have great potentials as promising energy storage medium for thermal or solar energy storage especially under mild conditions. Based on the plentiful chemistry of amino groups of FAs, we also proposed a new strategy for preparation of form-stable PCMs composites with enhanced FAs uptake due to the strong electrostatic interaction between basic amino groups of FAs and acidic groups of supporting materials, which may also open a new and versatile route to the construction of FAs-based PCMs composites for renewable and sustainable energy saving systems.

Performance analysis of a solar dryer integrated with the packed bed thermal energy storage (TES) system

This study presents the energy and exergy-based performances of a solar dryer integrated with packed bed (TES) as thermal energy storage medium. As a sample application, drying kinetics of orange slices was determined. The aim of this study is to evaluate the thermal storage potential of the packed bed by focusing on energy consumption and exergy-sustainability indicators. Experiments were repeated twice a day (sunshine hours and off-sunshine hours). The results indicated that solar dryer integrated with packed bed reduced the moisture content of orange slices from 93.5% to 10.28% (at the first experiment) and 10.76% (at the second experiment), respectively. Total useful energy consumption for both the two status were detected as 89.892 MJ and 88.11 MJ, respectively. The exergy efficiency for the drying system during the sunshine hours ranged from 50.18 to 66.58%.The exergy efficiency of the drying process, in case of using the stored thermal energy, also changed between 54.71 and 68.37%. Moreover, a mathematical model was developed to predict the change of the moisture ratio of orange slices during time. According to the results of the model, Modified Henderson and Pabis Model presented the optimum parameters for determining the drying kinetics of orange slices.

Plate type heat exchanger for thermal energy storage and load shifting using phase change material

The study presents an experimental investigation of a thermal energy storage vessel for load-shifting purposes. The new heat storage vessel is a plate-type heat exchanger unit with water as the working fluid and a phase change material (PCM) as the energy storage medium. The thermal characteristics of the heat exchanger such as heat transfer coefficient, effectiveness, efficiency, water exit temperature, heat storage rate, total energy storage capacity and storage time were experimentally evaluated as a function of various inlet conditions. The compact parallel plate design showed an enhanced the performance compared to conventional storage systems with an effectiveness up to 83.1% even when a PCM of low thermal conductivity is used. The proposed phase change energy storage system not only can deliver substantial benefits as a thermal energy storage medium, but also provides cost savings in infrastructure, equipment, and maintenance/operations compared to conventional systems.

Thermophysical property measurements on tetrabutylphosphonium sulfate ionic semiclathrate hydrate consisting of the bivalent anion

To develop the “hydrate thermal energy storage technology”, it is desired to reveal the mechanism of the thermophysical property manifestation on ionic semiclathrate hydrate. The influence of valence on thermophysical properties has not been investigated so far. In the present study, the phase equilibrium temperatures and the dissociation heats of tetrabutylphosphonium sulfate ((TBP)2SO4) ionic semiclathrate hydrate were experimentally studied. (TBP)2SO4 hydrate consists of the bivalent anion, SO42−. The highest phase equilibrium temperature was 6.5 °C at the mass fraction range from 0.363 to 0.384. The largest dissociation heat was (168.8 ± 2.4) kJ·kg−1 at the mass fraction 0.374. These values of the phase equilibrium temperature and the dissociation heat were respectively lower and smaller than those of the ionic semiclathrate hydrates with the monovalent anion. As a new choice for thermal energy storage medium, (TBP)2SO4 hydrate would be suitable to the automotive air conditioner and the cold chain for blood or perishable foods.