Thermal Storage Time Research Articles

Study on the thermal storage performance of high-temperature molten salt spheres packed bed using different heat transfer fluids

The high-temperature packed bed latent heat thermal energy storage system (PBLHTES) system is regarded as the key to the efficient operation of concentrating solar power (CSP) system. The heat transfer and storage materials determine the thermal performance of the thermal energy storage (TES) system. In this study, a discrete scheme for the PBLHTES system has been programmed, and a one-dimensional non-equilibrium model has been established. The numerical results are in good agreement with the experimental findings of the references. Originally, the effects of different fluids' thermodynamic characteristics on thermal performance are studied. Three widely used heat transfer fluids for high temperature working conditions, namely mixed nitrate salt, mixed chloride salt, and thermal oil, are applied for the established packed bed system, respectively. Then, three systems are numerically simulated, and sensitivity analyses of the Reynolds number, Stefan number, and sphere diameter are performed. According to the results, raising the Reynolds and Stefan numbers improves the energy storage rate but leads to an increase in heat transfer temperature difference and a decrease in exergy efficiency. Increasing Stefan number enhances the thermal storage capacity of three systems but causes irreversible loss. Differently, increasing the particle diameter not only extends the thermal storage time and increases the heat transfer temperature difference in all three systems but also decreases the energy storage rate and exergy efficiency. Furthermore, the decreasing slope of exergy efficiency with an increase in Reynolds and Stefan numbers is slowing down in systems 1 and 2 but growing in system 3. With the increase in sphere diameter, the decline slope is decreasing in all three systems. Overall, it is critical to choose the suitable HTF in a traditional or novel PBLHTES system to optimize thermal storage performance.

Influence of using clay block with increassed mass on energy performance of an office builidng in Nis

The objective of the research was to compare various types of clay blocks in terms of construction thermal inertia parameters and the influence they would have on the energy performance of an office building located in Nis. For this, a new type of clay block with increased mass is proposed, and a custom approach for determining all relevant indicators is described, intensively relying on building energy performance simulations. Fourteen configurations of external walls made of clay blocks, including the newly proposed block with increased mass, were investigated using EnergyPlus with a custom weather file to obtain construction thermal storage indicators, i.e., time lag and decrement factor. The results show the average decrement factor of less than 1% and the average time lag of approximately 9 hours for the newly proposed clay block, which is very similar to the values obtained for commercially available clay blocks. In addition, the same model of the building was used to check the influence that this increased mass has on the energy performance of the building served by a low temperature radiant and fan coil system. The results indicate the possibility of reducing heating energy consumption by 3.65% by using the increased mass clay block, while maintaining similar wall U-values, when compared with regularly used clay blocks, with a negligible change in cooling energy consumption.

Template-free facile preparation of mesoporous silica from fly ash for shaped composite phase change materials

Traditional sol-gel template preparation method for mesoporous silica has limited its large-scale production and applications due to low production quantity, complex preparation process and high cost. In this paper, we proposed a novel template-free process to prepare mesoporous silica-based materials by acid etching of activated fly ash to improve the support performance for shaped composite phase change materials. The mechanisms of mineral phase transformation and pore formation during preparation of mesoporous silica from fly ash were systematically investigated, and the structure, morphology and thermal properties of as-prepared shaped composite phase change materials (SCPCMs) were characterized and analyzed. The results show that stable mullite and quartz could be transformed into potassium aluminosilicate minerals after calcined with K2CO3, and mesoporous silica-based materials with different pore shapes and specific surface area ranging from 330 to 490 m2/g could be prepared from as-calcined fly ash. The PEG/MS-I (ink bottle-shaped material) achieved the largest loading efficiency of 64.88%, and the highest melting phase change enthalpy of 88.38 J/g, which is 30.7% and 57.7% higher than that of PEG/MS-S (silt-shaped material) and PEG/MS-W (wedge-shaped material), respectively. After 20 thermal cycles, the loss of melting enthalpy for PEG/MS-I was only 3%, and the thermal energy storage and release time were 23.1% and 17.0% shorter than that of pure PEG, respectively. In all, the PEG/MS-I composite exhibited reliable thermal storage performance and temperature regulation ability, which provides the feasibility of application of fly ash-derived composite phase change material in energy storage field.

Study on the thermal storage performance of a new cascade structure phase change thermal storage tank

Due to the intermittent and fluctuating nature of solar energy, phase change thermal storage technology plays a crucial role in the field of solar thermal energy utilization. As a current research hotspot, the organic combination of a cascade setup and a thermal storage tank can significantly improve the performance of thermal storage. To this end, a new physical model of cascaded phase change thermal storage has been designed, and a corresponding numerical model of three-dimensional unsteady states has been established based on the conventional cascade structure. The equations were solved using the finite-difference method and the phase change material (PCM) melting process was simulated using MATLAB based on C language numerical programming and the simulation results were compared with literature for validation. The effects on the liquid phase fraction and heat storage capacity of the cascaded phase change storage tank were investigated for each level of PCM arrangement, the height-to-diameter ratio of the storage tank and the inlet temperature of the heat transfer fluid. The results show that compared to conventional cascade thermal storage tanks, the new cascade phase change thermal storage tank can decrease the thermal storage time by 33 % and increase the thermal storage rate by 42 %, optimizing the disadvantages of the conventional structure which significantly reduces the heat transfer rate in the late melting stage. When the arrangement of PCM in the tank is modified, the melting time is shorter for the solution that arranges the PCM in the order of decreasing melting temperature as the distance from the heat exchanger wall or from the inlet increases, and the complete melting time of the PCM is reduced by 28 % and 30 % respectively compared to other solutions, and the heat storage rate is increased by 35 % and 37 % respectively. The larger the height-to-diameter ratio, the faster the rate of heat transfer from the heat exchange pipe to the outermost side of the tank, resulting in a 19 % and 45 % increase in heat storage rate for the height-to-diameter ratio of 5.92 compared to 5.00 and 4.12, respectively. When the inlet temperature is increased from 85 °C to 95 °C, the melting rate is increased by 32 % due to the increased heat transfer temperature difference. The results presented in this paper can provide some theoretical reference for the optimal design of cascade phase change thermal storage units, etc.

Rational construction of citrus essential oil nanoemulsion with robust stability and high antimicrobial activity based on combination of emulsifiers

We have successfully constructed citrus essential oil (CEO, d-limonene is its main active component) nanoemulsion by the high-pressure homogenization method, whose droplet size, polydispersity index, and zeta potential were 34.23 nm, 0.235, and −25.87 mV, respectively. The effects of thermal treatment (−20–48 °C), pH (5–9), ionic strength (100–500 mM NaCl) and storage time (200 days) were examined on the physicochemical properties of all treatments. The antimicrobial activity of nanoemulsion was tested by determining the minimal inhibitory concentration against the four foodborne microorganisms (Escherichia coli (10 mg/mL), Staphylococcus aureus (0.150 mg/mL), Bacillus subtilis (0.312 mg/mL) and Saccharomyces cerevisiae (0.312 mg/mL)). Especially, compared with pure CEO, the antibacterial activity of its nanoemulsion against S. aureus (0.150 mg/mL) and B. subtilis (0.312 mg/mL) was increased by 43 and 86 times respectively. Industrial relevance: In this work, we constructed robust CEO nanoemulsions based on a combination of emulsifiers via the high-pressure homogenization method, which bring new insights into the preparation of nanoemulsions. There is great potential for nanoencapsulation of natural compounds in the field of food preservation. Furthermore, the results may provide valuable data for industrial scale-up application.

Numerical simulation of heat transfer for Al-Si@Al2O3 composite phase change heat storage particles

Composite phase change heat storage particles (CPCHSPs) parpered using metals and alloys with excellent thermal properties can be used in different fields such as solar thermal energy management, industrial waste heat recovery. Acquiring their heat transfer behavior in the thermal cycle process is the necessary for their utilization. Previous studies have focused mainly on low-temperature phase change heat storage materials, and the effect of thermal radiation has not been considered in their mathematical models. In this study, the combined effect of heat conduction, convective heat transfer, and thermal radiation was considered to simulate the heat transfer behavior during the melting/solidification of a CPCHSP. To ensure accurate simulations, a suitable value of the mushy zone parameter was selected (Amush = 107), and the results were verified experimentally. The results showed that when the thermal conductivity of the PCM remained lower than 20 W·m−1·K−1, the effect of radiation on the thermal storage time was greater than 10%. In the thermal cycle process, the Al-Si alloy melts from the bottom and moves upwards along the inner wall till completely melts, and then solidifies to form a “V” shape. An unstable position of the instant maximum value was observed during the melting/solidification process, and the overall maximum static pressure (Pmax, t) reached a peak value of 23 MPa after the Al-Si alloy had melted completely. Based on the Pmax, t observed, an air volume fraction of 18% is recommended in the optimized structural design of the CPCHSPs to maintain a low overall maximum static pressure for high heat storage.

Effect of Flow Channel Cross Section Shape on the Performance of Heat Storage Structure

A numerical simulation is carried out for the thermal storage process in a heat storage device with magnesia bricks as thermal energy storage medium. Three types of cross section shapes (square, hexagon, circle) of the flow channel are considered with the inlet air temperature as high as 1023K. The perssure drop, temperature distribution and temperature uniformity of the flow channel are obtained. The results show that the pressure drop of the flow channel with circle cross section is the lowest when the Reynolds number is less than 2300 (in this case the inlet velocity is 5m/s), While when the Reynolds number is more than 2300, the flow channel with square cross section has the lowest pressure drop. The thermal storage time of the heat storage device decreases with the increase of air velocity. The temperature distribution of the flow channel indicates that the flow channel with hexagon cross section has the best comprehensive performance.

IMMOBILIZATION AND APPLICATION OF PARTIAL PURIFIED LOVASTATIN PRODUCED FROM LOCAL ISOLATE ASPERGILLUS TERREUS A50 USING SOLID STATE FERMENTATION

This work was designed to study the free and immobilized partial purified lovastatin in various applications. The results of HMG-CoA reductase inhibition showed enzyme inhibition at 10 mM of standard and partial purified lovastatin with specific activity 0.056 and 0.062 U/mg protein respectively, compared with specific activity 0.277 U/mg protein without inhibitor. The results of the thermal stability and storage time on lovastatin for inhibition of HMG-CoA reductase demonstrated that the standard and partial purified lovastatin were stabled in temperatures between 20-40 ᵒC, then the stability begun to decrease at 45 ᵒC, while lovastatin was stable in storage time between 1- 8 hours, then the stability begun to decrease after ten hours at 40 ºC. The results of MIC for lovastatin were demonstrated that most tested concentration were showed antibacterial activity of free and immobilized partial purified lovastatin against Candida albicans, Escherichia coli, and Staphylococcus aureus with MIC values ranging from 15 to 75 µg/ml. Whereas the results of minimum bactericidal concentration (MBC) and minimum fungicidal concentration (MFC) showed that C. albicans, E. coli, and S. aureus had no growth with concentration ranging from 55 to 75, 55 to 75, and 30 to 75 µg/ml, respectively. As well as the results of the cytotoxic impact using MTT experiment indicated that partial purified lovastatin caused a reduction in cells viability (p ≤ 0.05) at a dose-dependent manner on MCF-7 cell lines, with a calculating IC50 of 138.1 µg/ml, compare with normal cell line (WRL 68 Cell Line) at IC50 of 198.7 µg/ml.

Modelling of variable‐speed refrigeration for fast‐frequency control in low‐inertia systems

In modern power systems, shiftable loads contribute to the flexibility needed to increase robustness and ensure security. Thermal loads are among the most promising candidates for providing such service due to the large thermal storage time constants. This study demonstrates the use of variable-speed refrigeration (VSR) technology, based on brushless DC motors, for the fast-frequency response. First, the authors derive a detailed dynamic model of a single-phase VSR unit suitable for time-domain and small-signal stability analysis in low-inertia systems. For analysing dynamic interactions with the grid, they consider the aggregated response of multiple devices. However, the high computational cost involved in analysing large-scale systems leads to the need for reduced-order models. Thus, a set of reduced-order models is derived through transfer function fitting of data obtained from time-domain simulations of the detailed model. The modelling requirements and the accuracy versus computational complexity trade-off are discussed. Finally, the time-domain performance and frequency-domain analyses reveal substantial equivalence between the full- and suitable reduced-order models, allowing the application of simplified models in large-scale system studies.

Experimental study on the storage and release characteristics of phase change materials with different nanomaterials as addictives

The effect of nanomaterials on the thermal behavior of Decanoic-Caprylic Acid (DA-CA) binary eutectic mixture was investigated experimentally. Different high thermal conductivity nanomaterials, including nano-sized iron oxide (Fe2O3), nano-sized copper (Cu), hydroxylated multi-walled carbon nanotubes (MWCNT-OH), and dispersant Span-60, were added into DA-CA, respectively. The nanomaterial-enhanced phase change materials (NePCMs) were prepared by the ultrasonic oscillation method. The effects of nanomaterials on the cool storage performance of DA-CA were studied from the types and concentrations of nanomaterials. The experimental results showed that as the nanomaterials mass concentration increased, the thermal conductivity increased first and then gradually stabilized. The thermal conductivity trend for the composites added to the nanomaterials was: 0.40 g·L−1 Fe2O3 > 0.10 g·L−1 MWCNT-OH > 0.30 g·L−1 Cu. DA-CA + 0.40 g·L−1 Fe2O3 exhibited the best thermal properties, and its thermal conductivity increased by 36.8%, and the thermal storage time decreased by 38%. After 500 times thermal stability test, the NePCMs still maintained the appropriate phase change temperature and high latent heat. Therefore, this material has potential as part of the cold chain logistics for fruit and vegetable preservation.

Analysis of heat transfer and flow in the solar chimney with the sieve-plate thermal storage beds packed with phase change capsules

A novel phase change heat storage for solar heating is proposed, where the phase change capsules (PCC) are piled up on the different sieve beds to form several porous heat storage layers, and the buoyancy force in solar chimney is utilized to drive the heating airflow in the system. Local thermal non-equilibrium (LTNE) is considered to be in the porous beds, so the heat transfer and flow in the porous thermal storage layer are analyzed based on the double energy equations and Brinkman-Forchheimer extended Darcy model, and the k-ε turbulent model combined with the above equations are also employed to study the effects of materials, porosity and particle size of PCC in the porous thermal storage as well as the characteristics of flow channel on the efficient of thermal storage. The simulations accord with the published experimental results. About 7%–25% higher thermal storage time occurs in the layer of PCC than that of Tuff and Basalt. The porosity and particle size in the porous layer have an impact on the thermal storage, and the better performance of thermal storage can be achieved at the optimized ratio of the width of flow channel to bed thickness in the system.

Use of Spectroscopic Techniques for a Rapid and Non-Destructive Monitoring of Thermal Treatments and Storage Time of Sous-Vide Cooked Cod Fillets.

In this work, the potential of spectroscopic techniques was studied to investigate heat-induced changes occurring during the application of thermal treatments on cod (Gadus morhua L.) fillets. Vacuum-packed samples were thermally treated in a water bath at 50, 60, 70 and 80 °C for 5 and 10 min, and further stored for one, four, and eight days at 4 ± 1 °C before analysis. Several traditional (including cooking loss, drip loss, texture, protein solubility, protein oxidation, and color) and spectroscopic (fluorescence and diffuse reflectance hyperspectral imaging) measurements were conducted on the same samples. The results showed a decrease in fluorescence intensity with increasing cooking temperature and storage time, while the impact of cooking time was only noticeable at low temperatures. Diffuse reflectance data exhibited a decrease in absorbance, possibly as a result of protein denaturation and increased scattering at higher cooking temperatures. Both fluorescence and diffuse reflectance data were highly correlated with color parameters, whereas moderate correlations were observed with most other traditional parameters. Support vector machine models performed better than partial least square ones for both classification of cod samples cooked at different temperatures and in prediction of the cooking temperature. The best classification result was obtained on fluorescence data, achieving an accuracy of 92.5%, while the prediction models resulted in a root mean square error of prediction of cooking temperature lower than 5 °C. Overall, the classification and prediction models showed good results, indicating that spectroscopic techniques, especially fluorescence hyperspectral imaging, have a high potential for monitoring thermal treatments in cod fillets.

Topology optimization of fins for energy storage tank with phase change material

Six models based on different fin configuration of the energy storage tank with phase change material were established. The fin structure of model 3 is designed by topology optimization method. The thermal storage and release process of the six models were calculated by numerical simulation method. The results show that according to the thermal storage and release process of model 2, fin of model 3 is designed by topology optimization method. Thermal storage and release process of model 3 are both satisfactory agreement with the topology optimization results. Uniformity of temperature and liquid fraction is also significantly improved. Moreover, the model 3 can reduce the thermal storage time by 70% compared to model 2 and reduce the thermal release time by 81%. Furthermore, by comparison with all the 6 models, model 3 with the fin design based on the topology optimization method is found to have the significant advantages of less fins, metal saving, and low weight.

Review of latent thermal energy storage systems for solar air‐conditioning systems

Solar air-conditioning is an important approach to satisfy the high demand for cooling given the global energy situation. The application of phase-change materials (PCMs) in a thermal storage system is a way to address temporary power problems of solar air-conditioning systems. This paper reviews the selection, strengthening, and application of PCMs and containers in latent thermal storage system for solar air-conditioning systems. The optimization of PCM container geometry is summarized and analyzed. The hybrid enhancement methods for PCMs and containers, and the cost assessment of latent thermal storage system are discussed. The more effective heat transfer enhancement using PCMs was found to mainly involve micro-nano additives. Combinations of fins and nanoadditives, nanoparticles and metal foam are the main hybrid strengthening method. However, the thermal storage effect of hybrid strengthening is not necessarily better than single strengthening. At the same time, the latent thermal storage unit has less application in the field of solar air-conditioning systems, especially regarding heat recovery, because of its cost and thermal storage time. The integration of latent thermal storage units and solar air-conditioning components, economic analysis of improvement technology, and quantitative studies on hybrid improvement are potential research directions in the future.

Evaluation of thermal performance through development of a PCM-based thermal storage control system integrated unglazed transpired collector in experimental pig barn

The application of unglazed transpired collectors (UTCs) in livestock barns is an excellent solution for air ventilation in winter, for reducing structural energy loss, and for improving indoor air quality. However, thermal energy generated within specific periods may overheat the inside of the livestock barns. Thus, this study developed and applied a PCM-based thermal control system for saving and utilizing excess thermal energy generated by the application of a UTC in a experimental pig barn, through which the corresponding temperature deviation and the thermal performance of the thermal storage system are analyzed. During the experimental period, the UTC plenum temperature rose up to 65 °C, which is approximately 35 °C higher than that of the outdoor air throughout the day. The nonlinear correlation between the amount of solar radiation and UTC efficiency was verified during the experimental period (R2=0.58). Throughout the heat storage stage, the excess heat energy generated at the UTC plenum had a verified heat storage efficiency of up to 85%, a daily average of 22%, and an effect of a temperature difference of the PCM of 22.6 °C. Additionally, an average daily efficiency of 57% and an effect of a temperature increase of 13.8 °C compared to the outdoor temperature were verified through the heat release stage. The average thermal storage time was about 5 h and 50 min and the average release time was about 2 h and 33 min. During the experimental period, the average energy generation in the UTC plenum was 13,548.21 kcal/day and the average storage and release energies were 7739.78 and 1793.47 kcal/day, respectively.

Thermodynamic Analysis of Packed Bed Thermal Energy Storage System

A packed-bed thermal energy storage (PBTES) device, which is simultaneously restricted by thermal storage capacity and outlet temperatures of both cold and hot heat transfer fluids, is characterized by an unstable operation condition, and its calculation is complicated. To solve this problem, a steady thermodynamics model of PBTES with fixed temperatures on both ends was built. By using this model, the exergy destruction, thermocline thickness, thermal storage capacity, thermal storage time, and other key parameters can be calculated in a simple way. In addition, the model explained the internal reason for the change of thermocline thickness during thermal storage and release processes. Furthermore, the stable operation of the PBTES device was analyzed, and it was found that higher inlet temperature of hot air, and lower temperature difference between cold and hot air can produce less exergy destruction and achieve a larger cycle number of stable operation. The work can be employed as the basis of the design and engineering application of PBTES.

Tropical fruit juice: effect of thermal treatment and storage time on sensory and functional properties.

Tropical fruits rich in polyphenols, ascorbic acid, and high antioxidant capacity can enhance the functional composition, flavor as well as the overall acceptance of their juices. The aim of this study was to evaluate the effects of pasteurization and storage time on the physical, chemical, and sensory quality parameters of two formulations of tropical fruit juice blends with high antioxidant capacity. Two formulations with different concentrations of acai, camu-camu, acerola, cashew apple, yellow mombin, and pineapple were pasteurized at 85°C for 30s, hot-filled in glass bottles, and stored in refrigerated conditions (5°C). Analyses for color, total antioxidant activity, total polyphenols, carotenoids, ascorbic acid, and sensory quality were performed before and after pasteurization as well as at 90 and 180day of storage. Pasteurization did not negatively affect the concentration of functional components and sensory properties. However, the storage time negatively influenced the sensory quality and reduced the ascorbic acid content of both the formulations. Further, the acceptability and the nutritional quality were still high in these products after 180-days of storage, thus, not preventing their consumption.

Study on the properties of a novel shape-stable epoxy resin sealed expanded graphite/paraffin composite PCM and its application in buildings

ABSTRACTIn this study, a novel phase change material (PCM) of epoxy resin sealed expanded graphite/paraffin composite was developed as an independent attachment for building applications. A relatively high thermal energy storage density and a high thermal conductivity (2.141 W/(m·K)) were obtained in the composite PCM. The mass fraction of paraffin in the composite PCM could reach 94% without leakage of liquid paraffin when being heated at 50°C for more than 3 h, and the thermal cycle stability was good. Moreover, the thermal storage and release properties of this composite PCM with different thicknesses were studied by numerical simulation. The results showed that the thermal storage and release time are proportional to the thickness of the composite PCM, and there was almost no temperature gradient during the thermal storage and release process, which indicated that the thermal conductivity of this kind of composite PCM was high enough for building applications.

Thermal storage characteristics for rectangular cavity with partially active walls

The work is directed at the numerical simulation of latent-heat thermal energy storage in a two-dimensional rectangular cavity with partially thermally active parts. The detailed transient computations are performed for the inclination angle varies from 0 to 90° based on horizontal ground, for the aspect ratio of the rectangular cavity varies from 0.5 to 2, and for the number of discrete heat source located in the heated wall varies from 1 to 4. Numerical results indicated that thermally active part heated by discrete heat sources is a promising alternative for high-efficient thermal energy storage, as the vector direction between gravitation and overall heat flux is opposite, and that the aspect ratio has significantly sensitized for the thermal behavior as the inclination angle is 90°. It is demonstrated that the optimized thermal storage behaviors are reached for the inclination angle of 0°, the aspect ratio of 0.5, and the number of discrete heat source of 4, with the requested thermal storage time reduced more than 40%. It is found that the formation of the multicellular flow structure during the early stage of melting process, while a merging of the small recirculating cells into larger ones is observed during the following stage.

Investigating the effect of graphene nanoplatelets on the thermal conductivity of KAl(SO4)2 · 12H2O

This article, taking phase change material (PCM) aluminum potassium sulfate dodecahydrate (KAl(SO4)2 · 12H2O) as the object of study, researches the effects of graphene nanoplatelets (GN) on the thermal conductivity of KAl(SO4)2 · 12H2O. Correlated analysis shows that KAl(SO4)2 · 12H2O can be combined with GN to form KAl(SO4)2 · 12H2O/GN composites. The thermal conductivity of KAl(SO4)2 · 12H2O/GN composites improves significantly with the increase of GN contents. When the content of GN up to 2.5 wt%, the thermal conductivity of the composites is 1.311 W/m · k, increasing by 120% compared with the pure KAl(SO4)2 · 12H2O, the thermal storage time reduces by 31.9%. Meanwhile, GN can improve the undercooling of KAl(SO4)2 · 12H2O. When the content of GN is 2.5 wt%, the minimum undercooling is 31.1 °C, reducing by 28.5% compared with the pure KAl(SO4)2 · 12H2O. X-ray diffractometry (XRD) analysis shows that the crystal structure of KAl(SO4)2 · 12H2O is basically unchanged with the composite of GN after circulation. In general, GN have a great effect on improving the thermal conductivity of KAl(SO4)2 · 12H2O and have a good application prospect in the field of phase change thermal storage.