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Experimental investigation on the use of water-phase change material storage in conventional solar water heating systems
Abstract
This paper presents an experimental investigation of the performance of water-phase change material (PCM) storage for use with conventional solar water heating systems. Paraffin wax contained in small cylindrical aluminum containers is used as the PCM. The containers are packed in a commercially available, cylindrical hot water storage tank on two levels. The PCM storage advantage is firstly demonstrated under controlled energy input experiments with the aid of an electrical heater on an isolated storage tank, with and without the PCM containers. It was found that the use of the suggested configuration can result in a 13–14 °C advantage in the stored hot water temperature over extended periods of time. The storage performance was also investigated when connected to flat plate collectors in a closed-loop system with conventional natural circulation. Over a test period of 24 h, the stored water temperature remained at least 30 °C higher than the ambient temperature. The use of short periods of forced circulation was found to have minimum effect on the performance of the system. Finally, the recovery effect and the storage performance of the PCM was analyzed under open-loop operation patterns, structured to simulate daily use patterns.
... During discharge, the average temperature of the storage tank dropped below the PCM melting temperature range (49-53 • C) within 6-12 h. Al-Hinti et al. [27] placed the PCM-filled aluminium bottles on two levels, as seen in Figure 8. The water temperature was maintained at 13-14 • C higher than the system without a PCM. ...
... During discharge, the average temperature of the storage tank dropped below the PCM melting temperature range (49-53 °C) within 6-12 h. Al-Hinti et al. [27] placed the PCM-filled aluminium bottles on two levels, as seen in Figure 8. The water temperature was maintained at 13-14 °C higher than the system without a PCM. ...
... The system with many small tubes could provide hot water for a longer time during the first discharge but a limited time in other discharges. A summary of the usage of LHTES modules inside the water storage tank is presented in Table 2. Al-Hinti et al. [27] Placed the PCM-filled aluminium bottles inside the hot water tank. Experimental The water temperature was maintained at 13-14 • C higher than the system without PCM. ...
Domestic water heating accounts for 15% to 27% of the total energy consumption in buildings in Australia. Over the past two decades, the latent heat thermal energy storage (LHTES) system has been widely investigated as a way to reduce fossil fuel consumption and increase the share of renewable energy in solar water heating. However, the research has concentrated on the geometric optimisation of the LHTES heat exchanger for the past few years, and this might not be sufficient for commercialisation. Moreover, recent review papers mainly discussed the development of a particular heat-transfer improvement technique. This paper presents perspectives on various solar hot water systems using LHTES to shift focus to on-demand performance studies, as well as structure optimisation studies for faster commercialisation. Future challenges are also discussed. Since the topic is an active area of research, this paper focuses on references that showcase the overall performance of LHTES-assisted solar hot water systems and cannot include all published work in the discussion. This perspective paper provides directional insights to researchers for developing an energy-efficient solar hot water system using LHTES.
... The use of water and PCM as thermal energy storage material has better thermal performance than conventional systems [13] [14]. PCM placed in the collector causes the exit water temperature to be more stable against fluctuations in the intensity of solar radiation [15] and increases the collector's performance [16]. The use of PCM in the SWH system can reduce thermal losses [17], prevent overheating in the collector [18], and increase the thermal efficiency of the collector [19]. ...
... The use of PCM capsules in SWH tanks has also been investigated experimentally. PCM is contained in vials [26], spherical capsules [12], vertical tube capsules [15], and horizontal cylindrical capsules [27]. For horizontally placed TES tanks, the capsules were arranged along the cross-section of the tank. ...
... The K-type thermocouples (6) were used to record heat transfer fluid (HTF) and PCM temperatures by an AT4532 multi-channel temperature meter data acquisition (9) and PC (10). A pump of Sharp SPS-109SN (15) was installed in the piping system after the TES tank. Figure 2 shows the arrangement of the capsules in the TES tank. The capsules are installed symmetrically where the axis of the capsule is parallel to the axis of the tank. ...
The encapsulation technique is one way to use latent heat storage material in a solar water heater tank. In this technique, several capsules may be arranged in the tank. In this study, the capsules were installed along the cross-section of the tank. There has been no discussion of which part of the capsule position has optimal heat energy with a capsule arrangement. Proper placement of the capsule arrangement can result in optimal thermal energy storage in the tank. This study aimed to investigate the effectiveness of installing capsules in a tank with different positions in terms of thermal energy storage. The study used an active solar water heater. The 24 capsules containing paraffin wax were arranged in a tank. The solar simulator was used as a heat source for the collector, and it was set at 1000 W/m2. The flow rate of water was 2 liters/minute. During the charging process, the water and paraffin wax temperature was recorded. The temperature evolution of water and paraffin wax obtained were used to analyze the thermal energy content. The results showed that the average heating rate for water and paraffin wax was 0.246 °C/min and 0.254 °C/min, respectively, so the capsule arrangement served as a suitable heat exchanger. The capsules installed at the top had an average heating rate increase of 111.4% compared to those at the bottom. Therefore, mounting the capsule at the top of the tank was more effective than placing it at the bottom.
... This is a result of better temperature modulation within the tank. Al-Hinti et al. [44] did an experiment on a hybrid tank system. The tank is of a total volume of 107.4 l with paraffin of volume 49.4 l. ...
... The initial temperature and the water mass flowrate in the storage have a direct effect on energy gains [45][46][47][48][49][50][51]. The higher mass flowrate induces a turbulent regime that enhances heat transfer and hence increase energy gains [44]. This is of special importance when the charging and discharging periods of the system are limited and can not be extended. ...
... Al-Hinti et al. [44] p Wu and Fang [45] p p ...
The aim of this paper is providing a detailed review for the applications of phase change materials (PCMs) in residential heating. The study focuses mainly on its use in domestic water heating systems. Different studies accounting for structural characterization, research methodology, and long term performance were carefully assessed. The gaps in the literature have been highlighted and recommendations for future studies have been presented. The technical gaps urge the need for research to be directed towards enhancing PCM properties in the domestic system, novel integration of PCM within the system, and optimization of system performance based on real-time accurate weather data. The economic opportunities for such systems were presented in different locations of the world by investigating different energy efficiency measures. The work presented herein identifies potential energy management opportunities that can significantly reduce our reliance on fossil fuels. Consequently, promoting a green future and mitigating greenhouse gas emissions. It is structured to provide guidance for researchers and engineers working in inclusion of PCMs in residential heating applications.
... During a 24 h trial, the stored water temperature remained 30 • C higher than the ambient temperature. One can use such devices for one's everyday routine [71]. ...
... The thermal properties of such an installation depend on the type of pools and fluid we use, the size of the facility, i.e., cross-sectional area and length, the slurry flow rate, and the temperature of the slurry inlet [81]. The device stores thermal energy during the day with sunshine and returns to the heating and cooling system of buildings on demand, where a second circuit is activated when the ambient temperature drops to the point that requires the commissioning of this device [7,71]. Depending on the thermal energy storage system, one can use these facilities for heating swimming pools, buildings, and other household appliances, depending on the system's architectural design. ...
Countries that do not have oil and natural gas but are forced to reduce pollution due to combustion have stimulated and developed new technologies for absorption, storage, and energy creation based on nanotechnology. These new technologies are up-and-coming because they will solve the problem without additional environmental burden. The first technology is based on phase change materials (PCMs) that store the thermal energy produced by the sun and release it when requested. In the context of this article, there is a discussion about some devices that arise from this technology. The second technology is based on light nano-traps that convert solar energy into heat, which is then stored by heating water or other methods. The third practice is to absorb solar energy from nanoparticles, producing electricity. These technologies' principles will be discussed and analyzed to understand their perspectives.
... The PCM encapsulation can be of different shapes. The packed bed made of PCM-filled aluminum cans Fig. 14 with SWHS was investigated by Al-Hinti et al. [61]. The performance of the system was analyzed for open and closed-loop operation of the system. ...
... Fig. 14. Schematic representing the packed bed type LHSU studied by (a) [60] and (b) [61]. ...
The fluctuating and discontinuous availability problem of solar energy can be significantly reduced by utilizing thermal storage, especially latent heat storage (LHS). The most practically feasible designs of integrating the solar water heating systems (SWHS) with LHS are integrated collector storage (ICS) and separate collector storage (SCS). In the present article, the ICS-SWHS-LHS and SCS-SWHS-LHS designs have been extensively reviewed. The effect of operating parameters viz. HTF inlet temperature and mass flow rate have also been reviewed. For the ICS-SWHS-LHS, the flat plate collector (FPC) designs have been extensively studied in the literature. However, the thermal efficiency of the evacuated tube collector (ETC) has been found significantly better than the FPC-ICS-SWHS-LHS. For the SCS-SWHS-LHS, the thermal performance of all the designs of latent heat storage units (LHSU) has been found approximately the same. The thermal storage capacity of shell and tube type LHSU has found a maximum of all studied designs. A comparison between the ICS-SWHS-LHS and SCS-SWHS-LHS designs has also been presented. Both the designs have some merits and demerits in their design, operation, and performance. This study would be helpful for researchers and designers in selecting a particular design for specific applications.
... Solar water heating system with PCM in the water tank is a classic hybrid system of "SHTES + LHTES", which is frequently investigated in the last decades. The studies showed that with PCM, the tank volume can be reduced [203][204][205], the effective operation time can be extended [206,207], and the system efficiency can be enhanced [208]. Nkwetta et al. [209] explored the thermal performance of a hybrid TES system with a PCM/water storage tank. ...
... Thus, there is great potential (large temperature difference) to recover this energy for water heating or space heating. Since PCM keeps a [205] water PCM solar water heating system extend the effective operational time [206] water PCM solar water heating system ESD enhanced by 39%, exergy efficiency enhanced by 16%, operation time extended by 25%, improvement in thermal stratification [207] water PCM solar water heating system significant enhancement in system efficiency [208] water PCM electricity water heating system improvement in ESD shift and/or smooth peak power demand [209] graphite refrigeration system compared to the systems "without PCM" and "without PCM nor ice", the energy consumption reduced by 6.7% and 17.1%, CO 2 emission reduced by 7.2% and 17.5%, respectively [219] constant temperature during the storage (melting) process, it can recover the high-temperature condensation heat stably without causing great fluctuations in the sorption TES system. In the charging process, turn on V1 and turn off V2, V3, the thermal energy transfers from the high-temperature vapor to the PCM. ...
Thermal energy storage (TES) technology is playing an increasingly important role in addressing the energy crisis and environmental problems. Various TES technologies, including sensible-heat TES, latent-heat TES, and thermochemical TES, have been intensively investigated in terms of principles, materials, and applications. A bibliometric study between 2000 and 2019 is conducted to show the evolution of TES technology and to predict future trends. While the existing studies are focused on basic TES, advanced/hybrid TES technologies have attracted increasing interest and demonstrated outstanding merits in overcoming the disadvantages of basic TES. To promote the advanced/hybrid TES technologies, a review is conducted to summarize the progress in advanced storage cycles, hybrid storage materials, and hybrid storage systems. The comprehensive literature review indicated that latent-heat TES has been the focus in the past years. While thermochemical TES and its hybrid TES technologies show the greatest research potential and become an emerging hot topic. Each advanced/hybrid TES technology has a certain improvement over basic TES, such as increasing the energy storage density or energy storage efficiency, reducing the charging temperature, enhancing the thermal conductivity of the sorbents, stabilizing the discharging temperature, or improving the performance of the integrated systems. Apart from the published results, some potential advanced/hybrid TES technologies are put forward to further enrich the TES family and to improve the TES performance. This work aims to facilitate the advancement of advanced/hybrid TES technologies.
... The extended surfaces on the tubes increase the solar collector's heat transfer rate and efficiency [15]. Incorporating the encapsulated PCM inside the water tank is a promising technique to maintain the water temperature near the PCM melting temperature and above ambient temperature [16,17]. The shell-and-tube heat storage unit consists of two cylindrical pipes in which. ...
... They found that compared to ANN and ANFIS, the SVM approach yielded the best results. During the course of a 24-hour test, Al-Hinti et al. 10 investigated different configurations for external PCM storage tanks and they found that there was a 13 C-14 C increase in water temperature as well as the inlet temperature spike of the same amount. According to Chen et al. 11 heat transfer performance for the two-temperature model may be significantly enhanced by using PCM of paraffin in conjunction with aluminium structure of foam porous. ...
The present study has been carried out to improve the overall efficiency of a conventional flat plate solar collector (FPSC) using two different heat storage phase change materials (PCMs). Two grades of paraffin wax—Paraffin‐P116 (PCM‐1) and Paraffin‐5838 (PCM‐2) as PCM are selected for the analysis based on their high heat fusion rate, low thermal conductivity, and suitable phase transition temperature. The present code has been validated with experimental results and it showed a maximum error of 6.43% in predicting the water outlet temperature. Absorber plate temperature, useful heat transfer rate, water outlet temperature and efficiencies are estimated to improve the performance of FPSC with and without PCM for various flow rates (15 lph and 30 lph) with two different weights of PCM (9 kg and 14 kg) for three different locations in India, [Chennai (13.0827° N, 80.2707° E), Bengaluru (12.9716° N, 77.5946° E), and Delhi (28.7041° N, 77.1025° E)]. The maximum increment in the efficiency of FPSC with the use of PCM‐1 is 19.59% and with the use of PCM‐2 is 16.53%. Using 14 kg of PCM‐1 with the conventional FPSC at water inlet flow rate of 15 lph increases the overall thermal efficiency up to 19.59% compared with conventional FPSC. The maximum increase in the percentage of efficiency with PCM‐1 from conventional FPSC for different cases of 15 lph‐09 kg is 16.34%, 15 lph‐14 kg is 19.59%, 30 lph‐09 kg is 14.57% and 30 lph‐14 kg is 18.45%. From the present study, it can be concluded that the overall efficiency of FPSC is increased with the use of 14 kg of PCM‐1 with conventional FPSC at the inlet water flow rate of 15 lph.
... 23,24 PCMs can store and release energy at a particular temperature and therefore possess high energy densities compared to sensible storage material like water. 25,26 Both numerical as well as experimental studies have been carried out to explore the performance of solar thermal devices with PCMs. Mehling et al 27 conducted a numerical and experimental study of FPC incorporated with PCM storage and observed hot water for 50% to 200% longer time. ...
In the last two decades, metallic particles of nano sizes (~10⁻⁹ m) have been tested profoundly in volumetric absorption solar collectors (VASC) due to their excellent optical properties and broadband absorption in the entire solar spectrum. However, very limited studies are available for understanding the performance of integrated energy storage VASC systems using nanofluids. For the experimental work presented here, a hybrid nanofluid of gold nanoparticles in Azadirachta indica leaves extract has been synthesized by chemical route. The prepared hybrid nanofluid has shown good absorption in 400 to 700 nm wavelength range and hence achieved high photo‐thermal conversion efficiency for tested VASC system. Furthermore, commercially available paraffin wax is used as a phase change material (PCM) in thermal energy storage (TES) and further integrated with VASC to analyze the thermal performance of the system even after sunshine hours. The real‐time experiments were conducted using different working fluids, and at three mass flow rates, that is, 0.008 kg/s, 0.016 kg/s, and 0.033 kg/s, respectively, during mild winter days in the tropical climate of India. The study revealed a photo‐thermal efficiency enhancement of about 17.1% when hybrid heat transfer fluid was used in the VASC system with TES as compared to base fluid water but without TES. During the heating period, the maximum thermal gain of the hybrid nanofluid was observed to be about 15°C higher than the ambient temperature at mass flow rate of 0.033 kg/s. Thermal efficiency enhancement of about 23.8%, 24%, and 24.1% was observed with hybrid nanofluid compared to base fluid water at a mass flow rate of 0.008 kg/s, 0.016 kg/s, and 0.033 kg/s, respectively, when PCM was kept inside the tank. Furthermore, a maximum zero loss efficiency of 83.8% was estimated at an optimal mass flow rate of 0.033 kg/s for the TES‐integrated VASC system.
... For this raison, we have to use a circulation pump to homogenize the temperature of water in the tank. [17] Fig. 12: Water temperature variation in the tank at different nodes ...
The continuous increase in the level of greenhouse gas emissions and the rise in fuel prices are the main driving forces behind the efforts for more effectively utilize various sources of renewable energy. In many parts of the world and specifically in Tunisia, the direct solar radiation is considered to be one of the most promising sources of energy. Annual sunshine can reach 3288 kWh/m2/year be 6 kWh/m2/day. A greenhouse using means active conventional heating consumes 1 litter of fuel/m2/year which leads to 10 kWh/m2/year. Tunisia surface of greenhouse crops is about 1000 hectares this corresponds to 107 l of foil and 108 kWh .In order to reduce the cost of heating the agricultural greenhouse we used the vacuum solar collectors .Their efficiency depends at the same time upon the ambient climatic conditions and the thermal performances of vacuum solar collectors. Capillary polypropylene exchangers are used to attenuate the differences between the diurnal and nocturnal air temperatures under the tunnel greenhouses. Water circulates in these exchangers at hydraulic closed circuit. In this work we have realized an experimental study of a solar energy heating system. Two types of studies have been done. During the day the suspended exchangers recover the energy in excess for the plants comfort. This recovered energy is stored into the greenhouse ground through the buried exchangers the first one concern the functioning temperature of the heating system installed near the greenhouse and used to heat the water stocked in a tank of 300 litters. In the second type, the energy stored in the ground will be restored through the underground exchangers during the night; thermal energy already stored in the tanks is brought back by the suspended exchangers to heat the air greenhouse. In order to prove the efficiency of our system, we present thermal results relative to the effect of the heater system on the greenhouse microclimate and the agronomic results of the greenhouse culture of tomato. These results are very interesting compared to an unheated greenhouse and had a high effect on tomato quality.
... Over the past three decades, numerous studies have focused on exploring the benefits of LTES, 1-5 comparing various LTES configurations, 6,7 developing novel classes of PCMs, 8,9 and implementing LTES in solar domestic hot water (SDHW) systems. [10][11][12][13] Due to the low thermal conductivity of most PCMs, the heat transfer rate within LTES systems is limited, resulting in a reduced phase change rate during charging and discharging periods. To address this, various approaches have been proposed to enhance the LTES rate and accelerate the phase change process. ...
To enhance the thermal characteristics of a solar collector storage system, this study investigates the performance of a rectangular thermal energy storage (TES) tank by incorporating cascade phase change materials (cascade‐PCMs). Three different commercially available PCMs (RT44HC, RT54HC, and RT62HC) with distinct melting temperatures are employed. These cascade‐PCMs are utilized as slabs in vertical rectangular modules, which are integrated into the water TES tank. The heat transfer fluid (HTF) in the flat‐plate solar collector captures solar energy and transfers it to the TES tank, where it is stored as latent thermal energy. A two‐dimensional (2D) numerical model, utilizing the enthalpy‐porosity approach and conservation equations, is developed to analyze the melting and heat transfer processes within the TES tank. The model is validated against previous experimental and numerical data. Performance evaluation of the cascade‐PCMs tank is conducted during a 9‐h charging period (from 8:00 am to 5:00 pm) under Marrakesh weather conditions in Morocco. An optimization study is carried out to determine the optimal height of each cascade‐PCM. The results suggest that an optimal design with heights of 23, 16, and 11 cm for RT44HC, RT54HC, and RT62HC respectively, offers improved melting and storage quality. The thermal characteristics of the TES tank incorporating cascade‐PCMs are compared to those of a TES tank filled with a single phase change material (single‐PCM) during the charging period. The findings indicate that the cascade‐PCMs achieve complete melting, while the single‐PCM only reaches a melting fraction of 0.903 at the end of the charging process. Furthermore, the optimal configuration of the cascade‐PCMs storage tank exhibits slightly higher sensible and latent thermal energy storage capacity compared to the single‐PCM tank. The combination of the solar collector with the cascade‐PCMs storage tank results in a 3.47% higher average collection efficiency when compared to the single‐PCM tank.
... Kapsul silindris aluminium diisikan paraffin wax dan diletakkan di dalam tangki PATS vertikal. Air di tangki penyimpanan tidak turun di bawah 45 °C selama 24 jam pengujian [16]. Kanimozi & Bapu [17] memasukkan kapsul silinder tembaga berisi paraffin ke dalam tangki PATS dan menyimpulkan bahwa PCM mampu meningkatkan penyimpanan energi sistem. ...
Integrasi air dan phase-change material (PCM) menarik diterapkan pada pemanas air tenaga surya (PATS). Teknik enkapsulasi PCM menggunakan kapsul dapat dilakukan di dalam tangki PATS. Sejauh ini, karakteristik termal di dalam tangki PATS posisi horizontal berisi PCM yang berkaitan dengan variasi debit air belum pernah diungkap. Penelitian ini bertujuan untuk menyelidiki karakteristik termal tangki PATS yang melibatkan PCM dengan variasi debit air. Eksperimen menggunakan PATS sistem aktif dengan volume tangki 60 liter. Kapsul silinder berjumlah 24 buah diisi paraffin wax dan dimasukkan ke dalam tangki PATS. Termokopel sebanyak 20 buah dipasang di sisi air dan paraffin wax. Proses charging dilakukan selama 160 menit. Variasi debit air yang digunakan adalah 1 lpm, 2 lpm dan 3 lpm. Data temperatur air dan paraffin wax digunakan untuk menganalisis kinerja termal PATS. Hasil karakteristik termal dari tiga eksperimen kemudian dibandingkan. Energi termal akumulatif yang diperoleh untuk debit aliran 1 lpm, 2 lpm dan 3 lpm masing-masing adalah 12,09 MJ, 14,08 MJ dan 16,59 MJ. Penambahan debit aliran air mampu meningkatkan unjuk kerja termal sistem PATS yang melibatkan PCM.The integration of water and phase-change materials (PCM) is interestingly applied to solar water heaters (SWH). PCM encapsulation technique using capsules can be carried out in an SWH tank. So far, the thermal characteristics in the horizontal position of the SWH tank containing PCM related to variations in water flow have not been revealed. This study investigates the thermal characteristics of SWH tanks involving PCM with variations in water discharge. This experiment uses an active SWH system with a tank volume of 60 liters. The 24 cylindrical capsules were filled with paraffin wax and put into the SWH tank. There were twenty thermocouples installed on the waterside and paraffin wax. The charging process is carried out for 160 minutes. Variations of water discharge used are 1 lpm, 2 lpm, and 3 lpm. Water temperature data and paraffin wax were used to analyze the thermal performance of SWH. The results of the thermal characteristics of the three experiments were then compared. The accumulative thermal energy obtained for flow rates of 1 lpm, 2 lpm, and 3 lpm was 12.09 MJ, 14.08 MJ, and 16.59 MJ, respectively. The addition of the water flow rate can increase the thermal performance of the SWH system involving PCM.
... Cependant, des problèmes physiques et techniques (surfusion, corrosion, stabilité-cyclage, toxicité) pénalisent aujourd'hui la compétitivité de cette solution : en moyenne, elle est 1.5à 4 fois plus onéreuse qu'une cuve de stockage en eau [33]. C'est pourquoi la complémentarité des stockages latent et sensible aétéétudiéeà plusieurs reprises dans le cadre de la fourniture d'eau chaude solaire : MCP intégré au ballon d'eau chaude [38], MCP intégré au capteur solaire [39], MCP situé entre les capteurs et le ballon d'eau chaude [40]. ...
Dans le contexte climatique et énergétique actuel, des solutions doivent être trouvées pour remplacer progressivement l'usage des énergies fossiles. Le solaire thermique est une ressource disposant d'un fort potentiel encore trop peu exploité en France à l'échelle industrielle. Dans ce contexte, les grandes installations solaires thermiques sont de plus en plus étudiées. Actuellement, la majorité des études porte sur l'optimisation du dimensionnement des centrales en se basant sur des stratégies de pilotage standard. Le présent manuscrit propose une méthodologie de résolution mathématique pour la simulation et l'optimisation dynamique d'une centrale solaire thermique. Ce type d'optimisation permet de prendre en compte la dynamique de ce système, et en particulier la dynamique lente d'un stockage d'énergie thermique, et est réalisée en exploitant les degrés de liberté du problème tel qu'on le pose. Ainsi, en laissant libres certains paramètres de design, l'optimisation dynamique permet d'optimiser simultanément le fonctionnement et le dimensionnement de la centrale. Les différents éléments d'une centrale solaire thermique (champ solaire, échangeur de chaleur, stockage thermique, pompes, canalisations) sont modélisés et forment un système d'équations algébro-différentielles. Nous détaillons la méthode de collocation orthogonale sur éléments finis permettant de discrétiser ces équations et d'obtenir ainsi un système comprenant uniquement des équations algébriques. Différents modèles sont confrontés à des données expérimentales issues de la centrale de Condat-sur-Vézère et leur précision est quantifiée. Le développement d'une méthode par simulations et initialisations successives nous a permis de réaliser la simulation dynamique d'une centrale solaire thermique. Cependant, certaines contraintes de fonctionnement (règles de pilotage nécessaires pour saturer les degrés de liberté) sont difficiles à formuler de façon cohérente et implémentable dans le logiciel GAMS utilisé dans ces travaux. L'intérêt de l'optimisation dynamique est de tirer profit des degrés de liberté du problème afin de minimiser/maximiser une fonction objectif (en respectant les contraintes du problème) sans avoir à formuler des contraintes pour saturer les variables d'intérêt. Un premier problème d'optimisation dynamique a été formulé puis résolu suivant une stratégie orientée-équation. Sur un horizon de temps de cinq jours et avec un dimensionnement de centrale fixé, nous avons maximisé les bénéfices liés à la vente de chaleur solaire à un consommateur en optimisant le fonctionnement de la centrale. Cela a notamment fait ressortir des stratégies parfois contre-intuitives permettant une amélioration significative de la fonction objectif par rapport à des pilotages plus « classiques ». En particulier, l'utilisation d'une inclinaison dynamique des capteurs s'est montrée efficace, d'une part, pour augmenter l'énergie captée par le champ solaire et, d'autre part, pour gérer d'éventuelles surchauffes en défocalisant les capteurs par rapport à la trajectoire de captation maximale. L'utilisation d'un stockage thermique a également été utile pour permettre le déphasage entre la production et la demande. La formulation d'un second problème d'optimisation, sur un horizon de temps d'un an, a permis de minimiser le coût moyen de la chaleur solaire vendue au consommateur (sur la durée du projet) en déterminant le dimensionnement optimal de la centrale et les profils temporels optimaux des variables de fonctionnement en fonction de la courbe de charge. Des difficultés ont été rencontrées, notamment pour conserver un fonctionnement cohérent sur la période d'optimisation. Finalement, nous avons listé un certain nombre de pistes qui pourraient potentiellement améliorer les résultats obtenus.
... In particular, the annulus between the two cylinders is partially depressurized containing a small amount of water in the bottom (4 at 15 • C) which acts as PCM. PCM materials can improve the thermal behaviour of solar devices by reducing thermal losses [28][29][30][31][32][33][34]. The vapor that is produced creates a heat diode transfer mechanism from the outer vessel to the inner water storage tank ( Figure 1). ...
The paper presents a design and operation analysis of an Integrated Collector Storage (ICS) solar water heater, which consists of an asymmetric Compound Parabolic Concentrating (CPC) reflector trough, while the water tank comprises two concentric cylinders. The annulus between these vessels is partially depressurized and contains a small amount of water in the bottom of the outer vessel which dominantly contributes to the heat transfer from the outer to the inner cylinder. A multi-criteria optimization algorithm is applied to re-evaluate the design specifications of the parabolic surface, thus modifying the design of the entire ICS system and predict the necessary number of units for achieving the highest possible effectiveness with minimized fabrication costs and environmental impacts. The environmental footprint of the device is assessed through Life Cycle Assessment (LCA). The produced thermal energy in conjunction with the environmental and economic results are evaluated as a function of different configuration parameters regarding the water storage conditions, the solar radiation and the total pressure inside the annulus. The ultimate aim of the evaluation process is to offer new perspectives on the design principles of environmentally friendly and cost-effective devices with improved thermal performance.
... Οη Griffiths et al. [15] κειέηεζαλ πεηξακαηηθά ηε δηαηήξεζε ηεο ζεξκόηεηαο ελόο ICSWH ρξεζηκνπνηώληαο PCM ζε κνξθή θνληάκαηνο. Παξόκνηα, νη Al-Hinti et al. [16] κειέηεζαλ πεηξακαηηθά έλαλ ζπκβαηηθό ζεξκαληήξα λεξνύ ρξεζηκνπνηώληαο θεξί παξαθίλεο σο πιηθό PCM. Τν πιενλέθηεκα ηνπ ζπζηήκαηνο απηνύ εληνπίδεηαη ζην γεγνλόο όηη ην ζεξκό λεξό ρξήζεο είλαη δηαζέζηκν γηα πεξηζζόηεξν ρξνληθό δηάζηεκα, αθόκα θαη πέξα από ηελ πεξίνδν ζέξκαλζεο. ...
... The usage of PCM module was noted to supply hot water for longer duration. Al-Hinti et al. [71] encapsulated paraffin wax in cylindrical aluminum containers and placed in a storage tank at two levels. The suggested design had an advantage of 13-14°C higher temperature over the storage tank without PCM. ...
Phase change materials (PCMs) have significant number of applications. PCMs plays a vital role in managing the supply and demand of the energy. The present work deals with the review of containers used for the phase change materials for different applications, namely, thermal energy storage, electronic cooling, food and drug transportation and solar water and space heating. The material and geometry of container plays a crucial role in the thermal performance of the system. The rectangular containers are the most preferred containers followed by the cylindrical one due to the fast charging of the PCMs. The most important properties of containers are; it should be leak proof, accommodate volume change and should have high thermal conductivity to improve the heat exchange. For encapsulated PCMs, the thermal and structural stability is very important in addition to the above properties. Aluminum is widely used container material due to it’s high thermal conductivity, good corrosion resistance and lower weight.KeywordsThermal energy storagePhase change materialsLatent heatEncapsulated phase change materials
... Nowadays, the investigators are concentrating on improving the heat storage of SWH by means of numerous materials of phase shift [11,12,13]. Al-Hinti et al. [14] collectors by putting paraffin wax as the PCM inside the water storage tank. Their research recorded that 55°C hot water temperature, including the drawn-off effect, can be produced during the daytime, and 30°C warm water temperature in the very next morning. ...
In this work, an effort has taken to improve the thermal storage capacity of the evacuated tube solar water heating (SWH) system by means of a new kind of twin-nano/paraffin as a thermal storage medium. Beforehand, the twin-nano/paraffin has been prepared by amalgamating 1% mass of twin-nanoparticles (comprising an equal quantity of SiO2 and CuO nanoparticles) within the paraffin. The experiments were performed in three cases, viz., without paraffin, with paraffin, and with twin-nano/paraffin under the real-time solar conditions on the clear sunny days. The thermal storage characteristics had been measured in terms of the hotness of available hot water in the storage tank during the second day morning. The experiment for the each case was performed for twenty four hours continuously from the first day morning to next morning. During the experiment, the water was drawn-off after twelve hours, i.e., at 6 p.m in the evening, so as to replicate the real-time hot water demand in households. The experiments proved that the integration of paraffin and further, twin-nano/paraffin enhanced the thermal storage capacity of the evacuated tube SWH, by improving the temperature of available hot water during the next morning. The results substantiated that the water temperature was augmented by 8.8 °C and 11.7 °C, respectively with paraffin and twin-nano/paraffin. The enhancement was noticed to be significantly higher for the case with twin-nano/paraffin.
... Usage of fin is efficient in PCM based heat exchanger when the PCM is of higher thermal conductivity, for example, copper and graphite matrix. Hinti et al. [2] experimentally claimed that using PCM based heat exchanger has higher efficiency than sensible heat storage. Usage of external or internal fins decreases PCM's solidification time, and fin thickness has less effect than the length of the fin [3]. ...
In these modern times, the requirement of the energy is not always constant but often periodic. In a hot climatic country like India, a large amount of energy is consumed in cooling application. A heat-exchanger which can store the thermal energy during off-peak hours and use the same energy during peak hours for cooling applications may flatten the periodic energy requirements. Water has a very high value of latent heat of fusion. This latent heat can be utilized to store the thermal energy and use it at a later stage for cooling purposes. The cooling temperature management will be more effective during the phase change process due to the constant fluid temperature. The present study analyzes the heat transfer performance of Ice-Freezing type phase change material (PCM) based heat-exchanger (HEX) during the solidification process. The prediction of solidification time and variation of heat transfer coefficient (HTC) under various configurations is performed. commercialized computational fluid dynamics (CFD) software, Fluent 19 is used to analyze the solidification phenomenon in water. To evaluate the optimum element size, Mesh-independent study is conducted on a single block. Initially, the single block is considered for analyzing the solidification process. The simulations are performed on multiple pipe with varying pitch. The results indicated a drastic change in solidification time as the pitch is decreased. An optimum pitch has to be decided based on the application. The transient variation of the HTC during the solidification process is studied. Initially, during the sensible cooling stage, the HTC decreases at a faster rate. While during the solidification process, the transient variation in HTC is less.
... As an excellent PCM for the photothermal transformation, paraffin wax is frequently used in the field of solar energy storage applications at the moderate and low temperatures, due to its favorable properties, such as having high latent heat of fusion and negligible super-cooling effect, being chemically stable and noncorrosive (Jurčević et al. 2020b;Meng and Zhang 2017). One of the applications of solar energy is buildings, where solar energy is exploited to obtain thermal comfort and air quality with minimum consumption of energy (Al-Hinti, Al-Ghandoor, and Maaly et al. 2010;Fazilati and Alemrajabi 2013). In building applications, the window filled with paraffin wax can reduce energy consumption while improving the indoor thermal environment and achieve the goal of comfort level under various climatic conditions (Li et al. 2016a). ...
Experimental investigation on thermal properties of Al 2 O 3 nanoparticles dispersed paraffin for thermal energy storage applications, Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, ABSTRACT Addition of Al 2 O 3 nanoparticles into paraffin wax is beneficial to improve the thermal conductivity of paraffin wax. Moreover, it has effect on the other thermophysical properties of paraffin wax such as the thermal diffusivity and volumetric heat capacity. In the present paper, the two-step method was used to prepare the nanofluids of Al 2 O 3 nanoparticles and paraffin wax and then the influence of temperature and volume fraction of Al 2 O 3 nanoparti-cles on the thermal conductivity, thermal diffusivity, and volumetric heat capacity of the nanofluids was investigated. The experimental results show that the changing trend of the above-mentioned properties of Al 2 O 3 /paraffin shows a slight regularity with increasing temperature. The thermal conductivity of nanofluids is enhanced at 20°C, and the largest thermal conductivity attained is 0.38 W/m·K at the volume fraction of 0.01%, which led to 40% augmentation, compared with paraffin. The thermal diffusivity of nanofluids with the volume fraction 0.01%, 0.1%, and 1% varies by −31%, 13.5%, and −21% in solid state, respectively. Moreover, the volumetric heat capacity fluctuates with the increase in temperature, and the volumetric heat capacity of nanofluids with the volume fraction 0.01% and 0.1% is higher than that of 1% in liquid state.
... Schematic cross-sectional view of a hot water storage tank with PCM containers insert. Adopted fromAl-Hinti et al. (2010) ...
In recent years, various energy sources and methods have been used to heat water in domestic and commercial buildings. The known sources for water heating include electrical energy and solar radiation energy in the urban regions or burning of firewood in the rural areas. Several water heating methods may be used such as electrical heating elements, solar concentrators, flat plate collectors and evacuated tube collectors. This thesis focuses on ways to further improve the system’s performance for water heating through the combined use of solar energy and solar concentrator technique. Furthermore, the study proposed an alternative design method for the hot water storage tank.The solar collector-supporting frame was designed and analysed using Solidworks®. The forces acting on the structural members were simulated to determine the capacity of the frame to sustain the load, and the possible regions on the supporting frame, which could potentially fail while in operation.Energy performance was simulated for five years of operation using Matlab Simulink® software. This simulation was based on the use of three different data. The first is a five-year weather database of the City of Tshwane in South Africa. The second is a hot water consumption profile for a typical household. The third is the cost of additional heating with electricity depending on the time of use. This simulation allowed the validation of the choices of the different elements of the heating system.This study allowed the development of an approach for the design of a solar heating system by optimising the dimensions of the different elements for a typical household and a specific region.In addition, the use of polymeric materials and other materials like polyurethane, salt and aluminium is possible for the development of a hot water storage tank based on their inherent properties.Extending the findings in this thesis will further improve the designs for solar concentrator technologies and solar water heating systems. Therefore, some recommendations and suggestions are highlighted in order to improve the overall system design, analysis and performance
... Besides the advantage of energy storage, integration of LHS having PCM can also additionally reduce the impact of radiation fluctuation in solar collectors [26]. Numerous studies can be found exploring this area involving different parameters such as lower thermal conductivity, storage density, thermal behaviour and performance, tank design etc to improve the quality [27][28][29][30][31]. With increasing importance given to the renewable energy assisted storage systems, charging/discharging or melting/solidification of PCM systems need to be studied carefully to identify suitable material, low melting time etc. ...
Solar assisted thermal energy storage systems have gained potential over last few years. The present study investigates the melting behaviour of PCM in an enclosure under two different boundary conditions representing outlet temperature pattern of a solar collector and is compared with results of a baseline case with isothermal heating. Output temperature of a coaxial evacuated tube for two typical months have been used in the study and with this coupling of solar collector output and PCM, thermal energy storage of a particular type of solar collector is assessed. Lauric acid, an organic phase change material is used for the analysis. Conduction and convection both being equally important in such problems, Bejan's heatline concept is invoked to the current problem to study the heat flow in phase change materials which imparts novelty of the presented work. 2-D numerical simulations are performed to imitate the phase change process in virtual environment applying "effective heat capacity" method. In the modelling of the problem, natural convection is handled by taking into consideration of Boussenisq approximation and the velocity in solid region is restricted by the Darcy law's source term. Comparison with baseline case shows, the output of February month delivers fastest melting. The utility of the evacuated tube is also seen here as it extracts 11.35 kJ and 7.33 kJ more solar energy which is stored in phase change material. Heatlines are not explored much to analyse the heat transfer in phase change material in previous studies and in the present work one such attempt is made which effectively illuminates the conduction and convection regime. Interestingly it shows the re-emergence of conduction process at a later point of time in liquid PCM. The visualization of heat flow also reveals that the liquid region acts as heat source for solid PCM.
... Finally, paraffin wax was found prosperous technology for increasing compact SWH systems thermal efficiency, which use heated material stored in solar collectors and rely on the environment . An experimental research by Al-Hiniti and his colleagues [15] examined the efficiency of solar water heating systems using phase changes content, PCM. A cylindrical storing tank containing paraffin wax PCM was used with a solar plate array packed in hot water. ...
The rapidly rising issue of declining the non-renewable resources available has focused the world attention on how renewable resources can be better used and harvested. Solar energy is one of the essential sources of renewable energy. Solar energy is a source of renewable energy for various applications in the world today. The present study is regarded as a summary of early studies on utilizing phase-change material in the use and storage of solar power. Due to its high thermal density, the isothermal nature and the easy power, the late thermosetting with the material is an advantageous way to store thermal energy. This paper summarizes how thermal energy can be efficiently stored via PCM in thermal energy storage systems of solar collectors. PCMs are isothermal, have higher density energy storage and are capable of operating in varying temperature environments. Therefore, an attempt was made in this paper to summarize an analysis of the various applications of phase change material (PCM), even solar collection device integrating PCMs.
This study illuminates the groundbreaking innovation and real-world utility of Latent Heat Thermal Energy Storage (LHTES) systems, unveiling an advanced and readily deployable solution for efficiently storing and releasing thermal energy. The Latent Heat Thermal Energy Storage (LHTES) system has been developed as a dispatchable solution for storing and releasing thermal energy. LHTES units use phase change materials (PCMs), which, through charging and discharging, store energy in the form of thermal energy. LHTES devices are more practical than alternative approaches because of their increased heat storage capacity, a sizable array of PCMs, and virtually isothermal behavior. LHTES systems also need one hermetic container with no salt pumps, pipelines, or heating trace requirement. One of the major challenges for such an LHTES system is the selection of proper PCMs to achieve the targeted applications. Despite significant efforts to improve the LHTE units, their efficacy and broader range of application remain limited. To address these issues, researchers have explored alternate techniques to enhance the efficacy of the PCM-based energy storage and exchange units. This review provides a comprehensive analysis of LHTES based on PCMs, focusing on exploring the potential of different techniques to improve their efficacy for enhanced thermal performance. The paper thoroughly scrutinizes the different aspects of phase change materials (PCM), methods of improvement in their performance, and different hybrid techniques. The present status of the PCMs-based advanced energy storage system is also presented systematically. Finally, challenges and future recommendations are also proposed for future researchers. The review's outcome reveals that hybridization techniques can potentially enhance the performance of PCMs-based energy storage units. This review work also covers the PCM-based energy storage system's economic aspects for long-term sustainability.
The use of a phase change material for the storage of latent heat is an ideal approach for the storage of thermal energy due to the high thermal density of storage, the isothermal nature of the storage process, and the ease with which it may be controlled. In recent years, there has been a rise in the use of latent heat storage systems for the purpose of energy conservation, solar heating systems, and waste heat recovery systems. The use of solar water heaters in practical settings has become more widespread. After providing a summary of the information that has been disseminated on the theoretical uses of water heaters, this article begins by examining the research that has been conducted on the practical applications of solar water heaters. This article includes covers methods to improve the efficiency of these systems as well as research on solar water heaters that combine phase change material with solar water collectors. This paper concludes with several suggestions for further research on phase change material-based water heaters. The completion of this review in a fruitful manner leads to a greater comprehension of the research and development of phase change material-based water heaters as well as the many methods by which these heaters might be improved.
Fossil fuel usage for heating applications must be reduced considering the issues related to the environment and the restriction of their resources. In this regard, attention is devoted to renewable energy sources to supply the energy requirements of different sectors. In the building sector, solar energy is harnessed for heating and cooling. Solar energy is applicable both directly and indirectly for heating using different technologies. The intermittent nature of solar energy obliges the use of storage units to make the solar systems applicable at night hours or during periods the low solar intensity. Various thermal energy storage materials have been utilized in different kinds of solar heaters to stabilize their performance, improve their reliability, and avoid issues related to variations in solar radiation. In this article, studies on the usage of thermal energy storage units in solar water heaters are reviewed and their key results are reflected. As one of the main conclusions of the reviewed works, it can be denoted that several factors such as the operation condition and characteristics of the storage unit are effective on the function of the systems combined with the thermal storage component. Aside from an increment in the operating hours of solar heaters, usage of storage units can boost both energy and exergy efficiencies. Furthermore, the study denotes that the power saving rate is influenced by the abundance of solar energy resources. In addition, it could be denoted that the performance of the systems is improvable by employing some ideas, such as the application of nanotechnology in storage materials.
Concentrated solar power facilities are becoming one of the most attractive power plants for converting solar energy into useful work. Solar thermal technology with improved energy efficiency and process temperature is being developed to lower the levelized cost of electricity. This paper examines recent advances in research and development of molten salt as a heat transfer fluid, along with its benefits and drawbacks for a concentrated solar thermal power plant. Significant progress has been achieved by improving the thermal stability and thermophysical characteristics of molten nitrate salt and chloride salt mixtures. Molten chloride salts with thermal stability above 800 o C and quaternary nitrate salt mixtures have been suggested for use as the next generation of concentrated solar power (CSP) technology by various researchers. Heat transfer fluid (HTF) with melting points below 71 o C has so far been developed using quaternary and ternary nitrate salt mixtures. So far, these potential molten salt mixtures are still facing competitive technical challenges such as high corrosivity and economic implications. Addressing some of these challenges within the short term may require the tradeoff of some thermophysical properties. However, further R&D work is necessary to show the applicability of these next-generation Thermal Energy Storage (TES) technologies in the real world.
The development of modern photovoltaic thermal systems (PV/T) is one of the most important steps in the application of using solar energy to produce both electricity and heat. Studies have shown that a system consisting of a heat-collecting tank the is most efficient system, in which the phase change materials (PCMs) are mixed with nanoparticles inside the system that are cooled by a cooling fluid (preferably a nanofluid). The PCMs have a high capacity to store energy in the form of latent heat. Nanoparticles are added to PCMs to treat and improve the low thermal conductivity of these materials. In this experimental study, nano-iron oxide III (Fe2O3 ) was added to paraffin wax in multiple mass fractions to evaluate the thermophysical changes that can be occur on the wax properties. Four samples of paraffin–nano-Fe2O3 were prepared with mass fractions of 0.5%, 1%,
2% and 3%, and their thermophysical properties were compared with pure paraffin (without nano additives). The results from this study showed that adding nano-Fe2O3 at any mass fraction increases the viscosity and density of the product. Thermal conductivity is improved by adding nano-Fe2O3 to paraffin wax by 10.04%, 57.14%, 76.19%, and 78.57% when adding mass fractions of 0.5%, 1%, 2%, and 3%, respectively. Stability tests showed that the prepared samples have excellent thermal stability (especially for 0.5% and 1% added nano-Fe2O3 ) to acceptable level of stability when adding 3% of nano-Fe2O3
. The nano-Fe2O3 paraffin PV/T system was tested outdoors to ensure its ability to operate in the harshest weather conditions of Baghdad city. The current experimental results indicated clear evidence of the success of the examined nano-PCM.
The low thermal conductivity of phase change materials (PCMs) is a crucial challenge in utilizing latent heat thermal energy storage (LHTES) systems. Incorporating fins into LHTES system is an effective approach to overcoming the low thermal conductivity of PCM and enhancing its performance. In the present study, computational fluid dynamics is used to investigate the effects of fin configurations and operating conditions on the performance of a shell-and-tube system assisted by fins. The heat transfer rate and liquid fraction are investigated to evaluate the thermal behavior of the proposed system. The enthalpy–porosity technique is employed to simulate the phase change. The temperature variations over time at different PCM locations are calculated and compared with the measured temperatures. The predicted results show that the fin thickness and the inlet temperature of the heat transfer fluid play a key role in reducing the melting and solidification time. The obtained results indicated that by increasing the fin thickness from 0.5 to 1 mm, the heat transfer rate increased by approximately 17%. Also, increasing the inlet temperature from 60 °C to 65 °C improved the heat transfer rate by 36.2%.
This paper presents the results of a 3D numerical model based on computational fluid dynamics (CFD) simulations to investigate the effect of placing cylindrical encapsulated PCM in a vertical hot water storage tank used in a household solar water heater with a mantle heat exchanger on thermal stratification. To validate the developed CFD model, an experiment was designed, and the numerical model was validated with the results from the experimental study. The influence of adding PCM in the tank on thermal stratification during discharging was analyzed for various parameters such as PCM type, its position, its amount, and its melting temperature. The results showed that the addition of the PCM into a mantled hot water tank increases the thermal stratification and the outlet water temperature in the tank during discharging mode according to without PCM case. In addition, placing the PCM tubes on the top part of the tank results in improvement of 4.98 °C (19.6 %) in the outlet water temperature compared to the case without PCM. It was found that the best thermal stratification was obtained in Case-7, where 56 pieces of PCM tubes filled with salt hydrate were placed at the top of the tank. In this case, the MIX number is 0.130, the Richardson number is 0.0930, and the exergy efficiency is 0.611.
This manuscript discusses one of the proposed methods for storing solar energy. Applications of PCMs, mono and binary nanofluids and molten salts as storage materials in solar energy are the major important techniques explained. A summary of various other solar energy storage materials that are currently under application is also presented. This paper overlooks the most current research in this specific field through the main focus of measuring absorption efficiency and effects of different particles on it with changed concentration and assessing thermophysical and storage properties of discussed materials. Presented studies expressed extraordinary efficiency enhancement and other outcomes of these materials. However, there are many problems associated with these materials that hindered their commercialization. These major problems include high costs, corrosion and erosion, pressure drop and friction factor appreciation and instability are also discussed.
In this study, a new phase change water tank (NPCWT) design with a vertical baffle was simulated. Unlike in traditional phase change water tank (TPCWT) designs, the phase change materials (PCMs) of the new design were concentrated on one side of the tank, and the baffle divides the tank into a phase-change zone and a non-phase change zone. The simulation results were first compared with experimental data to verify the accuracy of the simulation. Then, the FLUENT software package was used to compare the performance of the NPCWT with that of a common water tank (CWT) and a TPCWT of the same overall dimensions. The influence of the inlet flowrate on NPCWT performance was also studied. The heat storage and release performance of tanks were analyzed in terms of heat storage and release time, temperature distribution, and the utilization rate of the PCM. The simulation results show that the performance of the NPCWT is better than that of the other two designs. Compared with TPCWT, the heat storage time is reduced by 4.12%, while the heat release time is extended by 4.6%. It can also effectively solve the problem of the low utilization rate of PCM, and the heat storage capacity and other parameters are improved. The overall thermal performance of the NPCWT is at an optimum when the inlet flow rate is set to 0.2–0.3 m/s.
Bioactive constituents like vitamins, essential oils, enzymes, antioxidants and flavors have important significance but some properties like poor water solubility, low stability against temperature, light, oxygen and low bioavailability limit their usage in various applications. Herewith it has been significant to improve new encapsulation technologies to use bioactive compounds effectively. In this respect, nano capsulation holds promise in the improvement of biocompatibility, controlled release and the proper targeting of large quantities of living organisms. Nowadays, electrospun nanofibers with their unique structure are incredibly favorable materials that are important in numerous usage fields. Electrospinning is one of the economical and easy technologies to produce nanofiber/nanofibrous webs which have excellent properties like high surface area-to-volume ratio, being feather-light, nano-porous nature, adaptability in surface functionalities, good mechanical properties and high permeability. This process improves the physical and functional properties of nano and microstructures and assures highly effective encapsulation.
In the present work, an experimental assessment of the performance of a Solar Water Tank (SWT) integrated with Nano-enhanced Phase Change Material (Ne-PCM) and a Stirrer. Two configurations of SWT/Ne-PCMs, a spiral-type and a jacketed shell-type heat exchangers are designed and developed. These SWTs are integrated with the Nano-enhanced PCM within cylindrical capsules. A laboratory-scale experimental setup is conducted to examine the performance effect of the SWTs integrated with a propeller stirrer. In addition, an analysis of the effects of various process parameters including HTF flow rate and stirring speed was carried out. The results show that compared to the jacketed tank (without stirring), the completion time for the SWT/Ne-PCM charging and discharging processes (with a stirrer and a coil) is reduced by 12.5% and 23.51%, respectively.
In this study, a numerical model with variable mushy zone constants was developed based on the enthalpy-porosity method for the unconstrained melting of phase change material (PCM) encapsulated in cylindrical containers inside hot water tanks. In particular, a method for dynamically determining mushy zone constants was established. Mushy zone constants were explicitly calculated for each element in the solid region and updated at each iteration in the solution procedure of the model. The model showed satisfactory performance, with a mean absolute relative error of 5.2% between experimental measurements and numerical results. Based on this model, the unconstrained melting process of PCM and the influence of the aspect ratio of the cylindrical container were investigated. Results showed that contact melting accelerated the heat transfer of PCM at the bottom region and further enhanced the natural convection of liquid PCM at the side region. Moreover, the aspect ratio exerted little influence on the heat transfer coefficient at side wall surfaces. The correlation between the total melting time and aspect ratio was also calculated. The peak total melting time occurred for an aspect ratio of 5.49, and the smallest total surface area corresponded to an aspect ratio of 2. Clearly, larger total surface areas do not necessarily result in shorter total melting time. Further analysis indicated that flatter containers likely to be preferable to slenderer containers in practical designs. In addition, increasing the percentage of the bottom surface area to the total surface area can increase the average heat transfer coefficient of latent heat storage units.
Latent heat storage materials undergo phase changes to maintain a constant temperature environment and are fast emerging as a passive “green” technology for thermal management. Phase-change materials (PCMs) typically have poor thermal conductivities; however, their response to rapid fluctuations in temperature can be sluggish. Here, we explore the feasibility of adding various aluminum alloy (AlSi10Mg) structures to speed up the thermal response. The cooling performance of various geometries with the same mass density was first investigated, and the best performing geometries were then further optimized to investigate the possible weight savings. Our results indicate that, for unidirectional heat flux, designs with 3D periodicity, such as triply periodic minimal surfaces, do not perform as well as those with 1D (parallel plates) and 2D (honeycombs) periodicity. Furthermore, a strong correlation was found between the cooling performance and the interfacial area density. An expanding melt front, which leads to an increase in the interfacial area for heat transfer over time, and even heat distribution were also observed to be advantageous. After optimization, the honeycomb design with tapered triangular rods surrounded by the PCM matrix was able to achieve greatest weight savings for a given performance requirement. Compared to a thermal management panel consisting solely of the PCM, it was able to keep a heated surface cooler by 90% and also outperformed a pure Al panel despite being more than 40% lighter.
Use of solar energy has seen significant growth in recent years. One of the key areas of direct use of solar energy is domestic water heating. A properly designed solar water heater can provide most of the hot water required for residential applications in a cost-effective and environmental-friendly manner. A major requirement of solar water heaters is the control of the water delivery temperature from the solar heater. Consistent water temperature should be maintained at the outlet of the system as required for specific applications. Also, heating of water is dependent on the availability of solar energy which naturally varies during the daytime and can be affected significantly by local weather conditions. One of the ways to overcome this difficulty is to use an intermediate phase change material (PCM)-based energy storage system which stores part of the solar energy during peak supply and releases it during lean periods. This chapter presents a study on the use of PCM-based energy storage systems for solar water heating. At first, a brief description of solar water heating process is given. This is followed by a discussion on the use of energy storage systems for solar water heating. Subsequently, a CFD model is presented to simulate the charging and discharging of a PCM-based energy storage system. The model is based on the enthalpy method and can capture the evolution of melting and solidification of PCM due to the flow of heat transfer fluid in the energy storage unit. The effect of important parameters such as flow inlet temperature and velocity, storage unit dimensions, and charging time on melting and temperature evolution is analyzed in detail.
Phase change materials (PCM) for thermal energy storage in solar energy systems have been the subject of a great deal of research in the literature. Despite this, the research results pertaining to the efficacy of PCMs in enhancing system solar fraction are mixed. The current paper explores this issue numerically within a systems context. A typical solar domestic hot water system is considered. The PCMs are introduced as vertical cylindrical modules contained within the water tank, thus forming a hybrid PCM/water thermal storage. Water flowing along the length of tank is used as the heat transfer fluid. A model was developed based on the enthalpy-porosity method to solve for the phase change process within the PCM modules. The model was thoroughly validated and verified and predictions were in good agreement (less than 5% deviation) with results from the literature. The hybrid tank model was linked with the collector performance and the system was tested for typical days of Canadian weather with a dispersed demand profile. The solar fraction of the hybrid system was compared to that for an identical system using water-only as the thermal storage medium. The system analysis explores the impact of storage volume on solar fraction for systems with and without PCMs included. The systems approach is critical since it allows for the coupled effects of the thermal storage, solar collector, and household load to be incorporated. The analysis clearly shows that incorporation of PCMs into the thermal storage results in enhanced solar fraction at undersized tank volumes relative to the demand. In contrast, as the tank volume is increased, the benefit of the PCMs diminishes and identical performance is obtained between the two systems at large volumes. An energy balance of the system shows that, despite marginally increased heat losses from the hybrid tank, the benefits of the hybrid storage at small storage volumes are due to the reduction in the collector fluid inlet temperature which increases the pump run time and thus the solar energy collected and reduction of collector losses.
Phase change materials are widely used as thermal capacitors in solar thermal systems. The phase change materials with carbon materials could directly absorb the solar energy and transfer to water for building heating, while are rarely reported. In this work, an Ethylene-Propylene-Diene Monomer based phase change material with expanded graphite is prepared. The photo-thermal performance of the phase change material is investigated with combined experimental and numerical method. The SiO2 aerogel is first used as the thermal insulator in the solar thermal systems with the high transmittance and low thermal conductivity. The effect of the phase change material height and tube passes number on the photo-thermal performance of the phase change materials are calculated. The results show that the new material has a tensile strength of 3.6 MPa, enthalpy of 126.8 J g⁻¹，and thermal conductivity of 1.106 W m⁻¹ K⁻¹. The phase change material with SiO2 aerogel could resist heat lost on the surface. The phase change material has good photo-thermal performance in solar thermal systems, could heat more than 200 L of hot water at daytime.
The weakness of an outdoor solar water heater (SWH) experiments is the difficulty in determining its thermal behavior. The fluctuation of solar radiation intensity causes the supply of energy received by SWH also fluctuate. The result is that the thermal behavior of the SWH cannot be known for specific parameters. This paper aims to investigate the thermal behavior of an active type SWH containing paraffin wax using the constant heat flux method. A phase change material (PCM) inserted into the capsule. The capsules were arranged in a tank to form a heat exchanger (HE). The thermocouples were mounted both on the waterside and the PCM side. The solar simulator installed on the top of the collector, and the SHW system placed indoors. The heat flux and water flow were set at 1000 W/m² and 2 LPM, respectively. The temperatures of water and PCM for 143 minutes charging recorded. The data obtained were used to analyze the thermal behavior of water and PCM. The results showed that the average heating rate of water and PCM was 0.227 °C/min and 0.205 °C/min, respectively. The value of this adjacent average heating rate shows that HE has functioned well in removing heat energy from water. The accumulated thermal energy produced was 13.08 MJ. Indoor experiments can reveal the thermal behavior of the SWH-PCM systems.
Global warming is increasing at an alarming rate nowadays, and to control its after effects is the most challenging task at present. Several steps have been undertaken to minimize its after effects, and in this direction, researchers have focused on the utilization of easily available renewable energy resources. In this perspective, solar energy stands out as a viable option. Solar energy utilization is one of the most attractive and efficient ways to utilize renewable resources for power generation and heating purposes. Nanomaterials generated through modern nanotechnology techniques have been employed which provides more efficient heat transfer and improvement in the performance of solar water heating. Nanocupric oxide (CuO) has been used for enhancement of heat transfer, thermal conductivity, thermal diffusivity of paraffin, and increment in the output temperature. But the presence of nanoparticles reduces the specific heat of paraffin. Field emission scanning electron microscopy and energy-dispersive X-ray (EDAX) have been used to examine the morphology of CuO nanoparticles, paraffin wax, and nano-CuO-paraffin composite. The maximum heat transfer rate and Rayleigh number are obtained as 5.7 KW and 8.84 × 107 pertaining to CuO nano-doped PCM composite while maintaining an air gap of 4 cm between the absorber plate and the glazing.
Thermal energy storage and phase change materials (PCMs) have become one of the most important research subjects in recent years. The present paper first introduces the generalities including the properties, advantages and disadvantages of various PCMs. Then the heat transfer modeling and enhancement techniques of Melting and freezing process of PCMs are summarized. Afterwards the application of PCMs in solar, electrical, thermal management, construction, textile, food, and pharmaceutical systems are reviewed. Finally, the challenges and prospects in research and applications of PCMs are presented. Previous studies show that use of PCMs has great potential to reduce energy consumption in various applications leading to the reduction of carbon dioxide emissions and environmental pollution. Organic PCMs have been widely used and proposed by various researchers due to their better stability and recycling. Using nanoparticles improves the PCMs’ performance and the thermal conductivity of PCMs and phase change time depends on the shape of the nanoparticles and increases with nanoparticle concentration. Some challenges such as high cost, the destructive effect of nanoparticles and PCMs on the human body and the environment, and the durability of PCMs after long-term use should be considered in the future researches.
A new type of solar collector was developed and its short term thermal performance was investigated. The solar collector, which exhibited a net solar aperture area of 1.44 m2, consisted of two adjoining sections one filled with water and the other with a phase change material with a melting and freezing range of about 45–50°C, i.e. paraffin wax in this study. The phase change material functioned both as an energy storage material for the stabilisation, theoretically, of the water temperature and as an insulation material due to its low thermal conductivity value. The results of the study indicated that the water temperature exceeded 55°C during a typical day of high solar radiation and it was kept over 30°C during the whole night. Covering the collector surface with an insulation blanket at a time when the water temperature was at its maximum improved the energy conservation of the water significantly. The instantaneous thermal efficiency values were between about 22% and 80%. The present solar collector was much advantageous over the traditional solar hot water collectors in Turkey in terms of total system weight and the cost in particular.
Latent heat storage is one of the most efficient ways of storing thermal energy. Unlike the sensible heat storage method, the latent heat storage method provides much higher storage density, with a smaller temperature difference between storing and releasing heat. This paper reviews previous work on latent heat storage and provides an insight to recent efforts to develop new classes of phase change materials (PCMs) for use in energy storage. Three aspects have been the focus of this review: PCM materials, encapsulation and applications. There are large numbers of phase change materials that melt and solidify at a wide range of temperatures, making them attractive in a number of applications. Paraffin waxes are cheap and have moderate thermal energy storage density but low thermal conductivity and, hence, require large surface area. Hydrated salts have larger energy storage density and higher thermal conductivity but experience supercooling and phase segregation, and hence, their application requires the use of some nucleating and thickening agents. The main advantages of PCM encapsulation are providing large heat transfer area, reduction of the PCMs reactivity towards the outside environment and controlling the changes in volume of the storage materials as phase change occurs. The different applications in which the phase change method of heat storage can be applied are also reviewed in this paper. The problems associated with the application of PCMs with regards to the material and the methods used to contain them are also discussed.
Abstract
The time variations of the water temperatures at the midpoint of the heat storage tank and at the outlet of the collector in a conventional open-loop passive solar water-heating system combined with sodium thiosulfate pentahydrate-phase change material (PCM) were experimentally investigated during November and then enhancement of solar thermal energy storage performance of the system by comparing with those of conventional system including no PCM was observed. It was observed that the water temperature at the midpoint of the storage tank decreased regularly by day until the phase-change temperature of PCM after the intensity of solar radiation decreased and then it was a constant value of 45 °C in a time period of approximately 10 h during the night until the sun shines because no hot water is used. Heat storage performances of the same solar water-heating system combined with the other salt hydrates-PCMs such as zinc nitrate hexahydrate, disodium hydrogen phosphate dodecahydrate, calcium chloride hexahydrate and sodium sulfate decahydrate (Glauber's salt) were examined theoretically by using meteorological data and thermophysical properties of PCMs with some assumptions. It was obtained that the storage time of hot water, the produced hot water mass and total heat accumulated in the solar water-heating system having the heat storage tank combined with PCM were approximately 2.59–3.45 times of that in the conventional solar water-heating system. It was also found that the hydrated salts of the highest solar thermal energy storage performance in PCMs used in theoretical investigation were disodium hydrogen phosphate dodecahydrate and sodium sulfate decahydrate.
The performance of a compact phase change material (PCM) solar collector based on latent heat storage was investigated. In this collector, the absorber plate–container unit performs the function of both absorbing the solar energy and storing PCM. The solar energy was stored in paraffin wax, which was used as a PCM, and was discharged to cold water flowing in pipes located inside the wax. The collector's effective area was assumed to be 1 m2 and its total volume was divided into 5 sectors. The experimental apparatus was designed to simulate one of the collector's sectors, with an apparatus-absorber effective area of 0.2 m2. Outdoor experiments were carried out to demonstrate the applicability of using a compact solar collector for water heating. The time-wise temperatures of the PCM were recorded during the processes of charging and discharging. The solar intensity was recorded during the charging process. Experiments were conducted for different water flow rates of 8.3–21.7 kg/h. The effect of the water flow rate on the useful heat gain (Qu) was studied. The heat transfer coefficients were calculated for the charging process. The propagation of the melting and freezing front was also studied during the charging and discharging processes. The experimental results showed that in the charging process, the average heat transfer coefficient increases sharply with increasing the molten layer thickness, as the natural convection grows strong. In the discharge process, the useful heat gain was found to increase as the water mass flow rate increases.
The use of thermal energy storage (TES) systems is essential for solar power systems because of fluctuations in the solar energy input. Several classes of storage may be required for a single installation, depending on the type and scale of the solar power plant itself, and the nature of its integration with conventional utility systems. For heating and hot water applications, water and phase change materials (PCMs) constitute the principle storage media. Soil, rock and other solids are used as well. Water has the advantage of approximately 80% less volume than that of water for a temperature variation of 10°C, which is the difference between temperatures of a fully charged and a fully discharged storage tank. Some PCMs are viscous and corrosive, and must be segregated within the container in order to be used as a heat transfer medium. For heat storage, two PCMs must be available, unless heat pumping is employed. A variety of solids is also used; rock particles of 20 to 50 mm in size are most prevalent. Well-designed packed rock beds have several desirable characteristics for energy storage. The heat transfer coefficient between the air and the solid is high, the cost of the storage material is low, the conductivity of the bed is low when air flow is not present and a large heat transfer area can be achieved at low cost by reducing the size of particles. TES systems have also been suggested for storing thermal energy at medium (38–304°C) and high temperatures (120–566°C). For instance, systems in an oil-rock system for hot water and heat-recovery applications are examples of medium-temperature applications, while those in molten nitrate salt systems (an excellent storage medium) for steam production for process applications are for high temperatures. Oil-rock TES, in which the energy is stored in a mixture of oil and rock in a tank, is less expensive than molten nitrate salt TES, but is limited to low-temperature applications. However, this oil-rock TES has been proven successful for solar thermal applications. The selection of the type of TES depends on various factors such as the storage period (diurnal or seasonal), economic viability, operating conditions, etc. In this article, a study of TES systems (including materials) is presented particularly with solar thermal applications in mind. The evaluation of their performances, cost and economic viability, ease of installation, cleanliness, environmental impact, safety factors, technological usability and applicability are discussed.
Energy storage is one of the key technologies for energy conservation and therefore is of great practical importance. One of its main advantages is that it is best suited for solar thermal applications. This study deals with a comprehensive discussion of the evaluation and the selection of sensible and latent heat storage technologies, systems and applications in the field of solar energy. Several issues relating to energy storage are examined from the current perspective. In addition, some criteria, techniques, recommendations, checklists on the selection, implementation and operation of energy storage systems are provided for the use of energy engineers, scientists and policy makers. Copyright © 1999 John Wiley & Sons, Ltd.
The objective of the present work is to investigate experimentally the thermal behavior of a packed bed of combined sensible and latent heat thermal energy storage (TES) unit. A TES unit is designed, constructed and integrated with constant temperature bath/solar collector to study the performance of the storage unit. The TES unit contains paraffin as phase change material (PCM) filled in spherical capsules, which are packed in an insulated cylindrical storage tank. The water used as heat transfer fluid (HTF) to transfer heat from the constant temperature bath/solar collector to the TES tank also acts as sensible heat storage (SHS) material. Charging experiments are carried out at constant and varying (solar energy) inlet fluid temperatures to examine the effects of inlet fluid temperature and flow rate of HTF on the performance of the storage unit. Discharging experiments are carried out by both continuous and batchwise processes to recover the stored heat. The significance of time wise variation of HTF and PCM temperatures during charging and discharging processes is discussed in detail and the performance parameters such as instantaneous heat stored and cumulative heat stored are also studied. The performance of the present system is compared with that of the conventional SHS system. It is found from the discharging experiments that the combined storage system employing batchwise discharging of hot water from the TES tank is best suited for applications where the requirement is intermittent.
Thermal energy storage in general, and phase change materials (PCMs) in particular, have been a main topic in research for the last 20 years, but although the information is quantitatively enormous, it is also spread widely in the literature, and difficult to find. In this work, a review has been carried out of the history of thermal energy storage with solid–liquid phase change. Three aspects have been the focus of this review: materials, heat transfer and applications. The paper contains listed over 150 materials used in research as PCMs, and about 45 commercially available PCMs. The paper lists over 230 references.
Heat-of-fusion storage materials for low temperature latent heat storage in the temperature range 0–120°C are reviewed. Organic and inorganic heat storage materials classified as paraffins, fatty acids, inorganic salt hydrates and eutectic compounds are considered. The melting and freezing behaviour of the various substances is investigated using the techniques of Thermal Analysis and Differential Scanning Calorimetry. The importance of thermal cycling tests for establishing the long-term stability of the storage materials is discussed. Finally, some data pertaining to the corrosion compatibility of heat-of-fusion substances with conventional materials of construction is presented.
Hot water heat stores with stratification are a common technology used in solar energy systems and reuse of waste heat. Adding a PCM module at the top of the water tank would give the system higher storage density, and compensate heat loss in the top layer. The work presented here includes experimental results and numerical simulation of the system using an explicit finite-difference method. Experiments and simulations were carried out using different cylindrical PCM modules. With only 1/16 of the volume of the store being PCM, 3/16 of water at the top of the store was held warm for 50% to 200% longer and the average energy density was increased by 20% to 45%. Furthermore, these 3/16 of water were reheated by the heat from the module after being cooled down in only 20 min.