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High supercooling and single functionalization are the main barriers to the large-scale application of microencapsulated phase-change materials (PCMs) in the construction industry. To address these issues, we propose a new inorganic microencapsulated PCM, PW@CaWO4, which was synthesized via the in situ polymerization method using inorganic CaWO4 as shell and phase-change paraffin wax (PW) as core. We investigated the effects of different emulsifiers and core-to-shell ratios on microcapsule properties and found that the PW@CaWO4 microcapsules have regular spherical topography and good uniformity in particle size. During the synthesis process, the CaWO4 shell provides convenient conditions for heterogeneous nucleation of PW and effectively reduces the supercooling degree. The minimum supercooling degree of the PW@CaWO4 microcapsules is only 1.00 ± 0.08 °C, which is 3.41 °C lower than that of PW. Moreover, the PW@CaWO4 microcapsules can absorb ultraviolet radiation and exhibit fluorescence, which originates from the peculiar WO42– structure in the CaWO4 shell, eliminating the need for doping other light-activating ions into the shell. The newly prepared microcapsules possess several advantages, including suitable particle size, low supercooling, good heat storage, high thermal conductivity, good short-wave ultraviolet absorption, peculiar fluorescence, excellent proof of leakage, and so on. The microcapsules can be applied to fluorescent architectural energy-saving coatings.

A thermal diode is a device where the effective thermal conductivity in one direction is higher than that in the opposite direction. Among various types of thermal diodes reported in the literature, the phase-change thermal diode yields a greater thermal rectification performance. However, there are some limitations to the current phase-change thermal diodes, such as complex structures, complicated manufacturing procedures, and sophisticated working mechanisms. More importantly, some thermal diodes involve toxic, rare and expensive constituent materials. Hence, a simple water-vapour chamber thermal diode utilising the latent heat from pure water is designed, assembled and investigated, both experimentally and numerically in this study. The effects of the temperature gradient across the thermal diode, and the water-air volume ratio inside the water chamber on the heat transfer and thermal rectification performance of the water-vapour chamber thermal diode are examined. Mathematical models for anticipating the heat transfer performance of the proposed thermal diode are also built and verified by the experimental results. It should be noted that this is the first study to investigate this kind of thermal diode theoretically and experimentally. The findings reveal that the forward effective thermal conductivity of the thermal diode shows a 50 % enhancement when the hot side temperature rises from 40 ℃ to 70 ℃. A maximum diodicity of 1.43 is reported at the water-air volume ratio of 0.5. The results also indicate that the heat transfer and thermal rectification performances of the thermal diode is improved for a high water-air volume ratio. There are lots of applications for the thermal diode. In this study, a thermal diode based solar thermoelectric power system is established. The findings show that a maximum power output of 0.057 W is reported when the hot plate temperature is 120 ℃ and the cooling temperature is 10 ℃.

phase change phase change

Abstract Actuators that convert external stimuli to mechanical energy have aroused strong attention for emerging applications in robotics, artificial muscles, and other fields. However, their limited performance under harsh operating conditions evidenced by the low cycle life and hysteresis has restricted their practical applications. Here, a thermal-driven actuator based on layered metallic molybdenum disulfide (1T MoS2) nanosheets is demonstrated. The active actuator film exhibits fully reversible and highly stable (>99.296% in 2700 cycles) thermal-mechanical conversion over a wide temperature window (from −60 °C to 80 °C). Importantly, 1T MoS2 film shows a fast response with the bending rate and the recovery rate of >1.090 rad s−1 and >0.978 rad s−1, respectively. The assembled actuator can lift 20 times its weight over several centimeters for more than 200 cycles. This work, for the first time, demonstrates the thermoresponsive characteristics of 1T MoS2 in developing the thermal actuator, which may open new opportunities for various applications, such as robotics, artificial muscles, and human assist devices.

Covering thermal screen on the front roof is one of the most general methods to improve the thermal performance of the solar greenhouse in China. Thermal screen control, however, is operator-dependent and based on empirical strategies. In order to more effectively manage the thermal screen, an optimal control method based on solar radiation and temperature difference between indoor and outdoor was established. The influence of different factors on the control of greenhouse thermal screen is systematically analyzed and the control function of the greenhouse thermal screen was calculated. The empirical control formula was established based on simulation which lasted for 62 days. As a result, the two-factor control method can significantly improve the air temperature when the thermal screen is controlled, and it can increase the average air temperature by 0.53 °C. Comparing with temperature difference, solar radiation has a greater impact on the control of thermal screen. The control method based on temperature difference and solar radiation can save 7.2% energy in winter. The research can provide reference for energy saving and automatic control of Chinese solar greenhouse.

Le système solaire de chauffage de l'eau (SWH) est l'une des applications les plus pratiques de l'énergie solaire, considérée comme une source d'énergie disponible, économique et respectueuse de l'environnement pour répondre aux demandes énergétiques du monde. Dans cette revue, les systèmes SWH existants et les aspects de conception des principaux composants, par exemple le capteur solaire thermique, le réservoir de stockage, l'échangeur de chaleur, le fluide caloporteur, la plaque absorbante, etc., ont été largement étudiés. Les recherches récentes visant à améliorer davantage les systèmes SWH et les applications pratiques potentielles sont examinées de manière critique. De plus, un concept relativement nouveau dans les systèmes SWH, qui utilise des nanofluides dans les capteurs solaires comme fluide de transfert de chaleur a été étudié en termes de critères de conception pour le développement de systèmes SWH. Le collecteur plat fixe (FPC) et le collecteur parabolique composé de suivi à axe unique (CPC) présentent des rendements thermiques de 45 à 60 % (plage de fonctionnement : 25 à 100 °C) et de 30 à 50 % (plage de fonctionnement : 60 à 300 °C), respectivement. L'utilisation de structures de stratification thermique, par exemple des diffuseurs, des déflecteurs, des membranes, des tissus, etc., est un outil efficace pour réduire les pertes de chaleur du réservoir de stockage ainsi que pour récupérer la plus grande énergie du capteur solaire. Il a été constaté que le revêtement de nanomatériaux, par exemple de nickel, de cuivre, etc., réduisait la perte de chaleur arrière dans les systèmes SWJ, ce qui augmentait éventuellement les performances thermiques du système. Les nanofluides constitués de nanotubes de carbone à parois multiples (MWCNT) et d'Al2O3 ont augmenté l'efficacité du FPC de 28,3 et 35 %, respectivement. De plus, en utilisant des nanofluides de CuO, l'efficacité du collecteur d'un collecteur à tube sous vide typique (ETC) a été augmentée jusqu'à 12,4 %. Plusieurs recommandations futures potentielles pour améliorer les performances du système SWH ont été formulées. El sistema de calentamiento solar de agua (SWH) es una de las aplicaciones más convenientes de la energía solar, que se considera una fuente de energía disponible, económica y respetuosa con el medio ambiente para satisfacer las demandas energéticas del mundo. En esta revisión, se estudiaron exhaustivamente los sistemas SWH existentes y los aspectos de diseño de los componentes principales, por ejemplo, el colector térmico solar, el tanque de almacenamiento, el intercambiador de calor, el fluido de transferencia de calor, la placa absorbente, etc. Se revisan críticamente las investigaciones recientes para mejorar aún más los sistemas de SWH y las posibles aplicaciones prácticas. Además, se ha estudiado un concepto relativamente nuevo en los sistemas SWH, que utiliza nanofluidos en colectores solares como fluido de transferencia de calor en términos de criterios de diseño para el desarrollo de sistemas SWH. El colector de placa plana estacionaria (FPC) y el colector parabólico compuesto de seguimiento de un solo eje (CPC) presentan eficiencias térmicas del 45–60 % (rango de funcionamiento: 25–100 °C) y del 30–50 % (rango de funcionamiento: 60–300 °C), respectivamente. El uso de estructuras de estratificación térmica, por ejemplo, difusores, deflectores, membranas, telas, etc., es una herramienta eficaz para reducir las pérdidas de calor del tanque de almacenamiento, así como para recolectar la mayor energía del colector solar. Se descubrió que el recubrimiento de nanomateriales, por ejemplo, níquel, cobre, etc., reduce la pérdida de calor de la parte posterior en los sistemas SWJ, lo que finalmente aumenta el rendimiento térmico del sistema. Los nanofluidos que consisten en nanotubos de carbono multipared (MWCNT) y Al2O3 aumentaron la efectividad de FPC en un 28,3 y 35 %, respectivamente. Además, utilizando nanofluidos de CuO, la eficiencia del colector de un colector de tubo de vacío típico (ETC) aumentó hasta en un 12,4 %. Se establecieron varias posibles recomendaciones futuras para mejorar el rendimiento del sistema SWH. The solar water-heating (SWH) system is one of the most convenient applications of solar energy, which is considered an available, economical, and environmentally friendly energy source to fulfill the energy demands of the world. In this review, existing SWH systems and design aspects of major components e.g., solar thermal collector, storage tank, heat exchanger, heat transferring fluid, absorber plate, etc. were extensively studied. Recent research to further improve SWH systems and potential practical applications are critically reviewed. Moreover, a relatively new concept in SWH systems, which is using nanofluids in solar collectors as heat transfer fluid has been studied in terms of design criteria for the development of SWH systems. Stationary flat plate collector (FPC) and single-axis tracking compound parabolic collector (CPC) exhibit thermal efficiencies of 45–60 % (operating range: 25–100 °C) and 30–50 % (operating range: 60–300 °C), respectively. The use of thermal stratification structures e.g., diffusers, baffles, membranes, fabrics, etc. is an effective tool to reduce heat losses from the storage tank as well as to harvest the highest energy from the solar collector. Coating of nanomaterials e.g., nickel, copper, etc. was found to reduce the backside heat loss in SWJ systems which eventually increases the thermal performance of the system. Nanofluids consisting of multiwall carbon nanotubes (MWCNTs) and Al2O3 increased the effectiveness of FPC by 28.3 and 35 %, respectively. Moreover, using CuO nanofluids, the collector efficiency of a typical evacuated tube collector (ETC) was increased by up to 12.4 %. Several potential future recommendations for improving the performance of the SWH system were stated. يعد نظام تسخين المياه بالطاقة الشمسية (SWH) أحد أكثر التطبيقات ملاءمة للطاقة الشمسية، والتي تعتبر مصدر طاقة متاحًا واقتصاديًا وصديقًا للبيئة لتلبية متطلبات الطاقة في العالم. في هذه المراجعة، تمت دراسة أنظمة SWH الحالية وجوانب تصميم المكونات الرئيسية على سبيل المثال، المجمع الحراري الشمسي، خزان التخزين، المبادل الحراري، سائل نقل الحرارة، لوحة الامتصاص، إلخ. تتم مراجعة الأبحاث الحديثة لزيادة تحسين أنظمة SWH والتطبيقات العملية المحتملة بشكل نقدي. علاوة على ذلك، تمت دراسة مفهوم جديد نسبيًا في أنظمة SWH، والذي يستخدم السوائل النانوية في مجمعات الطاقة الشمسية كسائل لنقل الحرارة من حيث معايير التصميم لتطوير أنظمة SWH. يُظهر مجمع الألواح المسطحة الثابت (FPC) ومجمع القطع المكافئ المركب أحادي المحور (CPC) كفاءات حرارية بنسبة 45–60 ٪ (نطاق التشغيل: 25–100 درجة مئوية) و 30–50 ٪ (نطاق التشغيل: 60–300 درجة مئوية)، على التوالي. يعد استخدام هياكل التقسيم الطبقي الحراري، على سبيل المثال، الناشرات، والحواجز، والأغشية، والأقمشة، وما إلى ذلك، أداة فعالة لتقليل فقد الحرارة من خزان التخزين وكذلك لحصاد أعلى طاقة من المجمع الشمسي. وجد أن طلاء المواد النانوية مثل النيكل والنحاس وما إلى ذلك يقلل من فقدان الحرارة الخلفي في أنظمة SWJ مما يزيد في النهاية من الأداء الحراري للنظام. زادت السوائل النانوية التي تتكون من الأنابيب النانوية الكربونية متعددة الجدران (MWCNTs) و Al2O3 من فعالية FPC بنسبة 28.3 و 35 ٪ على التوالي. علاوة على ذلك، باستخدام السوائل النانوية CuO، تمت زيادة كفاءة المجمع لمجمع الأنبوب المفرغ النموذجي (ETC) بنسبة تصل إلى 12.4 ٪. تم ذكر العديد من التوصيات المستقبلية المحتملة لتحسين أداء نظام المستودع الآمن.

This study examines the impact of incorporating phase change material (PCM) in photovoltaic thermal (PVT) systems on their electrical and thermal performance. Although PVT systems have shown effectiveness in converting solar energy into both electricity and heat, there is a necessity for studies to investigate how integrating PCMs can further enhance performance. The study also aims to explore the effect of solar irradiation and coolant mass flow rate on the electrical and thermal output of both PVT and PVT-PCM systems. A graphical user interface was developed within the MATLAB Simulink under the weather conditions of Amman, Jordan. The results show that the incorporation of PCM in PVT systems significantly reduces solar cell temperature and increases electrical efficiency. The highest electrical efficiency of a PVT system with PCM was found to be 14%, compared to 13.75% in a PVT system without PCM. Furthermore, the maximum achievable electrical power in a PVT system with PCM was 21 kW, while in the PVT system without PCM it was 18 kW. The study also found that increasing the coolant mass flow rate in a PVT system with PCM further reduced PV cell temperature and increased electrical efficiency, while the electrical efficiency of both the PVT and PVT-PCM systems decreases as solar incident radiation flux increases, resulting in a significant rise in cell temperature. At an increased solar radiation level from 500 W/m2 to 1000 W/m2, the electrical efficiency of the PVT configuration decreases from 13.75% to 11.1%, while the electrical efficiency of the PVT-PCM configuration falls from 14% to 12%. The findings of this study indicate that the use of PCM in PVT systems can lead to significant improvements in energy production and cooling processes. The results provide valuable information for designing and optimizing PVT-PCM systems.

Thermal ratcheting is a critical phenomenon associated with the cyclic operation of dual-medium thermocline tanks in solar energy applications. Although thermal ratcheting poses a serious impediment to thermocline operation, this failure mode in dual-medium thermocline tanks is not yet well understood. To study the potential for the occurrence of ratcheting, a comprehensive model of a thermocline tank that includes both the heterogeneous filler region as well as the composite tank wall is formulated. The filler region consists of a rock bed with interstitial molten salt, while the tank wall is composed of a steel shell with two layers of insulation (firebrick and ceramic). The model accounts separately for the rock and molten-salt regions in view of their different thermal properties. Various heat loss conditions are applied at the external tank surface to evaluate the effect of energy losses to the surroundings. Hoop stresses, which are governed by the magnitude of temperature fluctuations, are determined through both a detailed finite-element analysis and simple strain relations. The two methods are found to yield almost identical results. Temperature fluctuations are damped by heat losses to the surroundings, leading to a reduction in hoop stresses with increased heat losses. Failure is prevented when the peak hoop stress is less than the material yield strength of the steel shell. To avoid ratcheting without incurring excessive energy loss, insulation between the steel shell and the filler region should be maximized.

A theoretical model for describing the heat transfer characteristics of a turbine-based combined cycle (TBCC) engine cabin was established in Matlab/Simulink to quickly predict the thermal protection performance for engine accessories. The model’s effectiveness was verified by comparing the numerical results with the experimental data. The effects of different heat insulation layer thicknesses and fuel temperatures on the thermal protection performance are discussed; based on these effects, the heat insulation layer of 5 mm and fuel of 353 K were chosen to design the thermal protection cases. Nineteen different thermal protection cases were proposed and evaluated by using the model. Two representative accessories were chosen for the evaluation of the thermal protection performance of these cases. For accessory 1 with an internal heat source of 1000 W and internal fuel access, the thermal protection effect of adding a heat insulation layer and ventilation was the best, which decreased the accessory temperature by 43 K. For accessory 2 without an internal heat source, the thermal protection effect of adding a heat insulation layer to the casing and fuel cooling was the most ideal, which decreased the accessory temperature by 190 K. In addition, a comprehensive assessment was made to compare the performances of thermal protection cases.