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Abstract This paper presented a novel method of dissipating solar photovoltaic heat based on the technology of micro-heat-pipe array and the utilization of photovoltaic-cell waste heat. This novel technology solved the problems of low PV electrical efficiency and thermal failure caused by high cell temperature, greatly increased the comprehensive utilization efficiency of solar energy, and extended the service life of photovoltaic modules. One-year experiments were conducted to investigate the electrical and thermal performance of a forced-circulation, household-type photovoltaic/thermal system based on micro-heat-pipe array in Beijing, China. Test results showed that on the four typical days in different seasons, the average electrical efficiencies were 13.76%, 11.92%, 13.71%, and 14.65%; the average thermal efficiencies were 31.62%, 33.07%, 24.99%, and 17.24%; and the average total efficiencies were 45.38%, 44.99%, 38.70%, 31.89%, respectively. The system met the demand of power supply on sunny days and the demand of hot water between March and November, except in cloudy days. These experimental results can provide basis and reference for practical applications of the system.

Abstract In this work, the combustion and emission fundamentals of high n-butanol/diesel ratio blend with 40% butanol (i.e., Bu40) in a heavy-duty diesel engine were investigated by experiment and simulation at constant engine speed of 1400 rpm and an IMEP of 1.0 MPa. Additionally, the impact of EGR was evaluated experimentally and compared with neat diesel fuel (i.e., Bu00). The results show that Bu40 has higher cylinder pressure, longer ignition delay, and faster burning rate than Bu00. Compared with Bu00, moreover, Bu40 has higher NOx due to wider combustion high-temperature region, lower soot due to local lower equivalence ratio distribution, and higher CO due to lower gas temperature in the late expansion process. For Bu40, EGR reduces NOx emissions dramatically with no obvious influence on soot. Meanwhile, there is no significant change in HC and CO emissions and indicated thermal efficiency (ITE) with EGR until EGR threshold is reached. When EGR rate exceeds the threshold level, HC and CO emissions increase dramatically, and ITE decreases markedly. Compared with Bu00, the threshold of Bu40 appears at lower EGR rate. Consequently, combining high butanol/diesel ratio blend with medium EGR has the potential to achieve ultra-low NOx and soot emissions simultaneously while maintaining high thermal efficiency level.

Abstract Techniques for evaluating water management are critical to diagnose the performance of polymer electrolyte membrane fuel cells (PEMFCs). Acoustic emission as a function of polarisation (AEfP) has been recently introduced as a non-invasive, non-destructive method to analyse the water generation and removal inside a PEMFC during polarisation. AEfP was shown to provide unique insight into water management within a conventional PEMFC and correlating it to cell performance. Here, AEfP is used to characterise the performance of fractal PEMFCs by evaluating the hydration conditions inside them. This is achieved by probing the water dynamics inside two different fractal flow-field based PEMFCs, namely 1-way and 2-way fractal PEMFCs, and measuring the corresponding acoustic activity generated from them. AEfP is performed on the fractal PEMFCs under relatively humid (70% RH) and fully humidified (100% RH) reactant relative humidity (RH) conditions. Flooding in the 2-way fractal PEMFC, as opposed to the 1-way fractal PEMFC, is demonstrated under different operating conditions by the relatively higher acoustic activity it generates. Corroborating evidence of flooding in the 2-way fractal flow-field under different conditions is provided by its polarisation curves, impedance tests and galvanostatic (current hold) measurements.

Abstract Water fuel emulsion has been widely studied with the advantages of saving energy, enhancing engine torque, improving engine performance, and reducing the pollutant emissions. However, it has unfavorable disadvantages such as phase separation and long ignition delay. Water fuel microemulsion with rhamnolipid as the surfactant was formed in this study and characterized in comparison to water fuel emulsion. Water fuel microemulsion was thermodynamically stable without phase separation after 90 days vs. the milky-white emulsion fuel, separated within 2 days. In the thermogravimetric analysis, the TG and DTG curves were shifted to higher temperatures as the increment of heating rate. However, the shift for emulsion at 40 K min −1 was inconspicuous, which implies the reduction in heat transfer, mass transfer, and vaporization rates and further the lengthened ignition delay upon combustion in diesel engine. The activation energies ( E a ) predicted by Ozawa–Flynn–Wall (OFW), Kissinger–Akhira–Sunose (KAS), and Starink’s methods indicate that the formation of microemulsion could decrease the activation energy of the fuel by about 5 kJ mol −1 , while the formation of emulsion would increase by 15 kJ mol −1 . The lower activation energy of microemulsion fuel is an indication of easy ignition or shortened ignition delay. Thus, microemulsification may be a more competitive technique for fuel upgrading compared to emulsification.

Abstract A new air-cooled gas-steam combined cycle cogeneration system with absorption heat pump for recovering waste heat from exhausted steam of the steam turbine to achieve double effects of waste heat recovery and water saving is proposed based on a conventional water-cooled gas-steam combined cycle cogeneration system in the paper. The property criteria variation is analyzed before and after modification. In addition, the exergy analyses of primary equipments are carried out based upon the exergy analysis theory. The results demonstrate that the net generating power is approximately increased by 11,082 kW, equivalent coal consumption is reduced by 2.71 g/kWh, the net overall thermal efficiency is improved by 0.91% with 334,245 kW heating load at 100% load of the gas turbine in the modified system. Besides, the overall exergy loss is decreased by 6448 kW and exergy efficiency is improved by 0.98%. The overall property of the whole system is improved. The results show that the property reduction caused by air-cooling modification can be made up by the property improvement due to waste heat recovery. Moreover, the cooling circulating water can be saved by 1196.34 kg/s. The presented measure can not only improve performance of the system but also simultaneously achieve energy and water saving on the premise of satisfying user needs, which has a wide application potential in the water-shortage regions.

Abstract Interest in solar chimney power plant (SCPP) has seen resurgence due to the continuously increasing awareness on environmental concerns, particularly greenhouse gas emissions from fossil fuels, since the 21st century. Although remarkable advances in the understanding of SCPP have been achieved through extensive theoretical, experimental, and numerical studies with different focuses on various aspects of the SCPP technology, no industrial scale SCPP has been built. In response to these new scientific advances and challenges for commercialization, seven questions, including parameter influences, turbine design, flow and heat transfer characteristics, similarity analysis, and hybrid systems, are presented in this work. In addition, answers and current understanding are included to provide succinct links to latest knowledge and identify areas that require further research.

De nouveaux systèmes de refroidissement renouvelables sont nécessaires dans le monde entier pour répondre à la demande croissante de refroidissement. Cette étude propose et démontre une nouvelle intégration du refroidissement par absorption solaire avec le stockage de chaleur latente afin de maximiser l'utilisation de l'énergie renouvelable pour le refroidissement dans des climats extrêmement chauds. Une analyse paramétrique a été réalisée dans TRNSYS pour identifier les paramètres critiques pour un dimensionnement optimal liés à la taille du champ solaire, au volume du réservoir, à l'isolation du réservoir, au point de consigne de chauffage auxiliaire et à l'angle d'inclinaison du collecteur. De plus, l'intégration a été comparée à un système de refroidissement par absorption solaire conventionnel utilisant un stockage de chaleur sensible (un réservoir d'eau chaude) et un système de refroidissement par compression de vapeur électrique. Les résultats montrent qu'une taille de champ solaire de 1,5 m2/kWc, un volume de réservoir de stockage de chaleur latente de 30 L/m2, une isolation adéquate inférieure à 0,8 W/m2.K et des températures de consigne appropriées pour la chaudière auxiliaire fournissent les performances optimales pour maximiser la fraction solaire. Par rapport au refroidissement par absorption solaire conventionnel, l'étude démontre comment le matériau à changement de phase (PCM) a augmenté la fraction solaire de 4,2 % (de 70,3 à 74,5 %) en raison d'une température stable plus élevée et de pertes de réservoir plus faibles (réduites de 44 %). En outre, malgré le coût d'investissement initial plus élevé du système de refroidissement solaire à base de PCM proposé par rapport au système de refroidissement par compression de vapeur, les résultats soulignent que le coût du cycle de vie est beaucoup plus faible dans les climats extrêmement chauds. Après 25 ans, le coût du cycle de vie a été réduit de 34 % par rapport à la compression de vapeur et de 9 % par rapport à un système de refroidissement solaire conventionnel. Par rapport à la technologie de réfrigérant à compression de vapeur, le système proposé peut économiser 31,6 % d'énergie primaire et 1 222 kg de CO2eq par an. Cette recherche fournit des informations précieuses sur la conception et l'intégration optimales du refroidissement renouvelable pour les applications résidentielles dans les régions extrêmement chaudes. Se requieren nuevos sistemas de refrigeración renovables en todo el mundo para hacer frente a la creciente demanda de refrigeración. Este estudio propone y demuestra una nueva integración de la refrigeración por absorción solar con el almacenamiento de calor latente para maximizar el uso de energía renovable para la refrigeración en climas extremadamente cálidos. Se realizó un análisis paramétrico en TRNSYS para identificar los parámetros críticos para el dimensionamiento óptimo relacionados con el tamaño del campo solar, el volumen del tanque, el aislamiento del tanque, el punto de ajuste de la calefacción auxiliar y el ángulo de inclinación del colector. Además, la integración se comparó con un sistema de enfriamiento por absorción impulsado por energía solar convencional que utiliza almacenamiento de calor sensible (un tanque de agua caliente) y un sistema de enfriamiento por compresión de vapor impulsado por electricidad. Los resultados muestran que un tamaño del campo solar de 1,5 m2/kWc, un volumen del tanque de almacenamiento de calor latente de 30 L/m2, un aislamiento adecuado por debajo de 0,8 W/m2.K y temperaturas de consigna adecuadas para la caldera auxiliar proporcionan el rendimiento óptimo para maximizar la fracción solar. En comparación con el enfriamiento por absorción solar convencional, el estudio demuestra cómo el material de cambio de fase (PCM) aumentó la fracción solar en un 4,2 % (de 70,3 a 74,5 %) debido a una mayor temperatura estable y menores pérdidas del tanque (reducidas en un 44 %). Además, a pesar del mayor coste de inversión inicial del sistema de refrigeración solar basado en PCM propuesto en comparación con el sistema de refrigeración por compresión de vapor, los hallazgos destacan que el coste del ciclo de vida es mucho menor en climas extremadamente cálidos. Después de 25 años, el coste del ciclo de vida se redujo en un 34 % en comparación con la compresión de vapor y en un 9 % en comparación con un sistema de refrigeración convencional impulsado por energía solar. En comparación con la tecnología de refrigerante por compresión de vapor, el sistema propuesto puede ahorrar el 31,6 % de la energía primaria y 1222 kgCO2eq al año. Esta investigación proporciona información valiosa sobre el diseño y la integración óptimos de la refrigeración renovable para aplicaciones residenciales en regiones extremadamente calurosas. Novel renewable cooling systems are required worldwide to address the growing demand for cooling. This study proposes and demonstrates a novel integration of solar-driven absorption cooling with latent heat storage to maximise the use of renewable energy for cooling in extremely hot climates. A parametric analysis was performed in TRNSYS to identify the critical parameters for optimal sizing related to the solar field size, tank volume, tank insulation, auxiliary heating set point, and collector tilt angle. Moreover, the integration was compared with a conventional solar-driven absorption cooling system using sensible heat storage (a hot water tank) and an electric-driven vapour compression cooling system. The results show that a solar field size of 1.5 m2/kWc, a latent heat storage tank volume of 30 L/m2, adequate insulation below 0.8 W/m2.K, and appropriate set-point temperatures for the auxiliary boiler provide the optimal performance to maximise the solar fraction. Compared with conventional solar-driven absorption cooling, the study demonstrates how the phase change material (PCM) increased the solar fraction by 4.2 % (from 70.3 to 74.5 %) due to higher stable temperature and lower tank losses (reduced by 44 %). In addition, despite the higher initial investment cost of the proposed PCM-based solar-driven cooling system compared to the vapour compression cooling system, the findings highlight that the life cycle cost is much lower in extremely hot climates. After 25 years, the life cycle cost was lowered by 34 % compared to vapour compression and by 9 % compared to a conventional solar-driven cooling system. Compared to vapour compression refrigerant technology, the proposed system can save 31.6 % of primary energy and 1222 kgCO2eq annually. This research provides valuable insights into the optimal design and integration of renewable cooling for residential applications in extremely hot regions. هناك حاجة إلى أنظمة تبريد متجددة جديدة في جميع أنحاء العالم لتلبية الطلب المتزايد على التبريد. تقترح هذه الدراسة وتوضح تكاملًا جديدًا للتبريد بالامتصاص المدفوع بالطاقة الشمسية مع التخزين الحراري الكامن لتعظيم استخدام الطاقة المتجددة للتبريد في المناخات الحارة للغاية. تم إجراء تحليل بارامتري في TRNSYS لتحديد المعلمات الحرجة للتحجيم الأمثل المتعلق بحجم الحقل الشمسي وحجم الخزان وعزل الخزان ونقطة ضبط التسخين الإضافية وزاوية إمالة المجمع. علاوة على ذلك، تمت مقارنة التكامل مع نظام تبريد الامتصاص التقليدي الذي يعمل بالطاقة الشمسية باستخدام تخزين الحرارة المعقول (خزان الماء الساخن) ونظام تبريد ضغط البخار الذي يعمل بالكهرباء. تظهر النتائج أن حجم الحقل الشمسي 1.5 متر مربع/كيلو واط مكعب، وحجم خزان تخزين الحرارة الكامن 30 لتر/متر مربع، والعزل الكافي أقل من 0.8 واط/متر مربع، ودرجات حرارة نقطة الضبط المناسبة للغلاية المساعدة توفر الأداء الأمثل لتحقيق أقصى قدر من الجزء الشمسي. مقارنة بالتبريد بالامتصاص التقليدي القائم على الطاقة الشمسية، توضح الدراسة كيف زادت مادة تغيير الطور (PCM) من الجزء الشمسي بنسبة 4.2 ٪ (من 70.3 إلى 74.5 ٪) بسبب ارتفاع درجة الحرارة المستقرة وانخفاض خسائر الخزان (انخفضت بنسبة 44 ٪). بالإضافة إلى ذلك، على الرغم من ارتفاع تكلفة الاستثمار الأولي لنظام التبريد المقترح القائم على الطاقة الشمسية PCM مقارنة بنظام تبريد ضغط البخار، فإن النتائج تسلط الضوء على أن تكلفة دورة الحياة أقل بكثير في المناخات الحارة للغاية. بعد 25 عامًا، انخفضت تكلفة دورة الحياة بنسبة 34 ٪ مقارنة بضغط البخار وبنسبة 9 ٪ مقارنة بنظام التبريد التقليدي الذي يعمل بالطاقة الشمسية. بالمقارنة مع تقنية تبريد ضغط البخار، يمكن للنظام المقترح توفير 31.6 ٪ من الطاقة الأولية و 1222 كجم من مكافئ ثاني أكسيد الكربون سنويًا. يوفر هذا البحث رؤى قيمة حول التصميم الأمثل ودمج التبريد المتجدد للتطبيقات السكنية في المناطق شديدة الحرارة.

Abstract Organic solvent upgrading Indonesian lignite was performed in a 1 L autoclave under moderate temperature. The chemical structure and functional groups transformation of lignite upgraded by two organic solvents (ethanol and n-hexane) were analyzed to explore the upgrading mechanism of solvent thermal treatment by using Fourier transform infrared (FTIR) and 13 C nuclear magnetic resonance (NMR). In addition, the characteristics of pyrolysis of treated samples were investigated using thermo gravimetric (TG) to clarify the variance of pyrolysis reactivity. Results showed that the carbon content and calorific value of upgraded lignite were significantly improved, and H/C and O/C ratios of treated samples were significantly reduced with the temperature increasing. The relative percentage of carbonyl and carboxyl carbon, oxygenated aliphatic carbon and methoxyl carbon of lignite upgraded at 300 °C decreased by 20–30%. However, the carbon-substituted and protonated aromatic carbon at 120–135 ppm and protonated aromatic carbon at 90–120 ppm were significantly increased after lignite was upgraded by the two solvents at above 200 °C. These transformations indicated that oxygen-containing functional group was substituted by hydrogen or carbon-substituent as temperature increased, and were intensified at above 200 °C. In addition, oxygen-loss in the treated samples was attributed to the loss of carbonyl group at 175 ppm, dihydric phenol at 147 ppm, and methoxyl group at 55 ppm. The activation energy of upgraded lignite at 300 °C were higher than those of raw lignite and upgraded lignite at 100 and 200 °C, indicating the low reactivity of pyrolysis of the treated lignite with the temperature increasing.