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[en] Carbon nanotube (CNT) is considered as a kind of potential adsorbent because of its large surface area, uniform micropores and unique physicochemical properties. The adsorption performance of ammonia on the packed multi-walled carbon nanotubes (MWCNTs) were studied in this paper. Firstly, the packed MWCNTs were characterized by the scanning electron microscope (SEM) and transmission electron microscopy (TEM). Secondly, the effect of working pressure and adsorbent temperature on the adsorption capacity of ammonia by the packed MWCNTs was investigated. Thirdly, Langmuir and Freundlich models were used to analyze the equilibrium adsorption data and the adsorption kinetics was also discussed using a classical gas diffusion model. The Freundlich isotherm model could elucidate well the adsorption of ammonia on the MWCNTs when compared to the Langmuir equation. The research results showed that the equilibrium adsorption amount of ammonia by the MWCNTs varied between 22.69 and 90.05 mg/g_C_N_T at the adsorbent temperature of 25–35 °C and working pressure of 0.368–0.744 MPa. It seems that the pure MWCNT is not appropriate to act as the adsorbent for the solid–gas adsorption refrigeration due to its low adsorption capacity. However, our research indicates that the MWCNTs can be used as additive to some other chemical adsorbents to improve their heat transfer characteristics. - Highlights: • Adsorption performance of ammonia on packed MWCNTs was studied. • Effects of working pressure and temperature on the adsorption capacity were investigated. • Adsorption equilibrium data and kinetics of ammonia on MWCNTs were analyzed. • Equilibrium adsorption amount of ammonia varied 22.69–90.05 mg/g_C_N_T at different temperatures and pressures
[en] Graphical abstract: Solid–gas thermochemical multilevel sorption thermal battery for cascaded thermal energy storage. - Highlights: • A novel solid–gas thermochemical multilevel sorption thermal battery for energy storage. • Cascaded solar heat storage using thermochemical multilevel sorption thermal battery. • Performance of the thermochemical multilevel sorption thermal battery is analyzed. • The proposed method has high energy density and broad working temperature range. • Energy density of the proposed method is sensitive to chemical global conversion. - Abstract: An innovative solid–gas thermochemical multilevel sorption thermal battery is developed for cascaded solar thermal energy storage to enhance the versatility and working reliability of solar heat storage system by widening the working temperature range. Solar thermal energy can be stored in the form of bond energy of sorption potential at different cascaded temperatures resulting from solid–gas thermochemical multilevel sorption processes. The operating principle and working performance of the thermochemical multilevel sorption thermal battery for energy storage is described and analyzed. Thermodynamic analysis showed that the proposed thermochemical multilevel sorption thermal battery has the potential capacity for meeting the challenge of solar heat storage during the random variation of low and high solar insolation with time by using cascaded thermal energy storage technology. An energy density higher than 1200 kJ/kg of reactant can be attained from the advanced energy storage system. The promising method can enhance the versatility and working reliability of solar heat storage due to its distinct advantages of high energy density and a wide range of solar collection temperature when compared with conventional heat storage methods. It has potential applications for energy management of renewable energy utilization and waste heat recovery in large-scale industrial processes.
[en] This paper describes the design feature of Beijing Shijingshan 3 x 200 MW Cogeneration Plant. The design optimized the scheme and system of 200 MW units for heating. The cogeneration plant has achieved comprehensive economic benefit in energy saving and environmental pollution reduction
[en] Based upon the fast development of energy efficiency, energy safety and use of renewable and sustainable energy, various energy systems related to residential refrigeration, power generation and storage have been developing. Some of them are in large scale application, while others are still under development. Current status of residential refrigeration, power generation and energy storage technologies have been briefly summarized in this paper. Also, future residential refrigeration, power generation and energy storage technologies are highlighted, and some roadmaps are discussed. -- Highlights: ▸ Current status and future development of residential refrigeration have been briefly summarized and discussed. ▸ Current status and future development of power generation have been briefly summarized and discussed. ▸ Current status and future development of energy storage have been briefly summarized and discussed
[en] Adsorption refrigeration and heat pump systems have been considered as important means for the efficient use of low-grade thermal energy of 60-150 oC. Sorption systems are merely thermodynamic systems based on heat exchangers, and therefore a good design to optimize heat and mass transfer with reaction or sorption processes is very important, for which the notable technique is the use of expanded graphite to improve both heat and mass transfer in the chemisorption beds. Studies have also shown the need to enhance the heat transfer in adsorption bed by matching with the efficient heat transfer of thermal fluids. Heat pipes and good thermal loop design coupled with adsorption beds could yield higher thermal performance of a sorption system. A novel design with passive evaporation, known as rising film evaporation coupled with a gravity heat pipe was introduced for high cooling output. It has also been shown that the performance of traditional heat and mass recovery in the sorption systems is limited, and novel arrangement of thermal fluid and refrigerant may improve the performance of sorption systems. Based upon the above researches, various sorption systems have been developed, and high performances have been reached. -- Highlights: →Heat transfer design in adsorption refrigeration systems is researched. →Solidified adsorbent is an effective way to improve the heat transfer. →Heat pipe and rising film evaporation could generate high cooling output. →With efficient design two adsorption systems are developed. →Double way and double effect cycle is introduced.
[en] The performance analyses of a sorption refrigeration system with different mass recovery processes are presented, in which compound adsorbent of CaCl2 and activated carbon is used to improve the mass and heat transfer performances of sorption bed. The heating, cooling and heat recovery processes between two sorption beds were performed by multifunction heat pipes without additional power consumption. The experimental Clapeyron diagrams showed that the cycles with mass recovery (MR), with heat and mass recoveries (HMR), and with mass and heat recoveries (MHR), have better thermodynamic performances when compared with the sorption cycle without mass recovery (MR0). The implementary order of mass recovery and heat recovery has strong influence on the efficacy of mass recovery while it has little influence on the efficacy of heat recovery. In sorption cycles with HMR and with MHR, the hot beds can be pre-cooled and cold beds can be pre-heated effectively during the switching process, and heat consumption from external heat source during desorption phase is thereby reduced. Mass recovery can enlarge cycled refrigerant mass due to the transfer of refrigerant gas between two sorption beds during mass recovery process. In comparison with sorption cycle with MR0, sorption cycles with MR, with HMR, and with MHR can generally improve the coefficient of performance (COP) and specific cooling power (SCP) by more than 20% and 16%, respectively. Especially, sorption cycle with MHR has the highest performance among different mass recovery processes due to the fact that MHR has the advantages of MR and HMR, and it can improve the COP by 46.7% when compared with the cycle with MR0
[en] An innovative multifunction heat pipe type sorption refrigeration system is designed, in which a two-stage sorption thermodynamic cycle based on two heat recovery processes was employed to reduce the driving heat source temperature, and the composite sorbent of CaCl2 and activated carbon was used to improve the mass and heat transfer performances. For this test unit, the heating, cooling and heat recovery processes between two reactive beds are performed by multifunction heat pipes. The aim of this paper is to investigate the cycled characteristics of two-stage sorption refrigeration system with heat recovery processes. The two sub-cycles of a two-stage cycle have different sorption platforms though the adsorption and desorption temperatures are equivalent. The experimental results showed that the pressure evolutions of two beds are nearly equivalent during the first stage, and desorption pressure during the second stage is large higher than that in the first stage while the desorption temperatures are same during the two operation stages. In comparison with conventional two-stage cycle, the two-stage cycle with heat recovery processes can reduce the heating load for desorber and cooling load for adsorber, the coefficient of performance (COP) has been improved more than 23% when both cycles have the same regeneration temperature of 103 deg. C and the cooling water temperature of 30 deg. C. The advanced two-stage cycle provides an effective method for application of sorption refrigeration technology under the condition of low-grade temperature heat source or utilization of renewable energy
[en] Highlights: • The dual magnetization reversal is observed in Y1−xHoxFe0.5Cr0.5O3. • The EB field transforms from negative to positive and then to negative. • A large exchange bias effect induced by Ho3+ doping is obtained in Y1−xHoxFe0.5Cr0.5O3. - Abstract: The polycrystalline ceramics of Y1−xHoxFe0.5Cr0.5O3 (x = 0, 0.05 and 0.1) are synthesized by a sol-gel method. The magnetization reversal and exchange bias effect are investigated in single phase bulk Y1−xHoxFe0.5Cr0.5O3. Magnetic Ho3+ ion as a dopant is introduced into the system to confirm the influence of A-site ion on the magnetic interactions. The dual reversal of exchange bias field for x = 0.05 is observed, and its characteristic temperatures are corresponding to the compensation temperatures of magnetization reversal. The exchange bias field of x = 0.1 is found to be ∼10.03 kOe at 4 K, revealing a large value compared with that of x = 0. A schematic diagram based on the competition between the single ion anisotropy and Dzyaloshinsky-Moriya interaction, and the antiparallel coupling between the Ho3+ moments and the canted Cr3+/Fe3+ moments, is used to understand the dual reversal phenomenon of magnetization and exchange bias effect.
[en] A dual-mode thermochemical sorption energy storage system using working pair of expanded graphite/SrCl2-NH3 was proposed for seasonal solar thermal energy storage. The proposed system has two working modes to produce useful heat with an expected temperature during the discharging phase according to the different ambient temperatures, including the direct heating supply and temperature-lift heating supply. Solar thermal energy is transformed into chemical bonds and stored in summer, and the stored energy is released in the form of chemical reaction heat in winter. The direct heating supply mode is adopted at a relatively high ambient temperature in winter. The effective energy storage density is higher than 700 kJ/kg and the corresponding system COP is 0.41 when the heat output temperature and ambient temperature are 35 °C and 15 °C, respectively. The specific heating power increases with the decrease of heat output temperature for a given ambient temperature. The temperature-lift heating supply mode is adopted to upgrade the heat output temperature at a low ambient temperature below 0 °C in winter. It can produce heat with a temperature above 70 °C although the ambient temperature is as low as −15 °C. It is desirable to further improve the system performance using low mass ratio and high global conversion. Experimental results showed the advanced dual-mode thermochemical sorption energy storage technology is feasible and effective for seasonal solar thermal energy storage. - Graphical abstract: Working temperature range of dual-mode thermochemical sorption energy storage system during the discharging phase in winter. - Highlights: • A dual-mode seasonal solar thermochemical sorption energy storage system is developed. • The sorption working pair is strontium chloride/expanded graphite-ammonia. • Two working modes can be performed according to the different heat requirements in winter. • Energy density and COP of direct heating supply mode are 706 kJ/kg and 0.41 respectively. • Temperature-lift heating supply mode can meet heat demand at low ambient temperature.
[en] Novel EVM/SrBr_2 composite sorbents with different salt contents were developed for low-temperature thermal energy storage (TES). Simulative sorption experiment was conducted to obtain the sorption kinetics diagram and identify threshold salt content that composite sorbents can hold without solution leakage. Distribution of salt embedded in EVM was observed by extreme-resolution scanning electron microscopy (ER-SEM). Thermochemical characterizations including desorption performance and desorption heat were fully investigated by analyzing simultaneous thermal analyzer (STA) results. Results reveal that sorption process of composite sorbents is divided into three parts: water adsorption of EVM, water adsorption of SrBr_2 crystal and liquid-gas absorption of SrBr_2 solution. Since SrBr_2 solution can be hold in macrospores of EVM, water uptake and energy storage density are greatly increased. It appears that the composite sorbent of EVMSrBr_240 is a promising material for thermal energy storage, with water uptake of 0.53 g/g, mass energy storage density of 0.46 kWh/kg and volume energy storage density of 105.36 kWh/m"3. - Highlights: • Vermiculite/SrBr_2 composite sorbents were developed for thermal energy storage. • Water uptake of composite sorbents is divided into three phases. • Energy storage density of each sorption phase is evaluated via calculations. • EVMSrBr_240 is chosen as optimal sorbent without solution leakage.