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[en] This paper analyzed the influence of working fluids selection and operation conditions on the cost-effectiveness performance and net power output of an ORC for low grade heat utilization. A net power output model has been proposed theoretically and compared with the theoretical data calculated from thermodynamic analysis, exhibiting excellent agreements with the theoretical data. The proposed net power output model theoretically indicates that Jacob number and the ratio of evaporating temperature and heat rejected temperature play essential roles in discriminating the net power output among various working fluids at the same operation condition. For a given condensing and evaporating temperature, it can be concluded theoretically that fluid with low Jacob number will show attractive performance in an ORC. The maximum net power output is determined by the heat source rather than working fluids with a low inlet temperature of heat source. Cost-effectiveness performance analysis reveals that the maximum net power output and the best CEP cannot be achieved at the same time and compromise must be made when choosing the most suitable organic working fluids in different ORC designs. -- Highlights: • A net power output model is proposed and compared with theoretical data. • For fixed operation condition, low Ja fluid shows attractive performance in ORC. • The heat source rather than working fluid determines ORC performance at low Ths,in • The peak Wnet and best CEP cannot be achieved at the same time, compromise must be made
[en] Ni-rich ternary layered oxides, (LiNi_x [M]_1_−_xO_2, x ≥ 0.5, M = Co and Mn), have become one of the mainstream cathode materials for next-generation lithium-ion batteries due to their high capacity and cost efficiency compared with LiCoO_2. However, the high-voltage operation of the Ni-rich oxides (>4.3 V) required for high capacity is inevitably accompanied with a rapid capacity decay over numerous cycles. In this work, we reported a surface coating of LiNi_0_._6Co_0_._2Mn_0_._2O_2 with Li_2Si_2O_5via a facile and efficient synthetic approach, which involves the employment of silicic acid (H_2SiO_3) as remover to react with the surface residual lithium compounds (e.g. Li_2CO_3 and LiOH) of LiNi_0_._6Co_0_._2Mn_0_._2O_2 and consequent formation of a robust and complete Li"+-conductive Li_2Si_2O_5 protective coating layer. The structure and morphology of the coated cathode materials are fully characterized by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Compared with the pristine LiNi_0_._6Co_0_._2Mn_0_._2O_2, coating with the Li"+-conductive Li_2Si_2O_5 is found to be very effective for improving the rate capability of the LiNi_0_._6Co_0_._2Mn_0_._2O_2 when evaluated at a high cut-off voltage up to 4.5 V. Specifically, 1 wt. % H_2SiO_3-treated LiNi_0_._6Co_0_._2Mn_0_._2O_2 electrode exhibits high discharge specific capacities of 213.9 and 121.6 mAh g"−"1 at 0.1 and 10 C, respectively, whereas the pristine electrode only shows 196.8 and 92.1 mAh g"−"1. Besides, the surface-modified LiNi_0_._6Co_0_._2Mn_0_._2O_2 electrode also manifests an enhanced long-term cycling stability (67% capacity retention after 200 cycles at 5 C), much better than the pristine electrode (52% retention) due to the robust protective effect of the Li_2Si_2O_5 coating layer. All these results indicate that the Li_2Si_2O_5-coated LiNi_0_._6Co_0_._2Mn_0_._2O_2 will be a promising cathode material for lithium-ion batteries with fascinating electrochemical energy storage capabilities. - Graphical abstract: Silicic acid is used as a remover to react with lithium residues (LiOH and Li_2CO_3) on the surface of LiNi_0_._6Co_0_._2Mn_0_._2O_2 and subsequently generate an ion-conductive coating layer of Li_2Si_2O_5 after heat treatment. The surface-coated cathode materials show a remarkably enhanced rate capability, discharge specific capacities, and cycling performance for Li-ion batteries. - Highlights: • H_2SiO_3 is used as a remover to react with lithium residues on LiNi_0_._6Co_0_._2Mn_0_._2O_2 surface. • A surface coating layer of Li"+-conductive Li_2Si_2O_5 is formed. • Coating layer improves the velocity of Li"+ migration on electrode surface. • Erosion from the HF and CO_2 on electrode is greatly suppressed.
[en] Highlights: • Thermodynamic analysis is presented for an improved A-CAES combined with PBTES system. • A mathematic model is developed, validated and used to simulate system performances. • PBTES heights have significant influence on the PBTES’s thermal behaviors and the system efficiencies. • The maximum cycle efficiency of the improved A-CAES system is 56.74%. - Abstract: Energy storage technology is a cutting-edge research in the field of new and renewable energy application. In this paper we introduce the concept of an energy storage based on adiabatic compressed air energy storage (A-CAES) combined with packed bed thermal energy storage (PBTES) system. First, the system thermodynamic performance of a typical single cycle is discussed and the effect of PBTES heights is analyzed. The results show that an overall efficiency in excess of 49% is achievable and the PBTES heights have significant influence on the thermal behavior of PBTES, as well as the overall efficiencies. Because there is still heat energy remaining in the packed bed until the discharge process is terminated, an improved A-CAES system with a heat recuperator is further proposed. It is found that this improved system shows a promotion of ∼5% compared with the first present A-CAES system. The cycle efficiency of the improved system increases with the increase of continuous cycles, and then reaches a stable value of 56.74% after around 25 cycles. The main conclusions drawn from this work will be helpful for future development of a high-efficiency A-CAES system combined with PBTES.
[en] Highlights: • A concentric-dispersion model is established for packed bed storage with PCM. • Effects of PCM diameter, inlet velocity and tank height on thermal behavior is investigated. • Particle diameter has significant influence on the charge efficiency. • A higher thermal storage tank is beneficial for higher charge efficiency. - Abstract: The behavior of a packed bed latent heat thermal energy storage system is analyzed in this paper. Molten salt is considered for the heat transfer fluid (HTF) with phase change material (PCM) capsules as the filler. The model developed uses the concentric-dispersion equations, except the phase change phenomena of PCM inside the capsules is analyzed by using enthalpy method. The equations are numerically solved by finite-difference approach, and the results obtained are validated against experiments from the literature. The effects of PCM capsule diameter (dp), fluid inlet velocity (uf) and storage tank height (H) on the temperature profiles of packed bed have been investigated. Also presented and discussed in a detail description of the charge efficiency for various working conditions. The results indicated that decreasing the size of PCM capsule and fluid inlet velocity, or increasing the storage height, results in an increase in the charge efficiency
[en] Highlights: • The effect of fin pitch, length and bending distance on thermal performance were presented. • The corresponding ReC values at the j and f slope changes are in the range of 2000–2100. • The numerical results showed a good agreement with the experimental data. • Local high Nu values near the channel inlet, decreasing through the flow directions. - Abstract: Experimental and numerical studies on the flow and heat transfer characteristics for an innovative offset strip fins compact heat exchangers were performed. First, five fin schemes were investigated with various air flow velocities and a constant inlet steam pressure by experiments. The Reynolds number ranged from 500 to 5000 at the air side. The experimental results indicated that the fin pitch (Pf), fin length (Lf) and fin bending distance (Cf) have a significant influence on thermal performance of fins. The Colburn factor j, friction factor f and ‘point of transition’ were calculated from the experimental data. Then, the thermal–hydraulic performances of the novel offset strip fins were analyzed numerically. The simulation results obtained are in agreement with experimental data. Based on these simulations, the maximum values for local Nu number are at the channel inlet which is due to the thermal entrance effect. The longitudinal vortexes near the fin region will increase velocity gradient and reduce the thickness of boundary layer to improve heat transfer. The main conclusion draws from this work will be helpful for future development and design of a high-efficiency heat exchangers involving offset strip fin structures
[en] Highlights: • A novel flat plate heat pipe (FPHP) was designed and performed. • Maximum HS temperature is lower than 60 °C when the heat load reaches 100 W. • The FPHP will spend less time to start up with the increase of heat flux. • Liquid FR and VD have a significant influence on thermal performance of FPHP. - Abstract: The heat transfer performance of a novel flat plate heat pipe (FPHP) for electronic cooling was investigated experimentally. A variety of performance tests of FPHP were carried out with different air flow velocities (1.5 m/s < u < 6 m/s), working fluid filling ratios (10% < FR < 50%), and the vacuum degrees (0.002 Pa < VD < 0.25 Pa). Using distilled water and acetone as working fluids, the influence of the above parameters on steady-state heat transfer characteristics of the FPHP was also examined. The experimental results indicated that the filling ratio and vacuum degree had a significant influence on thermal performance of FPHP. Compared with cooling performance using distilled water and acetone, the FPHP cooling component using acetone had a stronger heat dissipation capacity for the same filling ratio
[en] A high-efficiency numerical method is proposed for using coarse meshes to simulate the low-velocity impact behaviours of laminated composite structures with a relatively large number of layers. The interface strength corresponding to different levels of mesh refinement in the cohesive model is defined by deduced analytical expressions, the predictive capabilities of which are validated by measurements from double cantilever beam, end notched flexure and mixed-mode bending tests. A parameter known as saturation crack density is employed in damage evolution modelling to ensure the correct energy dissipation in coarse-mesh elements that may contain multiple cracks. Good agreement between the experimental and simulated results indicates the correctness of the proposed method for predicting impact mechanical responses and impact-induced damage. In addition, the results show that coarse-mesh models using the method proposed here not only yield consistent results, e.g., impact response curves and projected delamination area, with models with finer meshes but can also significantly improve computational efficiency. (paper)
[en] Highlights: • A novel humidification-dehumidification system is designed to enhance the evaporation capacity of the system. • Thermal performance of the novel system is better than conventional system without reflux. • A more rigorous mathematical model of humidifier and the solver programme are built. • The optimum value of the gas-liquid ratio for maximum evaporation capacity is near 1.17 regardless of conditions. - Abstract: A novel humidification-dehumidification (HDH) system is designed to enhance the evaporation capacity. A more rigorous mathematical model of humidifier is proposed. A simulation programme of the whole system is built. Theoretical investigation is performed to investigate the effect of various parameters on the evaporation capacity and gained input ratio. The results demonstrate that the reflux ratio and inlet solution temperature of the humidifier are proportional to the evaporation capacity. An optimum mass flow rate of air exists for which the evaporation capacity is maximized. The gained input ratio (GIR), defined as the ratio between the total latent heat of evaporated water and the external heat input, decreases with the increase in air mass flow rate and increases with the increase in the reflux ratio. The optimum value of the gas-liquid ratio for maximum evaporation capacity is near 1.17, regardless of conditions. A multi-index comprehensive evaluation is introduced to assess the overall performance of the system. And a practical case is carried out to illustrate how to select the optimum operational parameters under different circumstances.
[en] Different thickness coatings formed by multilayer laser cladding are widely employed in laser repairing and the wear resistance of them are concerned. Multilayer nickel-based alloy were fabricated on the surface of low alloy steel by laser-induction hybrid cladding. Orthogonal analysis was used to evaluate the influence of the number of coating layers, load and relative velocity on the wear resistance of the coating. Wear loss and friction coefficient were set as the evaluate indexes. Microstructure, element distribution and phase composition were investigated by optical microscope, energy dispersive spectrometer (EDS) and x-ray diffractometer (XRD). Microhardness and worn surface of coatings were also tested. The results showed that the number of coating layers had an effect on the wear resistance of nickel-based coating. With the increase of coating thickness, more uniform was happened to the crystal grain. The nickel-based alloy coating was mainly composed of Cr23C6, Cr7C3, CrB, FeNi3 and Fe23(C, B)6. The lowest hardness was shown in the single-layer coating with an average value of 818.0 HV0.2. The average hardness of the two-layer coating and three-layer coating was 6.88% and 16% higher than that of the single-layer one, respectively. The cross-sectional area of the worn surface was (0.64 ∼ 2.3) × 10−3 mm2 and the distribution of them was consistent with the distribution of wear loss. The wear mechanism of nickel-based coating in this friction system was abrasive wear. The good wear resistance of the nickel-based alloy coating was mainly due to the presence of dense fine crystal grain and hard phase. (paper)
[en] In this paper, we study the optimization of network traffic by considering the effects of node buffer ability and capacity. Two node buffer settings are considered. The node capacity is considered to be proportional to its buffer ability. The node effects on network traffic systems are studied with the shortest path protocol and an extension of the optimal routing [Phys. Rev. E 74 046106 (2006)]. In the diagrams of flux—density relationships, it is shown that a nodes buffer ability and capacity have profound effects on the network traffic