查看更多>>摘要：Gas separation properties of membranes are the significant parameters in CO2 capture process. It has been reported that membranes with high permeance and moderate CO2/N-2 selectivity are suitable for CO2 capture from coal-fired flue gas. However, with emerging high selectivity membrane and novel processes, it is essential to evaluate the influence of membrane selectivity on carbon capture performance, especially the significance of sub ambient membrane operation. In this work, a sub-ambient membrane-cryogenic hybrid process was designed for CO2 capture from coal fired and blast furnace flue gas. It was found that energy consumption of vacuum can be saved when membranes with high selectivity were operated at sub-ambient condition. The cost and energy consumption of the optimal cases for coal fired flue gas were 36.14 $/tCO(2) and 1.87 GJ/tCO(2) according to the economic evaluation. The parasite load decreased 7.11% over the base case of 168 MW. In addition, the capture cost and energy consumption of optimal case for blast furnace flue gas were 28.81 $/tCO(2) and 1.55 GJ/tCO(2), respectively. The parasite load decreased 15.55% over the base case of 17.81 MW. The designed hybrid processes presented competitive potential when applied in high CO2-content scenarios. In summary, the hybrid process based on membranes and cryogenic has been proven to have economic advantages under simulated conditions, indicating that it has the potential to be amplified by industrialization.
查看更多>>摘要：A novel multistage air-gap diffusion distillation (MS-AGDD) system powered by low-grade sensible heat (LGSH) was proposed for fully recovering heat from LGSH to produce freshwater. The effect of operating parameter variations on the system performances was investigated theoretically based on the epsilon-NTU model for AGDD. The operating parameters include the hot water inlet temperature (T-hs(in)), the feed seawater flowrate (V-c,n(in)), salinity (S-c,n(in)) and temperature (T-c,n(in)), the temperature differences at the hot end of heat exchanger (Delta t(h)) and at the cold end of coolers (Delta t(c)). Results showed that under the given structure and size parameters of the system and the operating conditions, the variation of T-hs(in), V-c,n(in) or Delta t(h) affected the system performances significantly, but the variation of S-c,n(in) n or Delta t(c) affected those relatively less. The total freshwater yield and the recovered heat from the hot water enlarged with the increase of T-hs(in) or V-c,n(in), but they decreased with the increase of Delta t(h). The gained out ratio (GOR) of the system increased with the increase of T-hs(in), but it decreased with the increase of V-c,n(in) or Delta t(h). The irreversibility of the system increased with the increase of T-hs(in) or Delta t(h), but it decreased with the increase of T-c,n(in) or V-c,n(in).
查看更多>>摘要：The performance of the ejector relies on the geometrical parameters and the fluid phase state. Although the optimization of geometries of the ejector has been conducted in previous studies, the influence of different optimization sequence of geometric parameters was ignored in previous literatures. To close the knowledge gap, the goal of this paper is to investigate whether different optimization sequences affect the ejector performance and whether the ejector performance is the same under different optimization sequences after multiple rounds of optimization. Therefore, three geometrical parameters, namely the constant-pressure mixing chamber length (L-pm), the constant-area mixing chamber length (L-am) and diameter (D-am), are selected for the optimization study; besides, multi-round optimization with six optimization sequences of these three parameters is conducted by CFD simulations under four different combinations of primary flow liquid volume fraction (LVF1) and sec-ondary flow liquid volume fraction (LVF2) (LVF1 = 0 plus LVF2 = 0, LVF1 = 0 plus LVF2 = 0.06, LVF1 = 0.06 plus LVF2 = 0, LVF1 = 0.06 plus LVF2 = 0.06) for the first time. The results showed that: (1) for each LVF combi-nation, the three optimal parameters and corresponding maximum ER produced by one round optimization of six different optimization sequences are evidently different; (2) after multiple rounds of optimization, for LVF1 = 0 plus LVF2 = 0 or LVF1 = 0.06 plus LVF2 = 0.06, ultimate optimal geometrical parameters and maximum ER are the same with each other for six optimization sequences, however, for LVF1 = 0 plus LVF2 = 0.06 or LVF1 = 0.06 plus LVF2 = 0, each of them still has two different ultimate maximum ER; (4) for those four combinations, different sequence takes different optimization rounds, recommended sequences are D-am -> L-am -> L-pm (S6), L-pm -> L-am -> D-am (S1) or L-pm -> D-am -> L-am (S2), and L-am -> L-pm -> D-am (S3) and D-am -> L-am -> L-pm, respectively; and (5) the ultimate optimal parameters and maximum ER in four combinations differ significantly because they are largely dependent on the inlet fluid states.
查看更多>>摘要：Transcritical CO2 air-source heat pump has been widely applied for its high efficiency in producing domestic hot water. However, it preforms poorly for space heating specially in cold region, because of the high return water temperature and single-phase heat transfer in gas cooler. To resolve this issue, a modified integrated CO2 heat pump system is proposed, which can operate in heating-water combined mode and space heating mode with radiator followed by fan-coil unit in space heating circuit. To improve its thermal comfort and reduce economic cost simultaneously, multi-objective optimization for maximizing space-heating energy and minimizing total annual cost is conducted, based on a new optimizing model, considering two modes simultaneously as a whole and employing new concept of artificial neural network group. The best individual in Pareto front is selected, with 6109.2$/year cost and 5.87 x 10(8)J heating energy. Corresponding optimal geometric parameters of components are obtained as follows, 0.378 m(2) high-temperature gas cooler transfer area, 0.468 m(2) low-temperature gas cooler heat transfer area, and 0.0015 m(3)/s compressor displacement. Moreover, effects of important factors (electric fee, water demand, and ambient temperature) on system performance are also investigated. This work presents a new optimizing model and reveals the excellent application potential of the new system.
查看更多>>摘要：This paper proposes a novel ejector-enhanced auto-cascade refrigeration cycle (NEARC). In the novel cycle, the ejector not only replaces an expansion valve to recover partial expansion work, but also greatly reduces the throttling loss of the other expansion valve connected to the evaporator. The energy and exergy analysis methods are used to evaluate and compare the performance of NEARC using R290/R170 with conventional auto-cascade refrigeration cycle (CARC) and previously proposed ejector-enhanced auto-cascade refrigeration cycle (EARC). The simulation results show that under all given working conditions, the COP and exergy efficiency of NEARC are superior to those of CARC, but not always superior to those of EARC. With the change of initial mass fraction of R290, the COP and exergy efficiency of the three cycles all have maximum values. The maximum COP and exergy efficiency of NEARC are 42.85% and 42.71% higher than those of CARC, and 18.10% and 17.99% higher than those of EARC, respectively. When initial mass fraction of R290 is about 0.5, CARC and EARC have the best performance, and NEARC performs best when initial mass fraction of R290 is about 0.7. The comparison results demonstrate that the novel cycle has great energy-saving potential.
查看更多>>摘要：In this study, a novel variable-length intake manifold is designed to increase the volumetric efficiency of a four cylinder gasoline engine. The proposed intake manifold is designed with four independent throttle bodies on its inlet duct, which are separately connected to the atmosphere. By opening and closing each one of these throttle bodies, a different length of the intake manifold is obtained. The novelty of this study lies in the fact that in addition to the variable-length system at each engine speed, it uses a different combination of opened throttle bodies to further increase volumetric efficiency. To demonstrate the efficiency of the novel design, a onedimensional model of the Stock engine is developed using the GT-Power software in wide-open throttle steady-state condition and then validated with experimental results. Five vital criteria are defined for evaluating all of the thermo-fluid, heat, and mass transfer characteristics of the engine. The result of using the novel proposed design indicates that the volumetric efficiency, brake torque, brake specific fuel consumption, brake thermal efficiency, and heat release rate of the engine compared to the stock intake manifold were improved by 6.33%, 7.23%, 0.83%, 1.77%, and 11.79% respectively. Based on the obtained results, the best performance is achieved at 3500 rpm almost in all conditions. At this condition, the air and fuel mass flow rates and brake power are 0.0574 kg/s, 0.0041 kg/s, and 56.42 kW, respectively.
查看更多>>摘要：Water scarcity is among the major crucial issues confronting humanity, caused by the world's growth in population, the socio-economic development and the global climate change. Several desalination technologies are available to tackle the increased freshwater water demand. Therefore, the solar energy-driven distillation is among the most conceivable alternatives for supplying safe water with reducing the energy cost. The conventional solar distiller is a sustainable and economical process. However, the overall productivity is generally low. In this study, conceptual improvements on the design and distillation process of a wick type solar still are presented for the purpose of overcoming the low efficiency of the classic system. The novelty of this study is presented in combining three ideas to improve the still efficiency through creating an alternative mode of condensation based on forced convection, achieving a substantial gain in the specific weight and automating the distillation process. Hence, reducing the heat losses and enhancing the still productivity are achieved while maintaining the simplicity of the distiller and without calling for any complicated or cost-intensive technology. Furthermore, this investigation offers an innovative analytical process based on mathematical modelling tools as well as, an experimental approach. The results inferred that the advanced system produces significantly high distillate outputs of about 4.03 L.m(-2).d(-1) for an average of 380 W.m(-2) of mean solar radiation. Thereafter, the numerical results were experimentally validated, and it was proven that the efficiency of the advanced solar still was enhanced by 32% in comparison to the conventional solar still. The physic-chemical and bacterial analysis of the produced water revealed that the improved solar still can supply good quality of drinking.
查看更多>>摘要：Albeit the exhaust gas recirculation (EGR) is widely used to reduce the nitrogen oxides (NOx) emissions from large marine two-stroke engines, several challenges emerge for the engine-turbocharging system matching considering the contradictory requirements of the engine and its subsystems operation. Such challenges become more pronounced in complex engine configurations that include parallel turbochargers and the EGR system along with cut out and bypass branches. This study aims at parametrically investigating a large marine twostroke engine equipped with an EGR system, two parallel turbochargers of different size, and cut out branches. The turbocharging system characteristics are selected targeting the minimisation of the engine specific fuel consumption whilst ensuring compliance with the respective NOx emissions limits and satisfying imposed constraints for the compressors operation. A detailed model of the zero/one dimensional type is developed in the GT-SUITE software and used to simulate the investigated engine along with its subsystems. Simulation runs are performed to investigate the engine with four different turbocharger configurations of varying capacity ratio and under various operating conditions in terms of the EGR rate and engine load. The simulation results are analysed to reveal the impact of the turbocharger selection of the engine performance and emissions parameters. Furthermore, modulation schemes with EGR blower speed control, exhaust gas bypass and cylinder bypass are investigated to overcome the mismatch on the engine components flow rates and avoid turbocharger operational issues. The derived results demonstrate that the lowest weighted BSFC is achieved for the case of 70:30 capacity ratio between the large and small turbochargers, whilst the engine operation with the EGR is associated with a 2.6% penalty in the weighted BSFC. The EGR blower speed control is found sufficient to avoid the compressor overspeed at high engine loads exhibiting the lower BSFC penalty, whereas the cylinder bypass control is appropriate for controlling the compressor speed at low engine loads. This study contributes on delineating the underlying parameters and interactions between the engine components for the investigated marine two-stroke engine and provides recommendations for the engine-turbocharging system matching procedure.
查看更多>>摘要：Improving of thermal efficiency is inevitable for further dissemination of adsorption heat pumps. Here, a highly heat-integrated multi-bed switching sequence for adsorption chillers is presented to maximize regeneration of both, sensible and latent heat. The thermal coupling of the beds is investigated together with properties of the adsorbent layer using a True-Moving-Bed approach. Results are compared to the limiting thermodynamic efficiency. To account for heat and mass transfer in a consolidated adsorbent together with the motion of the adsorbent beds, a spatially one + one dimensional model is used. Adsorbent layer thickness, process cycle time and heat regeneration are optimized for maximal thermal efficiency and a given specific power density. Due to the combined optimization of material properties and cycle design, a Coefficient of Performance of up to 1.57 could be reached which is 96% of the limiting thermodynamic efficiency.
查看更多>>摘要：To improve the temperature uniformity and cooling performance of the battery module, a hybrid battery thermal management system (BTMS) with liquid cooling and phase change materials (PCM) containing different expanded graphite contents is proposed. To adjust the heat transfer efficiency of composite phase change material (CPCM) along the direction of liquid flow, the segments of CPCM matrix contain different expanded graphite (EG) contents. Subsequently, the effects of the layout of CPCM matrix, length distribution of each segment, the structure parameters and cooling strategy on cooling performance of the battery module are investigated using computational fluid dynamics (CFD) model at 4C discharge rate and ambient temperature of 308.15 K. The results demonstrate that the maximum temperature (T-max) and temperature difference (Delta T) of BTMS adopting segmented layout III are significantly reduced by 1.3 K and 1.4 K respectively compared with layout I. Additionally, the layout III exhibits optimal cooling performance when length of each segment is 110 mm, 120 mm and 120 mm, respectively. Moreover, the T-max and Delta T decrease with increase of cell-to-cell spacing (L) and diameter of liquid channel (d), and Delta T is only 2.2 K under the condition of L(24)d(5) (L = 24 mm, d = 5 mm). During the C-1-charging and C-4-discharging cycles, the Tmax of BTMS with normal strategy remains at 319.5 K and Delta T lower than 3 K; furthermore the strategy of delayed liquid cooling can significantly reduce power consumption by 33.3 % without sacrificing the cooling performance.
NSTL
Elsevier