Flow electrification occurs when a dielectric liquid flows along the wall surface, and it may cause electrostatic hazards such as spark discharges. Flow electrification issues of liquid hydrogen ...should be carefully treated since its low electrical conductivity and dangerous flammability. In this study, flow electrification characteristics of liquid hydrogen in pipe flow are numerically investigated. A theoretical model coupling the electric field and the flow field is introduced to govern the behaviour and distribution of charges, and an interface discharge model is adopted to describe the charge transfer boundary condition. The theoretical model is validated by comparing the simulation with experiment data, and the results show a good agreement with the averaged related deviation below 10%. The result of a common case, with flow velocity u of 1 m/s, pipe radius a 0.01 m, and length L 1 m, shows that the charge density, streaming current, and the electric potential of liquid hydrogen flow are in the magnitude of 10−12 C·m−3, 10−16 A and 10−2 V, respectively. Flow parameters, including flow velocity and pipe size, have a certain effect on the flow electrification characteristics of liquid hydrogen flow. By dimensionless parameterization, it is found that Reynolds numbers (Re), r/a, and x/a are exactly three orthogonal parameters determining the charge density distribution. Furthermore, the effects of electrical conductivity on the distribution of charges and charge dissipation have also been discussed. Finally, the safety assessment of the liquid hydrogen transportation system has been discussed, with extra consideration of the impurities and gas-liquid two-phase flow regime. To sum up, this work presents an in-depth and comprehensive insight into the flow electrification of liquid hydrogen flow, which is of great significance to the transportation safety of liquid hydrogen.
•An interface discharge model is adopted to describe the boundary charge transfer.•Flow parameters, including flow velocity and pipe size, have certain influences.•Rising electrical conductivity leads to the saturation of streaming current.•Impurities and two-phase flow have extra influence on the safety assessment.
•The effects of bending number for buried pipes on thermal performance of HGHE.•Comparison of performance between the staggered and in-line arrangement.•Comprehensive influence of pipe spacing and ...buried depth were investigated.•The critical pipe spacing of HGHE was obtained.
With the advantages of lower installation cost and lower drilling technology requirement, the horizontal ground heat exchanger (HGHE) has attracted much attention. In this paper, the pipe arrangements with in-line and staggered are evaluated comparatively and the effects of the relative displacement of staggered pipes are investigated. Meanwhile, the comprehensive effects of bending number, pipe spacing and buried depth on thermal performance of HGHE are studied. The results show that the thermal performance of staggered arrangement outperformed that of in-line arrangement when the relative offset displacement is greater than 1/3. The thermal interference between adjacent buried pipes is the significant factors causing thermal resistance. For double-layered HGHE, the critical pipe spacing of first layer and second layer is 40d and 100d respectively. The buried depth has little effect on the thermal performance of HGHE.
•Annual performances of nine ET products were evaluated in 35 global river basins.•A water balance method corrected for the water storage change at annual time scale is used.•All ET products ...performed better in dry basins than in wet basins.•Most products could not adequately estimate the inter-annual variability and trends of ETwb.
Evapotranspiration (ET) plays a critical role in linking the water and energy cycles but is difficult to estimate at regional and basin scales. In this study, we present a worldwide evaluation of nine ET products (three diagnostic products, three land surface model (LSM) simulations and three reanalysis-based products) against reference ET (ETwb) calculated using the water balance method corrected for the water storage change at an annual time scale over the period 1983–2006 for 35 global river basins. The results indicated that there was no significant intra-category discrepancy in the annual ET estimates for the 35 basins calculated using the different products in 35 basins, but some products performed better than others, such as the Global Land surface Evaporation estimated using the Amsterdam Methodology (GLEAM_E) in the diagnostic products, ET obtained from the Global Land Data Assimilation System version 1 (GLDAS 1) with the Community Land Model scheme (GCLM_E) in LSM simulations, and ET from the National Aeronautics and Space Administration (NASA) Modern Era Retrospective-analysis for Research and Applications reanalysis dataset (MERRA_E) in the reanalysis-based products. Almost all ET products (except MERRA_E) reasonably estimated the annual means (especially in the dry basins) but systematically underestimated the inter-annual variability (except for MERRA_E, GCLM_E and ET simulation from the GLDAS 1 with the MOSAIC scheme – GMOS_E) and could not adequately estimate the trends (e.g. GCLM_E and MERRA_E) of ETwb (especially in the energy-limited wet basins). The uncertainties in nine ET products may be primarily attributed to the discrepancies in the forcing datasets and model structural limitations. The enhancements of global forcing data (meteorological data, solar radiation, soil moisture stress and water storage changes) and model physics (reasonable consideration of the water and energy balance and vegetation processes such as canopy interception loss) will undoubtedly improve the estimation of global ET in the future.
In this study, Computational Fluid Dynamics (CFD) technique is employed to investigate the effects of two important ejector geometry parameters: the primary Nozzle Exit Position (NXP) and the mixing ...section converging angle
θ
, on its performance. A CFD model is firstly established and calibrated by actual experimental data, and then used to create 95 different ejector geometries and tested under different working conditions. From 210 testing results, it is found that the optimum NXP is not only proportional to the mixing section throat diameter, but also increases as the primary flow pressure rises. On the other hand, the ejector performance is very sensitive to
θ
especially near the optimum working point. The entrainment ratio can vary as much as 26.6% by changing
θ
. A relatively bigger
θ
is required to better maximize the ejector performance when the primary flow pressure rises. The significance of the study is that these findings can be used to guide the adjustment of NXP and
θ
in order to obtain the best ejector system performance when the operating conditions are different from the on-design conditions.
A new theoretical model for the convergent nozzle ejector in the anode recirculation line of the polymer electrolyte membrane (PEM) fuel cell system is established in this paper. A velocity function ...for analyzing the flow characteristics of the PEM ejector is proposed by employing a two-dimensional (2D) concave exponential curve. This treatment of velocity is an improvement compared to the conventional 1D “constant area mixing” or “constant pressure mixing” ejector theories. The computational fluid dynamics (CFD) technique together with the data regression and parameter identification methods are applied in the determination of the velocity function's exponent. Based on the model, the anode recirculation performances of a hybrid PEM system are studied under various stack currents. Results show that the model is capable of evaluating the performance of ejector in both the critical mode and subcritical mode.
•The performance of plain, serrated and perforated fins was research experimentally.•j/f, j/f1/2 and j/f1/3 are used as the performance evaluation criteria.•The effects of heating condition and ...Prandtl number on heat transfer were studied.•A modified Colburn factor j was proposed based on the Prandtl number effects.
An experimental investigation is performed using liquid R113 to study the thermohydraulic characteristics of plate-fin heat exchanger with plain, serrated and perforated fins. Meanwhile, three performance evaluation criteria j/f, j/f1/2 and j/f1/3 are used to qualitative compare their comprehensive performance. Further, to study the effects of heating condition and Prandtl number on heat transfer, a numerical model of serrated fins is carried out. The fin channels with a uniform heat flux at bottom end or at both bottom and upper ends are studied as two types of heating conditions, namely, single-fold and two-fold modes. Besides, using air (Pr = 0.744), R113 (Pr = 9.02) and ethylene glycol (Pr = 51.65) aqueous solution as working media, the Prandtl number effect is discussed. The results reveal that the comprehensive performance of serrated fins is the best. Colburn factor j of single-fold mode is lower than that of two-fold mode. The Colburn factor j decreases as the Prandtl number increases in laminar flow and it is independent of Prandtl number in turbulent flow. A modified Colburn factor j based on the Manglik & Bergles correlation is proposed as functions of (Pr/Prair)−0.04827 in laminar flow. The conclusions provide the guidance on the design of plate fin heat exchanger.
In this paper, a CFD model calibrated by the experimental results from initial designed ejector is used to evaluate the influence of 6 key geometry parameters on the performance (entrainment ratio) ...of an air-cooled ejector cooling system and, consequently, to find the best design parameters. A new ejector according to the findings from the CFD simulation is then designed and used at the same air-cooled ejector system to verify the simulation results. From both simulation and testing results, we find that: 1) the optimal area ratio, the ratio of primary nozzle exist position and length of constant-area mixing section to primary nozzle diameter are lower than those of water-cooled ejector systems; 2) the optimal converging angle of constant-pressure mixing section and the ratio of primary nozzle exit position and length of constant-area mixing section to the diameter of constant-area mixing section are very close to those of water-cooled ejector systems; 3) substantial performance improvement can be achieved by using the new parameters in the ejector design.
► Study the influence of geometry parameters on the air-cooled ejector performance. ► CFD model is established and calibrated by the experimental results. ► The optimal γA are much lower than those of water-cooled ejector systems. ► The optimal NXP/Dn and Lm/Dn are lower than those of water-cooled ejector systems.
Soil moisture (SM) retrieved from satellite and spaceborn sensors provides useful parameters for earth system models (ESMs). The Climate Change Initiative (CCI) SM products released by the European ...Space Agency have been widely used in many humid/semi-humid climatic regions due to their relatively long-term record. However, the performance of these products in cold and arid regions, such as the Qinghai-Tibetan Plateau (QTP), is largely unknown, necessitating urgent evaluation and calibration in these areas. In this work, we evaluated the reliability and improved the accuracy of the active-passive combined CCI products (CCI-C) using in-situ measured SM contents (SMC) under different underlying surface conditions. First, some conventional models were used to investigate the relationship between the CCI-C and the in-situ observed SMC, yielding similar fitting performances. Next, the random forest method and multiple linear regression were used to contrast the conventional models to calibrate and validate the CCI-C SM product based on the in-situ observed SMC, and the random forest method was found to have the highest accuracy. However, calibration of the CCI-C SM data with the best-performed random forest method based on different spatial zonation methods, e.g., by climate, topography, land cover, and vegetation, resulted in distinct spatial patterns of SM. Compared to a widely-used satellite SM product, namely the Soil Moisture Active Passive (SMAP) SM dataset, the calibrated CCI-C SM data based on climatic and vegetation zonation were larger but had similar spatial patterns. This study also points to the value of the calibrated CCI-C SM product to support land surface studies on the QTP.
Information on disease process and pathogenicity mechanisms is important for understanding plant disease. Spring black stem and leaf spot caused by the necrotrophic pathogen Phoma medicaginis var. ...medicaginis Malbr. & Roum causes large losses to alfalfa. However, till now, little is known about alfalfa-P. medicagnis interactions and the pathogenicity mechanisms of the pathogen. Here, alfalfa inoculated with P. medicaginis was subjected to GC-MS based metabolic profiling. The metabolic response in P. medicaginis-inoculated and mock-inoculated alfalfa leaves was assessed at 2, 4, 6, 8, 12, 16, 20, 24, 26 and 28 days post inoculation. In total, 101 peaks were detected in the control and inoculated groups, from which 70 metabolites were tentatively identified. Using multivariate analysis, 16 significantly regulated compounds, including amino acids, nitrogen-containing compounds and organic acids, polyols, fatty acids, and sugars were tentatively identified (Variable importance values, VIP>1.0 and p <0.05). Among these metabolites, the levels of malate, 5-oxoproline, palmitic acid and stearic acid were increased significantly in P. medicaginis-infected alfalfa leaves compared to the controls. In contrast, the levels ofγ-aminobutyric acid and 2-pyrrolidinone were significantly decreased in infected leaves compared to the controls. Further metabolic pathway analysis of the 16 significantly regulated compounds demonstrated that glycolysis, the tricarboxylic acid cycle, and β-oxidation of fatty acids were significantly induced in the alfalfa leaves at later stages of P. medicaginis infection. The strong induction of tricarboxylic acid cycle pathways at later infection stages caused by the pathogen may induce senescence in the alfalfa leaves, leading to plant death. However, intermediate metabolites of these metabolic pathways, and inositol phosphate, glutathione, the metabolic pathways of some amino acids accumulated rapidly and strongly at early stages of infection, which may enhance the ability of alfalfa to resist necrotrophic P. medicaginis disease. Understanding metabolic pathways is essential for understanding pathogenesis.
An efficient cascade copper-catalyzed intermolecular Ullmann-type C–N coupling/enamine condensation reaction is described, in which ortho-acylanilines and alkenyl iodides converted to ...multisubstituted quinolines in good to excellent yields.
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