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  • PROPERTIES OF THE BOUNDARY FLUX OF A SINGULAR DIFFUSION PROCESS

    The authors study the singular diffusion equation(6)u/(6)t = div(pα|(△)u|p-2(△)u), (x,t) ∈ QT = Ω× (0,T),where Ω (C) Rn is a bounded domain with appropriately smooth boundary (6)Ω, p(x) =dist(x, (6)Ω), and prove that if α≥ p- 1, the equation admits a unique solution subject only to a given initial datum without any boundary value condition, while if 0 <α<p- 1, for a given initial datum, the equation admits different solutions for different boundary value conditions....

    2020-11-11 22:33:38浏览:29 boundaryfluxSingulardiffusiondegeneracy

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  • Transport Process of Isopropanol Aqueous Solution by Pervaporation

    To study the transport process of isopropanol aqueous solution by pervaporation, the transport model of isopropanol and that of water at 323 K in polyvinyl alcohol(PVA) membrane were obtained in this paper. Theoretical predictions agreed well with the experimental results. The interactional parameter between water and PVA membrane is less than that between isopropanol and PVA membrane, which shows that water is preferentially dissolved in PVA membrane. The plasticizing coefficient and diffusion coefficient at infinite dilution of water are larger than those of isopropanol,which shows that the dissolution and permeation in PVA membrane of water are greater than those of isopropanol. Both the interactional parameter between water and isopropanol in the membrane and that in feed rise with the increase of isopropanol content in feed, which shows that the larger isopropanol content is, the higher selectivity of the membrane is and the more remarkable separation effect of pervaporation is....

    2020-11-10 09:33:08浏览:53 modelpermeatefluxisopropanolwaterpervaporation

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  • Research on On-line detection system for natural gas pipeline

    Four methods for testing the thickness and defect of pipeline are compared and analyzed in this paper. The testing principle of magnetic leakage flux based on electromagnetism is discussed in detail. From the experiments of sensor character, the effects caused by some factors are found, which give some important information for sensor design, and this method is proved reasonable and effective. The mechanical and electrical structures of inspection equipment, as well as its working principle and technical features are introduced. In this paper, control flow and software design are discussed, too. This detection system has been successfully developed. Experiments show that this detection system has high resolution and can be put into practice....

    2020-09-13 23:35:02浏览:32 magneticfluxleakagemethodnaturalgaspipelinethicknessdefectcontrolflow

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  • Production and emission of phosphine gas from wetland ecosystems

    Phosphine is a part of an atmospheric link of phosphorus cycle on earth,which could be an important pathway for phosphorus transport in environment.Wetland ecosystems are important locations for global biogeochemical phosphorus cycle.In this study,production and emission fluxes of free phosphine from four wetlands types in southern China were observed in different seasons.The results showed that the concentration of phosphine liberated from wetlands was at pg/m3-ng/m3 level.The emission concentrations of different wetlands followed the sequence:paddy field(51.83±3.06)ng/m3≥marsh(46.54±20.55)ng/m3 > lake(37.05±22.74)ng/m3 ≥coastal wetland(1.71±0.73)ng/m3,the positive phosphine emission flux occurred in rice paddy field(6.67±5.18)ng/(m2·hr)and marsh(6.23±26.9)ng/(m2·hr),while a negative phosphine flux of(-13.11±35.04)ng/(m2·hr)was observed on the water-air interface of Lake Taihu,suggesting that paddy field and marsh may be important sources for phosphine gas in atmosphere,while lake may be a sink of atmospheric phosphine gas during the sampling period.Atmospheric phosphine levels and emission flux from Yancbeng marsh and rice paddy field varied in different seasons and vegetational zones.Both diffusion resistance in aqueous phase and temperature were dominating factors for the production and transportation of phosphine to atmosphere....

    2020-09-13 23:35:02浏览:17 phosphinefluxWetlandecosystems

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  • 不同结构聚砜超滤膜对聚乙二醇的过滤性能研究

    以N,N-二甲基甲酰胺(DMF)、N,N-二甲基乙酰胺(DMAc)、N-甲基吡咯烷酮(NMP)为溶剂,水为非溶剂,制备了不同结构的聚砜超滤膜,并考察其对超滤膜过滤性能测试体系-聚乙二醇水溶液的过滤性能.发现纯水通量主要是由超滤膜表面的孔结构所决定,孔径越大通量越高;聚乙二醇水溶液的过滤性能由膜表面的孔结构和截面结构所决定,膜表面的孔径越小、截面是海绵结构的超滤膜的截留率越高.并且通过理论模拟与动态激光光散射的数据比较,发现聚乙二醇的分子链在经过超滤膜时形态发生了明显变化....

    2020-07-10 14:39:05浏览:28 聚砜超滤膜通量截留率polysulfoneultrafiltrationfluxrejection

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  • Particle flux through the Huanghai Sea cold water mass

    Settling particulate matter (SPM) was collected by using sediment traps at four stations in a survey section from Qingdao to Cheju-do,across the Huanghai Sea cold water mass (HSCWM), in August 2002. The sediment traps were planted in three layers: the upper layer of the thermocline (ULT) above the HSCWM, the lower layer of the thermocline (LLT), and the bottom layer of water column (BL).To determine the particle flux, the contents of organic carbon (POC), organic nitrogen (PON), total carbon (PC), and total phosphorous(PP) in SPM were analyzed, and two flux models (Ⅰ and Ⅱ ) were improved to calculate the resuspension ratio, with an assumption in Model Ⅰ that the vertical flux of SPM in the LLT equals the net vertical flux of SPM in the whole water column. An X value, i.e., the fraction of the resuspension flux originating from the surficial sediments nearby the sampling station, was deduced from Model Ⅰ to estimate the contribution of lateral currents to the total resuspension flux. The results showed that inorganic particles, fecal pellets, and miscellaneous aggregates were the major types of SPM in the HSCWM, and the contents of POC, PON, PC, and PP all decreased with water depth. A great deal of fecal pellets found in the LLT indicates that the main space producing biogenic SPM is the thermocline,and especially the LLT, where the C/N ratio is lower than that in the ULT. The resuspension ratios, 90%~96% among stations, imply strong impact ofresuspension on particle flux in the BL. These values were not significantly different between the two flux models,suggesting that the hypothesis in Model Ⅰ that the flux in the LLT equaling the net flux to the bottom is acceptable for shallow waters with stratification like the HSCWM. The POC export ratio from the HSCWM ranges from 35% to 68%. It benefits from the short sinking distance in shallow water. The upwelling in the HSCWM enhanced the POC flux through the water mass, and the lateral currents provides up to being greater than 50% ofresuspension flux in the BL according to evaluation of the X value....

    2020-07-08 21:52:19浏览:18 settlingparticulatematterparticlefluxmodelresuspensionratiothermocline

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  • The Impact of Soil Freezing/Thawing Processes on Water and Energy Balances

    A frozen soil parameterization coupling of thermal and hydrological processes is used to investigate how frozen soil processes affect water and energy balances in seasonal frozen soil. Simulation results of soil liquid water content and temperature using soil model with and without the inclusion of freezing and thawing processes are evaluated against observations at the Rosemount field station. By comparing the simulated water and heat fluxes of the two cases, the role of phase change processes in the water and energy balances is analyzed. Soil freezing induces upward water flow towards the freezing front and increases soil water content in the upper soil layer. In particular. soil ice obviously prevents and delays the infiltration during rain at Rosemount. In addition, soil freezing/thawing processes alter the partitioning of surface energy fluxes and lead the soil to release more sensible heat into the atmosphere during freezing periods....

    2020-07-08 21:52:19浏览:27 frozensoilwaterandenergybalancesprocessessurfaceflux

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  • Treatment of oil/water emulsion by polyethylene glycol ultrafiltration membrane

    Polyethylene glycol(PEG) membranes with different molecular mass cut-offs were used to treat oil/water emulsion, and the effects of experimental conditions including pressure, temperature and different opera-ting modes on permeate flux and removal rate of chemical oxygen demand (CODCr) were studied. The results show that the permeate flux of ultrafiltration membrane is influenced by pressure and temperature; practical pressure is chosen to be 0.3-0.7 MPa for the PEG with molecular mass cut-offs of 8 000 and 0.7-1.0 MPa for the PEG with molecular mass cut-offs of 2 500; and the practical temperature is chosen to be 25-32 ℃. Different operating modes of ultrafiltration also influence the permeate flux and removal rate of CODCr. The ultrafiltration membrane of intermittent cross-flow operating mode is easier to be influenced by blocky polarization and contamination than that of sequential cross-flow operating mode. Removal rate of CODCr in intermittent cross-flow and sequential cross-flow condition can be maintained at about 93%....

    2020-07-08 08:49:41浏览:25 wateremulsionultrafiltrationmembranepermeatefluxchemicaloxygen

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  • Key technique of a detection sensor for coal mine wire ropes

    Wire ropes, employed extensively in coal mine hoists and transportation systems are subject to damage due to wear,corrosion and fatigue. The extent of damage and the carrying capacity of ropes are closely related to the sense of safety by staff and equipments. Magnetic flux leakage detection method (MFL), as an effective method, is these days widely used in detection of bro-ken strands of wire ropes. In order to improve the accuracy of detection of flaws in wire ropes by magnetic flux leakage (MFL), the effect of the distance between a sensor and the surface of a wire rope (i.e., lift-off) on detection by magnetic flux leakage was in-vestigated. An analysis of the main principles for the choice of lift-off is described by us and a new method that improves the struc-ture of the detector is proposed from the point of view of the design of a magnetic circuit, to restrain the impact of fluctuations of sensor lift-off. The effect of this kind of method is validated by simulation and computation. The results show that the detection sensitivity is markedly increased by this method. Furthermore, the signal-to-noise ratio (SNR) can be increased by over 28%. This method will lend itself to offer reliable scientific information to optimize the structure of excitation devices and improve the accu-racy of MFL detection....

    2020-06-12 16:17:32浏览:1388 coalminewireropemagneticfluxleakagedetectionlift-off

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  • 炉管壁面热通量对裂解反应影响的数值模拟

    利用计算流体力学软件Fluent模拟了KTI裂解炉单根GK-V型炉管内的流动、传热和化学反应,并将计算结果与工业数据对比,验证了厂模型的准确性.研究发现,在沿裂解炉管长的轴向方向上,根据主导过程的不同,可以将炉管分为3段:传热段、一次反应段和二次反应段.计算结果表明,在其它模型参数不变的情况下,分别增加和减少壁面的热通量,乙烯质量分数随热通量增加而升高,丙烯质量分数随热通量增加而降低....

    2020-03-24 09:22:53浏览:1440 乙烯裂解炉热通量计算流体力学数值模拟ethylenepyrolyzerheatfluxcomputationalfluiddynamics

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