Temperature Distributions in Single Cell of Polymer Electrolyte Fuel Cell Simulated by an 1D Multi-plate Heat-Transfer Model and a 3D Numerical Simulation Model

The purpose of this study is to verify an 1D multi-plate heat-transfer model estimating the temperature distribution on the interface between polymer electrolyte membrane and catalyst layer at cathode in single cell of polymer electrolyte fuel cell, which is named as reaction surface in this study, with a 3D numerical simulation model solving many governing equations on the coupling phenomena in the cell. The results from both models/simulations agreed well. The effects of initial operation temperature, flow rate, and relative humidity of supply gas on temperature distribution on the reaction surface were also investigated. It was found in both 1D and 3D simulations that, the temperature rise （i.e., Treact-Tini） of the reaction surface from initial operation temperature at 70℃ was higher than that at 80℃ irrespective of flow rate of supply gas. The effect of relative humidity of supply gas on Treact- Tini near the inlet of the cell was small. Compared to the previous studies conducted under the similar operation conditions, the Treact - Tini calculated by 1D multi-plate heat-transfer model in this study as well as numerical simulation using 3D model was reasonable.

Indoor experiment and numerical simulation study of ammonia-nitrogen migration rules in soil column

The riverbank soil is a natural purifying agent for the polluted river water(Riverbank filtration, RBF). This is of great importance to groundwater safety along the riverbank. This paper examines the migration and transformation rules of ammonia-nitrogen in three typical types of sand soil using the indoor leaching experiment of soil column, and then makes comparison with the indoor experiment results in combination with the numerical simulation method. The experiment process shows that the change in ammonia-nitrogen concentration goes through three stages including "removal-water saturation-saturation". As the contents of clay particles in soil sample increase, the removal of ammonia-nitrogen from soil sample will take more time and gain higher ratio. During the removal period, the removal ratio of Column 1, Column 2 and Column 3 averages 68.8%(1-12 d), 74.6%(1-22 d) and 91.1%(1-26 d). The ammonia-nitrogen removal ratio shows no noticeable change as the depth of soil columns varies. But it is found that the ammonia-nitrogen removal ratio is the least of the whole experiment when the soil columns are at the depth of 15 cm. It can be preliminary inferred that the natural purifying performance of soil along the river for ammonia-nitrogen in river water mainly depends on the proportion of fine particles in soil. HYDRUS-1D model is used to simulate this experiment process, analyze the change of the bottom observation holes by time and depth in three columns(the tenth day), and make comparison with the experiment result. The coefficients of determination for fitting curves of Column 1, Column 2 and Column 3 are 0.953, 0.909, 0.882 and 0.955, 0.740, 0.980 separately. Besides, this paper examines the contribution of absorption, mineralization and nitrification in the simulation process. In the early removal stage, mineralization plays a dominant role and the maximum contribution rate of mineralization is 99%. As time goes by, absorption starts to function and gradually assumes a dominant position. In the middle and late removal stage, nitrification in Column 1 and Column 2 makes more contribution than mineralization. So the experiment result of the ammonia-nitrogen concentration is 0.6% and 2.4% lower than that in effluent and the maximum contribution ratio of nitrification is -4.53% and -5.10% respectively when only the function of absorption is considered. The mineralization in Column 1 and Column 2 in the middle and late removal stage still plays a more important role than nitrification. So the experiment result is 1.4% higher than that in effluent and the maximum contribution ratio of nitrification is -2.51% when only the function of absorption is considered. Therefore, absorption, mineralization and nitrification make different contributions during different part of the stage. This means that the natural purifying performance of soil along the river for ammonia-nitrogen in river water not only depends on the proportion of fine particles in soil, but depends on the mineralization and nitrification environment. This can offer some insights into the protection and recovery of groundwater along the riverbank.

Numerical simulations of flow and sediment transport within the Ning-Meng reach of the Yellow River,northern China

Effective management of a river reach requires a sound understanding of flow and sediment transport generated by varying natural and artificial runoff conditions. Flow and sediment transport within the Ning-Meng reach of the Yellow River（NMRYR）, northern China are controlled by a complex set of factors/processes, mainly including four sets of factors：（1） aeolian sediments from deserts bordering the main stream;（2） inflow of water and sediment from numerous tributaries;（3） impoundment of water by reservoir/hydro-junction; and（4） complex diversion and return of irrigation water. In this study, the 1-D flow ＆ sediment transport model developed by the Yellow River Institute of Hydraulic Research was used to simulate the flow and sediment transport within the NMRYR from 2001 to 2012. All four sets of factors that primarily control the flow and sediment transport mentioned above were considered in this model. Compared to the measured data collected from the hydrological stations along the NMRYR, the simulated flow and sediment transport values were generally acceptable, with relative mean deviation between measured and simulated values of 〈15%. However, simulated sediment concentration and siltation values within two sub-reaches（i.e., Qingtongxia Reservoir to Bayan Gol Hydrological Station and Bayan Gol Hydrological Station to Toudaoguai Hydrological Station） for some periods exhibited relatively large errors（the relative mean deviations between measured and simulated values of 18% and 25%, respectively）. These errors are presumably related to the inability to accurately determine the quantity of aeolian sediment influx to the river reach and the inflow of water from the ten ephemeral tributaries. This study may provide some valuable insights into the numerical simulations of flow and sediment transport in large watersheds and also provide a useful model for the effective management of the NMRYR.

Numerical Feasibility Study of a Wax Cold Flow Approach for Subsea Tie-In Flowlines Using a 1D Mechanistic Multiphase Flow Simulator

This work is a thermo-fluid numerical case study to investigate the size and performance of a system that eliminates needs for insulating, heating and inhibiting chemically the deposition of wax in subsea tie-in flowlines. For short, we call this type of systems “Cold Flow”. The particular system analyzed in this study consists of a reactor unit at the inlet to the flowline, where the thermal solubility of the wax-creating molecules is reduced by cooling. Subsequently, solid wax is deposited in the reactor piping and wax free crude is entering the flowline. The reactor is regenerated periodically. The reactor-pipeline system was modelled using a commercial flowline simulator, with transient, thermal, multiphase and deposition capabilities. The basic layout used was a transportation pipeline of 8 km and 6.69 in ID with a mass flow rate of 17.51 kg/s, a water cut (WC) of zero and an inlet temperature of 70°C. The wax appearance temperature (cloud point) of the crude is 22°C and the seabed temperature is 4°C. Three types of reactors have been simulated: a non-insulated pipe section, a passive cooler with a bundle of parallel pipes and an active cooler. Sensitivity analyses have been performed for all three cases varying the external convective coefficient, the reactor pipeline diameter and the WC. For a non-insulated pipeline section cooler, the required length is of the same order of magnitude as the main flowline, implying that such a solution is impractical for short flowline distances or when a compact deployment is desired. For the passive cooler case, the required length was half of that in the previous case;thus it is still significant. For the active cooler reactor, the required cooling duty was 2.2 MW. In all three cases, the pipe-flow dynamics were analyzed, and the pigging arrangement complexity has been qualitatively addressed. However, the detailed design falls out of the scope of this study.

Estimation of evapotranspiration from artificial forest in mountainous areas of western Loess Plateau based on HYDRUS-1D model

Evapotranspiration is the most important expenditure item in the water balance of terrestrial ecosystems,and accurate evapotranspiration modeling is of great significance for hydrological,ecological,agricultural,and water resource management.Artificial forests are an important means of vegetation restoration in the western Loess Plateau,and accurate estimates of their evapotranspiration are essential to the management and development of water use strategies for artificial forests.This study estimated the soil moisture and evapotranspiration based on the HYDRUS-1D model for the artificial Platycladus orientalis(L.)Franco forest in western mountains of Loess Plateau,China from 20 April to 31 October,2023.Moreover,the influence factors were identified by combining the correlation coefficient method and the principal component analysis(PCA)method.The results showed that HYDRUS-1D model had strong applicability in portraying hydrological processes in this area and revealed soil water surplus from 20 April to 31 October,2023.The soil water accumulation was 49.64 mm;the potential evapotranspiration(ETp)was 809.67 mm,which was divided into potential evaporation(Ep;95.07 mm)and potential transpiration(Tp;714.60 mm);and the actual evapotranspiration(ETa)was 580.27 mm,which was divided into actual evaporation(Ea;68.27 mm)and actual transpiration(Ta;512.00 mm).From April to October 2023,the ETp,Ep,Tp,ETa,Ea,and Ta first increased and then decreased on both monthly and daily scales,exhibiting a single-peak type trend.The average ratio of Ta/ETa was 0.88,signifying that evapotranspiration mainly stemmed from transpiration in this area.The ratio of ETa/ETp was 0.72,indicating that this artificial forest suffered from obvious drought stress.The ETp was significantly positively correlated with ETa,and the R2 values on the monthly and daily scales were 0.9696 and 0.9635(P<0.05),respectively.Furthermore,ETa was significantly positively correlated with temperature,solar radiation,and wind speed,and negatively correlated with relative humidity and precipitation(P<0.05);and temperature exhibited the highest correlation with ETa.Thus,ETp and temperature were the decisive contributors to ETa in this area.The findings provide an effective method for simulating regional evapotranspiration and theoretical reference for water management of artificial forests,and deepen understanding of effects of each influence factors on ETa in arid areas.

Migration and fate of polycyclic aromatic hydrocarbons in bioretention systems with different media:experiments and simulations

Polycyclic aromatic hydrocarbons(PAHs)present significant risks to human health owing to their carcinogenic,teratogenic,and mutagenic properties.The contamination of surface water with PAHs via runoff has become a prominent source of water pollution.While the capacity of bioretention systems to remove PAHs from runoff is recognized,the dynamics of PAH migration and degradation in these systems are not well-understood.This study aims to explain the migration and fate of PAHs in bioretention systems through a series of experiments and model simulations.This study constructed bioretention systems with three different media types and found that these systems achieved PAH load reductions exceeding 92%.Notably,naphthalene(NAP),fluoranthene(FLT),and pyrene(PYR)tended to accumulate in the media’s upper layer,at depths of 10 to 40 cm.To further analyze the migration and fate of PAHs during multi-site rainfall events and across prolonged operation,we applied the HYDRUS-1D model under three distinct scenarios.The findings of this study indicated that NAP degraded in 40 d,whereas FLT and PYR showed incomplete degradation after 120 d.During continuous rainfall events,there was no clear pattern of PAH accumulation;however,FLT and PYR persisted in the bioretention systems.The combination of experimental and simulation findings highlights the inevitable accumulation of PAHs during extended use of bioretention systems.This research provides a theoretical basis for improving operational efficiency,advancing PAH degradation in bioretention systems,and reducing their toxicity.

Numerical Modeling of Shallow Water Table Behavior with Lisse Effect

Air entrapment is an important consideration in environments with shallow water tables and sandy soil, like the condition of highly conductive sandy soils and flat topography in Florida, USA. It causes water table rises in soils, which are significantly faster and higher than those in soils without air entrapment. Two numerical models, Integrated Hydrologic Model (IHM) and HYDRUS-1D (a single-phase, one-dimensional Richards′ equation model) were tested at an area of west central Florida to help further understanding the shallow water table behavior during a long term air entrapment. This investigation employed field data with two modeling approaches to quantify the variation of air pressurization values. It was found that the air pressurization effect was responsible at time up to 40 cm of water table rise being recorded by the observation well for these two models. The values of air pressurization calculated from IHM and HYDRUS-1D match the previously published values. Results also indicated that the two numerical models did not consider air entrapment effect (as the predictive parameters remain uncertain) and thus results of depth to water table from these models did not compare to the observations for these selected periods. Incorporating air entrapment in prediction models is critical to reproduce shallow water table observations.

Controlling of NO_x Emitted from a Diesel Engine Fueled on Biodiesel: Theoretical Modeling and Experimental Evaluation

The development of a diesel engine model using one-dimensional （1-D） fluid-dynamic engine simulation codes,and its validation using experimental measurements are described in this paper.The model was calibrated by running the engine on an electric dynamometer at eight steady-state operating conditions.The refined engine model was used to predict the oxides of nitrogen （NOx） less than those measured earlier in the experiments,and hence to recommend changes in the engine for the verification of the results.The refined engine model is greatly influenced by the start of injection angle （ψ）,ignition delay （φ）,premix duration （DP）,and main duration （DM） for the prediction of reduced NOx emissions.It is found that optimum ψ is 6.5° before top dead center （BTDC）.At this angle,the predicted and experimental results are in good agreement,showing only a difference of up to 4%,6.2%,and 7.5% for engine performance,maximum combustion pressure （Pmax）,and NOx,respectively.

耦合空压机通路的商用车进气噪声仿真分析

为了对商用车的进气管口噪声进行预测,提出了空压机通路一维仿真模型建立方法,建立空压机-发动机耦合仿真模型,在主要阶次噪声频率点处对噪声频率和噪声幅值进行准确预测,同时对来自空压机和发动机的阶次噪声进行识别。利用耦合模型研究了空压机通路的噪声特点以及在该通路上的降噪措施与效果。结果表明,空压机噪声有着典型的脉冲噪声特点,在处理该种类型的噪声时,不同种类消声器的布置顺序会对最终的消声效果产生明显影响。

Estimating Soil Hydraulic Parameters Characterizing Rainwater Infiltration and Runoff Properties of Dryland Floodplains

The two-layered (0 - 50 and 50 - 250 mm) surface horizon hydraulic parameters of three dryland floodplain soil-types under aquafer water management in Postmasburg, Northern Cape Province of South Africa were estimated with HYDRUS-1D model. Time dependent water infiltration measurements at 30 and 230 mm depths from simulated rainfalls on undisturbed 1 m2 small plots with intensities of 1.61 (high), 0.52 (medium) and 0.27 (low) mm·min-1, were minimised using a two-step inversion. Firstly, separate optimisation of the van Genuchten-Mualem model parameters for the two surface-horizon layers and secondly, simultaneous optimisation for the joint two-layered horizon with first step optimal parameters entered as initial values. The model reproduced transient water-infiltration data very well with the Nash-Sutcliffe model efficiency coefficient (NSE) of 0.99 and overestimated runoff (NSE;0.27 to 0.98). The upper surface horizon had highly optimised and variable parameters especially θs and Ks. Optimal Ks values from higher soil surface bulk-density (≥1.69 g·cm-3) were lower by at least one order of magnitude to double ring infiltrometers and water infiltration properties were different (P < 0.05) for the high rainstorm due to raindrop impact and surface crusting. Optimal α and n parameter values corresponded well with texture of the Addo (Greysols), Augrabies (Ferralsols) and Brandvlei (Cambisols) soil types. However, θs and Ksshowed greater sensitivity to model output and exerted greater influence on dryland floodplain water-infiltration and runoff characteristics. Increasing rainfall simulation period to attain near-surface saturated conditions and inclusion of surface ponding data in the inverse problem could considerable improve model prediction of hydro-physical parameters controlling surface-subsurface water distribution in fluvial environments.

基于一二维耦合模型和水库调度的长江宜宾河段洪水遭遇与淹没分析

【目的】宜宾市地处金沙江与岷江汇合处,且有横江、南广河及其他重要支流汇入,因此洪水遭遇组合复杂,且受金沙江下游向家坝-溪洛渡等梯级水库调度影响明显,其水文水动力计算对下游各城镇河段防洪规划及减灾政策制定具有重要意义。【方法】通过构建一二维水动力学耦合数学模型,采用实测洪水验证的分析方法对长江宜宾河段(含重要支流汇入段)的洪水组合进行分析,选取了1961年、1966年两个典型年并对比有无金沙江下游梯级水库调洪的影响,计算各河段和沿岸城镇100 a、50 a及20 a一遇的洪水淹没。【结果】结果表明:(1)当发生超标洪水时,城区主要洪水漫溢淹没分布在宜宾的安边镇、柏溪街道,翠屏区西郊街道以及岷江菜坝镇飞机坝段。(2)不管是1961典型年(岷江为主要来水)还是1966典型年(金沙江为主要来水),岷江流域均受灾较重;其中西郊街道和大观楼街道的洪水主要受金沙江来水和岷江洪水顶托作用明显;岷江漫溢洪水为宜宾城区外洪的主要来源,岷江是宜宾市的防洪重点。【结论】结合防洪工程分布及现有堤防建设情况,菜坝镇飞机坝片区现有的20 a一遇洪水的堤防无法满足实际防洪标准需求;西郊街道滨江公园和备战码头,由于未形成防洪封闭圈,城区局部地区仍处于不设防状态;柏溪镇堤防防洪标准20 a一遇偏低,黑河(柏树溪)受到金沙江回水影响会造成柏溪镇严重洪灾。金沙江在向家坝水库的调蓄作用下,即使发生100 a或超过50 a一遇超标洪水,中心城区均不超过40 a一遇,宜宾城区受金沙江洪水影响相对较小,受岷江回水影响较大。

Changes of Vertical Groundwater Recharge with Increase in Thickness of Vadose Zone Simulated by One-Dimensional Variably Saturated Flow Model

The thickness of vadose zone plays a critical role in vertical groundwater recharge. The decline of water table since the past decades due to long-term groundwater over-exploitation has resulted in deep vadose zone in North China Plain. One-dimensional variably saturated flow models were established by Hydrus-1D software and simulations were run under steady and continuous declining water table respectively to estimate the impact of increase in thickness of vadose zone on recharge process, quantity and recharge time. Luancheng area was selected to estimate recharge quantity considering steady and continuous declining water table. The simulation results show that the increase in thickness of vadose zone delays recharge process to water table. The recharge quantity decreases first and then remains stable with the decline of water table. Under the condition of declining water table, the evaluation of recharge by the flux at water table overestimates the recharge quantity. The average annual recharge rate of Luancheng area is 134 mm/a.

珠江三角洲一维河网与三维河口耦合水质模型模拟与验证

在一维与三维耦合水动力、悬沙模型的基础上,构建了珠江三角洲一维与三维耦合水质模型。模型中包括浮游植物-氮-磷-碳-溶解氧循环,并考虑颗粒物在底泥与水体界面的再悬浮过程。选择了三个代表性时段(1999年1月、1999年7月与2000年)进行水质模拟,并采用相应水期的实测资料进行验证。结果表明,耦合水质模型计算效果良好,较好地再现了整个研究区域内各水质要素的时空分布规律,成功描述了珠江三角洲河网与河口区的动力与生物化学变化过程。

基于GIS技术的河流污染动态模拟系统

本文论述了稳态均匀流场中的一维河流水质扩散模型,并在此模型的基础上,基于GIS二次开发技术开发了河流污染动态模拟系统。该系统以乐山市涌斯江支流段的地理底图及基本数据为例,实现了对河流污染情况的动态模拟。通过对该系统的一系列操作,可以对河段任意位置污染物浓度进行自动查询和修改,从而为河流水质污染的监测和管理提供可视化参考依据。

n型单晶硅衬底少子寿命对n-PERC电池性能的影响

采用PC1D模拟软件模拟不同少子寿命的硅片条件下电阻率、扩散方块电阻、结深对n-PERC电池性能的影响。结果表明,随着硅片少子寿命的延长,电池效率提高。通过对实际生产中少子寿命和硅片径向不均匀度的研究,得出n-PERC电池使用硅片的最佳少子寿命值。

直喷汽油机爆震试验与一维模拟研究

一维整机仿真中,爆震是需要考虑的重要因素之一.本文采用试验和模拟结合的方法对比了两类常用爆震模型,分析了其适用范围、准确性及误差产生的原因,并提出模型可能的修正方向.试验结果表明,利用循环占有率法可较为准确地确定临界爆震点火提前角.仿真结果表明,动力学拟合模型对于不同转速、压缩比和进气温度的模拟具有较好的准确性,而经验公式模型则对不同当量比、温度和压缩比的模拟准确性较好.两类模型各自有其适用范围,均需要进一步优化和修正.

一维简化模型地铁列车火灾热释放速率

基于最新《车辆防火要求》及相关材料的燃烧特性数据,以成都地铁2号线列车为例,通过区别处理铺地材料和其他可燃材料并设定引燃条件,建立新型地铁列车一维火灾蔓延模型,计算得到其时变火灾热释放速率,并预测相应的火灾蔓延过程和燃尽时间。结果表明,单节典型地铁列车的最大火灾热释放速率约为4.5 MW,特征燃尽时间约为2 000 s。将计算结果与FDS模拟结果进行对比,证明模型具有较高的可靠性,且计算过程大为简化,可为地铁防火设计提供参考。

三峡库区枝状河网水动力过程实时模拟

基于圣维南控制方程组,针对三峡库区朱沱—坝址河段,采用θ半隐方法离散动量方程的水位梯度项,运用欧拉-拉格朗日方法求解动量方程的对流项,利用有限体积法离散连续性方程,结合预测校正法将枝状河网稀疏线性系统分解为若干三对角子系统,建立了一种可实现河网系统速度-压力耦合问题简单、快速及高精度求解的一维枝状河网水流数学模型。选用2005年、2006年实测水位资料对该模型进行率定与验证,水位计算误差一般<10cm,流量计算误差一般<5%,数学模型计算结果与实测资料符合较好,表明模型精度较高。在单核串行效率测试中,模型模拟1 a水流过程耗时约23.7 s,实现了三峡库区枝状河网水动力过程的实时模拟。

Effect of pH on transport of Pb^(2+),Mn^(2+),Zn^(2+) and Ni^(2+) through lateritic soil: Column experiments and transport modeling

This study investigated the effects of pH on the transport of Pb 2＋ , Mn 2＋ , Zn 2＋ and Ni 2＋ through lateritic soil columns. Model results by fitting the symmetric breakthrough curves （BTCs） of bromide （Br ） with CXTFIT model suggested that physical non-equilibrium processes were absent in the columns. The heavy metal BTCs were, however, asymmetrical and exhibited a tailing phenomenon, indicating the presence of chemical non-equilibrium processes in the columns. The retardation factors of Pb 2＋ were the largest of the four metal ions at both pH 4.0 （33.3） and pH 5.0 （35.4）. The use of Langmuir isotherm parameters from batch studies with HYDRUS-1D did not predict the BTCs well. Rather the two-site model （TSM） described the heavy metal BTCs better than the equilibrium linear/nonlinear Langmuir model. The fraction of instantaneous sorption sites （ f ） of all four metal ions on the lateritic soil was consistently about 30%–44% of the total sorption sites.

高速气体与椭圆柱云相互作用的数值研究

高速颗粒流在天文、自然灾害、工业安全、医疗工业和国防等领域有着重要应用。采用基于分层流模型的直接数值模拟方法,对平面激波与椭圆柱云的相互作用进行数值研究,重点关注椭圆柱横截面的不同长短轴之比和椭圆柱横截面长轴与来流方向所成角度对流场的影响,从气体来流方向上的速度、x轴和y轴方向上的均方根速度、动能、内能和湍动能的分布上进行分析,对能量在计算域的上游区域、椭圆柱云区域和下游区域进行定量分析。同时针对椭圆柱改进了一维体积平均模型,利用该模型拟合了由直接数值模拟得到的反射激波和透射激波位置,获得了最适配的一维体积平均模型中的人工有效阻力系数,并探讨此系数的分布规律。