scholarly journals Mathematical Model of Ammonium Nitrogen Transport to Runoff with Different Slope Gradients under Simulated Rainfall

Water ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 675 ◽  
Author(s):  
Weimin Xing ◽  
Peiling Yang ◽  
Chang Ao ◽  
Shumei Ren ◽  
Yao Xu
Keyword(s):  
Mathematical Model ◽  
Mass Transfer ◽  
Transfer Coefficient ◽  
Rainfall Intensity ◽  
Overland Flow ◽  
Nutrient Transport ◽  
Ammonium Nitrogen ◽  
Time Dependent ◽  
Nitrogen Transport ◽  
Slope Gradient

The removal of nutrients by overland flow remains a major source of non-point pollution in agricultural land. In this study, a mathematical model of ammonium nitrogen transport from soil solution to overland flow was established. The model treated the mass transfer coefficient (km) as a time-dependent parameter, which was not a constant value as in previous studies, and it was evaluated with a four-slope gradient and three rainfall intensities. The kinematic-wave equation for overland flow was solved by an approximately semi-analytical solution based on Philip’s infiltration model, while the diffusion-based mass conversation equation for overland nutrient transport was solved numerically. The results showed that the simulated runoff processes and ammonium nitrogen concentration transport to the overland flow agreed well with the experimental data. Further correlation analyses were made to determine the relationships between the slope gradient, rainfall intensity and the hydraulic and nutrient transport parameters. It turned out that these parameters could be described as a product of exponential functions of slope gradient and rainfall intensity. Finally, a diffusion-based model with a time-dependent mass transfer coefficient was established to predict the ammonium nitrogen transport processes at the experimental site under different slope gradients and rainfall intensities.

Analysis of Fouling Characteristic in Enhanced Tubes Using Multiple Analogies

2010 ◽  
Author(s):  
Wei Li ◽  
Guanqiu Li ◽  
Zhengjiang Zhang ◽  
Zhiming Xu ◽  
Shanrang Yang
Keyword(s):  
Mathematical Model ◽  
Mass Transfer ◽  
Heat Flux ◽  
Transfer Coefficient ◽  
Cooling Tower ◽  
Comprehensive Analysis ◽  
Von Karman ◽  
Enhanced Tubes ◽  
Plain Tube ◽  
Von Kármán

This paper provides a comprehensive analysis on cooling tower fouling data taken from seven 15.54 mm I.D. helically ribbed, copper tubes and a plain tube at Re = 16000. A new mathematical model has been developed. The mass transfer coefficient Km is calculated through three analogies, which are Prandtl analogy, Von-Karman analogy, and j factor analogy. Fouling deposition is assumed to be determined by two processes, which are corresponding to heat flux and fluid friction. Von-Karman analogy is proved the best analogy among the three. Series of semi-theoretical fouling correlations as a function of the product of area indexes and efficiency indexes were developed. They were applicable to different internally ribbed geometries. The correlations can be directly used to assess the fouling potential of enhanced tubes in actual cooling tower water situations.

Simulation of Runoff for Varying Mulch Coverage on a Sloped Surface

2013 ◽  
Vol 409-410 ◽  
pp. 339-343 ◽  
Author(s):  
Su Fang Cui ◽  
Ying Hua Pan ◽  
Quan Yuan Wu ◽  
Zhen Hua Zhang ◽  
Bao Xiang Zhang
Keyword(s):  
Soil Erosion ◽  
Rainfall Intensity ◽  
Overland Flow ◽  
Soil Surface ◽  
Northwest China ◽  
Slope Gradient ◽  
Soil Infiltration ◽  
Infiltration Capacity ◽  
Coverage Ratio ◽  
Runoff Volume

The use of thin plastic film to cover slope surfaces can lead to slope runoff and soil erosion in Loess hilly areas in northwest China. Three main factors (slope, rainfall intensity, and coverage ratio) were selected to analyze variations in runoff dynamics for a Lou soil surface and to obtain a theoretical foundation for practical application. The results indicate that for a fixed rainfall intensity and coverage ratio, a critical slope gradient close to 26.8% was observed. For a fixed coverage ratio and slope gradient, the cumulative runoff volume increased with the rainfall intensity. Overland flow varied with the coverage ratio and this can be attributed to increases in the cumulative runoff volume and runoff velocity with increasing coverage ratio. The experimental results show that for double-ridge cultivation with film mulching, the best coverage ratio is 50:150. This ratio not only reduces moisture evaporation and promotes soil conservation, but also effectively improves rainwater utilization and reduces soil erosion. In addition, for slope gradients exceeding 26.8%, runoff decreases and the soil infiltration capacity increases, so a slope gradient of 26.836.4% is optimal for the local cultivation model.

A Pilot Study on Time-Dependent Dissolution of CO2 in Oil for Prediction of Gas Kick Behaviors in Non-Aqueous Fluids

2019 ◽  
Author(s):  
Mahendra Kunju ◽  
James Nielsen ◽  
Yuanhang Chen ◽  
Otto L. Santos ◽  
Wesley C. Williams ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
High Pressures ◽  
Liquid System ◽  
Time Dependent ◽  
Drilling Fluids ◽  
Volumetric Mass Transfer Coefficient ◽  
Point Pressure ◽  
Dependent Mass

Abstract The influx of gas from formations during drilling or when the well is left undisturbed during tripping, logging, and flow check can dissolve very quickly in Non-aqueous drilling fluids (NAF). The dissolved gas can stay unnoticeable till the gas comes out of solution below bubble point pressure closer to surface. The objective of the paper is to develop a model to predict the time dependent mass transfer of CO2 in oil at subcritical pressures and validate the model using experimental results. Since CO2 is soluble in oil, the interaction between solvent and solute can help us understand the dissolution and mass transfer mechanism of CO2 in oil. A model has been developed by incorporating factors that drive the interaction and the rate of gas loading into the liquid to predict the time-dependent mass transfer. A 1.5 inch vertical low pressure apparatus is used to conduct experiments by injecting CO2 into pressurized static column of oil. Pressure inside the pipe, and mass of CO2 injected are varied to study their effects on mass transfer. Boundary conditions for this model are provided from experimentally obtained data of volumetric mass transfer coefficient of the injected gas and liquid system at gas injection flow rate. The developed time-dependent model has been validated using the data collected from the tests. The volumetric mass transfer coefficient is found to change with pressure. This model can be extended to experiments under high-pressures to replicate the downhole conditions. The model can be modified to include desorption to predict the loading and unloading of gas in NAF, and gas oil ratios at depths along the annulus in a real well.

scholarly journals Slope–velocity equilibrium and evolution of surface roughness on a stony hillslope

2017 ◽  
Vol 21 (6) ◽  
pp. 3221-3229 ◽  
Author(s):  
Mark A. Nearing ◽  
Viktor O. Polyakov ◽  
Mary H. Nichols ◽  
Mariano Hernandez ◽  
Li Li ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Rainfall Intensity ◽  
Overland Flow ◽  
Surface Condition ◽  
Relative Increase ◽  
Unique Function ◽  
Slope Gradient ◽  
Hydraulic Roughness ◽  
Artificial Rainfall ◽  
Discharge Rates

Abstract. Slope–velocity equilibrium is hypothesized as a state that evolves naturally over time due to the interaction between overland flow and surface morphology, wherein steeper areas develop a relative increase in physical and hydraulic roughness such that flow velocity is a unique function of overland flow rate independent of slope gradient. This study tests this hypothesis under controlled conditions. Artificial rainfall was applied to 2 m by 6 m plots at 5, 12, and 20 % slope gradients. A series of simulations were made with two replications for each treatment with measurements of runoff rate, velocity, rock cover, and surface roughness. Velocities measured at the end of each experiment were a unique function of discharge rates, independent of slope gradient or rainfall intensity. Physical surface roughness was greater at steeper slopes. The data clearly showed that there was no unique hydraulic coefficient for a given slope, surface condition, or rainfall rate, with hydraulic roughness greater at steeper slopes and lower intensities. This study supports the hypothesis of slope–velocity equilibrium, implying that use of hydraulic equations, such as Chezy and Manning, in hillslope-scale runoff models is problematic because the coefficients vary with both slope and rainfall intensity.

Research on Mass Transfer Coefficient Measurement Model of External-Loop Airlift Reactor

2012 ◽  
Vol 512-515 ◽  
pp. 2405-2411
Author(s):  
Qian Wu ◽  
Ma Lin Liu ◽  
Tong Wang Zhang
Keyword(s):  
Mathematical Model ◽  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Measurement Model ◽  
Airlift Reactor ◽  
Continuous Stirred Tank Reactor ◽  
Volumetric Mass Transfer Coefficient ◽  
External Loop ◽  
Coefficient Measurement

A mathematical model considering the inter-phase mass transfer both in the down-comer and the riser of an external-loop airlift reactor was established in this paper. The calculated global volumetric mass transfer coefficient based on the assumption of continuous stirred tank reactor (CSTR) was different from the local volumetric mass transfer coefficients by the newly proposed mathematical model and the difference was discussed. The effects of mass transfer in the down-comer, the hydrodynamic pressure and the experimental time on the mass transfer coefficient measurement model have been studied in detail. And it was also proved that only the global volumetric mass transfer coefficient, but not the local volumetric mass coefficient, can be obtained from a time-concentration curve in the external-loop airlift reactor.

Predictions of capillary oxygen transport in the presence of fluorocarbon additives

1998 ◽  
Vol 275 (6) ◽  
pp. H2250-H2257 ◽  
Author(s):  
Charles D. Eggleton ◽  
Tuhin K. Roy ◽  
Aleksander S. Popel
Keyword(s):  
Mathematical Model ◽  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Oxygen Transport ◽  
Retractor Muscle ◽  
Additional Increase ◽  
Fluorocarbon Emulsion

A mathematical model of capillary oxygen transport was formulated to determine the effect of increasing plasma solubility, e.g., by the addition of an intravascular fluorocarbon emulsion. The effect of increased plasma solubility is studied for two distributions of fluorocarbon, when the fluorocarbon droplets are uniformly distributed throughout the plasma and when the fluorocarbon droplets are concentrated in a layer adjacent to the endothelium. The model was applied to working hamster retractor muscle at normal and lowered hematocrit. The intracapillary mass transfer coefficient was found to increase by 18% as the solubility was increased by a factor of 1.7 at a hematocrit of 43%. An additional increase of 6% was predicted when the solubility increase was concentrated in the layer adjacent to the endothelium. At a hematocrit of 25%, the intracapillary mass transfer coefficient increased 14% when the solubility was increased by a factor of 1.7.

Investigation on heat and mass transfer characteristics for a zeolite-coated heat exchanger using comparatively low-temperature energy: Heating humidification mode and cooling dehumidification mode

2020 ◽  
pp. 1420326X2094229
Author(s):  
Beungyong Park ◽  
Sihwan Lee
Keyword(s):  
Mathematical Model ◽  
Mass Transfer ◽  
Heat Exchanger ◽  
Low Temperature ◽  
Transfer Coefficient ◽  
Heat And Mass Transfer ◽  
Air Conditioning ◽  
Environmental Control ◽  
Moisture Removal ◽  
Transfer Characteristics

Desiccant-based hybrid air-conditioning technologies are currently being developed to reduce energy consumption and enhance the effectiveness of indoor thermal environmental control in buildings. The purpose of this study is to propose a compact desiccant-based outdoor air-conditioning system that directly uses heated desorption and cooled adsorption with comparatively low-temperature energy, and to propose a mathematical model for the system by investigating the heat and mass transfer characteristics of a zeolite-coated heat exchanger (ZCHE). To study the heat and mass transfer characteristics of the ZCHE, the moisture removal capacity and the moisture removal regeneration were measured at various heat source temperatures and water flow rates using an experimental model. The measured values were adopted as boundary condition for mathematical model. The results show that the air-conditioning performance of the ZCHE is strongly dependent on the water temperature under constant air conditions. The humidification capacity of the ZCHE was measured 25.0 g at 5 kW heat capacity and the humidification capacity was measured 10.2 g at 0.6 kW cooling capacity. The relative errors of mass transfer coefficient and heat transfer coefficient are ±3.6% and ±3.8%, respectively. Moreover, the proposed mathematical model fitted well with measured values.

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