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Balance Approach (balance + approach)
Kinds of Balance Approach Selected AbstractsRecharge Through a Regional Till Aquitard: Three-Dimensional Flow Model Water Balance ApproachGROUND WATER, Issue 3 2000Richard E. Gerber In southern Ontario, vertical leakage through a regionally extensive till is the primary source of recharge to underlying aquifers used for domestic and municipal water supply. Since leakage is largely controlled by the bulk hydraulic conductivity (K) of the aquitard, accurate estimates of K are necessary to quantify the resource. Considerable controversy exists regarding estimates of K for this aquitard, which vary according to the scale of the test method. For the till matrix, estimates from core samples and slug tests consistently range from 10,11 to 10,10 m/s. Isotopic evidence (3H), on the other hand, indicates that nonmatrix structures such as sand lenses, erosional surfaces, joints, and fractures significantly enhance till permeability. This is confirmed by slug test, pump test, recharge, and water balance studies, which show that K varies over seven orders of magnitude (10,12 to 10,5 m/s). To provide a regional estimate of bulk K and a reliable estimate of vertical recharge through the Northern Till, a numerical ground water flow model was constructed for the Duffins and Petticoat Creek drainage hasin. The model was calibrated to measurements of hydraulic head and estimates and measurements of base flow throughout the basin. This model demonstrates that the vertical hydraulic conductivity (Kv) for the Northern Till ranges from 5 × 10,10 to 5 × 10,9 m/s, values that are up to 2.5 orders of magnitude greater than matrix K estimates. Regional recharge through the Northern Till is estimated to range from 30 to 35 mm/a. [source] Modelling lake stage and water balance of Lake Tana, EthiopiaHYDROLOGICAL PROCESSES, Issue 25 2009Yirgalem A. Chebud Abstract The level of Lake Tana, Ethiopia, fluctuates annually and seasonally following the patterns of changes in precipitation. In this study, a mass balance approach is used to estimate the hydrological balance of the lake. Water influx from four major rivers, subsurface inflow from the floodplains, precipitation, outflow from the lake constituting river discharge and evapotranspiration from the lake are analysed on monthly and annual bases. Spatial interpolation of precipitation using rain gauge data was conducted using kriging. Outflow from the lake was identified as the evaporation from the lake's surface as well as discharge at the outlet where the Blue Nile commences. Groundwater inflow is estimated using MODular three-dimensional finite-difference ground-water FLOW model software that showed an aligned flow pattern to the river channels. The groundwater outflow is considered negligible based on the secondary sources that confirmed the absence of lake water geochemical mixing outside of the basin. Evaporation is estimated using Penman's, Meyer's and Thornwaite's methods to compare the mass balance and energy balance approaches. Meteorological data, satellite images and temperature perturbation simulations from Global Historical Climate Network of National Oceanographic and Atmospheric Administration are employed for estimation of evaporation input parameters. The difference of the inflow and outflow was taken as storage in depth and compared with the measured water level fluctuations. The study has shown that the monthly and annually calculated lake level replicates the observed values with root mean square error value of 0·17 and 0·15 m, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source] Comparison of seven models for estimation of evapotranspiration and groundwater recharge using lysimeter measurement data in GermanyHYDROLOGICAL PROCESSES, Issue 18 2005C.-Y. Xu Abstract This study evaluates seven evapotranspiration models and their performance in water balance studies by using lysimeter measurement data at the Mönchengladbach hydrological and meteorological station in Germany. Of the seven evapotranspiration models evaluated, three models calculate actual evapotranspiration directly using the complementary relationship approach, i.e. the CRAE model of Morton, the advection,aridity (AA) model of Brutsaert and Stricker, and the GG model of Granger and Gray, and four models calculate first potential evapotranspiration and then actual evapotranspiration by considering the soil moisture condition. Two of the four potential evapotranspiration models belong to the temperature-based category, i.e. the Thornthwaite model and the Hargreaves model, and the other two belong to the radiation-based category, i.e. the Makkink model and the Priestley,Taylor model. The evapotranspiration calculated by the above seven models, together with precipitation, is used in the water balance model to calculate other water balance components. The results show that, for the calculation of actual evapotranspiration, the GG model and the Makkink model performed better than the other models; for the calculation of groundwater recharge using the water balance approach, the GG model and the AA models performed better; for the simulation of soil moisture content using the water balance approach, four models (GG, Thornthwaite, Makkink and Priestley,Taylor) out of the seven give equally good results. It can be concluded that the lysimeter-measured water balance components, i.e. actual evapotranspiration, groundwater recharge, soil moisture, etc., can be predicted by the GG model and the Makkink model with good accuracy. Copyright © 2005 John Wiley & Sons, Ltd. [source] Daily streamflow modelling and assessment based on the curve-number techniqueHYDROLOGICAL PROCESSES, Issue 16 2002Jin-Yong Choi Abstract A cell-based long-term hydrological model (CELTHYM) that can be integrated with a geographical information system (GIS) was developed to predict continuous stream flow from small agricultural watersheds. The CELTHYM uses a cell-by-cell soil moisture balance approach. For surface runoff estimation, the curve number technique considering soil moisture on a daily basis was used, and release rate was used to estimate baseflow. Evapotranspiration was computed using the FAO modified Penman equation that considered land-use-based crop coefficients, soil moisture and the influence of topography on radiation. A rice paddy field water budget model was also adapted for the specific application of the model to East Asia. Model sensitivity analysis was conducted to obtain operational information about the model calibration parameters. The CELTHYM was calibrated and verified with measured runoff data from the WS#1 and WS#3 watersheds of the Seoul National University, Department of Agricultural Engineering, in Hwaseong County, Kyounggi Province, South Korea. The WS#1 watershed is comprised of about 35·4% rice paddy fields and 42·3% forest, whereas the WS#3 watershed is about 85·0% forest and 11·5% rice paddy fields. The CELTHYM was calibrated for the parameter release rate, K, and soil moisture storage coefficient, STC, and results were compared with the measured runoff data for 1986. The validation results for WS#1 considering all daily stream flow were poor with R2, E2 and RMSE having values of 0·40, ,6·63 and 9·69 (mm), respectively, but validation results for days without rainfall were statistically significant (R2 = 0·66). Results for WS#3 showed good agreement with observed data for all days, and R2, E2 and RMSE were 0·92, 0·91 and 2·23 (mm), respectively, suggesting potential for CELTHYM application to other watersheds. The direct runoff and water balance components for watershed WS#1 with significant areas of paddy fields did not perform well, suggesting that additional study of these components is needed. Copyright © 2002 John Wiley & Sons, Ltd. [source] The effect of cell size distribution during the cooling stage of cryopreservation without CPAAICHE JOURNAL, Issue 8 2010S. Fadda Abstract A novel model capable of quantitatively describing and predicting intracellular ice formation (IIF) as a function of temperature in a cell population characterized by a size distribution is proposed. The model overcomes the classical approach which takes into account a population of identically sized cells. The size distribution dynamics of a cell population in response to water osmosis and IIF occurrence during the cooling stage of a standard cryopreservation protocol without using cryoprotective agent (CPA) is simulated by means of a suitable population balance approach. Specifically, the model couples the classical water transport equation developed by Mazur1 to the quantitative description of nucleation and diffusion-limited growth of ice crystals in the framework of a 1-D population balance equation (PBE). It is found that IIF temperature depends on the cell size, i.e., it is higher for larger cells. Correspondingly, the probability of IIF (PIIF) results to be dependent on the initial size distribution of the cell population. Model's parameters related to the osmotic behavior of the cell population and to IIF kinetics are obtained by comparison between theoretical results and suitable experimental data of isolated rat hepatocytes available in the literature. Model reliability is successfully verified by predicting the experimental data of PIIF at different, constant cooling rates with better accuracy as compared to the theoretical approaches available in the literature. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Flocculation of biological cells: Experiment vs. theoryAICHE JOURNAL, Issue 7 2003Binbing Han Flocculation of biological cells is important in the biotechnology industry, as it could lead to improved efficiencies for bioreactor harvesting operations such as microfiltration. Experimental studies for flocculation of yeast and CHO cells using cationic polyelectrolytes suggest the existence of a steady-state, self-similar floc size distribution. The experimentally determined floc size distributions were modeled using a population balance approach. For flocculated yeast suspensions, the variation of the floc volume fraction with dimensionless particle diameter is predicted by the population balance model assuming a binary breakage distribution function. However, the variation of floc number fraction with dimensionless particle diameter is better predicted assuming a log normal fragment distribution function probably due to the presence of submicron-sized yeast cell debris. For CHO cell flocs, the floc volume and number fractions are predicted using a log normal fragment distribution function. CHO cells are far more fragile than yeast cells. Thus, individual CHO cells in a CHO cell floc can lyse leading to the formation of a number of small particles. [source] Determination of fluidized bed granulation end point using near-infrared spectroscopy and phenomenological analysisJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2005W. Paul Findlay Abstract Simultaneous real-time monitoring of particle size and moisture content by near-infrared spectroscopy through a window into the bed of a fluidized bed granulator is used to determine the granulation end point. The moisture content and particle size determined by the near-infrared monitor correlates well with off-line moisture content and particle size measurements. The measured particle size is modeled using a population balance approach, and the moisture content is shown to follow accepted models during drying. Given a known formulation, with predefined parameters for peak moisture content, final moisture content, and final granule size, the near-infrared monitoring system can be used to control a fluidized bed granulation by determining when binder addition should be stopped and when drying of the granules is complete. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:604,612, 2005 [source] MANAGEMENT OF FLOOD CONTROL SUMPS AND POLLUTANT TRANSPORT,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2001Edward H. Smith ABSTRACT: Levee sump systems are used by many riverine communities for temporary storage of urban wet weather flows. The hydrologic performance and transport of stormwater pollutants in sump systems, however, have not been systematically studied. The objective of this paper is to present a case study to demonstrate development and application of a procedure for assessing the hydraulic performance of flood control sumps in an urban watershed. Two sumps of highly variable physical and hydraulic characteristics were selected for analysis. A hydrologic modeling package was used to estimate the flow hydrograph for each outfall as part of the flow balance for the sump. To validate these results, a water balance was used to estimate the total runoff using sump operational data. The hydrologic model calculations provide a satisfactory estimate of the total runoff and its time-distribution to the sump. The model was then used to estimate pollutant loads to the sump and to the river. Although flow of stormwater through a sump system is regulated solely by flood-control requirements, these sumps may function as sedimentation basins that provide purification of stormwater. A sample calculation of removals of several conventional pollutants in the target sumps using a mass balance approach is presented. [source] Copolymer Sequence Distributions in Controlled Radical PolymerizationMACROMOLECULAR REACTION ENGINEERING, Issue 2-3 2009Amin Zargar Abstract Although simulations of polymerizations have been performed using population-balance and method-of-moments techniques to determine the properties of copolymers, the method used most often to estimate copolymer composition distribution is based on probabilistic arguments and is not entirely compatible with the population balance approach. In this paper, a model based on the method of moments is presented that determines not only the molecular weight and copolymer composition characteristics, but also allows prediction of the copolymer distribution. The method is applied to controlled-radical polymerization. Batch polymerizations are simulated to illustrate the effect of composition drift, and shot polymerizations are simulated to show the potential to produce copolymers with customized sequence distributions. [source] Prediction of the Bivariate Molecular Weight-Long Chain Branching Distribution in High-Pressure Low-Density Polyethylene AutoclavesMACROMOLECULAR THEORY AND SIMULATIONS, Issue 6 2007Apostolos Krallis Abstract In the present study a population balance approach is described to follow the time evolution of bivariate molecular weight-long chain branching (MW-LCB) distributions in high pressure low density polyethylene autoclaves. The model formulation is based on a sectional grid method, the so-called fixed pivot technique (FPT). According to this method, the ,live' and ,dead' polymer chain populations are assigned to a selected number of discrete points. Then, the resulting dynamic discrete-continuous molar species equations for ,live' and ,dead' polymer chains are solved at the specified grid points. It is shown that a very good agreement exists between theoretical results and experimental data which proves the capability of the FPT method in calculating the joint MW-LCB distribution for branched polymers. [source] Momentum Balance for Two-Phase Horizontal Pipe Flow Part 2: Testing of ModelsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1-2 2004P. L. Spedding Momentum balance models were tested against reliable data for both holdup and pressure drop. The best prediction performance was achieved using a model that considered the actual shape of the liquid phase in the pipe. In such circumstances the momentum balance calculation tended to under predict both the holdup and pressure drop for some of the annular and stratified regimes. Suggestions are made for improvements in the momentum balance approach. [source] A hybrid model of anaerobic E. coli GJT001: Combination of elementary flux modes and cybernetic variablesBIOTECHNOLOGY PROGRESS, Issue 5 2008Jin Il Kim Flux balance analysis (FBA) in combination with the decomposition of metabolic networks into elementary modes has provided a route to modeling cellular metabolism. It is dependent, however, on the availability of external fluxes such as substrate uptake or growth rate before estimates can become available of intracellular fluxes. The framework classically does not allow modeling of metabolic regulation or the formulation of dynamic models except through dynamic measurement of external fluxes. The cybernetic modeling approach of Ramkrishna and coworkers provides a dynamic framework for modeling metabolic systems because of its focus on describing regulatory processes based on cybernetic arguments and hence has the capacity to describe both external and internal fluxes. In this article, we explore the alternative of developing hybrid models combining cybernetic models for the external fluxes with the flux balance approach for estimation of the internal fluxes. The approach has the merit of the simplicity of the early cybernetic models and hence computationally facile while also providing detailed information on intracellular fluxes. The hybrid model of this article is based on elementary mode decomposition of the metabolic network. The uptake rates for the various elementary modes are combined using global cybernetic variables based on maximizing substrate uptake rates. Estimation of intracellular metabolism is based on its stoichiometric coupling with the external fluxes under the assumption of (pseudo-) steady state conditions. The set of parameters of the hybrid model was estimated with the aid of nonlinear optimization routine, by fitting simulations with dynamic experimental data on concentrations of biomass, substrate, and fermentation products. The hybrid model estimations were tested with FBA (based on measured substrate uptake rate) for two different metabolic networks (one is a reduced network which fixes ATP contribution to the biomass and maintenance requirement of ATP, and the other network is a more complex network which has a separate reaction for maintenance.) for the same experiment involving anaerobic growth of E. coli GJT001. The hybrid model estimated glucose consumption and all fermentation byproducts to better than 10%. The FBA makes similar estimations of fermentation products, however, with the exception of succinate. The simulation results show that the global cybernetic variables alone can regulate the metabolic reactions obtaining a very satisfactory fit to the measured fermentation byproducts. In view of the hybrid model's ability to predict biomass growth and fermentation byproducts of anaerobic E. coli GJT001, this reduced order model offers a computationally efficient alternative to more detailed models of metabolism and hence useful for the simulation of bioreactors. [source] Modelling lake stage and water balance of Lake Tana, EthiopiaHYDROLOGICAL PROCESSES, Issue 25 2009Yirgalem A. Chebud Abstract The level of Lake Tana, Ethiopia, fluctuates annually and seasonally following the patterns of changes in precipitation. In this study, a mass balance approach is used to estimate the hydrological balance of the lake. Water influx from four major rivers, subsurface inflow from the floodplains, precipitation, outflow from the lake constituting river discharge and evapotranspiration from the lake are analysed on monthly and annual bases. Spatial interpolation of precipitation using rain gauge data was conducted using kriging. Outflow from the lake was identified as the evaporation from the lake's surface as well as discharge at the outlet where the Blue Nile commences. Groundwater inflow is estimated using MODular three-dimensional finite-difference ground-water FLOW model software that showed an aligned flow pattern to the river channels. The groundwater outflow is considered negligible based on the secondary sources that confirmed the absence of lake water geochemical mixing outside of the basin. Evaporation is estimated using Penman's, Meyer's and Thornwaite's methods to compare the mass balance and energy balance approaches. Meteorological data, satellite images and temperature perturbation simulations from Global Historical Climate Network of National Oceanographic and Atmospheric Administration are employed for estimation of evaporation input parameters. The difference of the inflow and outflow was taken as storage in depth and compared with the measured water level fluctuations. The study has shown that the monthly and annually calculated lake level replicates the observed values with root mean square error value of 0·17 and 0·15 m, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||||||||