Mass Balance Principles Research Articles

A New Measurement Model for Main Steam Flow of Power Plants

Abstract Accuracy of existing measurement models for main steam flow in power plants is always unsatisfied. In this paper, a model with higher accuracy for main steam flow measurement was proposed. Accurate values of main steam flow can be obtained based on principle of mass balance when unit is at a steady state. Because of volume sections such as cooling wall and super heater, this model isn’t suitable for dynamic-state unit. Another measuring model based on Flugel formula can give exact change trends of main steam flow when unit is at a dynamic state. However, its accuracy is unsatisfied. Therefore, this paper took advantages of the two models, fusing them together in frequency domain with complementary filter method. Simulation results show that new model not only gives accurate steam flow when unit is at a steady state but also provides exact change trends of main steam flow.

Mathematical and Computational Models of Oxidative and Nitrosative Stress

The importance of nitric oxide (NO), superoxide (O2-), and peroxynitrite (ONOO-), interactions in physiologic functions and pathophysiological conditions such as cardiovascular disease, hypertension, and diabetes have been established extensively in in vivo and in vitro studies. Despite intense investigation of NO, O2-, and ONOO- biochemical interactions, fundamental questions regarding the role of these molecules remain unanswered. Mathematical models based on fundamental principles of mass balance and reaction kinetics have provided significant results in the case of NO. However, the models that include interaction of NO, O2-, and ONOO- have been few because of the complexity of these interactions. Not only do these mathematical and computational models provided quantitative knowledge of distributions and concentrations of NO, O2-, and ONOO- under normal physiologic and pathophysiologic conditions, they also can help to answer specific hypotheses. The focus of this review article is on the models that involve more than one of the 3 molecules (NO, O2-, and ONOO-). Specifically, kinetic models of O2- dismutase and tyrosine nitration and biotransport models in the microcirculation are reviewed. In addition, integrated experimental and computational models of dynamics of NO/O2-/ONOO- in diverse systems are reviewed.

Development and Validation of a Model to Predict Air Temperatures and Humidities in the Headspace of Partially Filled Stored Grain Silos

During storage, headspace conditions play an important role in affecting the physical, chemical, and biological activities of living organisms in the upper layer of a grain mass. A model was developed using energy and mass balance principles to predict temperature and relative humidity of the headspace air in a partially filled silo. The formulation of the headspace domain had nine control volumes (nine temperatures and RH values) with the grain and roof surfaces as boundaries. Solar radiation and convective heat transfer were used as the driving factors for heat transfer in the headspace. Humidity transfer due to the air mass flow rate was considered the driving factor behind changes in headspace RH. The periodic changes in solar radiation and wind speed induced temperature and humidity variations in the silo headspace. The predicted results were validated using observed data. The standard error of predicted versus observed headspace air and wall temperatures was in the range of 2.3°C to 5.3°C and 3.1°C to 5.5°C, respectively. The standard error of predicted versus observed headspace humidities was around 7%. The developed model is considered sufficiently accurate and reliable to predict air temperature and relative humidity at multiple locations in the headspace of a grain storage silo.

Upscaling geochemical reaction rates accompanying acidic CO2‐saturated brine flow in sandstone aquifers

Network flow models were used to simulate the flow of CO2‐saturated brine in the pore networks corresponding to three different sandstones. The simulations were used to study upscaling of anorthite and kaolinite reaction rates from pore to core scales. Unique to our simulations is the use of computed tomography to capture the mineral distribution in the samples as well as the sample pore network. The upscaled reaction rates determined from these simulations incorporate mass balance principles and microscale reaction rate laws and capture the physical, mineral, and flow heterogeneities in the network. These upscaled rates were compared with upscaled rates predicted by a continuum model and by a volume‐averaged‐concentration method. For the anorthite reaction, which remains far from equilibrium, the volume‐averaged reaction rate exceeded the reaction rate of the network model by 18% to 46%. While the continuum model rate also exceeded the network model rate by −1% to 53%, its predicted values were generally better than the volume‐averaged method. The kaolinite reaction is near equilibrium and is heavily influenced by the form of the microscale rate law in the precipitation regime. Three alternate rate laws were tested, which produced significantly different predictions for the bulk reaction rates. For all three rate laws, continuum and volume‐averaged reaction rates incorrectly predicted the magnitude of the kaolinite reaction rate (disagreements of −700% to 55%), and the predicted reaction type, dissolution versus precipitation, was also often opposite to that of the network model. Finally, for both anorthite and kaolinite, all upscaled reaction rates showed significant flow rate dependence.

A simplified conception model for salt marsh sedimentation rate calculation: Response to changing suspended sediment concentration—A case study of Wanggang salt marsh, Jiangsu Province, China

Situated at the junction of land and sea, coastal salt marshes are very sensitive to global environmental changes. Existing numerical models simulating the vertical growth of coastal salt marshes are under the conditions of low suspended sediment concentration (SSC), but under high SSC, such as in the Jiangsu coast of China, the models need to be refined. In this paper, based on the mass balance principle, a refined zero-dimensional time-stepped model is applied after considering the average suspended sediment concentration (ASSC). The statistical results of in situ observation data show that there is an obvious positive linear relationship between ASSC and maximum inundation height, and an obvious positive exponential one between inundation time and inundation height. Using the short-term measurement values for the input parameters and incorporating the above-mentioned relationship between SSC and inundation height, the sedimentation rates are calculated, and the results are similar to previous data. In addition, some factors and hydrodynamic processes that were ignored or simplified could influence the calculated value.

Gross primary production variability associated with meteorology, physiology, leaf area, and water supply in contrasting woodland and grassland semiarid riparian ecosystems

Understanding ecosystem‐atmosphere carbon exchanges in dryland environments has been more challenging than in mesic environments, likely due to more pronounced nonlinear responses of ecosystem processes to environmental variation. To better understand diurnal to interannual variation in gross primary productivity (GPP) variability, we coupled continuous eddy‐covariance derived whole ecosystem gas exchange measurements with an ecophysiologic model based on fundamental principles of diffusion, mass balance, reaction kinetics, and biochemical regulation of photosynthesis. We evaluated the coupled data‐model system to describe and understand the dynamics of 3 years of growing season GPP from a riparian grassland and woodland in southern Arizona. The data‐model fusion procedure skillfully reproduced the majority of daily variation GPP throughout three growing seasons. While meteorology was similar between sites, the woodland site had consistently higher GPP rates and lower variability at daily and interannual timescales relative to the grassland site. We examined the causes of this variation using a new state factor model analysis that partitioned GPP variation into four factors: meteorology, physiology, leaf area, and water supply. The largest proportion of GPP variation was associated with physiological differences. The woodland showed a greater sensitivity than the grassland to water supply, while the grassland showed a greater sensitivity to leaf area. These differences are consistent with hypotheses of woody species using resistance mechanisms, stomatal regulation, and grassland species using resilience mechanisms, leaf area regulation, in avoiding water stress and have implications for future GPP sensitivity to climate variability following wood‐grass transitions.

Morphology and Particle Size Distribution Controls of Droplet-to-Macroporous/Hollow Particles Formation in Spray Drying Process of Colloidal Mixtures Precursor

The morphology control of droplet-to-macroporous/hollow particles formation using an ultrasonically spray-drying method as well as correlation between the droplet and particle size distribution of generated particles using a precursor of colloidal mixtures of polystyrene latex (PSL) and negatively charged silica nanoparticles were demonstrated. Porous particles were successfully produced by negatively charged PSL colloids. On the other hand, positively charged PSL colloids tended to generate hollow particles. The measured particle size distribution (PSD) of hollow particles agreed well with the calculated PSD using a mass balance principle of droplet to drying particles of silica and PSL composites. However, for porous particle formation, the measured PSD was smaller than the calculated PSD. The effects of PSL and silica colloids concentrations on a starting material as well as process residence time on the final porous particles were also investigated. A high PSL colloid concentration, low silica colloid...

Dynamic modeling and simulation of greenhouse environments under several scenarios: A web-based application

Greenhouse crop production systems are located throughout the world within a wide range of climatic conditions. To achieve environmental conditions favorable for plant growth, greenhouses are designed with various components, structural shapes, and numerous types of glazing materials. They are operated differently according to each condition. To improve the pedagogy and the understanding of the complexity and dynamic behavior of greenhouse environments with different configurations, an interactive, dynamic greenhouse environment simulator was developed. The greenhouse environment model, based on energy and mass balance principles, was implemented in a web-based interactive application that allowed for the selection of the greenhouse design, weather conditions, and operational strategies. The greenhouse environment simulator was designed to be used as an educational tool for demonstrating the physics of greenhouse systems and environmental control principles. Several scenarios were simulated to demonstrate how a specific greenhouse design would respond environmentally for several climate conditions (four seasons of four geographical locations), and to demonstrate what systems would be required to achieve the desired environmental conditions. The greenhouse environment simulator produced realistic approximations of the dynamic behavior of greenhouse environments with different design configurations for 28-h simulation periods.

Sustainable Root Zone Salinity and Shallow Water Table in the Context of Land Retirement

This study uses five years of field data from the Land Retirement Demonstration Project located in western Fresno County of California to develop a comprehensive theoretical and numerical modeling framework to evaluate the specific site conditions required for a sustainable land retirement outcome based on natural drainage. Using field data, principles of mass balance in a control volume, the HYDRUS-1D software package for simulating one-dimensional movement of water, heat, and multiple solutes in variably-saturated media, and a model-independent parameter optimizer, the processes of soil water and solute movement in root zone and deep vadose zone were investigated. The optimization of unsaturated soil hydraulic parameters and downward flux (natural drainage) from the control volume against observed vadose zone salinity levels and shallow groundwater levels yield difficult to obtain natural drainage rate as a function of water table height within the control volume. The results show that the unsaturated s...

A hierarchical analysis of terrestrial ecosystem model Biome-BGC: Equilibrium analysis and model calibration

The increasing complexity of ecosystem models represents a major difficulty in tuning model parameters and analyzing simulated results. To address this problem, this study develops a hierarchical scheme that simplifies the Biome-BGC model into three functionally cascaded tiers and analyzes them sequentially. The first-tier model focuses on leaf-level ecophysiological processes; it simulates evapotranspiration and photosynthesis with prescribed leaf area index (LAI). The restriction on LAI is then lifted in the following two model tiers, which analyze how carbon and nitrogen is cycled at the whole-plant level (the second tier) and in all litter/soil pools (the third tier) to dynamically support the prescribed canopy. In particular, this study analyzes the steady state of these two model tiers by a set of equilibrium equations that are derived from Biome-BGC algorithms and are based on the principle of mass balance. Instead of spinning-up the model for thousands of climate years, these equations are able to estimate carbon/nitrogen stocks and fluxes of the target (steady-state) ecosystem directly from the results obtained by the first-tier model. The model hierarchy is examined with model experiments at four AmeriFlux sites. The results indicate that the proposed scheme can effectively calibrate Biome-BGC to simulate observed fluxes of evapotranspiration and photosynthesis; and the carbon/nitrogen stocks estimated by the equilibrium analysis approach are highly consistent with the results of model simulations. Therefore, the scheme developed in this study may serve as a practical guide to calibrate/analyze Biome-BGC; it also provides an efficient way to solve the problem of model spin-up, especially for applications over large regions. The same methodology may help analyze other similar ecosystem models as well.

Assessment of total urban metabolism and metabolic inefficiency in an Irish city-region

This paper aims to measure product and waste flows in an Irish city-region using the principles of metabolism and mass balance. An empirical indicator to measure resource efficiency, using a ratio of waste disposal as a function of product consumption, was developed and it was found that total materials metabolic inefficiency fell by 31% from 0.13 in 1996 to 0.09 in 2002. The paper concludes by analyzing the strengths and weaknesses of this indicator and its potential application in the field of sustainable consumption and resource efficiency as well as making suggestions to improve and strengthen the indicator.

Effect of particle spatial distribution on particle deposition in ventilation rooms

We used simulations and experimental tests to investigate indoor particle deposition during four commonly used ventilation modes, including ceiling supply, side-up supply, side-down supply and bottom supply. We used a condensation monodisperse aerosol generator to generate fine diethylhexyl sebacate (DEHS) particles of different sizes along with two optical particle counters that measured particle concentration at the exhaust opening and inside a three-dimensional ventilated test room. We then simulated particle deposition using the same ventilation modes with computational fluid dynamics (CFD) method. Our simulated results indicate that mean deposition velocity/rate for particles 0.5–10 μm (aerodynamic diameter) is not affected by different ventilation modes. However, both our experimental and simulated results indicate that the deposition loss factor, a parameter defined based on mass balance principle to reflect the influence of particle distribution on deposited particle quantity, differ significantly by ventilation mode. This indicates that ventilation plays an important role in determining particle deposition due to the apparent differences in the spatial distribution of particles. The particle loss factor during ventilation modes characterized by upward air flow in the room is smaller than that of mixing ventilation; however this trend was strongly influenced by the relative location of the inlets, outlets and aerosol source.

Dynamics and spatial variability of near-bottom sediment exchange in the Yangtze Estuary, China

This study was conducted to examine the spatial variations in the exchange between near-bottom suspended and sea-bottom sediments in the Yangtze Estuary and adjacent region, as well as to explore the fate of suspended sediments in the study area. The relationship between the sand, silt, and clay contents of the sediments was analyzed by log-ratio analysis, which revealed a non-linear function for selective deposition and a wide range of grain-size distributions in the estuary. This finding does not conform to the nearly constant clay/silt ratios reported for other tidal basins around the world, due to non-linear sediment mixing under complex hydrodynamic conditions. The sediment exchange processes in the Yangtze Estuary were quantified based on the principle of mass balance. The average grain-size distribution of near-bottom suspended sediments from the estuary showed that approximately 49% of the riverine sediments accumulated in the mouth bar area, while the rest, which is primarily composed of fine-grained sediments, is transferred to the outer estuary and deposited in the form of flocs. The spatial distribution of the sediment exchange ratios demonstrated that small amounts of suspended sediment were deposited onto the seabed of the upper estuary (exchange ratio < 0.1), because the fine-grained suspended sediments in this region were transported to the mouth bar area by the ebb-dominated tidal flow. The sediment exchange ratios in the outer estuary also showed very low values (<0.1) due to the oceanic currents offshore that prevented the diffusion of riverine sediments further seaward. Intensive sediment exchange occurred in the inner estuary due to the sand-mud mixing which was controlled by bidirectional tidal flows. In addition, a high sediment exchange ratio occurred in the muddy area (>0.8) seaward of the river mouth, which implies that this is the present-day depocenter of Yangtze mud. The sediment exchange rates obtained by combining the dimensionless exchange ratios and bulk sediment accumulation rates, were found to be 2–3 cm/yr in the muddy depocenter, which extends to the south of the river mouth (from 122° E to 123° E longitude, at 31° N latitude).

Exploring Estuarine Nutrient Susceptibility

The susceptibility of estuaries to nutrient loading is an important issue that cuts across a range of management needs. We used a theory-driven but data-tested simple model to assist classifying estuaries according to their susceptibility to nutrients. This simple nutrient-driven phytoplankton model is based on fundamental principles of mass balance and empirical response functions for a wide variety of estuaries in the United States. Phytoplankton production was assumed to be stoichiometrically proportional to nitrogen load and an introduced "efficiency factor" intended to capture the myriad processes involved in converting nitrogen load to algal production. A Markov Chain Monte Carlo algorithm of Bayesian inference was then employed for parameter estimation. The model performed remarkably well for chlorophyll estimates, and the predicted estimates of primary production, grazing, and sinking losses are consistent with measurements reported in the literature from a wide array of systems. Analysis of the efficiency factor suggests that estuaries with the ratio of river inflow to estuarine volume (Q/V) greater than 2.0 per year are less susceptible to nutrient loads, and those with Q/V between 0.3 and 2.0 per year are moderately susceptible. This simple model analysis provides a first-order screening tool for estuarine susceptibility classification.

Mathematical model for efficient water flow management

Abstract A mathematical model for the optimization of pump scheduling in a water distribution system is proposed. The water system we consider works without a large water storage facility and hence the mass balance principle is the base for the model. A result concerning the pressure drop after T -junctions is the main simplification we propose. An optimization problem is formulated and solved by a Branch and Bound method for a real water distribution system using data from a small city in Serbia.

Incorporating Ecological Data and Associated Uncertainty in Bioaccumulation Modeling: Methodology Development and Case Study

Bioaccumulation models predict internal concentrations of hydrophobic chemicals by incorporating key gain/loss processes reflecting the ecology of the exposed species and the characteristics of the chemical. Here, we propose a new methodology that uses ecological data and the principle of mass balance in food webs to estimate bioaccumulation in food webs. To this end, we combine linear inverse models (LIMs) that estimate food web flows based on mass balance with a mechanistic bioaccumulation model (OMEGA). In a case study we show that uncertainty ranges on bioaccumulation predictions were on average estimated a factor of 4 lower by LIM-OMEGA than by an OMEGA application that does not consider mass balance within food webs, most notably for chemicals with log Kow > 5, reflecting an increasing importance of uptake through food ingestion for those chemicals. Ranges of internal concentrations predicted by LIM-OMEGA were smaller in enclosures with fish, as strong predation pressure from the latter on mesozooplankton constrains food web flows and thus bioaccumulation.

Creatinine Kinetics and the Definition of Acute Kidney Injury

Acute kidney injury (AKI) is a common and devastating medical condition, but no widely accepted definition exists. A recent classification system by the Acute Dialysis Quality Initiative (RIFLE) defines AKI largely by percentage increases in serum creatinine (SCr) over baseline. The Acute Kidney Injury Network defines the first stage by either an absolute or a percentage increase in SCr. To examine the implications of various definitions, we solved differential equations on the basis of mass balance principles. We simulated creatinine kinetics after AKI in the setting of normal baseline kidney function and stages 2, 3, and 4 chronic kidney disease (CKD). The percentage changes in SCr after severe AKI are highly dependent on baseline kidney function. Twenty-four hours after a 90% reduction in creatinine clearance, the rise in SCr was 246% with normal baseline kidney function, 174% in stage 2 CKD, 92% in stage 3 CKD, and only 47% in stage 4 CKD. By contrast, the absolute increase was nearly identical (1.8 to 2.0 mg/dl) across the spectrum of baseline kidney function. Time to reach a 50% increase in SCr was directly related to baseline kidney function: From 4 h (normal baseline) up to 27 h for stage 4 CKD. By contrast, the time to reach a 0.5-mg/dl increase in SCr was virtually identical after moderate to severe AKI (>50% reduction in creatinine clearance). We propose an alternative definition of AKI that incorporates absolute changes in SCr over a 24- to 48-h time period.

A study on synthetic regional environmental policies for utilising biomass resources

Due to the principles of mass balance, there is a trade-off between regional water pollution and global warming. However, local governments in charge of water pollution control usually try to reduce water pollution loads without thinking of the influences on global warming. This study aims to formulate a simulation/evaluation model that reflects material balance and evaluates the regional environmental policies with utilising biomass resources. In the simulation, introduction of biomass utilisation plants was chosen as an effective tool to reduce environmental pollutants and substitution occurs between nitrogen monoxide and Total Nitrogen during the emission of nitrogen into the environment. These results implies that promotion of biomass resource utilisation can improve both the environment and economy and policy making for water quality improvement should also take into account the effects on global warming of policy measures. Eliminating vertically divided administrative functions becomes essential for resolution of global environmental problems.

Statistical theory of multiple-site linear wall-adsorption capillary Chromatography

Based on the mass-balance principle, a particular diffusion equation to describe the movement of solute molecules in the stagnant layer of multiple-site solid surfaces is constructed. From the equation, the moments of residence time in a step on multiple-site surfaces are derived. Similarly, the moments in a step in the mobile phase are also derived from a diffusion-drift equation. According to the probability theory, there exists a general relationship between the moments of an elution curve and the moments in a step. Through this relationship, the expressions of the elution-curve moments are derived from the step moments. In this paper, the details related to multiple-site linear wall-adsorption capillary chromatography are described and added in the equations to determine the step moments. The resultant expressions of the elution-curve moments involve various factors, such as adsorption–desorption rate constants, equilibrium constants, axial and radial dispersions in the mobile phase. Afterwards, the moment expressions are used to analyze the peak tailing. The results show that a small quantity of sites with a slow desorption rate will lead to a large peak asymmetry.

A Mathematical Model of Liver Cell Aggregation In Vitro

The behavior of mammalian cells within three-dimensional structures is an area of intense biological research and underpins the efforts of tissue engineers to regenerate human tissues for clinical applications. In the particular case of hepatocytes (liver cells), the formation of spheroidal multicellular aggregates has been shown to improve cell viability and functionality compared to traditional monolayer culture techniques. We propose a simple mathematical model for the early stages of this aggregation process, when cell clusters form on the surface of the extracellular matrix (ECM) layer on which they are seeded. We focus on interactions between the cells and the viscoelastic ECM substrate. Governing equations for the cells, culture medium, and ECM are derived using the principles of mass and momentum balance. The model is then reduced to a system of four partial differential equations, which are investigated analytically and numerically. The model predicts that provided cells are seeded at a suitable density, aggregates with clearly defined boundaries and a spatially uniform cell density on the interior will form. While the mechanical properties of the ECM do not appear to have a significant effect, strong cell-ECM interactions can inhibit, or possibly prevent, the formation of aggregates. The paper concludes with a discussion of our key findings and suggestions for future work.