Multizonal Model Research Articles

Quasi-Dimensional Multi-Zone Modeling of Methane-Diesel Dual-Fuel Combustion

Strict CO2 emission and fuel economy regulations are motivating the developers of internal combustion engines to consider alternative fuels. Dual-fuel NG diesel engines are attractive due to minimal design changes, ability to maintain high compression ratio of the diesel baseline, and elimination of driver’s range anxiety. A typical overarching goal is to maximize the substitution ratio, but the higher complexity of the dual-fuel engine comes with challenges, such as the knock limit at high load, combustion instability at low load and methane slip. Development of dual-fuel engine and its control strategies can benefit from predictive simulations, capable of providing deep insights into combustion and emission formation. They can dramatically lower the time and cost for explorations of design and optimizing engine control strategies. Even when experimental data is available, the simulation can provide useful additional insight by predicting value of parameters that are not easy to measure from experimental setup. This paper presents development of a Quasi-D multi-zone combustion model of a heavy-duty dual-fuel engine. The approach marries the best features of the multi-zonal diesel spray model with the turbulent flame entrainment model for the premixed charge of NG and air/EGR. The diesel combustion model developed in this study is based on the framework proposed by Hiroyasu et al. (Hiroyasu, 1985) with several improvements in its sub-models. Regarding the combustion of the premixed charge, a new way of modeling the flame front area during NG flame propagation is proposed. The NG flame is assumed to initiate from the outer boundary of diesel spray and propagates into the space in the direction perpendicular to the diesel spray envelope. The algorithm incorporates geometrical information of all spatial constraints and it can provide a universal solution for various piston or cylinder head designs. The diesel and NG combustion models run concurrently to arrive at a complete prediction of the heat release history of both fuels, based on detailed information about the evolution of diesel spray, ignition and flame propagation of NG-air mixture.

Pressure transient analysis for multi-vug composite fractured vuggy carbonate reservoirs

Vugs usually exist dispersedly in the formation of fractured vuggy carbonate reservoirs. The vug volume is an important parameter, owing to its significant contribution to oil reserves. However, at present, no reliable method is available for estimating the vug volume. This paper presents an analytical multi-zonal composite reservoir well test model that can determine the vug volume.First, the mathematical model is established according to the simplified physical model, and the analytical solution to the mathematical model is derived using Laplace transform. Second, based on the analytical solution, the type curves of dimensionless wellbore pressure and derivative versus dimensionless time, are plotted through numerical inversion. We use the two-vug model as an example to recognize the flow characteristics, and observe that 10 distinct flow regimes exist with two concaves. Furthermore, by comparing the single-vug and multi-vug models, an interesting finding is that one more concave will be added into the derivative curve when one more vug is present in the formation. The vug volume can be obtained by means of the pressure transient analysis. Also, the characteristics of our model are further exhibited by comparing it with the dual porosity model and the conventional composite model. And, a comparison with the conventional composite model and a field case are conducted to verify the validity and reliability of the proposed model in this study. Finally, the effects of each parameter on the pressure and derivative responses are analyzed. The pressure behavior is influenced by the mobility ratio, storage ratio, vug storage constant, and region radius. The mobility and storage ratios mainly affect the vug storage regimes, while the vug storage constant has an important impact on the concave depth and location, and the radial flow regime is dominated by the region radius.

Zonal modelling of a counter-current spray drying tower

A generic multi-zonal modelling methodology for spray drying towers is proposed to provide relatively quick (seconds) simulations on desktop computers for decision making on changing process parameters for automatic process control. A multi-zonal model comprises combinations of all or some of six differing zones: plug-flow, semi-plug-flow and well-mixed zones in either co- or counter-current flow. This approach is demonstrated by predicting the dried powder characteristics of a detergent powder from a pilot-scale counter-current spray drying tower. The types, sizes and locations of the different zones are obtained by a detailed analysis of predictions from a previous 3-dimensional Computational Fluid Dynamics (CFD) simulation of gas and particle flow dynamics and drying kinetics within the tower. The multi-zonal model consists of seven zones – five in counter-current and two in co-current flow. The trends of the predicted gas temperature profiles are close to those from the CFD results. The particle exit temperature, moisture content and residence times over the full particle size distribution (PSD) range are very close to the CFD values unlike the previous simulated results from our plug-flow model. The outcome clearly demonstrates that the prerequisite to have a sound conceptual model of spray drying towers, such as the multi-zonal model developed here, is a detailed knowledge of the gas and particle flow fields within the tower.

Turbulent rectangular compound open channel flow study using multi-zonal approach

In this paper, an improved Shiono–Knight model (SKM) has been proposed to calculate the rectangular compound open channel flows by considering a multi-zonal (MZ) approach in modelling turbulence and secondary flows across lateral flow direction. This is an effort to represent natural flows with compound shape more closely. The proposed model improves the estimation of secondary flow by original SKM model to increase the accuracy of depth-averaged velocity profile solution formed within the transitional region between different sections (i.e. between main-channel and floodplain) of compound channel. This proposed MZ model works by sectioning intermediate zones between floodplain and main-channel for running computation in order to improve the modelling accuracy. The modelling results have been validated using the experimental data by national UK Flood Channel Facility. It has been proven to work reasonably well to model secondary flows within the investigated compound channel flow cases and hence produce better representation to their flow lateral velocity profile.

Development of a bi-equilibrium model for biomass gasification in a downdraft bed reactor

This work proposes a simple and accurate tool for predicting the main parameters of biomass gasification (syngas composition, heating value, flow rate), suitable for process study and system analysis. A multizonal model based on non-stoichiometric equilibrium models and a repartition factor, simulating the bypass of pyrolysis products through the oxidant zone, was developed. The results of tests with different feedstocks (corn cobs, wood pellets, rice husks and vine pruning) in a demonstrative downdraft gasifier (350kW) were used for validation. The average discrepancy between model and experimental results was up to 8 times less than the one with the simple equilibrium model. The repartition factor was successfully related to the operating conditions and characteristics of the biomass to simulate different conditions of the gasifier (variation in potentiality, densification and mixing of feedstock) and analyze the model sensitivity.

Estimation of air infiltration for Australian housing energy analysis

This study presents an integrated air flow model for AccuRate, a benchmark housing energy star-rating tool widely used in Australia. The model was developed by implementing a network multi-zonal infiltration model into an existing large opening model. Case studies using 10 houses in Melbourne, Australia, showed that on average the predicted infiltration rates are within 12.6% of the blower-door test results with a standard deviation of 1.6%. The model study also showed that on average the infiltration rates of the 10 houses could be reduced around 52% by sealing major air leakage pathways, which can result in an average of 7% reduction in the annual space heating and cooling loads for the 10 houses. It was also found that an annual hourly energy performance simulation using the new air flow model requires around 15 min in comparison with around 1 min using the existing simple infiltration model in the AccuRate engine.

The Multi-zonal Balance Model of Temperature Distribution in Data Center

For better characterizing the heat distribution of data centers, Multi-zone Model are considered in this paper, modularizing the cold and hot aisle space of a data center into several regular modules. Upon studying the thermal transmission between every two modules, the heat distribution of all cold and hot aisles in a data center was figured out. Firstly, while considering the thermal transmission, Multi-zone Heat-mass Balanced Model, a model improved from a traditional one, was established. Three modules, which are wall flow module, thermal plume module and thermal transmission module, consists the model. The model characterizes the thermal transmission in both vertical and horizontal direction by integrating the heat conduction of walls, wall convective heat exchange and convective heat exchange among sub-regions. Then, Multi-zone Heat Distribution Model were built by combining the established modules, wall flow module, thermal plume module and thermal transmission module, with Heat-mass Balanced Model. The new model makes the contribution to a detailed characterization of cold-and-hot-aisle-space heat distribution in a data center. Finally, the heat distribution model, combined with data in a case, was numerically simulated. Comparing the simulation results with data in the case, conclusion can be made that the Multi-zone Heat Distribution Model enjoys well consistency and robustness.

Hybrid LES–multizonal modelling of the uranium oxalate precipitation

Oxalic precipitation is usually applied to process radioactive wastes or to recover actinides from a multicomponent solution. Due to their later handling and use, actinide precipitates have to satisfy strict requirements. In nuclear environment where experiments are limited, simulation may be the only way to test different industrial configurations in order to adjust industrial campaigns. In this manuscript, the modelling of the tetravalent uranium oxalate precipitation in an unbaffled reactor is achieved using a hybrid multizonal/CFD model. The population balance is solved according to the moment method in a multizonal model entirely parameterised through computational fluid dynamics calculations based on large-eddy simulation (LES) and a sub-grid model of micromixing. The modelling is applied to show how the specificity of flow field in an unbaffled reactor can have a noticeable effect on the uranium oxalate properties.

Multizonal thermochemical modelling of heavy metal transfer in incineration plants

Heavy metals enter an incineration plant as trace components in the fuel and are inhomogeneously distributed into the ash streams exiting the plant. Their concentration in the respective ash streams mainly depends on their chemical properties, especially on their volatility. Several authors already modelled the chemical state within an incinerator by one single thermochemical equilibrium calculation and achieved qualitative characterization of the heavy metals’ behavior. In the work at hand, a multizonal thermochemical process model of an incineration plant is developed. The chemical reactions within the incinerator are modelled as a sequence of thermochemical equilibria. Reaction kinetic as well as mass transport related inhibitions are accounted for by choosing a proper model structure. Test calculations for a waste and a biomass fired incinerator show that the model is capable of simulating the distribution of As, Cd, and Sn into the ash streams with better quantitative accuracy compared to the abovementioned single-equilibrium approach. The distribution of Cu and Pb is found to be closely coupled to the volatility of Cl on the grate.

Development of an Entrained Flow Gasifier Model for Process Optimization Study

Coal gasification is a versatile process to convert a solid fuel in syngas, which can be further converted and separated in hydrogen, which is a valuable and environmentally acceptable energy carrier. Different technologies (fixed beds, fluidized beds, entrained flow reactors) are used, operating under different conditions of temperature, pressure, and residence time. Process studies should be performed for defining the best plant configurations and operating conditions. Although “gasification models” can be found in the literature simulating equilibrium reactors, a more detailed approach is required for process analysis and optimization procedures. In this work, a gasifier model is developed by using AspenPlus as a tool to be implemented in a comprehensive process model for the production of hydrogen via coal gasification. It is developed as a multizonal model by interconnecting each step of gasification (preheating, devolatilization, combustion, gasification, quench) according to the reactor configuration, that is an entrained flow reactor. The model removes the hypothesis of equilibrium by introducing the kinetics of all steps and solves the heat balance by relating the gasification temperature to the operating conditions. The model allows to predict the syngas composition as well as quantify the heat recovery (for calculating the plant efficiency), “byproducts”, and residual char. Finally, in view of future works, the development of a “gasifier model” instead of a “gasification model” will allow different reactor configurations to be compared.

Computational issues in hybrid multizonal/computational fluid dynamics models

AbstractHybrid multizonal/computational fluid dynamics (CFD) models provide a means of introducing a more realistic description of fluid mechanics and mixing phenomena within process models. The solution of the CFD submodel implicitly defines a function relating one or more of the variables in the multizonal model (the function outputs) in terms of another subset of the variables (the function inputs). This paper is concerned with the accurate and efficient evaluation of this function using local approximate models (LAMs) that may have a general mathematical structure, or be based on physical correlations. Practical issues relating to the robustness of the solution of hybrid models are also considered, and a general architecture for the software interface between the multizonal and CFD submodels is presented. The effectiveness and efficiency of the overall approach are tested by two applications relating, respectively, to a stirred‐tank chemical reactor fitted with a cooling jacket and to a stirred‐tank bioreactor. © 2005 American Institute of Chemical Engineers AIChE J, 2005

The Lowry Model Revisited: Incorporating a Multizonal Input‐Output Model into an Urban Land Use Allocation Model

This paper formulates a new generation of Lowry‐style models that combine a multizonal input‐output model and an urban land use allocation model. Three different types of models are proposed: 1) an unconstrained model, 2) a primal of a linear programming approach that includes land supply constraints, and 3) a modified dual of the linear programming approach that allocates land based on additional conditions of economic efficiency. The modified dual formulation improves upon the limitations of Lowry models and their derivatives. First, the proposed model has sound theoretical underpinnings that incorporate the production theory of input‐output models and the behavioral theory of optimization models. Second, the proposed model allocates land on the basis of economic efficiency by imposing a procedure that equalizes shadow prices. And third, the proposed model is an optimization model that fully accounts for the spatial and sectoral relationships of multiplier effects determining land use demand.

Multiple Radon Entry Modeling in a House with a Cellar

ABSTRACT Combining a computational fluid dynamics (CFD) model and a multi-zonal model, a study was carried out on radon entry through the complex substructure of a house with a cellar. The uniqueness of the radon entry problem in this type of house was due to the involvement of two radon entry routes to two chambers: the cellar and the living area of the house. Soil gas carrying radon was driven through the two routes by two coupled disturbance pressures in the chambers. The effects of temperature differences were considered as another driving force for the radon entry. Examined in this study were the effects of the geometry of the substructure, air permeability of the soil, air-tightness of the cellar shell, and cellar ventilation on radon entry to both the cellar and the living area. The ground floor covering on top of the soil outside a cellar wall increased radon entry through this wall by about 68%, as radon built up to a very high level under the covering. The effect of cellar ventilation was found as follows: the cellar ventilation created a layer of airflow in the soil under the ground floor; the flow passed over a crack in the ground floor, the entry route to the living area, diluting the radon in the area. Hence, the soil gas entering the living area carried less radon. Cellar ventilation seems more effective in reducing radon entry to the living area in a more permeable soil and leaky cellar shell; a moderate cellar ventilation condition achieved 77% reduction in radon entry to the area. When permeability of these two materials was lower and soil radon content remained the same, the chances of radon entry was also lower; hence, the indoor radon level was lower and no radon control was needed. When such soil contains high radon concentration, other mitigation measures must be sought.

Dispersion of Automotive Alternative Fuel Vapors within a Residence and Its Attached Garage

Abstract A study was undertaken to investigate the use of mass balance modeling techniques to predict air pollution concentrations in residential settings where the source is evaporative emissions of alternative fuels emitted in the attached garage. Field study measurements of the spatial and temporal distribution of evaporative emissions in an attached garage were used to conduct this investigation. In this field study, known quantities of methanol were allowed to evaporate in the garage. Methanol concentrations were then measured and simulated in the garage. Because chemical and physical properties of this contaminant are clearly understood, it was possible to simulate the concentrations inside the remainder of the house. A multi-zonal mass balance model (CONTAM88) was used to predict the across-residence spatial and temporal distribution of concentrations of evaporative emissions from a methanol source inside the attached garage. The model's input data include physical characteristics of the house; parameters characterizing the leakiness of the house; heat, ventilation and air-conditioning system characteristics; fixed airflow data from vent registers; on-site meteorological measurements; and information on the contaminant source. Before using the model to simulate methanol dispersions, the model's performance was tested. Sulfur hexafluoride (SF6) measurements were taken throughout the residence and garage. The model was used to predict interzonal airflow rates and SF6 concentration distributions within the garage and the house, as well as to investigate the well-mixed zone assumption for the garage. Modeling results show that predicted garage SF6 concentrations agreed reasonably well with the measured concentrations under mixed conditions, but the model underpredicted the SF6 concentrations within rooms of the house where mixing was probably incomplete. Methanol simulation results showed that the model underpredicted by approximately 15 percent the garage methanol concentration after methanol emissions stopped. This study found that evaporative emissions in an attached garage have a tendency to infiltrate the house, with rooms adjacent to the garage showing the highest levels of methanol concentrations. Thus automotive evaporative emissions may represent a source of indoor pollution and human exposure in a residential attached garage and also in other critical locations of the residence.

Modelización aplicada al diseño de sistemas de control en el horno alto

The production of pig iron in blast furnaces resists automatic control strategies due to the lack of knowledge about physical and chemical phenomena taking place inside the reactor. High dimensions lead to important dead times and lags. As a consequence it is very difficult to quantify control actions from actual process measurements. A simplified multizonal mathematical model has been proposed that allowed the description of a given blast furnace excluding hearth. Parameters underlying the model have been identified and, under appropriate assumptions, temperature and composition profiles have been established. The analysis of model predictions has been illustrated with steady-state responses to typical control actions.

Comprehensive Regional Socioeconomic Simulation System

This paper describes a comprehensive regional socioeconomic simulation system by using a personal computer. The system is composed of an interactive macroframe model (KMF model), a multizonal socioeconomic simulation model (OURS model), an interactive data retrieval and display subsystem (IDRS), and four kinds of data bases. In the system, the Kansai region of Japan is used as an example. The KMF model forecasts the employment by industrial sectors and the population in the whole Kansai region. The forecasted results are used as the exogenous variables of the OURS model. In the OURS model, the whole region is divided into 120 zones and fundamental socioeconomic indicators, such as population, employment, and land-use area, are forecasted for each zone. The IDRS subsystem helps the model user easily retrieve and display the required data in investigating the simulation results. In this paper, the problem of population aging in Osaka, Japan, is analyzed as an example of the applications of the constructed system. It is anticipated that the system can be used in regional policy-making for each zone.

Multizonal Model of Industrial Activities Based on Journey‐Time Model

A large‐scale regional‐simulation model constructed to forecast industrial activities in disaggregated regions is described. Since the disaggregated subregions (zones) are very close geographically, mutual influences among them cannot be ignored in forecasting future activities in each zone. Based on state‐variable representation, the variation of employment by industrial sectors taken as state variables that represent industrial activities in each zone is described. It is shown that the representation can be simplified to a linear equation with respect to unknown parameters by introducing a previously defined potential, if some reasonable assumptions are postulated. For the purpose of making a positive study, the Kansai region (in the western part of Japan), disaggregated into 120 zones, is taken as an example. First, a submodel is constructed to estimate journey time between zones, which is necessary to calculate the values of various employment and population potentials in each zone. Second, taking emp...

Multizonal Simulation Model of Population

This paper describes a model to forecast population categorized by sex, five-year age groups, and zones. The region under consideration is the Kansai region in Japan, which is disaggregated into 120 zones. Population is estimated as the sum of the closed population and the net social increase. The total net social increase for each zone is estimated on the basis of such variables in each zone as: (1) Demand for labor force determined by industrial developments; (2) increment in labor force; and (3) increment in housing stock. The social increase by sex and age groups is estimated by using the migration rate by sex and age groups (migration pattern) for each zone. One of the main characteristics of the model is that the migration pattern for each zone is taken as one of the endogenous variables which vary according to the development of various socioeconomic activities in each zone. The final test of the constructed model has been performed, and it has been confirmed that the model has sufficient validity. Some of the simulation results are also presented.