Numerical Simulations of a Circulating Fluidized Bed with a Square Cross-Section

In this study, both 2D and 3D numerical simulations of a well-documented circulating fluidized bed with a square cross-section were conducted. With some assumptions, a series of 2D simulations was first carried out to study the influence of grid resolution, initial flow field, and boundary condition on the flow hydrodynamics. It was found that 2D simulations under-predicted the solids inventory even with the finest grid (10-particle-diameter grid size). On the other hand, a 3D simulation with relatively coarse grid was found in better agreement with the experimental data. Differences between 2D and 3D simulations were briefly discussed

HIGH PERFORMANCE COMPUTING: CLEAN COAL GASIFIER DESIGNS USING HYBRID PARALLELIZATION

One of the targets for coal gasification in the near future is capturing 90% of the carbon with less than a 10% increase in cost of electricity. Aggressive goals like this will require innovative gasifier designs to reach the market place quickly, with less risk, and in an economically viable way. Researchers at the National Energy Technology Laboratory (NETL) are collaborating with industry, academia, and other national labs on multiphase computational models like the legacy code MFIX (Multiphase Flow with Interphase eXchange) which can help design, operate, and scale-up clean coal gasifiers to meet the challenges or a carbon constrained world. In fact, NETL has hosted a series of multiphase workshops which has produced a multiphase flow science technology roadmap to achieve the goal “that by 2015 multiphase science based computer simulations play a significant role in the design, operation, and troubleshooting of multiphase flow devices in fossil fuel processing plants”. In this study, we present our experience of porting MFIX, an open source multiphase computational fluid dynamic model, to a high performance computing platform and how the resulting high fidelity simulations are impacting the design of clean coal gasifiers of tomorrow. Inherent to these gasifiers is the various time and length scales which require very high spatial resolution, large number of iterations with small time-steps to resolve and predict the spatiotemporal variations in gas and solids volume fractions, velocities, temperatures with any associated phase change and chemical reactions. These requirements resulted in perhaps the largest known simulations of gas-solids reacting flows, providing detailed information about the gas-solids flow structure, pressure, temperature and species distribution in the gasifier. From a computational science perspective, we found that global communication has to be reduced to achieve scalability to 1000s of cores and hybrid parallelization can yield substantial improvement in time-to-solution when utilizing thousands of multi-core processors

Process Modeling Phase I Summary Report for the Advanced Gas Reactor Fuel Development and Qualification Program

This report summarizes the results of preliminary work at Oak Ridge National Laboratory (ORNL) to demonstrate application of computational fluid dynamics modeling to the scale-up of a Fluidized Bed Chemical Vapor Deposition (FBCVD) process for nuclear fuels coating. Specifically, this work, referred to as Modeling Scale-Up Phase I, was conducted between January 1, 2006 and March 31, 2006 in support of the Advanced Gas Reactor (AGR) Program. The objective was to develop, demonstrate and "freeze" a version of ORNL's computational model of the TRI ISOtropic (TRISO) fuel-particle coating process that can be specifically used to assist coater scale-up activities as part of the production of AGR-2 fuel. The results in this report are intended to serve as input for making decisions about initiating additional FBCVD modeling work (referred to as Modeling Scale-Up Phase II) in support of AGR-2. The main computational tool used to implement the model is the general-purpose multiphase fluid-dynamics computer code known as MFIX (Multiphase Flow with Interphase eXchanges), which is documented in detail on the DOE-sponsored website http://www.mfix.org. Additional computational tools are also being developed by ORNL for post-processing MFIX output to efficiently summarize the important information generated by the coater simulations. The summarized information includes quantitative spatial and temporal measures (referred to as discriminating characteristics, or DCs) by which different coater designs and operating conditions can be compared and correlated with trends in product quality. The ORNL FBCVD modeling work is being conducted in conjunction with experimental coater studies at ORNL with natural uranium CO (NUCO) and surrogate fuel kernels. Data are also being obtained from ambient-temperature, spouted-bed characterization experiments at the University of Tennessee and theoretical studies of carbon and silicon carbide chemical vapor deposition kinetics at Iowa State University. Prior to the current scale-up activity, considerable effort has gone in to adapting the MFIX code to incorporate the unique features of fuel coating reactors and also in validating the resulting simulation features with experimental observations. Much of this work is documented in previous AGR reports and publications (Pannala et al., 2004, Pannala et al., 2005, Boyalakuntla et al., 2005a, Boyalakuntla et al., 2005b and Finney et al., 2005). As a result of the previous work described above, the ORNL coater model now has the capability for simulating full spatio-temporal details of the gas-particle hydrodynamics and gas-particle heat and mass transfer in the TRISO coater. This capability provides a great deal of information about many of the processes believed to control quality, but the model is not yet sufficiently developed to fully predict coating quality for any given coater design and/or set of operating conditions because the detailed chemical reaction kinetics needed to make the model fully predictive are not yet available. Nevertheless, the model at its current stage of development already provides the most comprehensive and detailed quantitative information available about gas flows, solid flows, temperatures, and species inside the coater during operation. This level of information ought to be highly useful in expediting the scale-up process (e.g., in correlating observations and minimizing the number of pilot-scale tests required). However, previous work had not yet demonstrated that the typical design and/or operating changes known to affect product quality at the lab scale could be clearly discriminated by the existing model. The Modeling Scale-Up Phase I work was initiated to produce such a demonstration, and two detailed examples are discussed in this report

Automotive Underhood Thermal Management Analysis Using 3-D Coupled Thermal-Hydrodynamic Computer Models: Thermal Radiation Modeling

The goal of the radiation modeling effort was to develop and implement a radiation algorithm that is fast and accurate for the underhood environment. As part of this CRADA, a net-radiation model was chosen to simulate radiative heat transfer in an underhood of a car. The assumptions (diffuse-gray and uniform radiative properties in each element) reduce the problem tremendously and all the view factors for radiation thermal calculations can be calculated once and for all at the beginning of the simulation. The cost for online integration of heat exchanges due to radiation is found to be less than 15% of the baseline CHAD code and thus very manageable. The off-line view factor calculation is constructed to be very modular and has been completely integrated to read CHAD grid files and the output from this code can be read into the latest version of CHAD. Further integration has to be performed to accomplish the same with STAR-CD. The main outcome of this effort is to obtain a highly scalable and portable simulation capability to model view factors for underhood environment (for e.g. a view factor calculation which took 14 hours on a single processor only took 14 minutes on 64 processors). The code has also been validated using a simple test case where analytical solutions are available. This simulation capability gives underhood designers in the automotive companies the ability to account for thermal radiation - which usually is critical in the underhood environment and also turns out to be one of the most computationally expensive components of underhood simulations. This report starts off with the original work plan as elucidated in the proposal in section B. This is followed by Technical work plan to accomplish the goals of the project in section C. In section D, background to the current work is provided with references to the previous efforts this project leverages on. The results are discussed in section 1E. This report ends with conclusions and future scope of work in section F

Common mental disorders among adult members of 'left-behind' international migrant worker families in Sri Lanka

BACKGROUND: Nearly one-in-ten Sri Lankans are employed abroad as International migrant workers (IMW). Very little is known about the mental health of adult members in families left-behind. This study aimed to explore the impact of economic migration on mental health (common mental disorders) of left-behind families in Sri Lanka. METHODS: A cross-sectional survey using multistage sampling was conducted in six districts (representing 62% of outbound IMW population) of Sri Lanka. Spouses and non-spouse caregivers (those providing substantial care for children) from families of economic migrants were recruited. Adult mental health was measured using the Patient Health Questionnaire. Demographic, socio-economic, migration-specific and health utilization information were gathered. RESULTS: A total of 410 IMW families were recruited (response rate: 95.1%). Both spouse and a non-spouse caregiver were recruited for 55 families with a total of 277 spouses and 188 caregivers included. Poor general health, current diagnosed illness and healthcare visit frequency was higher in the non-spouse caregiver group. Overall prevalence of common mental disorder (CMD; Depression, somatoform disorder, anxiety) was 20.7% (95%CI 16.9-24.3) with 14.4% (95%CI 10.3-18.6) among spouses and 29.8% (95%CI 23.2-36.4) among non-spouse caregivers. Prevalence of depression (25.5%; 95%CI 19.2-31.8) and somatoform disorder 11.7% (95%CI 7.0-16.3) was higher in non-spouse caregiver group. When adjusted for age and gender, non-returning IMW in family, primary education and low in-bound remittance frequency was associated with CMD for spouses while no education, poor general health and increased healthcare visits was significantly associated in the non-spouse caregiver group. CONCLUSIONS: To our knowledge, this is one of the first studies to explore specific mental health outcomes among adult left-behind family members of IMW through standardized diagnostic instruments in Sri Lanka and in South Asian region. Negative impact of economic migration is highlighted by the considerably high prevalence of CMD among adults in left-behind families. A policy framework that enables health protection whilst promoting migration for development remains a key challenge for labour-sending nations

Spatiotemporal Compound Wavelet Matrix Framework for Multiscale/Multiphysics Reactor Simulation: Case Study of a Heterogeneous Reaction/Diffusion System

We present a mathematical method for efficiently compounding information from different models of species diffusion from a chemically reactive boundary. The proposed method is intended to serve as a key component of a multiscale/ multiphysics framework for heterogeneous chemically reacting processes. An essential feature of the method is the merging of wavelet representations of the different models and their corresponding time and length scales. Up-and-downscaling of the information between the scales is accomplished by application of a compounding wavelet operator, which is assembled by establishing limited overlap in scales between the models. We show that the computational efficiency gain and potential error associated with the method depend on the extent of scale overlap and wavelet filtering used. We demonstrate the method for an example problem involving a two-dimensional chemically reactive boundary and first order reactions involving two species

A new model for a drying droplet

A new model for droplet drying is suggested. This model is based on the analytical solutions to the heat transfer and species diffusion equations inside spherical droplets. Small solid particles dispersed in an ambient evaporating liquid, or a non-evaporating substance dissolved in this liquid, are treated as non-evaporating components. Three key sub-processes are involved in the process of droplet drying within the new model: droplet heating/cooling, diffusion of the components inside the droplets, and evaporation of the volatile component. The model is used to analyse the drying of a spray consisting of chitosan dissolved in water. After completion of the evaporation process, the size of the residual solid ball predicted by the model is consistent with those observed experimentally

The Colombo Twin and Singleton Follow-up Study: a population based twin study of psychiatric disorders and metabolic syndrome in Sri Lanka

BACKGROUND: The disease burden related to mental disorders and metabolic syndrome is growing in low-and middle-income countries (LMIC). The Colombo Twin and Singleton Study (COTASS) is a population-based sample of twins and singletons in Colombo, Sri Lanka. Here we present prevalence estimates for metabolic syndrome (metS) and mental disorders from a follow-up (COTASS-2) of the original study (COTASS-1), which was a mental health survey. METHODS: In COTASS-2, participants completed structured interviews, anthropometric measures and provided fasting blood and urine samples. Depressive disorder, depressive symptoms, anxiety symptoms, post-traumatic stress disorder (PTSD) and hazardous alcohol use were ascertained with structured psychiatric screens (Composite International Diagnostic Interview (CIDI), Beck Depression Inventory (BDI-II), Generalised Anxiety Disorder Questionnaire (GAD-7), PTSD Checklist - Civilian Version (PCL-C), and Alcohol Use Disorders Identification Test (AUDIT)). We defined metS according to the International Diabetes Federation (IDF) criteria and the revised National Cholesterol Education Programme Adult Treatment Panel (NCEP ATP III) criteria. We estimated the prevalence of psychiatric disorders and metS and metS components, and associations with gender, education and age. RESULTS: Two thousand nine hundred thirty-four twins and 1035 singletons were followed up from COTASS-1 (83.4 and 61.8% participation rate, respectively). Prevalence estimates for depressive disorder (CIDI), depressive symptoms (BDI ≥ 16), anxiety symptoms (GAD-7 ≥ 10) and PTSD (PCL-C DSM criteria) were 3.8, 5.9, 3.6, and 4.5% respectively for twins and 3.9, 9.8, 5.1 and 5.4% for singletons. 28.1 and 30.9% of male twins and singletons respectively reported hazardous alcohol use. Approximately one third met the metS criteria (IDF: 27.4% twins, 44.6% singletons; NCEP ATP III: 30.6% twins, 48.6% singletons). The most prevalent components were central obesity (59.2% twins, 71.2% singletons) and raised fasting blood glucose or diabetes (38.2% twins, 56.7% singletons). CONCLUSION: MetS was highly prevalent in twins, and especially high in singletons, whereas the prevalence of mental disorders was low, but consistent with local estimates. The high levels of raised fasting plasma glucose and central obesity were particularly concerning, and warrant national diabetes prevention programmes