Simultaneous estimation of states and inputs in a planar solid oxide fuel cell using nonlinear adaptive observer design

An adaptive nonlinear observer design for the planar solid oxide fuel cell (SOFC) is presented in this work. This observer is based on a lumped parameter model of the SOFC and it can simultaneously estimate the inputs and the states of the system. Considering the inputs as unknown parameters is advantageous because some of the input parameters are not practically measurable in a SOFC stack. The asymptotic stability of the proposed observer is proven using the Lyapunov function method and is based on the concept of input-to-state stability for cascaded systems. The simulations show that the developed observer can track the temperature and species concentration profiles in the planar SOFC during step changes in the input variables and can simultaneously predict the input variables. The adaptive observer presented is valid for a wide operating range, requires fewer variables to be measured, and is robust to fluctuations in the input variables

Effect of a cluster on gas–solid drag from lattice Boltzmann simulations

Fast fluidization of fine particles leads to formation of particle clusters, which significantly affects the drag force between the phases. Existing gas–solid drag models, both empirical and theoretical, do not account for the effect of the clusters on the drag force, and as a result, the computational studies using them are unable to capture the inherent heterogeneity of fast fluidization beds. The limitation of the current drag models is generally attributed to poor understanding of the effect of the clusters. In this study, the effect of a single cluster on the drag force has been investigated by conducting lattice Boltzmann simulations of gas–particle flow under a wide range of the overall voidage and particle Reynolds numbers. It was observed that simulations with the particles in a cluster configuration gave considerably lower drag than those with particles in a random arrangement. Furthermore, for the cluster voidage between maximum to 0.7, a significant drag reduction was observed when the inter-particle distances within a cluster was decreased. The simulations with a constant cluster voidage of 0.7 showed that the drag force decreased on decreasing the overall voidage from the maximum voidage to approximately 0.96; however any further decrease in the overall voidage caused a steep increase in the drag force. The results of this study are important in quantifying the drag reduction due to the formation of clusters

Synthesis and applications of porous non-silica metal oxide submicrospheres

© 2016 Royal Society of Chemistry. Nowadays the development of submicroscale products of specific size and morphology that feature a high surface area to volume ratio, well-developed and accessible porosity for adsorbates and reactants, and are non-toxic, biocompatible, thermally stable and suitable as synergetic supports for precious metal catalysts is of great importance for many advanced applications. Complex porous non-silica metal oxide submicrospheres constitute an important class of materials that fulfill all these qualities and in addition, they are relatively easy to synthesize. This review presents a comprehensive appraisal of the methods used for the synthesis of a wide range of porous non-silica metal oxide particles of spherical morphology such as porous solid spheres, core-shell and yolk-shell particles as well as single-shell and multi-shell particles. In particular, hydrothermal and low temperature solution precipitation methods, which both include various structure developing strategies such as hard templating, soft templating, hydrolysis, or those taking advantage of Ostwald ripening and the Kirkendall effect, are reviewed. In addition, a critical assessment of the effects of different experimental parameters such as reaction time, reaction temperature, calcination, pH and the type of reactants and solvents on the structure of the final products is presented. Finally, the practical usefulness of complex porous non-silica metal oxide submicrospheres in sensing, catalysis, biomedical, environmental and energy-related applications is presented

Computational fluid dynamics simulation of LNG pool fire radiation for hazard analysis

In this paper, a three-dimensional computational fluid dynamics (CFD) model has been conducted on liquefied natural gas (LNG) pool fire radiation. Besides the general governing equations (continuity, energy and momentum), three key components as viscous model of large eddy simulation (LES), non-premixed combustion model, and radiation model for pool fire radiation have been considered to take account of the unsteady and pulsed burning flames, which are especially important in capturing characteristics of large LNG pool fire. The experimental data from Montoir series field tests of LNG pool fire, which could demonstrate a relatively complete performance of large LNG pool fire, have been applied to validate the CFD model of fire radiation. The relative error is less than 10% and the results are in good agreement with the test data. CFD model performs better than the commonly used engineering model as Solid Flame Model. The verified CFD model is then applied to perform a hazard analysis for a LNG satellite station. The spacing distances between facilities (e.g. LNG tanks and vaporizers) and ignition source have been evaluated numerically to avoid thermal radiation damage. It is concluded that the spacing distance between AAV banks and impoundment walls should be enlarged

Computational fluid dynamics analysis of liquefied natural gas dispersion for risk assessment strategies

Computational fluid dynamics (CFD) simulations have been conducted for dense gas dispersion of liquefied natural gas (LNG). The simulations have taken into account the effects of gravity, time-dependent downwind and crosswind dispersion, and terrain. Experimental data from the Burro series field tests, and results from integral model (DEGADIS) have been used to assess the validity of simulation results, which were found to compare better with experimental data than the commonly used integral model DEGADIS. The average relative error in maximum downwind gas concentration between CFD predictions and experimental data was 19.62%.The validated CFD model was then used to perform risk assessment for most-likely-spill scenario at LNG stations as described in the standard of NFPA 59A (2009) “Standard for the Production, Storage and Handling of Liquefied Natural Gas”. Simulations were conducted to calculate the gas dispersion behaviour in the presence of obstacles (dikes walls). Interestingly for spill at a higher elevation, e.g., tank top, the effect of impounding dikes on the affected area was minimal. However, the impoundment zone did affect the wind velocity field in general, and generated a swirl inside it, which then played an important function in confining the dispersion cloud inside the dike. For most cases, almost 75% of the dispersed vapour was retained inside the impoundment zone. The finding and analysis presented here will provide an important tool for designing LNG plant layout and site selection

Effect of Dilute Acid - Alkaline Pretreatment on Rice Husk Composition and Hydrodynamic Modeling with CFD

The high cellulosic content of rice husk can be utilized as a feedstock for pulp and biofuel. Pretreatment is necessary to break the bonds in the complex lignocellulose matrices addressing the cellulose access. This work aims to utilize the rice husk using dilute acid and alkaline pretreatment experimentally and CFD modeling. The study consists of three series of research. The first stage was the dilute acid pretreatment with sulfuric acid concentration of 1% to 5% (v/v) at 85°C for 60 minutes, and alkaline pretreatment with NaOH concentration of 1% to 5% (w/v) at 85oC for 30 minutes separately. The second stage used the combination of both pretreatment. Moreover the last stage of research was hydrodynamic modeling of pretreatment process by CFD (ANSYS FLUENT 16). The experimental results showed that the lowest lignin content after acid pretreatment was about 10.74%. Alkaline pretreatment produced the lowest lignin content of 4.35%. The highest cellulose content was 66.75 % for acid-alkaline pretreatment. The lowest content of lignin was about 6.09% for acid-alkaline pretreatment. The lowest performance of alkaline pretreatment on HWS (hot water solubility) of about 7.34% can be enhanced to 9.71% by using a combination alkaline-acid. The combined pretreatments result hemicellulose of about 9.59% (alkaline-acid) and 9.27% (acid-alkaline). Modeling results showed that the mixing area had the minimum pressure of about -6250 Pa which is vortex leading minimum efficiency of mixing. The rice husk flowed upward to the upper level and mixed with reagent in the perfect mixing. &nbsp