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Middleton, WI, United States

Drennan S.A.,Convergent Science Inc.
Western States Section of the Combustion Institute Spring Technical Meeting 2014 | Year: 2014

Computational Fluid Dynamic (CFD) combustion simulations of gas turbine combustion have become increasingly useful in the design and development of lower emissions, higher performing engines. However, mesh generation for traditional CFD continues to represent a significant portion of the time required to conduct CFD simulations. This paper presents the application of an automatically generated Cartesian meshing approach to a liquid fueled gas turbine combustor for Large Eddy Simulation (LES) simulations. The model combustor used in this study is a single can with a generic fuel/air mixer employing radial and axial swirlers for multi-zone combustion. The spray is modeled with discrete injections of droplets to simulate an air-blast atomizer. A modified cut-cell Cartesian method is used that eliminates the need for the computational grid to be morphed with the geometry of interest while still representing the true boundary shape. This approach allows for the use of simple orthogonal grids and completely automates the mesh generation process. The meshing approach utilizes Adaptive Mesh Refinement (AMR) to resolve the domain near geometric features and in regions near the spray and flame front. AMR allows the use of a very fine computational mesh in the vicinity of the spray and high temperature reaction zones while keeping the overall cell count relatively low. Mesh sensitivity studies are presented with modifications in the global mesh size and in mesh refinement near effusion cooled surfaces. These reacting flow results use a detailed reaction mechanism to simulate Jet-A liquid fuel. Cell-size recommendations from the above studies are used to further explore grid convergence for RANS and LES-based simulations.

Raju M.,Convergent Science Inc. | Khaitan S.,Iowa State University
International Journal of Hydrogen Energy | Year: 2011

Small hybrid wind systems are capable of storing and supplying power for residential applications. In this paper, the excess wind energy is converted into hydrogen by electrolysis and is stored in a metal hydride. Metal hydride beds are known for their high volumetric capacity compared to the compressed hydrogen storage, and offers hydrogen storage at a reasonable operating temperature and pressure. A system simulation model is developed in Matlab/Simulink platform for the dynamics of the metal hydride hydrogen storage system, which is charged by the wind energy. The thermal loads of the metal hydride storage system is met by passing water at ambient temperature for cooling the bed while hydrogen is being absorbed. The effect of the transient turbulent wind velocity profile on the storage system is analyzed. The thermal management of the storage system plays an important role in the overall design, and hence it is discussed in detail. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Raju M.,Convergent Science Inc. | Khaitan S.K.,Iowa State University
Journal of Power Sources | Year: 2012

This paper deals with the storage of excess wind energy, in a hybrid wind power system, in the form of compressed hydrogen. A system simulation model is developed in Matlab/Simulink platform for the charging and discharging dynamics of compressed hydrogen storage system integrated with the wind turbine and the fuel cell. Wind model is used to estimate the power generation in the wind turbine. When the wind power generation exceeds the load, the excess power is diverted to the electrolyzer to produce hydrogen. As and when the pressure inside the electrolyzer builds, a compressor is operated intermittently (for higher efficiency) to divert the hydrogen into high pressure cylinders. When demand exceeds the power generation, fuel cell supplies the power to the load. A number of fuel cell stacks are provided to meet the required load. The overall efficiency of the storage system, defined as the ratio of the useful energy derived from the storage system to the energy diverted to the storage system is found to be 24.5% for the compressed hydrogen storage based system. © 2012 Elsevier B.V. All rights reserved.

Khaitan S.K.,Iowa State University | Raju M.,Convergent Science Inc.
International Journal of Hydrogen Energy | Year: 2012

In small hybrid wind systems, excess wind energy is stored for later use during the deficit power generation. Excess wind energy can be stored as hydrogen in a metal hydride storage bed and reused later to generate power using a fuel cell. This paper deals with the discharge dynamics of the coupled fuel cell and metal hydride storage bed during the power extraction. Thermal coupling of the fuel cell and metal hydride bed is also discussed. The waste heat generated in the fuel cell is removed using a water coolant. The exit fuel cell coolant stream is passed through the metal hydride storage bed to supply the necessary heat required for desorption of hydrogen from the bed. This will also lead to a reduction in the load on the radiator. The discharge dynamics and the thermal management of the coupled system are demonstrated through a system simulation model developed in Matlab/Simulink platform. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Khaitan S.K.,Iowa State University | Raju M.,Convergent Science Inc.
International Journal of Hydrogen Energy | Year: 2012

Typical compressed air energy storage (CAES) based gas turbine plant operates on natural gas or fuel oils as fuel for its operation. However, the use of hydro-carbon fuels will contribute to carbon emissions leading to pollution of the environment. On the other hand, the use of hydrogen as fuel for the gas turbine will eliminate the carbon emissions leading to a cleaner environment. Hydrogen can be produced using renewable energy sources like wind, solar etc. Storage of hydrogen is a bottleneck for such a system. A high capacity sodium alanate metal hydride bed is used in this study to store the hydrogen. The dynamics of the CAES based gas turbine plant operating with hydrogen fuel is presented along with discharge dynamics of the metal hydride bed. The heat required for desorbing the hydrogen from the metal hydride bed is provided partly by the hot flue gas exiting from the low pressure turbine and partly by external heating. Thus some of the heat from the flue gas is extracted. A novel multiple bed strategy is employed for efficient desorption. Each bed consists of a shell and tube, with alanate in the shell and heating fluid flowing through the helical coiled tube. Hydrogen combustor is modeled using a simplified Continuous Stirred Tank Reactor (CSTR) assumption in CANTERA. The NOx emissions in the low pressure turbine exhaust stream are presented. Copyright © 2012 Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

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