The Experts below are selected from a list of 15 Experts worldwide ranked by ideXlab platform
G. R. St. Pierre - One of the best experts on this subject based on the ideXlab platform.
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Application of a counter-current Gaseous diffusion model to the oxidation of hafnium carbide at 1200 to 1530°C
Oxidation of Metals, 1993Co-Authors: G. R. Holcomb, G. R. St. PierreAbstract:A counter-current Gaseous diffusion model is presented to describe the oxidation of hafnium carbide between 1200 and 1530°C. The model separates the porous hafnia scale into two gas diffusion regions separated by a flame front, where O 2 and CO react to form CO 2.In the outer region, O 2 and CO 2 counter-diffuse; in the inner region, CO 2 and CO counter-diffuse. The concentration gradients of each Gaseous Specie in the pores of the hafnia are determined and the rate of oxidation is calculated. A porosity of 2% and a pore radius of 0.01 μm are representative of the values observed in hafnia during the early stages of HfC oxidation. These values lead to predictions of parabolic rate constants that are close to those measured by thermogravimetric analysis. In addition, the predicted and measured parabolic rate constants are shown to have the same dependence upon temperature and oxygen partial pressure.
G. R. Holcomb - One of the best experts on this subject based on the ideXlab platform.
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Application of a counter-current Gaseous diffusion model to the oxidation of hafnium carbide at 1200 to 1530°C
Oxidation of Metals, 1993Co-Authors: G. R. Holcomb, G. R. St. PierreAbstract:A counter-current Gaseous diffusion model is presented to describe the oxidation of hafnium carbide between 1200 and 1530°C. The model separates the porous hafnia scale into two gas diffusion regions separated by a flame front, where O 2 and CO react to form CO 2.In the outer region, O 2 and CO 2 counter-diffuse; in the inner region, CO 2 and CO counter-diffuse. The concentration gradients of each Gaseous Specie in the pores of the hafnia are determined and the rate of oxidation is calculated. A porosity of 2% and a pore radius of 0.01 μm are representative of the values observed in hafnia during the early stages of HfC oxidation. These values lead to predictions of parabolic rate constants that are close to those measured by thermogravimetric analysis. In addition, the predicted and measured parabolic rate constants are shown to have the same dependence upon temperature and oxygen partial pressure.
Jan Pribis - One of the best experts on this subject based on the ideXlab platform.
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Algorithm and simulation of heat conduction process for design of a thin multilayer technical device
Applied Thermal Engineering, 2016Co-Authors: Alexander Ayriyan, Ján Buša, Eugeny E. Donets, Hovik Grigorian, Jan PribisAbstract:Abstract A model of a multilayer device with non-trivial geometrical structure and nonlinear dependencies of thermodynamic material properties at cryogenic temperatures is suggested. A considered device, called cryogenic cell, is intended for use in multicharged ion sources for pulse injection of Gaseous Species into ionization space of ion sources. The main requirement for the cryogenic cell operation is the permanent opening and closing for Gaseous Species injection in a millisecond range, while cell closing is provided by freezing of the Gaseous Specie at the outer surface of the cell and the cell opening – by the corresponding pulse heating of the cell surface up to definite temperature. The thermal behavior of the device in a millisecond time range is simulated. The algorithm for solving the non-stationary heat conduction problem with a time-dependent periodical heating source is suggested. The algorithm is based on finite difference explicit–implicit method. The OpenCL realization of the algorithm is discussed. The optimal particular choice of the parameters to provide the required pulse temperature regime of the designed cryogenic cell for the chosen working gas is presented. Based on these results further optimization can be formulated.
Walter W. Yuen - One of the best experts on this subject based on the ideXlab platform.
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On the utilization of the mean beam length concept in the evaluation of radiative heat transfer in isothermal three-dimensional non-gray system
International Journal of Heat and Mass Transfer, 2015Co-Authors: Walter W. YuenAbstract:The mean beam length concept, which is defined traditionally for the evaluation of emission of a gas volume to its surrounding boundary, is generalized to apply to three-dimensional surface–surface and volume–surface radiative exchange with an intervening non-gray N2/CO2/H2O/soot mixture at one atmosphere. The concept is demonstrated to be effective in providing a simple, efficient and accurate approach to compute radiative heat transfer in non-gray three-dimensional mixtures. Using numerical data generated for a rectangular enclosure, the mean beam lengths are shown to depend mainly on the total partial pressure of the absorbing gas and soot volume fraction. The mean beam length’s dependence on the mixture temperature and the fractional proportion of the individual Gaseous Specie does not have a strong influence on the mixture total absorptance and emittance. The Hottel’s constant mean beam length approach is shown to be accurate only in the prediction of the emittance of a non-luminous mixture (i.e. without soot). For the mixture absorptance and the emittance/absorptance of a luminous mixture, the Hottel’s approach is generally inaccurate. A neural network, MBL-NNET, is developed to correlate the mean beam length data for the mixture in the enclosure. The two neural networks (MBL-NNET and RAD-NNET) are shown to be an effective approach in the evaluation of radiation heat transfer in practical engineering systems.
Alexander Ayriyan - One of the best experts on this subject based on the ideXlab platform.
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Algorithm and simulation of heat conduction process for design of a thin multilayer technical device
Applied Thermal Engineering, 2016Co-Authors: Alexander Ayriyan, Ján Buša, Eugeny E. Donets, Hovik Grigorian, Jan PribisAbstract:Abstract A model of a multilayer device with non-trivial geometrical structure and nonlinear dependencies of thermodynamic material properties at cryogenic temperatures is suggested. A considered device, called cryogenic cell, is intended for use in multicharged ion sources for pulse injection of Gaseous Species into ionization space of ion sources. The main requirement for the cryogenic cell operation is the permanent opening and closing for Gaseous Species injection in a millisecond range, while cell closing is provided by freezing of the Gaseous Specie at the outer surface of the cell and the cell opening – by the corresponding pulse heating of the cell surface up to definite temperature. The thermal behavior of the device in a millisecond time range is simulated. The algorithm for solving the non-stationary heat conduction problem with a time-dependent periodical heating source is suggested. The algorithm is based on finite difference explicit–implicit method. The OpenCL realization of the algorithm is discussed. The optimal particular choice of the parameters to provide the required pulse temperature regime of the designed cryogenic cell for the chosen working gas is presented. Based on these results further optimization can be formulated.