S. Ghiaasiaan | Georgia Institute of Technology (original) (raw)
Papers by S. Ghiaasiaan
In Conventional and Miniature Systems, 2007
International Journal of Energy for a Clean Environment, 2017
SPIE Proceedings, 2017
The optimum small satellite (SmallSat) cryocooler system must be extremely compact and lightweigh... more The optimum small satellite (SmallSat) cryocooler system must be extremely compact and lightweight, achieved in this paper by operating a linear cryocooler at a frequency of approximately 300 Hz. Operation at this frequency, which is well in excess of the 100-150 Hz reported in recent papers on related efforts, requires an evolution beyond the traditional Oxford-class, flexure-based methods of setting the mechanical resonance. A novel approach that optimizes the electromagnetic design and the mechanical design together to simultaneously achieve the required dynamic and thermodynamic performances is described. Since highly miniaturized pulse tube coolers are fundamentally ill-suited for the sub-80K temperature range of interest because the boundary layer losses inside the pulse tube become dominant at the associated very small pulse tube size, a moving displacer Stirling cryocooler architecture is used. Compact compressor mechanisms developed on a previous program are reused for this design, and they have been adapted to yield an extremely compact Stirling warm end motor mechanism. Supporting thermodynamic and electromagnetic analysis results are reported.
International Journal of Multiphase Flow, 2008
Heat Transfer, Volume 3, 2002
ABSTRACT The hybrid artificial neural network-first principle modeling (ANN-FPM) is a powerful an... more ABSTRACT The hybrid artificial neural network-first principle modeling (ANN-FPM) is a powerful and flexible methodology that can be particularly useful for complex multi-phase flow processes. In this method the flow state variables are obtained from the solution of conservative equations using first principle-based closure relations whenever possible, and using trained artificial neural networks for poorly-understood rate processes. The ANN-FPM methodology is applied to a set of experimental data representing critical heat flux in a uniformly heated horizontal annular test section cooled with water. The first principle method is based on numerical solution of one-dimensional two-phase equilibrium conservation equations with velocity slip represented by an algebraic slip ratio correlation. The critical heat flux is predicted using trained neural networks that use local hydrodynamic parameters estimated by the first principle method. It is shown that the methodology works well for the studied data.
Suarez/Light, 2012
Controlled diffusion solidification (CDS) involves mixing two precursor alloys at different therm... more Controlled diffusion solidification (CDS) involves mixing two precursor alloys at different thermal mass and subsequently casting the resultant mixture into near net shaped cast components. The process enables casting of Aluminum wrought alloys into near net shaped components by circumventing the problem of hot tearing by obtaining a non-dendritic morphology of the primary Al phase. The study presents the favorable process and alloy parameters to enable sound shaped casting of 7050 Al wrought alloy (Al-Zn-Mg-Cu) by the CDS process along with the mechanical tensile properties under various heat treatment conditions. The tilt pour gravity casting process was used for this study to demonstrate the ability to cast high integrity components with high strength and ductility.
In Conventional and Miniature Systems, 2007
In Conventional and Miniature Systems, 2007
In Conventional and Miniature Systems, 2007
In Conventional and Miniature Systems, 2007
In Conventional and Miniature Systems, 2007
Convective Heat and Mass Transfer
Convective Heat and Mass Transfer
In Conventional and Miniature Systems, 2007
Convective Heat and Mass Transfer
Convective Heat and Mass Transfer
Nuclear Engineering and Design, 1985
Abstract The numerical solution of the transient heat conduction in the fuel rods of light water ... more Abstract The numerical solution of the transient heat conduction in the fuel rods of light water reactors is studied in this paper, for the purpose of selecting an efficient, economic and accurate solution procedure to be used in fast running codes. The radial heat conduction equations are presented in terms of ordinary time dependent differential equations that are subsequently integrated. Comparisons were carried out using the lumped capacitance method, the method of lines, and the integral method with parabolic temperature profiles. The temperature-time history of the fuel pellet and cladding, predicted by the various methods, is shown for slow and fast transients representing the uncovery and reflood phases of a loss of coolant accident. It was found that the integral method, with parabolic temperature profiles in both the fuel pellet and cladding, was the most economic and gave sufficiently accurate predictions.
International Journal of Heat and Mass Transfer, 1994
Industrial & Engineering Chemistry Research, 2006
Industrial & Engineering Chemistry Research, 2003
In Conventional and Miniature Systems, 2007
International Journal of Energy for a Clean Environment, 2017
SPIE Proceedings, 2017
The optimum small satellite (SmallSat) cryocooler system must be extremely compact and lightweigh... more The optimum small satellite (SmallSat) cryocooler system must be extremely compact and lightweight, achieved in this paper by operating a linear cryocooler at a frequency of approximately 300 Hz. Operation at this frequency, which is well in excess of the 100-150 Hz reported in recent papers on related efforts, requires an evolution beyond the traditional Oxford-class, flexure-based methods of setting the mechanical resonance. A novel approach that optimizes the electromagnetic design and the mechanical design together to simultaneously achieve the required dynamic and thermodynamic performances is described. Since highly miniaturized pulse tube coolers are fundamentally ill-suited for the sub-80K temperature range of interest because the boundary layer losses inside the pulse tube become dominant at the associated very small pulse tube size, a moving displacer Stirling cryocooler architecture is used. Compact compressor mechanisms developed on a previous program are reused for this design, and they have been adapted to yield an extremely compact Stirling warm end motor mechanism. Supporting thermodynamic and electromagnetic analysis results are reported.
International Journal of Multiphase Flow, 2008
Heat Transfer, Volume 3, 2002
ABSTRACT The hybrid artificial neural network-first principle modeling (ANN-FPM) is a powerful an... more ABSTRACT The hybrid artificial neural network-first principle modeling (ANN-FPM) is a powerful and flexible methodology that can be particularly useful for complex multi-phase flow processes. In this method the flow state variables are obtained from the solution of conservative equations using first principle-based closure relations whenever possible, and using trained artificial neural networks for poorly-understood rate processes. The ANN-FPM methodology is applied to a set of experimental data representing critical heat flux in a uniformly heated horizontal annular test section cooled with water. The first principle method is based on numerical solution of one-dimensional two-phase equilibrium conservation equations with velocity slip represented by an algebraic slip ratio correlation. The critical heat flux is predicted using trained neural networks that use local hydrodynamic parameters estimated by the first principle method. It is shown that the methodology works well for the studied data.
Suarez/Light, 2012
Controlled diffusion solidification (CDS) involves mixing two precursor alloys at different therm... more Controlled diffusion solidification (CDS) involves mixing two precursor alloys at different thermal mass and subsequently casting the resultant mixture into near net shaped cast components. The process enables casting of Aluminum wrought alloys into near net shaped components by circumventing the problem of hot tearing by obtaining a non-dendritic morphology of the primary Al phase. The study presents the favorable process and alloy parameters to enable sound shaped casting of 7050 Al wrought alloy (Al-Zn-Mg-Cu) by the CDS process along with the mechanical tensile properties under various heat treatment conditions. The tilt pour gravity casting process was used for this study to demonstrate the ability to cast high integrity components with high strength and ductility.
In Conventional and Miniature Systems, 2007
In Conventional and Miniature Systems, 2007
In Conventional and Miniature Systems, 2007
In Conventional and Miniature Systems, 2007
In Conventional and Miniature Systems, 2007
Convective Heat and Mass Transfer
Convective Heat and Mass Transfer
In Conventional and Miniature Systems, 2007
Convective Heat and Mass Transfer
Convective Heat and Mass Transfer
Nuclear Engineering and Design, 1985
Abstract The numerical solution of the transient heat conduction in the fuel rods of light water ... more Abstract The numerical solution of the transient heat conduction in the fuel rods of light water reactors is studied in this paper, for the purpose of selecting an efficient, economic and accurate solution procedure to be used in fast running codes. The radial heat conduction equations are presented in terms of ordinary time dependent differential equations that are subsequently integrated. Comparisons were carried out using the lumped capacitance method, the method of lines, and the integral method with parabolic temperature profiles. The temperature-time history of the fuel pellet and cladding, predicted by the various methods, is shown for slow and fast transients representing the uncovery and reflood phases of a loss of coolant accident. It was found that the integral method, with parabolic temperature profiles in both the fuel pellet and cladding, was the most economic and gave sufficiently accurate predictions.
International Journal of Heat and Mass Transfer, 1994
Industrial & Engineering Chemistry Research, 2006
Industrial & Engineering Chemistry Research, 2003