S. Ghiaasiaan - Profile on Academia.edu (original) (raw)
Papers by S. Ghiaasiaan
Unit Conversions
In Conventional and Miniature Systems, 2007
International Journal of Energy for a Clean Environment, 2017
In this study, the key components of combined cycles designed for waste energy recovery from auto... more In this study, the key components of combined cycles designed for waste energy recovery from automobile engines have been virtually designed for being light weight, small sized without compromising strengths, and based on integration with the existing components of an automobile. A simulation was performed to examine the amount of waste energy that could be recovered and the consequential increase in the overall thermal effi ciency through the use of Kalina, ethanol, and steam cycles using the Engineering Equation Solver soft ware under typical engine operating conditions. It was observed that the steam cycle was bett er for recovering energy from the exhaust gas in the higher temperature range (689 o C to 160 o C) and the Kalina cycle was bett er for recovering energy from the exhaust gas and the cooling water in the lower temperature range (122 o C to 80 o C) among the three cycles. It was found that using this combination of cycles, about 5 kW of power could be extracted from the waste energy. The next thing was to determine the amount of space, weight, and design to incorporate a system of cycles like this with an automobile. The combined cycle generation, a process widely used in existing power plants, has become a viable option for automotive applications due to the advances in the materials science, nanotechnology, and MEMS (Micro-Electro Mechanical Systems) devices. Critical components of the best performing cycles have been designed using computer-aided engineering for the minimization of weight and space, and integration with the typical components of an automobile.
Development of a miniature Stirling cryocooler for LWIR small satellite applications
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
Single-phase and two-phase flow pressure drops caused by flow area expansion and contraction were... more Single-phase and two-phase flow pressure drops caused by flow area expansion and contraction were measured using air and water. The test section consisted of two capillaries with 0.84 mm and 1.6 mm diameters. For single-phase flow, the Reynolds numbers defined based on the smaller diameter capillary covered the range 160-11,000. For two-phase flow, the all-liquid Reynolds number based on the smaller capillary varied in the 410-1020 range, and the flow quality varied in the 0.018-0.2 range. The single-phase flow loss coefficients for both flow area expansion and contraction were empirically correlated. For two-phase flow, the data indicated the occurrence of significant velocity slip, and the one-dimensional homogeneous flow model utterly disagreed with the data. For flow area expansion the one-dimensional slip flow model along with an Armand-type slip ratio correlation could predict the data well. For flow area contraction, the one-dimensional slip flow model along with the slip ratio expression of Zivi agreed with the data very well, provided that no venacontracta was considered.
Hybrid Neural Network-First Principles Modeling of Critical Heat Flux in a Thin Annular Channel
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.
Near Net Shaped Casting of 7050 Al Wrought Alloy by CDS Process: Microstructure and Mechanical Properties
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.
Collision Integrates for the Lennard–Jones Potential Model
In Conventional and Miniature Systems, 2007
Thermodynamic Properties of Saturated Liquid and Vapor for Selected Refrigerants
In Conventional and Miniature Systems, 2007
Two-Phase Flow in Small Flow Passages
In Conventional and Miniature Systems, 2007
The Drift Flux Model and Void–Quality Relations
In Conventional and Miniature Systems, 2007
Thermodynamic and Single-Phase Flow Fundamentals
In Conventional and Miniature Systems, 2007
Summary of Some Useful Heat Transfer and Friction-Factor Correlations
Convective Heat and Mass Transfer
Transport Properties of Saturated Water and Steam
Convective Heat and Mass Transfer
Frequently Used Notation
In Conventional and Miniature Systems, 2007
Internal Laminar Flow
Convective Heat and Mass Transfer
Thermophysical and Transport Fundamentals
Convective Heat and Mass Transfer
Heat conduction in nuclear fuel rods
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
The combined heat and mass transfer during the evaporation of a superheated spherical droplet sdb... more The combined heat and mass transfer during the evaporation of a superheated spherical droplet sdbject to an external flow field composed of its own saturated vapor, when the droplet and its surrounding vapor contain a tracer amount of a volatile transferred species, is numerically modeled. The droplet mass transfer model is an extension of the Kronig and Brink method to variable droplet radius. Gas-side heat and mass transfer are treated using the quasi-steady film theory. Calculated parameteric results, demonstrating the effects of important parameters when the partition coefficient of the transferred species is much larger than one, are presented.
Industrial & Engineering Chemistry Research, 2006
Taylor flow, a flow regime characterized by Taylor bubbles separated by liquid slugs that do not ... more Taylor flow, a flow regime characterized by Taylor bubbles separated by liquid slugs that do not contain entrained micro bubbles, is a predominant gas-liquid two-phase flow regime in capillaries and minichannels (channels with hydraulic diameters in the 0.1-1 mm range), and it occurs in monolithic catalytic converters and other multiphase reactors. Taylor flow regime is morphologically relatively simple and has been modeled in the past using computational fluid dynamics (CFD) methods. However, most of the past CFD models have either assumed a fixed gas-liquid interfacial geometry or have modeled the gas-liquid interphase movement based on the method of spines, which imposes some restrictions on the free movement of the interface. In this study, we examine the feasibility of CFD modeling of the Taylor flow regime in capillaries by using the volume-of-fluid (VOF) technique for the motion of the gas-liquid interphase. It is shown that such a model predicts well the experimental data and empirical correlations relevant to the hydrodynamics of capillaries. Improved correlations for slug length and pressure drop in capillaries are also suggested based on available experimental data.
Flow Regime Identification in Gas/Liquid/Pulp Fiber Slurry Flows Based on Pressure Fluctuations Using Artificial Neural Networks
Industrial & Engineering Chemistry Research, 2003
Unit Conversions
In Conventional and Miniature Systems, 2007
International Journal of Energy for a Clean Environment, 2017
In this study, the key components of combined cycles designed for waste energy recovery from auto... more In this study, the key components of combined cycles designed for waste energy recovery from automobile engines have been virtually designed for being light weight, small sized without compromising strengths, and based on integration with the existing components of an automobile. A simulation was performed to examine the amount of waste energy that could be recovered and the consequential increase in the overall thermal effi ciency through the use of Kalina, ethanol, and steam cycles using the Engineering Equation Solver soft ware under typical engine operating conditions. It was observed that the steam cycle was bett er for recovering energy from the exhaust gas in the higher temperature range (689 o C to 160 o C) and the Kalina cycle was bett er for recovering energy from the exhaust gas and the cooling water in the lower temperature range (122 o C to 80 o C) among the three cycles. It was found that using this combination of cycles, about 5 kW of power could be extracted from the waste energy. The next thing was to determine the amount of space, weight, and design to incorporate a system of cycles like this with an automobile. The combined cycle generation, a process widely used in existing power plants, has become a viable option for automotive applications due to the advances in the materials science, nanotechnology, and MEMS (Micro-Electro Mechanical Systems) devices. Critical components of the best performing cycles have been designed using computer-aided engineering for the minimization of weight and space, and integration with the typical components of an automobile.
Development of a miniature Stirling cryocooler for LWIR small satellite applications
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
Single-phase and two-phase flow pressure drops caused by flow area expansion and contraction were... more Single-phase and two-phase flow pressure drops caused by flow area expansion and contraction were measured using air and water. The test section consisted of two capillaries with 0.84 mm and 1.6 mm diameters. For single-phase flow, the Reynolds numbers defined based on the smaller diameter capillary covered the range 160-11,000. For two-phase flow, the all-liquid Reynolds number based on the smaller capillary varied in the 410-1020 range, and the flow quality varied in the 0.018-0.2 range. The single-phase flow loss coefficients for both flow area expansion and contraction were empirically correlated. For two-phase flow, the data indicated the occurrence of significant velocity slip, and the one-dimensional homogeneous flow model utterly disagreed with the data. For flow area expansion the one-dimensional slip flow model along with an Armand-type slip ratio correlation could predict the data well. For flow area contraction, the one-dimensional slip flow model along with the slip ratio expression of Zivi agreed with the data very well, provided that no venacontracta was considered.
Hybrid Neural Network-First Principles Modeling of Critical Heat Flux in a Thin Annular Channel
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.
Near Net Shaped Casting of 7050 Al Wrought Alloy by CDS Process: Microstructure and Mechanical Properties
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.
Collision Integrates for the Lennard–Jones Potential Model
In Conventional and Miniature Systems, 2007
Thermodynamic Properties of Saturated Liquid and Vapor for Selected Refrigerants
In Conventional and Miniature Systems, 2007
Two-Phase Flow in Small Flow Passages
In Conventional and Miniature Systems, 2007
The Drift Flux Model and Void–Quality Relations
In Conventional and Miniature Systems, 2007
Thermodynamic and Single-Phase Flow Fundamentals
In Conventional and Miniature Systems, 2007
Summary of Some Useful Heat Transfer and Friction-Factor Correlations
Convective Heat and Mass Transfer
Transport Properties of Saturated Water and Steam
Convective Heat and Mass Transfer
Frequently Used Notation
In Conventional and Miniature Systems, 2007
Internal Laminar Flow
Convective Heat and Mass Transfer
Thermophysical and Transport Fundamentals
Convective Heat and Mass Transfer
Heat conduction in nuclear fuel rods
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
The combined heat and mass transfer during the evaporation of a superheated spherical droplet sdb... more The combined heat and mass transfer during the evaporation of a superheated spherical droplet sdbject to an external flow field composed of its own saturated vapor, when the droplet and its surrounding vapor contain a tracer amount of a volatile transferred species, is numerically modeled. The droplet mass transfer model is an extension of the Kronig and Brink method to variable droplet radius. Gas-side heat and mass transfer are treated using the quasi-steady film theory. Calculated parameteric results, demonstrating the effects of important parameters when the partition coefficient of the transferred species is much larger than one, are presented.
Industrial & Engineering Chemistry Research, 2006
Taylor flow, a flow regime characterized by Taylor bubbles separated by liquid slugs that do not ... more Taylor flow, a flow regime characterized by Taylor bubbles separated by liquid slugs that do not contain entrained micro bubbles, is a predominant gas-liquid two-phase flow regime in capillaries and minichannels (channels with hydraulic diameters in the 0.1-1 mm range), and it occurs in monolithic catalytic converters and other multiphase reactors. Taylor flow regime is morphologically relatively simple and has been modeled in the past using computational fluid dynamics (CFD) methods. However, most of the past CFD models have either assumed a fixed gas-liquid interfacial geometry or have modeled the gas-liquid interphase movement based on the method of spines, which imposes some restrictions on the free movement of the interface. In this study, we examine the feasibility of CFD modeling of the Taylor flow regime in capillaries by using the volume-of-fluid (VOF) technique for the motion of the gas-liquid interphase. It is shown that such a model predicts well the experimental data and empirical correlations relevant to the hydrodynamics of capillaries. Improved correlations for slug length and pressure drop in capillaries are also suggested based on available experimental data.
Flow Regime Identification in Gas/Liquid/Pulp Fiber Slurry Flows Based on Pressure Fluctuations Using Artificial Neural Networks
Industrial & Engineering Chemistry Research, 2003