This paper gives results of an experimental study to determine the effect that a surface reaction... more This paper gives results of an experimental study to determine the effect that a surface reaction has on a boundary layer flow. An innovative technique has been developed to visualize the effect a surface reaction has on a flat plate boundary layer flow. A mixture of mineral oil and hexanoic acid flowed at low Reynolds number over a metal plate embedded with a small piece of sodium. The reaction between the hexanoic acid and the sodium metal produced hydrogen bubbles, which rose to the surface. Upstream of the reaction, dye was injected into the laminar flow, and the interaction between the bubbles and the dye was recorded. Results show that bubble entrainment stretch and bend the dye filaments, convect fluid away from the reaction, and create vortices downstream and to the sides of the reaction. These results show that a surface reaction can introduce velocity fluctuations into an otherwise laminar flow. Farther downstream the flow relaminarizes.
There have been significant efforts by the heat transfer community to investigate the melting phe... more There have been significant efforts by the heat transfer community to investigate the melting phenomenon of materials. These efforts have included the analytical development of equations to represent melting, numerical development of computer codes to assist in modeling the phenomena, and collection of experimental data. The understanding of the melting phenomenon has application in several areas of interest, for example, the melting of a Phase Change Material (PCM) used as a thermal storage medium as well as the melting of the fuel bundle in a nuclear power plant during an accident scenario. The objective of this research is two-fold. First a numerical investigation, using computational fluid dynamics (CFD), of melting with internal heat generation for a vertical cylindrical geometry is presented. Second, to the best of authors knowledge, there are very limited number of engineering experimental results available for the case of melting with Internal Heat Generation (IHG). An exper...
The Stefan problem with internal heat generation can be found in various industrial applications.... more The Stefan problem with internal heat generation can be found in various industrial applications. In particular, this problem describes melting of nuclear fuel rods during a reactor emergency. The present study reports on numerical modeling of the heat conduction equation and the Stefan equation with an application of the method of catching of the front into a space grid node. To solve numerically the heat conduction equation we realized an implicit four-node scheme using the Thomas method and iteration procedure.
We study the evolution of the solid-liquid interface during melting and solidification of a mater... more We study the evolution of the solid-liquid interface during melting and solidification of a material with constant internal heat generation and prescribed heat flux at the boundary for a plane wall and a cylinder. The equations are solved by splitting them into transient and steady-state components and then using separation of variables. This results in an ordinary differential equation for the interface that involves infinite series. The initial value problem is solved numerically, and solutions are compared to the previously published quasi-static solutions. We show that when the internal heat generation and the heat flux at the boundary are close in value to each other, the motion of the phase change front takes longer to reach steady-state than when the values are farther apart. As the difference between the internal heat generation and the heat flux increases, the transient solutions become more dominant and the numerical solution of the phase change front does not reach steady...
A nonlinear, first-order ordinary differential equation that involves Fourier-Bessel series terms... more A nonlinear, first-order ordinary differential equation that involves Fourier-Bessel series terms has been derived to model the time-dependent motion of the solid-liquid interface during melting and solidification of a material with constant internal heat generation in cylindrical coordinates. The model is valid for all Stefan numbers. One of the primary applications of this problem is for a nuclear fuel rod during meltdown. The numerical solutions to this differential equation are compared to the solutions of a previously derived model that was based on the quasi-steady approximation, which is valid only for Stefan numbers less than one. The model presented in this paper contains exponentially decaying terms in the form of Fourier-Bessel series for the temperature gradients in both the solid and liquid phases. The agreement between the two models is excellent in the low Stefan number regime. For higher Stefan numbers, where the quasi-steady model is not accurate, the new model diff...
The principal purpose of this study is to understand the entropy generation rate in bypass, trans... more The principal purpose of this study is to understand the entropy generation rate in bypass, transitional, boundary-layer flow better. The experimental work utilized particle image velocimetry (PIV) and particle tracking velocimetry (PTV) to measure flow along a flat plate. The flow past the flat plate was under the influence of a negligible “zero” pressure gradient, followed by the installation of an adverse pressure gradient. Further, the boundary layer flow was artificially tripped to turbulence (called “bypass” transition) by means of elevated freestream turbulence. The entropy generation rate was seen to behave similar to that of published computational fluid dynamics (CFD) and direct numerical simulation (DNS) results. The observations from this work show the relative decrease of viscous contributions to entropy generation rate through the transition process, while the turbulent contributions of entropy generation rate greatly increase through the same transitional flow. A basi...
This paper gives results of an experimental study to determine the effect that a surface reaction... more This paper gives results of an experimental study to determine the effect that a surface reaction has on a boundary layer flow. An innovative technique has been developed to visualize the effect a surface reaction has on a flat plate boundary layer flow. A mixture of mineral oil and hexanoic acid flowed at low Reynolds number over a metal plate embedded with a small piece of sodium. The reaction between the hexanoic acid and the sodium metal produced hydrogen bubbles, which rose to the surface. Upstream of the reaction, dye was injected into the laminar flow, and the interaction between the bubbles and the dye was recorded. Results show that bubble entrainment stretch and bend the dye filaments, convect fluid away from the reaction, and create vortices downstream and to the sides of the reaction. These results show that a surface reaction can introduce velocity fluctuations into an otherwise laminar flow. Farther downstream the flow relaminarizes.
There have been significant efforts by the heat transfer community to investigate the melting phe... more There have been significant efforts by the heat transfer community to investigate the melting phenomenon of materials. These efforts have included the analytical development of equations to represent melting, numerical development of computer codes to assist in modeling the phenomena, and collection of experimental data. The understanding of the melting phenomenon has application in several areas of interest, for example, the melting of a Phase Change Material (PCM) used as a thermal storage medium as well as the melting of the fuel bundle in a nuclear power plant during an accident scenario. The objective of this research is two-fold. First a numerical investigation, using computational fluid dynamics (CFD), of melting with internal heat generation for a vertical cylindrical geometry is presented. Second, to the best of authors knowledge, there are very limited number of engineering experimental results available for the case of melting with Internal Heat Generation (IHG). An exper...
The Stefan problem with internal heat generation can be found in various industrial applications.... more The Stefan problem with internal heat generation can be found in various industrial applications. In particular, this problem describes melting of nuclear fuel rods during a reactor emergency. The present study reports on numerical modeling of the heat conduction equation and the Stefan equation with an application of the method of catching of the front into a space grid node. To solve numerically the heat conduction equation we realized an implicit four-node scheme using the Thomas method and iteration procedure.
We study the evolution of the solid-liquid interface during melting and solidification of a mater... more We study the evolution of the solid-liquid interface during melting and solidification of a material with constant internal heat generation and prescribed heat flux at the boundary for a plane wall and a cylinder. The equations are solved by splitting them into transient and steady-state components and then using separation of variables. This results in an ordinary differential equation for the interface that involves infinite series. The initial value problem is solved numerically, and solutions are compared to the previously published quasi-static solutions. We show that when the internal heat generation and the heat flux at the boundary are close in value to each other, the motion of the phase change front takes longer to reach steady-state than when the values are farther apart. As the difference between the internal heat generation and the heat flux increases, the transient solutions become more dominant and the numerical solution of the phase change front does not reach steady...
A nonlinear, first-order ordinary differential equation that involves Fourier-Bessel series terms... more A nonlinear, first-order ordinary differential equation that involves Fourier-Bessel series terms has been derived to model the time-dependent motion of the solid-liquid interface during melting and solidification of a material with constant internal heat generation in cylindrical coordinates. The model is valid for all Stefan numbers. One of the primary applications of this problem is for a nuclear fuel rod during meltdown. The numerical solutions to this differential equation are compared to the solutions of a previously derived model that was based on the quasi-steady approximation, which is valid only for Stefan numbers less than one. The model presented in this paper contains exponentially decaying terms in the form of Fourier-Bessel series for the temperature gradients in both the solid and liquid phases. The agreement between the two models is excellent in the low Stefan number regime. For higher Stefan numbers, where the quasi-steady model is not accurate, the new model diff...
The principal purpose of this study is to understand the entropy generation rate in bypass, trans... more The principal purpose of this study is to understand the entropy generation rate in bypass, transitional, boundary-layer flow better. The experimental work utilized particle image velocimetry (PIV) and particle tracking velocimetry (PTV) to measure flow along a flat plate. The flow past the flat plate was under the influence of a negligible “zero” pressure gradient, followed by the installation of an adverse pressure gradient. Further, the boundary layer flow was artificially tripped to turbulence (called “bypass” transition) by means of elevated freestream turbulence. The entropy generation rate was seen to behave similar to that of published computational fluid dynamics (CFD) and direct numerical simulation (DNS) results. The observations from this work show the relative decrease of viscous contributions to entropy generation rate through the transition process, while the turbulent contributions of entropy generation rate greatly increase through the same transitional flow. A basi...
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Papers by John Crepeau