Two-phase combustion problems involving hydrocarbons and oxygen, or air, represent a very complic... more Two-phase combustion problems involving hydrocarbons and oxygen, or air, represent a very complicated research topic. This is due to the co-existence of several complex physical phenomena, each with its own length and time scale that is yet to be studied and understood. In this paper, a computational model suitable for dense sprays is suggested to initiate further research in this area. An Eulerian-Eulerian formulation for conservation equations in both phases is proposed. The model couples the gas and liquid phases by mixing, evaporation, and combustion via the source terms that appear in conservation equations. The combustion model is described through a multi-step finite rate chemical kinetics approach, which is fully coupled to the flowfield to describe species mass fraction, production/destruction, and the subsequent gas phase properties. The discretization method is based on the Total Variation Diminishing (TVD) scheme, which is accurate, robust and very efficient. TVD is capa...
International Journal of Numerical Methods for Heat & Fluid Flow, Jun 1, 2006
PurposeTo address the effects of velocity profile at the discharge air grille (DAG) on the amount... more PurposeTo address the effects of velocity profile at the discharge air grille (DAG) on the amount of entrained air into an open refrigerated display case (ORDC).Design/methodology/approachThe performance of an ORDC was studied by CFD, DPIV and LDV. The actual measured velocity profile at the DAG and total flow rate of the display case at its nominal operating conditions are used as guidelines throughout the CFD modeling.FindingsIt was found that a skewed parabolic profile with the peak shifted towards the inner section of the case generates the minimum entrainment and demonstrates that with simple changes to the geometry of the DAG, a significant reduction in the entrainment rate could be achieved.Research limitations/implicationsThis study finds the optimum infiltration rate of a manufactured ORDC. A fundamental study is currently being done to address all the effective parameters that can affect the infiltration rate of any ORDCs.Originality/valueThis paper presents this fact that the velocity profile at the DAG has a significant impact on the infiltration rate and electricity consumption of ORDCs. In turn, the velocity profile is dependent on the geometry and shape of the air passage before DAG. Thus, the analysis of the effect of the geometry on the velocity should seriously be taken into consideration by the case manufacturers.
Air curtains in open refrigerated vertical display cases are designed for creating an invisible b... more Air curtains in open refrigerated vertical display cases are designed for creating an invisible barrier between the cold air inside and the warm air outside of the case. A modular display case is built to allow the variation of flow and geometrical parameters. This unit is used 1) to directly measure the infiltration rate as a function of all of these parameters by using a tracer gas, and 2) to understand the fluid dynamics of the air curtain, by using Particle Image Velocimetry (PlY) technique. Based on this study, an artificial neural network (ANN) program was developed that assisted the researchers in specifying those flow parameters and geometrical configurations that minimized the infiltration rate, and the cooling load thereafter. A display case, based on these design specifications, was fabricated and tested. A 13 percent reduction in the infiltration rate was produced which translates into $200 M savings, and approximately 0.5 M tons of reduction in green house gases in the United States. The temperature of the food was also monitored, and in all cases met the Food and Drug Administration (FDA) requirements. The research also indicated a potential additional 13-15 percent- improvement in savings
ABSTRACT After depositing a wetting liquid onto a porous medium surface, and under the influence ... more ABSTRACT After depositing a wetting liquid onto a porous medium surface, and under the influence of the capillary pressure, the liquid is imbibed into porous medium creating a wetted imprint. The flow within the porous medium does not cease once all liquid is imbibed, but it continues as a secondary capillary flow, where the liquid flows from large pores into small pores along the liquid interface. The flow is solved using the capillary network model, and influence of the boundary condition on the liquid distribution within porous medium is investigated. The porous medium boundaries can be defined as open or closed boundaries, where an open boundary is treated as a part of the liquid interface. In contrast, the closed boundary is defined as a static entity, in which the potential condition for flow to take place is never satisfied. By defining the porous medium boundaries as open or closed, one is able to obtain a very different liquid distribution within the porous medium. The liquid saturation profiles along the principal flow direction ranging from constant, to steadily decreasing, to the profile with a local maximum, are found numerically. Finally, it is shown that these saturation profiles are also related to the geometrical dimension that is perpendicular to the pertinent boundary, and changing the boundary type from open to closed allows the liquid distribution within porous medium to be controlled.
Journal of the Acoustical Society of America, Feb 1, 1999
The effect of the leading and trailing edge geometries on the production of tones associated with... more The effect of the leading and trailing edge geometries on the production of tones associated with the flow of low-speed subsonic air over a cavity were investigated experimentally and numerically. The leading edge geometries considered in the study included an overhang (simulating car door gaps) and an overhang with delta tabs such as used to control jet noise. The trailing edge geometries used in the investigations included sloped and rounded impingement regions. The numerical results documented the periodic fluctuations of the transverse velocity, pressure, and density of the shear layer and the resulting cavity pressures. The periodic vortex behavior in the cavity mouth and impingement region was also studied numerically to predict possible configurations for sound suppression. Experimental investigations of the cavity sound-pressure levels were used to determine the validity of the numerical simulations and the predicted cavity configurations for sound suppression.
It is evident that improvements in performance of refrigerated units (cabinets, display cases, et... more It is evident that improvements in performance of refrigerated units (cabinets, display cases, etc.) is becoming a necessity. Some of these improvements are focused on the hardware involving the compressor, evaporator, lighting design and heat transfer of such units. However, additional gains in the performance of refrigerated cabinets can be achieved by altering the airflow pattern and characteristics inside (or outside) these cabinets. This chapter summarizes ongoing research on this, to demonstrate the application of a hybrid approach which combines computational fluid dynamics (CFD) and experimental methods to understand and map the airflow pattern and characteristics. The main focus is on open vertical refrigerated display cases (OVRDCs). The chapter discusses the infiltration rate in OVRDCs by using hybrid CFD and experimental tools. CFD provides detailed local information about the fluid flow, giving insight into ways to alter a design for better performance
To create a system that can greatly enhance the ability to predict the outcome of a chemical atta... more To create a system that can greatly enhance the ability to predict the outcome of a chemical attack event in terms of the existing level of an agent’s concentratio
Two-phase combustion problems involving hydrocarbons and oxygen, or air, represent a very complic... more Two-phase combustion problems involving hydrocarbons and oxygen, or air, represent a very complicated research topic. This is due to the co-existence of several complex physical phenomena, each with its own length and time scale that is yet to be studied and understood. In this paper, a computational model suitable for dense sprays is suggested to initiate further research in this area. An Eulerian-Eulerian formulation for conservation equations in both phases is proposed. The model couples the gas and liquid phases by mixing, evaporation, and combustion via the source terms that appear in conservation equations. The combustion model is described through a multi-step finite rate chemical kinetics approach, which is fully coupled to the flowfield to describe species mass fraction, production/destruction, and the subsequent gas phase properties. The discretization method is based on the Total Variation Diminishing (TVD) scheme, which is accurate, robust and very efficient. TVD is capa...
International Journal of Numerical Methods for Heat & Fluid Flow, Jun 1, 2006
PurposeTo address the effects of velocity profile at the discharge air grille (DAG) on the amount... more PurposeTo address the effects of velocity profile at the discharge air grille (DAG) on the amount of entrained air into an open refrigerated display case (ORDC).Design/methodology/approachThe performance of an ORDC was studied by CFD, DPIV and LDV. The actual measured velocity profile at the DAG and total flow rate of the display case at its nominal operating conditions are used as guidelines throughout the CFD modeling.FindingsIt was found that a skewed parabolic profile with the peak shifted towards the inner section of the case generates the minimum entrainment and demonstrates that with simple changes to the geometry of the DAG, a significant reduction in the entrainment rate could be achieved.Research limitations/implicationsThis study finds the optimum infiltration rate of a manufactured ORDC. A fundamental study is currently being done to address all the effective parameters that can affect the infiltration rate of any ORDCs.Originality/valueThis paper presents this fact that the velocity profile at the DAG has a significant impact on the infiltration rate and electricity consumption of ORDCs. In turn, the velocity profile is dependent on the geometry and shape of the air passage before DAG. Thus, the analysis of the effect of the geometry on the velocity should seriously be taken into consideration by the case manufacturers.
Air curtains in open refrigerated vertical display cases are designed for creating an invisible b... more Air curtains in open refrigerated vertical display cases are designed for creating an invisible barrier between the cold air inside and the warm air outside of the case. A modular display case is built to allow the variation of flow and geometrical parameters. This unit is used 1) to directly measure the infiltration rate as a function of all of these parameters by using a tracer gas, and 2) to understand the fluid dynamics of the air curtain, by using Particle Image Velocimetry (PlY) technique. Based on this study, an artificial neural network (ANN) program was developed that assisted the researchers in specifying those flow parameters and geometrical configurations that minimized the infiltration rate, and the cooling load thereafter. A display case, based on these design specifications, was fabricated and tested. A 13 percent reduction in the infiltration rate was produced which translates into $200 M savings, and approximately 0.5 M tons of reduction in green house gases in the United States. The temperature of the food was also monitored, and in all cases met the Food and Drug Administration (FDA) requirements. The research also indicated a potential additional 13-15 percent- improvement in savings
ABSTRACT After depositing a wetting liquid onto a porous medium surface, and under the influence ... more ABSTRACT After depositing a wetting liquid onto a porous medium surface, and under the influence of the capillary pressure, the liquid is imbibed into porous medium creating a wetted imprint. The flow within the porous medium does not cease once all liquid is imbibed, but it continues as a secondary capillary flow, where the liquid flows from large pores into small pores along the liquid interface. The flow is solved using the capillary network model, and influence of the boundary condition on the liquid distribution within porous medium is investigated. The porous medium boundaries can be defined as open or closed boundaries, where an open boundary is treated as a part of the liquid interface. In contrast, the closed boundary is defined as a static entity, in which the potential condition for flow to take place is never satisfied. By defining the porous medium boundaries as open or closed, one is able to obtain a very different liquid distribution within the porous medium. The liquid saturation profiles along the principal flow direction ranging from constant, to steadily decreasing, to the profile with a local maximum, are found numerically. Finally, it is shown that these saturation profiles are also related to the geometrical dimension that is perpendicular to the pertinent boundary, and changing the boundary type from open to closed allows the liquid distribution within porous medium to be controlled.
Journal of the Acoustical Society of America, Feb 1, 1999
The effect of the leading and trailing edge geometries on the production of tones associated with... more The effect of the leading and trailing edge geometries on the production of tones associated with the flow of low-speed subsonic air over a cavity were investigated experimentally and numerically. The leading edge geometries considered in the study included an overhang (simulating car door gaps) and an overhang with delta tabs such as used to control jet noise. The trailing edge geometries used in the investigations included sloped and rounded impingement regions. The numerical results documented the periodic fluctuations of the transverse velocity, pressure, and density of the shear layer and the resulting cavity pressures. The periodic vortex behavior in the cavity mouth and impingement region was also studied numerically to predict possible configurations for sound suppression. Experimental investigations of the cavity sound-pressure levels were used to determine the validity of the numerical simulations and the predicted cavity configurations for sound suppression.
It is evident that improvements in performance of refrigerated units (cabinets, display cases, et... more It is evident that improvements in performance of refrigerated units (cabinets, display cases, etc.) is becoming a necessity. Some of these improvements are focused on the hardware involving the compressor, evaporator, lighting design and heat transfer of such units. However, additional gains in the performance of refrigerated cabinets can be achieved by altering the airflow pattern and characteristics inside (or outside) these cabinets. This chapter summarizes ongoing research on this, to demonstrate the application of a hybrid approach which combines computational fluid dynamics (CFD) and experimental methods to understand and map the airflow pattern and characteristics. The main focus is on open vertical refrigerated display cases (OVRDCs). The chapter discusses the infiltration rate in OVRDCs by using hybrid CFD and experimental tools. CFD provides detailed local information about the fluid flow, giving insight into ways to alter a design for better performance
To create a system that can greatly enhance the ability to predict the outcome of a chemical atta... more To create a system that can greatly enhance the ability to predict the outcome of a chemical attack event in terms of the existing level of an agent’s concentratio
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Papers by Homayun Navaz