A. Horimek - Academia.edu (original) (raw)

Papers by A. Horimek

Research paper thumbnail of Natural Convection Cooling of a Heat Source Placed at the Bottom of a Square Cavity. Effect of Source Length, Position, Thermal Condition and Prandtl Number

International Journal of Heat and Technology, 2020

Cooling process of a heat source placed at the bottom side of a cold-walled cavity (TC) by means ... more Cooling process of a heat source placed at the bottom side of a cold-walled cavity (TC) by means of natural convection has been studied numerically in this work. Two thermal conditions have been assumed at the source (q-imposed or T-imposed). The effects of Rayleigh number (Ra=10+3→10+6), source length (SL=0.1→1.0), source position (D) compared to left side, in addition to the effect of the number of Prandtl (Pr=0.71→10+2) were analyzed with ample details. For a source at the center of the bottom side, results showed an increase of flow and temperature disturbance with increasing Ra and/or SL, with an enhancement of both local and mean Nusselt numbers. Particular exceptions were noticed for high Ra values for the second heating type. For all considerations, the case of SL=0.1 makes an exception where a very good heat exchange rate is recorded. When the source is no longer centered, Clearer difference between this case and the previous one was recorded, especially for small D values....

Research paper thumbnail of Laminar Forced Convection of a Pseudoplastic Thermo dependent Fluid in an Annular Horizontal Duct

Arab Gulf Journal of Scientific Research

In this work, the problem of thermal development for laminar forced convection of a pseudoplastic... more In this work, the problem of thermal development for laminar forced convection of a pseudoplastic thermo dependent fluid in a concentric annular horizontal duct is numerically addressed. Three thermal conditions are assumed: inner cylinder subjected to an imposed heat flux while the outer is insulated; then the inverse; and finally both cylinders are heated with the same heat flux densities. All computations are carried out from the entrance up to the thermal fully developed stage for a flow already developed dynamically. The study objective is to illustrate the effects of the rheological index (n), aspect ratio (r1), thermodependency (Pn) and heating mode on velocity profiles and Nusselt number evolution in addition to thermal entrance length. The results show an improvement in heat exchange with the shear-thinning of the fluid. The outer Nusselt decreases as r1 decreases while the inner one improves. Overall, the thermodependency has a similar effect to that of the shear-thinning....

Research paper thumbnail of Laminar Flow for a Newtonian Thermodependent Fluid in an Eccentric Horizontal Annulus

This work focused on the numerical study of forced convection, for a thermodependent Newtonian fl... more This work focused on the numerical study of forced convection, for a thermodependent Newtonian fluid in an eccentric horizontal annular duct. The inner and outer cylinders were heated with constant heat flux. The governing equations were solved numerically by a finite difference method with implicit scheme. The dynamic profile was assumed to be fully developed while the temperature profile was assumed uniform at the entrance. The aim of this work was to present the effects of eccentricity on the dynamic and thermal fields along the duct. The thermodependency effect of the fluid was also examined, and some interesting results regarding the reduction of the dynamic blocking phenomenon of the flow in the narrow part of the duct for large eccentricities were presented. These results reduce the strictness of precautions for neglecting axial diffusion when making computations in such geometries.

Research paper thumbnail of Laminar mixed convection in an eccentric annular horizontal duct for a thermodependent non-Newtonian fluid

International Journal of Heat and Mass Transfer, 2011

The present work focuses on the study of mixed convection of a purely viscous shear-thinning flui... more The present work focuses on the study of mixed convection of a purely viscous shear-thinning fluid in a horizontal annular eccentric duct. The inner and outer cylinders are heated with constant and uniform heat flux densities. The objective of this work is to study the effect of the variation of eccentricity, rheological behavior of the fluid as well as the thermodependency of the rheological parameters on the reorganization of the flow and thermal stratification caused by the buoyancy forces. At the entrance of the heating zone, the dynamic regime is assumed to be established and the temperature profile uniform. The conservation equations are solved numerically using a finite difference method with implicit schemes. A secondary azimuthal flow, induced by natural convection, develops downstream of the inlet section. This flow creates a stratification of the thermal field on a given section of the duct, which intensifies downstream from the entrance. On the other hand, the decrease in consistency with increasing temperature near the heated walls produces a centrifugal radial flow towards the walls. The presence of an eccentricity induces in turn a significant effect on the main dynamic field and the stratification of the thermal field. Two cases of upward and downward eccentricity are treated. These show that an upward shift increases the stratification of the thermal field, while the stratification begins to weaken from a certain amount of eccentricity in the case of downward shift. This represents an important result in terms of possible industrial applications. We may indeed conclude that an appropriate choice of downward eccentricity can reduce the thermal stratification, observed experimentally in the case of a concentric heated annular duct [1], when this stratification is undesirable. The choice of this eccentricity depends on rheological and thermal properties of the fluid.

Research paper thumbnail of Laminar Forced Convection of a Pseudoplastic Thermodependent Fluid in an Annular Horizontal Duct

Arab GulfJournal of Scientific Research, 2015

In this work, the problem of thermal development for laminar forced convection of a pseudoplastic... more In this work, the problem of thermal development for laminar forced convection of a pseudoplastic thermodependent fluid in a concentric annular horizontal duct is numerically addressed. Three thermal conditions are assumed: inner cylinder subjected to an imposed
heat flux while the outer is insulated; then the inverse; and finally both cylinders are heated with the same heat flux densities. All computations are carried out from the entrance up to the thermal fully developed stage for a flow already developed dynamically.The study objective is to illustrate the effects of the rheological index (n), aspect ratio (r1), thermodependency (Pn) and heating mode on velocity profiles and Nusselt number evolution in addition to thermal entrance length. The results show an improvement in heat exchange with the shear-thinning of the fluid. The outer Nusselt decreases as r1 decreases while the inner one improves. Overall, the thermodependency has a similar effect to that of the shear-thinning. A very important result shows the reduction in thermal length with increasing n and/or Pn. Simple, accurate and widely valid correlations are provided for Nusselt number and thermal entrance length under different conditions.

Research paper thumbnail of Natural Convection Cooling of a Heat Source Placed at the Bottom of a Square Cavity. Effect of Source Length, Position, Thermal Condition and Prandtl Number

International Journal of Heat and Technology, 2020

Cooling process of a heat source placed at the bottom side of a cold-walled cavity (TC) by means ... more Cooling process of a heat source placed at the bottom side of a cold-walled cavity (TC) by means of natural convection has been studied numerically in this work. Two thermal conditions have been assumed at the source (q-imposed or T-imposed). The effects of Rayleigh number (Ra=10+3→10+6), source length (SL=0.1→1.0), source position (D) compared to left side, in addition to the effect of the number of Prandtl (Pr=0.71→10+2) were analyzed with ample details. For a source at the center of the bottom side, results showed an increase of flow and temperature disturbance with increasing Ra and/or SL, with an enhancement of both local and mean Nusselt numbers. Particular exceptions were noticed for high Ra values for the second heating type. For all considerations, the case of SL=0.1 makes an exception where a very good heat exchange rate is recorded. When the source is no longer centered, Clearer difference between this case and the previous one was recorded, especially for small D values....

Research paper thumbnail of Laminar Forced Convection of a Pseudoplastic Thermo dependent Fluid in an Annular Horizontal Duct

Arab Gulf Journal of Scientific Research

In this work, the problem of thermal development for laminar forced convection of a pseudoplastic... more In this work, the problem of thermal development for laminar forced convection of a pseudoplastic thermo dependent fluid in a concentric annular horizontal duct is numerically addressed. Three thermal conditions are assumed: inner cylinder subjected to an imposed heat flux while the outer is insulated; then the inverse; and finally both cylinders are heated with the same heat flux densities. All computations are carried out from the entrance up to the thermal fully developed stage for a flow already developed dynamically. The study objective is to illustrate the effects of the rheological index (n), aspect ratio (r1), thermodependency (Pn) and heating mode on velocity profiles and Nusselt number evolution in addition to thermal entrance length. The results show an improvement in heat exchange with the shear-thinning of the fluid. The outer Nusselt decreases as r1 decreases while the inner one improves. Overall, the thermodependency has a similar effect to that of the shear-thinning....

Research paper thumbnail of Laminar Flow for a Newtonian Thermodependent Fluid in an Eccentric Horizontal Annulus

This work focused on the numerical study of forced convection, for a thermodependent Newtonian fl... more This work focused on the numerical study of forced convection, for a thermodependent Newtonian fluid in an eccentric horizontal annular duct. The inner and outer cylinders were heated with constant heat flux. The governing equations were solved numerically by a finite difference method with implicit scheme. The dynamic profile was assumed to be fully developed while the temperature profile was assumed uniform at the entrance. The aim of this work was to present the effects of eccentricity on the dynamic and thermal fields along the duct. The thermodependency effect of the fluid was also examined, and some interesting results regarding the reduction of the dynamic blocking phenomenon of the flow in the narrow part of the duct for large eccentricities were presented. These results reduce the strictness of precautions for neglecting axial diffusion when making computations in such geometries.

Research paper thumbnail of Laminar mixed convection in an eccentric annular horizontal duct for a thermodependent non-Newtonian fluid

International Journal of Heat and Mass Transfer, 2011

The present work focuses on the study of mixed convection of a purely viscous shear-thinning flui... more The present work focuses on the study of mixed convection of a purely viscous shear-thinning fluid in a horizontal annular eccentric duct. The inner and outer cylinders are heated with constant and uniform heat flux densities. The objective of this work is to study the effect of the variation of eccentricity, rheological behavior of the fluid as well as the thermodependency of the rheological parameters on the reorganization of the flow and thermal stratification caused by the buoyancy forces. At the entrance of the heating zone, the dynamic regime is assumed to be established and the temperature profile uniform. The conservation equations are solved numerically using a finite difference method with implicit schemes. A secondary azimuthal flow, induced by natural convection, develops downstream of the inlet section. This flow creates a stratification of the thermal field on a given section of the duct, which intensifies downstream from the entrance. On the other hand, the decrease in consistency with increasing temperature near the heated walls produces a centrifugal radial flow towards the walls. The presence of an eccentricity induces in turn a significant effect on the main dynamic field and the stratification of the thermal field. Two cases of upward and downward eccentricity are treated. These show that an upward shift increases the stratification of the thermal field, while the stratification begins to weaken from a certain amount of eccentricity in the case of downward shift. This represents an important result in terms of possible industrial applications. We may indeed conclude that an appropriate choice of downward eccentricity can reduce the thermal stratification, observed experimentally in the case of a concentric heated annular duct [1], when this stratification is undesirable. The choice of this eccentricity depends on rheological and thermal properties of the fluid.

Research paper thumbnail of Laminar Forced Convection of a Pseudoplastic Thermodependent Fluid in an Annular Horizontal Duct

Arab GulfJournal of Scientific Research, 2015

In this work, the problem of thermal development for laminar forced convection of a pseudoplastic... more In this work, the problem of thermal development for laminar forced convection of a pseudoplastic thermodependent fluid in a concentric annular horizontal duct is numerically addressed. Three thermal conditions are assumed: inner cylinder subjected to an imposed
heat flux while the outer is insulated; then the inverse; and finally both cylinders are heated with the same heat flux densities. All computations are carried out from the entrance up to the thermal fully developed stage for a flow already developed dynamically.The study objective is to illustrate the effects of the rheological index (n), aspect ratio (r1), thermodependency (Pn) and heating mode on velocity profiles and Nusselt number evolution in addition to thermal entrance length. The results show an improvement in heat exchange with the shear-thinning of the fluid. The outer Nusselt decreases as r1 decreases while the inner one improves. Overall, the thermodependency has a similar effect to that of the shear-thinning. A very important result shows the reduction in thermal length with increasing n and/or Pn. Simple, accurate and widely valid correlations are provided for Nusselt number and thermal entrance length under different conditions.