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Titre : Investigation des échanges convectifs dans diverses configurations Type de document : texte imprimé Auteurs : Issam Rezaiguia, Auteur ; Mahfoud Kadja, Directeur de thèse Editeur : constantine [Algérie] : Université Constantine 1 Année de publication : 2014 Importance : 142 f. Format : 30 cm. Note générale : 2 copies imprimées disponibles
Langues : Français (fre) Catégories : Français - Anglais
Génie MécaniqueTags : convection naturelle nanofluides cavité triangulaire angle d'inclinaison simulation numérique microcanaux chute de pression transfert thermique conjugué fraction solide comportement non-Newtonien natural convection nanofluids triangular cavity inclination angle numerical simulation microchannels pressure drop conjugate heat transfer solid fraction non-Newtonian behavior الحمل الحراري الطبيعي مائع نانوي تجويف ثلاثي الشكل زاوية الميل محاكاة العددية قنوات ميكروية هبوط الضغط نقل الحرارة نسب الحيود للذرات الصلبة سلوك غير نيوتوني Index. décimale : 620 Génie Mécanique Résumé : This thesis reports the results of two studies: the first one concerns natural convection in isosceles triangular cavities with a partially active base while the second one concerns heat transfer in microchannels.
The first study considers natural convection cooling of a heat source located on the bottom wall of an inclined isosceles triangular enclosure filled with a Cu water-nanofluid. The right and left walls of the enclosure are both maintained cold at constant equal temperatures, while the remaining parts of the bottom wall are insulated. The study has been carried out for a Rayleigh number in the range 104 ≤ Ra ≤ 106, for a heat source length in the range 0.2 ≤ ε ≤ 0.8, for a solid volume fraction in the range 0.0 ≤ � ≤ 06 and for an inclination angle in the range 00 ≤ δ ≤ 450. Results are presented in the form of streamline contours, isotherms, maximum temperature at the heat source surface and average Nusselt number. It is noticed that the addition of Cu nanoparticles enhances the heat transfer rate and therefore cooling effectiveness for all values of Rayleigh number, especially at low values of Ra. The effect of the inclination angle becomes more noticeable as one increases the value of Ra. For high Rayleigh numbers, a critical value for the inclination angle of δ = 150 is found for which the heat source maximum temperature is highest.
The second study investigates heat transfer in microchannels machined in heat dissipating sinks. The fluid used is a nanofluid whose properties are temperature dependent. The energy dissipation is evaluated for various solid fraction contents along with the cooling effectiveness of this modern type of heat exchangers. The shape of the channels is also investigated. The evaluation parameter used for thermal energy dissipation is the Nusselt number while that used for cooling effectiveness is the static pressure drop between the inlet and the outlet of the microchannel. Conjugate convection-conduction energy conservation equations have been solved along with mass and momentum conservation equations in order to determine these parameters.
The results obtained showed important heat transfer augmentation with solid fraction at the expense of an increased pressure drop, i.e high pumping cost (therefore low cooling effectiveness). The microchannel inlet section geometry was also found to contribute to the values of the Nusselt number and pressure drop. Among the tested geometries (elliptical, rectangular, trapezoidal) the rectangular section provided the best compromise between heat transfer augmentation and pumping cost. At the end of the study, a comparison was made between the results obtained by assuming Newtonian rheology and those obtained with non-Newtonian rheological behavior of the same nanofluid sample. It was found that the assumption of non-Newtonian rheological behavior of nanofluids gives higher Nusselt number values and much lower pressure drops.
Diplôme : Doctorat en sciences En ligne : ../theses/gmecanique/REZ6773.pdf Format de la ressource électronique : Permalink : https://bu.umc.edu.dz/md/index.php?lvl=notice_display&id=9837 Investigation des échanges convectifs dans diverses configurations [texte imprimé] / Issam Rezaiguia, Auteur ; Mahfoud Kadja, Directeur de thèse . - constantine [Algérie] : Université Constantine 1, 2014 . - 142 f. ; 30 cm.
2 copies imprimées disponibles
Langues : Français (fre)
Catégories : Français - Anglais
Génie MécaniqueTags : convection naturelle nanofluides cavité triangulaire angle d'inclinaison simulation numérique microcanaux chute de pression transfert thermique conjugué fraction solide comportement non-Newtonien natural convection nanofluids triangular cavity inclination angle numerical simulation microchannels pressure drop conjugate heat transfer solid fraction non-Newtonian behavior الحمل الحراري الطبيعي مائع نانوي تجويف ثلاثي الشكل زاوية الميل محاكاة العددية قنوات ميكروية هبوط الضغط نقل الحرارة نسب الحيود للذرات الصلبة سلوك غير نيوتوني Index. décimale : 620 Génie Mécanique Résumé : This thesis reports the results of two studies: the first one concerns natural convection in isosceles triangular cavities with a partially active base while the second one concerns heat transfer in microchannels.
The first study considers natural convection cooling of a heat source located on the bottom wall of an inclined isosceles triangular enclosure filled with a Cu water-nanofluid. The right and left walls of the enclosure are both maintained cold at constant equal temperatures, while the remaining parts of the bottom wall are insulated. The study has been carried out for a Rayleigh number in the range 104 ≤ Ra ≤ 106, for a heat source length in the range 0.2 ≤ ε ≤ 0.8, for a solid volume fraction in the range 0.0 ≤ � ≤ 06 and for an inclination angle in the range 00 ≤ δ ≤ 450. Results are presented in the form of streamline contours, isotherms, maximum temperature at the heat source surface and average Nusselt number. It is noticed that the addition of Cu nanoparticles enhances the heat transfer rate and therefore cooling effectiveness for all values of Rayleigh number, especially at low values of Ra. The effect of the inclination angle becomes more noticeable as one increases the value of Ra. For high Rayleigh numbers, a critical value for the inclination angle of δ = 150 is found for which the heat source maximum temperature is highest.
The second study investigates heat transfer in microchannels machined in heat dissipating sinks. The fluid used is a nanofluid whose properties are temperature dependent. The energy dissipation is evaluated for various solid fraction contents along with the cooling effectiveness of this modern type of heat exchangers. The shape of the channels is also investigated. The evaluation parameter used for thermal energy dissipation is the Nusselt number while that used for cooling effectiveness is the static pressure drop between the inlet and the outlet of the microchannel. Conjugate convection-conduction energy conservation equations have been solved along with mass and momentum conservation equations in order to determine these parameters.
The results obtained showed important heat transfer augmentation with solid fraction at the expense of an increased pressure drop, i.e high pumping cost (therefore low cooling effectiveness). The microchannel inlet section geometry was also found to contribute to the values of the Nusselt number and pressure drop. Among the tested geometries (elliptical, rectangular, trapezoidal) the rectangular section provided the best compromise between heat transfer augmentation and pumping cost. At the end of the study, a comparison was made between the results obtained by assuming Newtonian rheology and those obtained with non-Newtonian rheological behavior of the same nanofluid sample. It was found that the assumption of non-Newtonian rheological behavior of nanofluids gives higher Nusselt number values and much lower pressure drops.
Diplôme : Doctorat en sciences En ligne : ../theses/gmecanique/REZ6773.pdf Format de la ressource électronique : Permalink : https://bu.umc.edu.dz/md/index.php?lvl=notice_display&id=9837 Exemplaires (1)
Code-barres Cote Support Localisation Section Disponibilité REZ/6773 REZ/6773 Thèse Bibliothèque principale Thèses Disponible Approche numérique de la convection naturelle thermo-solutale dans une cavité rectangulaire poreuse saturée de fluide et à orientation variable. / Abdelhakim Latreche
Titre : Approche numérique de la convection naturelle thermo-solutale dans une cavité rectangulaire poreuse saturée de fluide et à orientation variable. Type de document : texte imprimé Auteurs : Abdelhakim Latreche, Auteur ; Mahfoud Djezzar, Directeur de thèse Editeur : جامعة الإخوة منتوري قسنطينة Année de publication : 2019 Importance : 101 f. Format : 30 cm. Note générale : 2 copies imprimées disponibles Langues : Français (fre) Catégories : Français - Anglais
PhysiqueTags : Physique Energétique: Photothermique Transfert de chaleur et de masse milieux poreux convection naturelle Double
diffusion modèle de Darcy-Brinkmann-Forchheimer volumes finis Heat and mass transfer porous media natural convection Double diffusion Darcy-Brinkmann-Forchheimer model finite volumes انتقال الحرارة والكتلة الوسائط المسامية الحمل الحراري الانتشار المزدوج نموذج دارسي
برينكمان-فورخايمر الحجوم المتناهيةIndex. décimale : 530 Physique Résumé :
In this thesis, heat and mass transfers by natural convection in porous media have been studied numerically. The horizontal walls are subjected to constant temperatures and impermeable to solute transport in the first case and at constant temperatures and
concentrations in the second case, while the vertical walls are thermally insulated and are subjected to constant concentrations in the first case, and are considered adiabatic in the second case. The phenomenon of thermo-solutal convection is governed by the conservation equations of mass, momentum, energy and concentration. The porous media are modeled according to the general model of Darcy and Darcy-Brinkman-Forchheimer respectively. The convective flow is governed by different control parameters, namely the angle of inclination (α ), the Rayleigh number (Ra), the ratio of the forces of volume (N), the number of Prandtl (Pr),the number of Lewis (Le), the Darcy number (Da) the form factor (A) and the porosity ε of the porous matrix. The finite volume method was used to solve the basic equations in porous media. Regarding the validation of the calculation code, the agreement obtained between our results and those available in the literature proved to be excellent. The influence of physical and geometrical parameters is examined. In the first case, five solutions characterized by multicellular and single-cell clockwise / counterclockwise, natural / antinatural flows were obtained in the case of the intermediate regime with the variation of the inclination, the structure of the flow intensifies and the transfers of Heat and average mass increase as │N│ increases. In the second case, two solutions characterized by multicellular (-90° ≤α≤0°) and single-cell trigonometric (0°<α≤90°) flows were obtained, the intensity of the flow decreases with increasing of α in both directions, while there was an increase in heat transfer and mass up to inclination 45° and 60° respectively. The structure of the flow intensifies and the average heat and mass transfers increase with the increase of N, Ra and A while the contrary has been found with Le except the mass transfer which keeps its increase.
Diplôme : Doctorat en sciences En ligne : ../theses/physique/LAT7514.pdf Format de la ressource électronique : Permalink : https://bu.umc.edu.dz/md/index.php?lvl=notice_display&id=11353 Approche numérique de la convection naturelle thermo-solutale dans une cavité rectangulaire poreuse saturée de fluide et à orientation variable. [texte imprimé] / Abdelhakim Latreche, Auteur ; Mahfoud Djezzar, Directeur de thèse . - جامعة الإخوة منتوري قسنطينة, 2019 . - 101 f. ; 30 cm.
2 copies imprimées disponibles
Langues : Français (fre)
Catégories : Français - Anglais
PhysiqueTags : Physique Energétique: Photothermique Transfert de chaleur et de masse milieux poreux convection naturelle Double
diffusion modèle de Darcy-Brinkmann-Forchheimer volumes finis Heat and mass transfer porous media natural convection Double diffusion Darcy-Brinkmann-Forchheimer model finite volumes انتقال الحرارة والكتلة الوسائط المسامية الحمل الحراري الانتشار المزدوج نموذج دارسي
برينكمان-فورخايمر الحجوم المتناهيةIndex. décimale : 530 Physique Résumé :
In this thesis, heat and mass transfers by natural convection in porous media have been studied numerically. The horizontal walls are subjected to constant temperatures and impermeable to solute transport in the first case and at constant temperatures and
concentrations in the second case, while the vertical walls are thermally insulated and are subjected to constant concentrations in the first case, and are considered adiabatic in the second case. The phenomenon of thermo-solutal convection is governed by the conservation equations of mass, momentum, energy and concentration. The porous media are modeled according to the general model of Darcy and Darcy-Brinkman-Forchheimer respectively. The convective flow is governed by different control parameters, namely the angle of inclination (α ), the Rayleigh number (Ra), the ratio of the forces of volume (N), the number of Prandtl (Pr),the number of Lewis (Le), the Darcy number (Da) the form factor (A) and the porosity ε of the porous matrix. The finite volume method was used to solve the basic equations in porous media. Regarding the validation of the calculation code, the agreement obtained between our results and those available in the literature proved to be excellent. The influence of physical and geometrical parameters is examined. In the first case, five solutions characterized by multicellular and single-cell clockwise / counterclockwise, natural / antinatural flows were obtained in the case of the intermediate regime with the variation of the inclination, the structure of the flow intensifies and the transfers of Heat and average mass increase as │N│ increases. In the second case, two solutions characterized by multicellular (-90° ≤α≤0°) and single-cell trigonometric (0°<α≤90°) flows were obtained, the intensity of the flow decreases with increasing of α in both directions, while there was an increase in heat transfer and mass up to inclination 45° and 60° respectively. The structure of the flow intensifies and the average heat and mass transfers increase with the increase of N, Ra and A while the contrary has been found with Le except the mass transfer which keeps its increase.
Diplôme : Doctorat en sciences En ligne : ../theses/physique/LAT7514.pdf Format de la ressource électronique : Permalink : https://bu.umc.edu.dz/md/index.php?lvl=notice_display&id=11353 Exemplaires (1)
Code-barres Cote Support Localisation Section Disponibilité LAT/7514 LAT/7514 Thèse Bibliothèque principale Thèses Disponible
Titre : Transfert convectif dans une cavité totalement ou partiellement occupée par une matrice poreuse en ETL ou HETL Type de document : texte imprimé Auteurs : Abderrahim Bourouis, Auteur ; Abdeslam Omara, Auteur Editeur : جامعة الإخوة منتوري قسنطينة Année de publication : 2016 Importance : 131 f. Format : 30 cm. Note générale : 2 copies imprimées disponibles
Langues : Français (fre) Catégories : Français - Anglais
PhysiqueTags : Physique Energétique Convection Mixte Conjuguée Convection Naturelle Milieu Poreux Hors Équilibre Thermique Local Phase Solide Phase Fluide Volumes Finis Conjugate Mixed Convection Natural Convection Porous Medium Local Thermal non Equilibrium Solid Phase Fluid Phase Finite-Volume Method حمل حراري مختلط حمل حراري طبیعي وسط مسامي عدم التوازن الحراري الموضعي طور مائع طور صلب الحجوم المنتھیة Index. décimale : 530 Physique Résumé : In this work, a numerical study of convective heat transfer in confined fluid and porous media was considered. The fluid flow is governed by the Navier–Stokes equations in the fluid region whereas the Darcy–Brinkman–Forchheimer model in the porous region. The finite volume method is used in order to discrete the governing equations, and the SIMPLE algorithm is used to treat the coupling pressure-velocity.
Initially, the first application is to examine the effects of the Richardson number (Ri = 0.1, 1, 10) and thermal conductivity ratio (Rk = 0.1, 1, 10, 100) on the heat transfer by conjugate mixed convection and conduction in a lid-driven enclosure with thick vertical porous layer. The left vertical moving wall of enclosure takes two different directions, (upward or downward moving wall). In this study, the compression of isotherms in the porous layer is observed at low conductivity ratio, while at large conductivity ratio, isotherms span the fluid filled part of the enclosure. It is also observed that average Nusselt numbers along the right hot wall and along the fluid-porous layer interface tend to zero at large and low thermal conductivity ratio, respectively.
For the second application, we have considered a thermal non-equilibrium approach on
natural convection in a square porous cavity with partial active vertical walls. Depending on the location of hot part and cold part, respectively on the left and right side walls, two cases are considered: Upper-Lower and Lower-Upper active walls. The two equations model is used to take into account separately local temperatures of the fluid and the solid. The effect of the Rayleigh number, Darcy number, inter-phase heat transfer coefficient and modified conductivity ratio is examined. The obtained results reveal that the location of the hot and cold parts on the vertical side walls has a significant influence on the flow structure and the rate of heat transfer within the enclosure.
Diplôme : Doctorat en sciences En ligne : ../theses/physique/BOU6987.pdf Format de la ressource électronique : Permalink : https://bu.umc.edu.dz/md/index.php?lvl=notice_display&id=10407 Transfert convectif dans une cavité totalement ou partiellement occupée par une matrice poreuse en ETL ou HETL [texte imprimé] / Abderrahim Bourouis, Auteur ; Abdeslam Omara, Auteur . - جامعة الإخوة منتوري قسنطينة, 2016 . - 131 f. ; 30 cm.
2 copies imprimées disponibles
Langues : Français (fre)
Catégories : Français - Anglais
PhysiqueTags : Physique Energétique Convection Mixte Conjuguée Convection Naturelle Milieu Poreux Hors Équilibre Thermique Local Phase Solide Phase Fluide Volumes Finis Conjugate Mixed Convection Natural Convection Porous Medium Local Thermal non Equilibrium Solid Phase Fluid Phase Finite-Volume Method حمل حراري مختلط حمل حراري طبیعي وسط مسامي عدم التوازن الحراري الموضعي طور مائع طور صلب الحجوم المنتھیة Index. décimale : 530 Physique Résumé : In this work, a numerical study of convective heat transfer in confined fluid and porous media was considered. The fluid flow is governed by the Navier–Stokes equations in the fluid region whereas the Darcy–Brinkman–Forchheimer model in the porous region. The finite volume method is used in order to discrete the governing equations, and the SIMPLE algorithm is used to treat the coupling pressure-velocity.
Initially, the first application is to examine the effects of the Richardson number (Ri = 0.1, 1, 10) and thermal conductivity ratio (Rk = 0.1, 1, 10, 100) on the heat transfer by conjugate mixed convection and conduction in a lid-driven enclosure with thick vertical porous layer. The left vertical moving wall of enclosure takes two different directions, (upward or downward moving wall). In this study, the compression of isotherms in the porous layer is observed at low conductivity ratio, while at large conductivity ratio, isotherms span the fluid filled part of the enclosure. It is also observed that average Nusselt numbers along the right hot wall and along the fluid-porous layer interface tend to zero at large and low thermal conductivity ratio, respectively.
For the second application, we have considered a thermal non-equilibrium approach on
natural convection in a square porous cavity with partial active vertical walls. Depending on the location of hot part and cold part, respectively on the left and right side walls, two cases are considered: Upper-Lower and Lower-Upper active walls. The two equations model is used to take into account separately local temperatures of the fluid and the solid. The effect of the Rayleigh number, Darcy number, inter-phase heat transfer coefficient and modified conductivity ratio is examined. The obtained results reveal that the location of the hot and cold parts on the vertical side walls has a significant influence on the flow structure and the rate of heat transfer within the enclosure.
Diplôme : Doctorat en sciences En ligne : ../theses/physique/BOU6987.pdf Format de la ressource électronique : Permalink : https://bu.umc.edu.dz/md/index.php?lvl=notice_display&id=10407 Exemplaires (1)
Code-barres Cote Support Localisation Section Disponibilité BOU/6987 BOU/6987 Thèse Bibliothèque principale Thèses Disponible
Titre : Modélisation du transfert thermique par convection naturelle dans les géométries pratiques. Type de document : texte imprimé Auteurs : Mabrouk Guestal, Auteur ; Mahfoud Kadja, Directeur de thèse Editeur : جامعة الإخوة منتوري قسنطينة Année de publication : 2018 Importance : 240 f. Format : 30 cm. Note générale : 2 copies imprimées disponibles
Langues : Français (fre) Catégories : Français - Anglais
Génie MécaniqueTags : G. Mécanique: Énergétique Convection naturelle Convection naturelle tridimensionnelle Enceinte cylindrique horizontale Enceinte sphérique Chauffe-eau solaire chauffage partiel volumes finis Nanofluide Nanotubes Natural convection Three-dimensional natural convection Horizontal cylindrical enclosure Spherical enclosure Solar water heater partial heating Finite volume Nanofluid Nanotube الحمل الحراري الطبیعي الحمل الحراري الطبیعي ثلاثي الأبعاد حاویة أسطوانیة أفقیة حاویة كرویة سخان الماء الشمسي تسخین جزئي الحجوم المنتھیة سوائل النانو أنابیب النانو Index. décimale : 620 Génie Mécanique Résumé : The objective of this doctoral thesis is to study the thermal and dynamic structures of the flow resulting from natural convection heat transfer within different practical geometries, applying the most recent methods used to improve the heat transfer. For this reason, two studies on this subject have been carried out. In the first study, a numerical study was carried out on heat transfer by natural convection using two nanofluides inside a horizontal cylindrical enclosure with partial heating of its lower part at constant temperature or constant heat flux, the length of the heat source is changed from 5% to 25% of the total perimeter of the enclosure, the rest of the unheated parts of the bottom wall are considered as adiabatic, the two side parts of the enclosure are considered at a low constant temperature, each one of them has a length of 25% of the total perimeter of the enclosure, the top part of the enclosure is considered as adiabatic, it has a length of 25% of the total perimeter. To analyze the effect of using nanofluids with different particles volume fractions on heat transfer inside cylindrical horizontal enclosures, two nanofluids (Cu-water, TiO2-water) were used with volume fraction of nanoparticles being varied in the range of 0 corresponding to pure water) to 0.05. The steady state forms of Navier-Stokes equations and the equations of conservation of mass and energy in twodimensional cylindrical coordinates have been solved by the finite volume method and the SIMPLE algorithm was used for the pressure-velocity coupling. The Rayleigh number was varied in the interval 103 to 106. This research is characterized by a detailed analysis of the effect of changing both the Rayleigh number, the heated length and the value of nanoparticles volume fraction on the dynamic and thermal fields, on the percentage enhancement of the average Nusselt numbers, and also on the variation of the temperature and the vertical velocity component at the vertical and horizontal central lines of the enclosure. The results obtained were summarized in the form of correlation equations of the average Nusselt number as a function of the heated length, the Rayleigh number and volume fraction for both types of nanofluids. In the second study, a numerical study was carried out on the effect of using two techniques for the optimization of heat transfer by natural convection in a three-dimensional spherical enclosure of solar water heater. The outer wall (solar collector) is considered as a heated wall at a constant temperature, the wall which is located behind the solar collector is considered as adiabatic wall. In the enclosure there is a spiral tube, its wall is under a low temperature which increases linearly in terms of enclosure height. The first technique is to exploit nanotechnology using two types of nanofluids Cu-Water and CNT-Water, to improve the heat transfer in the enclosures of spherical solar water heaters, the volume fraction of nanoparticles was varied in the range of 0 (corresponding to pure water) to 0.05. The second technique involves making geometric modifications to the enclosure of spherical solar water heater to improve the natural convection heat transfer, these modifications consist in creating concentric annular orifices in the lower part of the internal adiabatic wall of the solar water heater, the number of annular orifices varies from 1 to 6. The Rayleigh number was varied in the interval 104 to 106. The steady state forms of Navier-Stokes equations and the equations of conservation of mass and energy in three-dimensional spherical coordinates have been solved by the finite volume method. The SIMPLE algorithm was used for the pressure-velocity coupling. This research is characterized by a detailed analysis of the effect of changing both the Rayleigh number, the number of annular orifices and the value of nanoparticles volume fraction on the dynamic and thermal fields and on the heat transfer and its percentage improvement. The results obtained were summarized in the form of correlation equations of the average Nusselt number as a function of the Rayleigh number, the number of annular orifices and the volume fraction of the nanofluid. Through the results obtained in all the studies carried out in the frame of this doctoral thesis, a very important theorem has been reached on the improvement of heat transfer by natural convection in enclosures. The application of this theorem can revolutionize the field of performance improvement of various thermal engineering systems whose operating principle depends on heat transfer by natural convection.
Note de contenu : Annexes. Diplôme : Doctorat en sciences En ligne : ../theses/gmecanique/GUE7495.pdf Format de la ressource électronique : Permalink : https://bu.umc.edu.dz/md/index.php?lvl=notice_display&id=11327 Modélisation du transfert thermique par convection naturelle dans les géométries pratiques. [texte imprimé] / Mabrouk Guestal, Auteur ; Mahfoud Kadja, Directeur de thèse . - جامعة الإخوة منتوري قسنطينة, 2018 . - 240 f. ; 30 cm.
2 copies imprimées disponibles
Langues : Français (fre)
Catégories : Français - Anglais
Génie MécaniqueTags : G. Mécanique: Énergétique Convection naturelle Convection naturelle tridimensionnelle Enceinte cylindrique horizontale Enceinte sphérique Chauffe-eau solaire chauffage partiel volumes finis Nanofluide Nanotubes Natural convection Three-dimensional natural convection Horizontal cylindrical enclosure Spherical enclosure Solar water heater partial heating Finite volume Nanofluid Nanotube الحمل الحراري الطبیعي الحمل الحراري الطبیعي ثلاثي الأبعاد حاویة أسطوانیة أفقیة حاویة كرویة سخان الماء الشمسي تسخین جزئي الحجوم المنتھیة سوائل النانو أنابیب النانو Index. décimale : 620 Génie Mécanique Résumé : The objective of this doctoral thesis is to study the thermal and dynamic structures of the flow resulting from natural convection heat transfer within different practical geometries, applying the most recent methods used to improve the heat transfer. For this reason, two studies on this subject have been carried out. In the first study, a numerical study was carried out on heat transfer by natural convection using two nanofluides inside a horizontal cylindrical enclosure with partial heating of its lower part at constant temperature or constant heat flux, the length of the heat source is changed from 5% to 25% of the total perimeter of the enclosure, the rest of the unheated parts of the bottom wall are considered as adiabatic, the two side parts of the enclosure are considered at a low constant temperature, each one of them has a length of 25% of the total perimeter of the enclosure, the top part of the enclosure is considered as adiabatic, it has a length of 25% of the total perimeter. To analyze the effect of using nanofluids with different particles volume fractions on heat transfer inside cylindrical horizontal enclosures, two nanofluids (Cu-water, TiO2-water) were used with volume fraction of nanoparticles being varied in the range of 0 corresponding to pure water) to 0.05. The steady state forms of Navier-Stokes equations and the equations of conservation of mass and energy in twodimensional cylindrical coordinates have been solved by the finite volume method and the SIMPLE algorithm was used for the pressure-velocity coupling. The Rayleigh number was varied in the interval 103 to 106. This research is characterized by a detailed analysis of the effect of changing both the Rayleigh number, the heated length and the value of nanoparticles volume fraction on the dynamic and thermal fields, on the percentage enhancement of the average Nusselt numbers, and also on the variation of the temperature and the vertical velocity component at the vertical and horizontal central lines of the enclosure. The results obtained were summarized in the form of correlation equations of the average Nusselt number as a function of the heated length, the Rayleigh number and volume fraction for both types of nanofluids. In the second study, a numerical study was carried out on the effect of using two techniques for the optimization of heat transfer by natural convection in a three-dimensional spherical enclosure of solar water heater. The outer wall (solar collector) is considered as a heated wall at a constant temperature, the wall which is located behind the solar collector is considered as adiabatic wall. In the enclosure there is a spiral tube, its wall is under a low temperature which increases linearly in terms of enclosure height. The first technique is to exploit nanotechnology using two types of nanofluids Cu-Water and CNT-Water, to improve the heat transfer in the enclosures of spherical solar water heaters, the volume fraction of nanoparticles was varied in the range of 0 (corresponding to pure water) to 0.05. The second technique involves making geometric modifications to the enclosure of spherical solar water heater to improve the natural convection heat transfer, these modifications consist in creating concentric annular orifices in the lower part of the internal adiabatic wall of the solar water heater, the number of annular orifices varies from 1 to 6. The Rayleigh number was varied in the interval 104 to 106. The steady state forms of Navier-Stokes equations and the equations of conservation of mass and energy in three-dimensional spherical coordinates have been solved by the finite volume method. The SIMPLE algorithm was used for the pressure-velocity coupling. This research is characterized by a detailed analysis of the effect of changing both the Rayleigh number, the number of annular orifices and the value of nanoparticles volume fraction on the dynamic and thermal fields and on the heat transfer and its percentage improvement. The results obtained were summarized in the form of correlation equations of the average Nusselt number as a function of the Rayleigh number, the number of annular orifices and the volume fraction of the nanofluid. Through the results obtained in all the studies carried out in the frame of this doctoral thesis, a very important theorem has been reached on the improvement of heat transfer by natural convection in enclosures. The application of this theorem can revolutionize the field of performance improvement of various thermal engineering systems whose operating principle depends on heat transfer by natural convection.
Note de contenu : Annexes. Diplôme : Doctorat en sciences En ligne : ../theses/gmecanique/GUE7495.pdf Format de la ressource électronique : Permalink : https://bu.umc.edu.dz/md/index.php?lvl=notice_display&id=11327 Exemplaires (1)
Code-barres Cote Support Localisation Section Disponibilité GUE/7495 GUE/7495 Thèse Bibliothèque principale Thèses Disponible
Titre : Approche numérique de la convection naturelle dans une enceinte férmée délimitée par deux cylindres elliptiques horizontaux centrés et deux plans diamétraux Type de document : texte imprimé Auteurs : Fouzia Bendjaballah ; Univ. de Constantine, Éditeur scientifique ; M. Djezzar, Directeur de thèse Année de publication : 2007 Importance : 75 f. Note générale : 01 Disponible à la salle de recherche 02 Disponibles au magazin de la B.U.C. 01 CD Langues : Français (fre) Catégories : Français - Anglais
PhysiqueTags : Convection naturelle Formulation vorticité-fonction de courant Equations de Boussinesq Espaces annulaires Cavités annulaires Eceintes férmées Cylindres elliptiques Index. décimale : 530 Physique Diplôme : Magistère En ligne : ../theses/physique/BEN4967.pdf Permalink : https://bu.umc.edu.dz/md/index.php?lvl=notice_display&id=3535 Approche numérique de la convection naturelle dans une enceinte férmée délimitée par deux cylindres elliptiques horizontaux centrés et deux plans diamétraux [texte imprimé] / Fouzia Bendjaballah ; Univ. de Constantine, Éditeur scientifique ; M. Djezzar, Directeur de thèse . - 2007 . - 75 f.
01 Disponible à la salle de recherche 02 Disponibles au magazin de la B.U.C. 01 CD
Langues : Français (fre)
Catégories : Français - Anglais
PhysiqueTags : Convection naturelle Formulation vorticité-fonction de courant Equations de Boussinesq Espaces annulaires Cavités annulaires Eceintes férmées Cylindres elliptiques Index. décimale : 530 Physique Diplôme : Magistère En ligne : ../theses/physique/BEN4967.pdf Permalink : https://bu.umc.edu.dz/md/index.php?lvl=notice_display&id=3535 Exemplaires (1)
Code-barres Cote Support Localisation Section Disponibilité BEN/4967 BEN/4967 Thèse Bibliothèque principale Thèses Disponible
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