Natural convection within water-zno nanofluid-filled hemispherical enclosure with a cubic electronic device

This work qualifies and quantifies the nanofluidic natural convective phenomena occurring in a hemispherical enclosure used for electronics applications. This cavity consists of a disk thermally insulated on its rear face, an active cube centered on the disk which generates a constant heat flux and an isothermal dome. The disc of the cavity remains horizontal while its dome is oriented either upwards or downwards. The considered nanofluid is a mixture of water with metallic ZnO nanoparticles. In order to examine the influence of these nanoparticles on the natural convective heat transfer, three values of the volume fraction considered: 0% (pure water), 1% and 5%. The dimensionless governing system of the problem under consideration is solved by means of the control volume method in combination with the SIMPLE algorithm. The structured mesh is composed of triangular surfacic elements and tetrahedral in the volumic domain. Temperature and velocity distributions are presented for some configurations and convective heat transfer is examined for all processed ones. The natural convective heat transfer is quantified by means of Nusselt-Rayleigh-Prandtl correlations.Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .International centre for heat and mass transfer.American society of thermal and fluids engineers

Influence of Gemetrical and Thermal Parameters on the Thermal Comportment of a Pin-on-Disk System

Strong temperature gradients are often the cause of malfunctions taking place in mechanical systems which associate two rubbing solids. This work presents the thermal behaviour of a system consisting on a rotating disk in rubbing contact with a pin. Immersed in an environment characterized by a surface conductance h and a temperature Tf , the disk is subjected to localised heat flux generated by the friction with the pin, eccentric with respect to the rotating axis of the disk. Several parameters intervene decisively on the local heat transfer and therefore on the temperature of the contact surface between the two solids in friction. In addition to the conductance, other parameters as the angular velocity of the disk, the frictional heat flux or the pin diameter and its off center with respect to the disk rotation axis, play a major role in the thermal exchange. The present work examines the influence of such parameters on the thermal solution. An analytical expression is proposed for the calculation of the 3D disk´s temperature. The presented thermal cartographies make possible to locate the zones of the system undergoing the greatest temperature gradients and thus the associated spots of mechanical rupture. Results are compared with other analytical solutions found in the specialized literatu

Aerodynamics in the open channel of the Sistan-type wind-mill with vertical axis wind turbine

International Journal of Numerical Methods for Heat and Fluid FlowThe purpose of this paper is to examine the details of the air mass flow and aerodynamical phenoména across a channel containing a large vertical axis wind turbine. The considered model reproduces as closely as possible the real assembly of the Sistan-type wind-mill whose top is open. The technical results of this work could be used for the restoration and operation of this assembly whose historical and architectural values are recognized.L'objectif de cet article est d’examiner les détails d'un écoulement dans un canal contenant une turbine à axe vertical. Les résultats techniques de ce travail pourront être utilisés pour la restauration et la mise en service de ce dispositif dont la valeur historique et architecturale est reconnue

Heat transfer in a conical gap using H2O–Cu nanofluid and porous media. Effects of the main physical parameters

Heat transfer around a conical antenna is quantified in this work. Cooling of this active electronic component is ensured by a medium of high porosity saturated by a H2O–Cu nanofluid with a volume fraction varying between 0% and 5%. The ratio between the thermal conductivity of the porous materials and that of the water (base fluid) ranges from 4 to 41.2, the null value corresponding to a heat transfer without porous media (only nanofluid). The conical enclosure's aspect ratio varies in the 0.2–0.6 range, being its base inclined between 0° (horizontal base with cone's top oriented upwards) and 180° range (horizontal base with cone's top oriented downwards). The associated Rayleigh number varies within the 3.32x105-6.74x107 range. Heat transfer by natural convection is quantified for any configuration combining these five parameters and presented via a correlation allowing determination of the average Nusselt number. This study shows that heat transfer increases when the cone is tilted. For a given aspect ratio, the maximum is reached when the cone is vertical with the top pointing down. This observation remains valid in the overall Rayleigh number range. The average Nusselt number enhancement varies between 20 and 70%, according on the considered cavity's aspect ratio. This study complements a recent one restricted to the case of a cone whose horizontal base is located at the bottom, being 0.2 the aspect ratio of the enclosure

Transient natural convection in closed and inclined cubical enclosures. Application to electronic equipment thermal regulation

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.Certain electronic components are very sensitive to temperature variations during their operations. This is true particularly for electronic systems containing high density integrated circuits, which are increasingly a characteristic of today’s equipment due to the ever evolving process of miniaturisation. The correct operation of such electronic systems is related to their thermal state. Therefore, thermal regulation is required for their proper dynamic operation. This regulation is complex in the case of a high level of integration and confinement to small spaces. The proper sizing of the closed or limited opening casing is, therefore, necessary in order to ensure the correct operation of the equipment in confined spaces. This paper presents a treatment of the particular case of the transient natural 2D convection in a cubical enclosure filled with air. The active walls are differentially heated and maintained isothermic. These walls can remain vertical, but can also be inclined with respect to the gravity field. The dynamic and thermal fields within the case are analysed numerically using the finite volume method. An experimental test rig is developed for the thermal analysis by examining the temperature distribution in the immediate vicinity of the hot wall, which simulates the electronic equipment.cs201

Thermal state of a concentric quarter spherical enclosure subjected to air free convection

The average temperature difference between the walls of a cavity consisting of two concentric quarter spheres and subjected to an air natural convective flow was determined. The work was performed numerically through volume control method based on the SIMPLE algorithm. The thermal state was determined for several combinations of the aspect ratio varying from 0.05 to 0.35 and Rayleigh number with elevated values reaching 6.76 × 1011. A new correlation has been proposed, allowing thermal sizing of this type of cavity which could be used in different fields of engineering such as electronics and building. © 2021, Akadémiai Kiadó, Budapest, Hungary

Thermal state of a conical antenna cooled by means of nanofluid saturated porous media

Thermal state of a conical antenna used for big data transfer was determined in this work. Its cooling is provided through porous media saturated with water-based copper nanofluid (NF) whose volume fraction varies in the 0% (pure water)-10% range. Otherwise, the ratio between the thermal conductivity of the highly porous material and that of the fluid base (water) varies between 4 and 41.2. The solution is obtained by means of 3D numerical approach based on the volume control method using the SIMPLE algorithm in the large 3.32×105-6.74×107 Rayleigh number range. The average temperature of the antenna can be determined with the correlation proposed in this work for any combination of the thermal conductivity ratio, volume fraction and Rayleigh number. This new and original correlation makes it possible to determine the optimal values of these three influencing parameters to ensure the correct antenna's operation. © 2022 World Scientific Publishing Company

Influence of geometrical and thermal parameters on the thermal component of a pin-on-disk system

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.Strong temperature gradients are often the cause of malfunctions taking place in mechanical systems which associate two rubbing solids. This work presents the thermal behaviour of a system consisting on a rotating disk in rubbing contact with a pin. Immersed in an environment characterized by a surface conductance h ͚. and a temperature T ͚ ,the disk is subjected to localised beat flux generated by the friction with the pin, eccentric with respect to the rotating axis of the disk. Several parameters intervene decisively on the local heat transfer and therefore on the temperature of the contact surface between the two solids in friction. In addition to the conductance, other parameters as the angular velocity of the disk, the frictional heat flux or the pin diameter and its off­-center with respect to the disk rotation axis, play a major role in the thermal exchange. The present work examines the influence of such parameters on the thermal solution. An analytical expression is proposed for the calculation of the 3D disk's temperature. The presented thermal cartographies make possible to locate the zones of the system undergoing the greatest temperature gradients and thus the associated spots of mechanical rupture. Results are compared with other analytical solutions found in the specialized literature.ej201