Thermal state of electronic assemblies applied to smart building equipped with QFN64 device subjected to natural convection

The performance and reliability of electronic components and assemblies strongly depend on their thermal state. The knowledge of the temperature distribution throughout the assembly is therefore an essential element to ensure their correct operation. This is the main objective of this work that examines the case of a conventional assembly equipped with a quad flat nonlead QFN64 subjected to free convection. This active electronic package is welded on a PCBwhich may be inclined by an angle varying between 0° and 90° (horizontal and vertical positions respectively) and generates during its operation a high power ranging from 0.1 to 1W.Thermoregulation of the assembly is ensured by natural convection, given its many well known advantages in this engineering field. Accurate relationships are proposed to determine the temperature on different areas of the device and the PCB. They are determined by means of a 3D numerical survey based on the finite volume method confirmed by measurements on an actual installation. These relationships allow reliability improvement of these electronicassemblies widely used in many engineering fields, as computing industry, mobile telephony, home automation, automotive, embarked electronics and smart building considered in this survey. The present survey complements a recent study which quantifies the natural convective heat transfer on the considered electronic assembly equipped with the QFN64 device, for thesame power range and angle of inclination

Enhancement of natural convection for improvement of Trombe wall performance. An experimental study

This experimental work shows that the natural convective heat transfer in the active enclosure of a conventional Trombe wall assembly is enhanced by the interposition of transparent and vertical partitions. Quantification of the average Nusselt number corresponding to both versions with and without partitions was carried out by means of a 1/5 scale assembly. The glass cover is maintained isothermal at cold temperature while the active wall generates a variable heat flux simulating the incident solar radiation. The distance between the two active and parallel walls is variable. Four ratios between this distance and the height of the wall are considered, associated with a wide range of Rayleigh number reaching 4.1×109. An error calculation is carried out for all the processed configurations, taking into account the experimental uncertainties of the measured physical parameters. The maximum error found on the average Nusselt number is low, of about 5%. Measurements made by means of an interstitial medium without partitions are consistent with the results of other work carried out by experimental and numerical approaches in specific ranges of Rayleigh number. This study reveals the partitions effectiveness, since the natural convective heat transfer's increase lies between 10.0% and 14.4% according to the considered configuration. Correlations are proposed in the present work in order to calculate the average natural convective Nusselt number for the conventional Trombe wall without partitions and for its improved version, for any aspect ratio and in the whole range of the considered Rayleigh number. They contribute to the optimization of the thermal design of this interesting assembly

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

Transient thermal characteristics of airborne electronic equipment with discrete hot bands in square cavities

This study is concerned with the thermal regulation of electronic circuits confined in a closed cubical air-filled cavity. The hot active wall, which represents the electronic equipment, is composed of three parallel discrete heat source bands subjected to a constant heat flux, separated by two adiabatic bands. The second active wall is an isothermal cold plate and is facing the hot wall. The cavity channel is considered adiabatic. Transient heat exchanges through 2D natural convection are analysed for several configurations obtained through varying the inclination angle of the active wall with respect to gravity. The numerical approach conducted with the finite volumes method allowed the derivation of the thermal and dynamic characteristics of the cavity. The thermal evolution of the sources does not show any local temperature peaks that could exceed the maximum allowable temperature set by the electronic components manufacturers. This guarantees the normal operation of the equipment. The numerical analysis is complemented by experimental measurements that validate the used model and allow the correct sizing of the airborne electronic circuits.Transient natural convection Imposed heat flux Electronic applications Inclined air-filled cavity Discrete sources Finite volumes method Experimental data

Temperature solution of one-dimensional modeling of rapid transient heat transfer around a cylindrical body

The aim of the present paper is to provide a numerical solution of the heat transfer equation into and along the wall of a cylindrical profile in a very high-speed flow. A series of diagrams are derived. They allow to calculate the time-dependent temperature at any point on the surface as well as inside the body. The profile, which is initially at a uniform temperature, is suddenly submitted to a convective and/or radiative heat flux around its surface. These diagrams provide useful data on extremely rapid heat transfer phenomena, i.e., at very low Fourier (Fo) numbers. They can be used regardless the dimensions, thermophysical characteristics of the body, and thermal characteristics of the wall, i.e., at any Biot (Bi) number. They provide a reliable shortcut for the understanding of the thermal behavior of the projectile abrasion in a ram accelerator operation. The analytical aspect of the problem is detailed in the case of a long, i.e., one dimensional, cylindrical geometry, but the diagrams can be used for 2D transient phenomena, in relation with the solution of the infinite plate, which has been developed earlier for the same range of Fourier and Biot numbers. The general equation that is presented in the paper is quite complex to solve for some Fo-Bi combinaisons. Therefore, a numerical procedure was developed in order to account fore some important divergence problems that may occur during the calculation in these specific cases. The accuracy of the present diagrams has been strongly improved in comparison with that of the same type of plots, which are available in the literature and turn out to yield a poor accuracy for some specific Fo-Bi combinaisons

Thermal behavior of an active electronic dome contained in a tilted hemispherical enclosure and subjected to nanofluidic Cu-water free convection

This study examines the thermal behavior of a hemispherical electronic component subjected to a natural nanofluidic convective flow. During its operation, this active dome generates a high power, leading to Rayleigh number values reaching 4.56×109. It is contained in a hemispherical enclosure and the space between the dome and the cupola is filled with a monophasic water-based copper nanofluid whose volume fraction varies between 0 (pure water) and 10%. According to the intended application, the disc of the enclosure may be tilted at an angle ranging from 0° to 180° (horizontal disc with dome facing upwards and downwards, respectively). The numerical solution has been obtained by means of the volume control method. The surface average temperature of the dome has been determined for many configurations obtained by combining the Rayleigh number, the cavity’s tilt angle and the nanofluid volume fraction which vary in wide ranges. The temperature fields presented for several configurations confirm the effects of natural convection. The results clearly highlight the effects of these influence parameters on the thermal state of the assembly. The study shows that some combinations of the Rayleigh-tilt angle-volume fraction are incompatible with a normal operating system at steady state and that a thermoregulation is required. The correlation of the temperature-Rayleigh-Prandtl-angle type proposed in this work allows to easily carry out the thermal dimensioning of the considered electronic assembly.</p