N. Alilat

THREE-DIMENSIONAL CALCULATION OF TEMPERATURE IN A ROTATING DISK SUBJECTED TO AN ECCENTRIC CIRCULAR HEAT SOURCE AND SURFACE COOLING

This article derives, for the first time, an appropriate analytical solution for the calculation of three-dimensional temperature distribution inside a rotating disk subjected to an eccentric circular heat source and surface cooling. This problem is encountered in, among others, the pin-on-disk frictional device, thrust ball bearing, or machining in a lathe. In order to obtain this solution under an explicit and simple form, we assume that the cooling occurs over the whole frictional surface of the disk, including the heated region. A numerical study, using the finite-volume method, is also conducted in order to define the limits of validity of the above assumption. It is shown that the analytical solution is accurate for a wide range of heat convection coefficients ( h ≤ 1,000 W/m2K for high Peclet numbers and h ≤ 5,000 W/m2K for low ones).

Nu-Ra correlations for natural convection at high Ra numbers in air-filled tilted hemispherical cavities with dome oriented upwards. Disk submitted to constant heat flux

Purpose – The purpose of this paper is to propose correlations between Nusselt and Rayleigh numbers for the case of inclined and closed air-filled hemispherical cavities. The disk of such cavities is subjected to a constant heat flux. The study covers a wide range of Rayleigh numbers from 5×107 to 2.55×1012. Design/methodology/approach – Correlations are obtained from numerical approach validated by experimental measurements on some configurations, valid for several angles of inclination of the cavity between 0° (horizontal disk) and 90° (vertical disk) in steps of 15°. Findings – The statistical analysis of a large number of calculations leads to reliable results covering laminar, transitional and turbulent natural convection heat transfer zones. Practical implications – The proposed correlations provide solutions for applications in several fields of engineering such as solar energy, aerospace, building, safety and security. Originality/value – The new relations proposed are the first published for high...

Fast transient conduction in infinite plate subject to violent thermal effects

Abstract This work is an implement to a study that was conducted for long cylinders and spheres undergoing fast processes characterized by low Fourier numbers (Fo). It allows to solve some complex 2D and 3D problems involving the specific thermal boundary conditions examined in this survey. Analytical solutions for fast transient conduction in infinite plate subject to sudden and violent thermal effects on its surface are presented in this paper. The numerical solutions are presented in the form of simple diagrams that can be easily and readily used in some engineering applications. These data are useful for the optimization of numerical codes in fluid mechanics in association with heat transfer and inverse methods for the determination of thermal characteristics of the surface phenomena in various cases. These diagrams are for specific ranges of Fo and Bi numbers corresponding to the fast transient problems characterized by low Fourier numbers, associated with a large combination of dimensions of the body and values of thermal surface conductance (large range of Bi). These diagrams constitute a substantial improvement (especially for violent and sudden thermal effects) of the well known Heisler’s charts. A numerical solution is proposed. It overcomes the problems due to a too slow convergence. The main difficulty is encountered when solving characteristic equations based on a combination of the parameters involved in the particular equations of temperature and energy which may take asymptotic values for the specific phenomena addressed in this study. The results are successfully compared to those based on a different calculation procedure. It is for example the case for thermo-mechanics problem due to the braking using the tablet-disk system.

Nu–Ra–Pr correlations for nanofluidic natural convection in tilted hemispherical enclosures with an active disk

ABSTRACT This work qualifies and quantifies the natural convective phenomena occurring in a hemispherical enclosure filled with ZnO-Water monophasic nanofluid with a volume fraction varying between 0% (pure water) and 10%. The dome of the cavity is kept isothermal while its circular base generates a power varying between 0.5W and 400W. The disc can be inclined with respect to the horizontal plane by an angle varying between 0 and 180° (horizontal disk with a dome facing upwards and downwards respectively). The 3D numerical approach is carried out with the finite volume method based on the SIMPLE algorithm. The temperature and velocity distributions are presented and the convective heat transfer is examined for all processed configurations. The nanofluidic convective heat transfer is quantified by means of correlations of the Nusselt-Rayleigh-Prandtl-tilt angle type. They allow to optimize the thermal design of these cavities used in the field of electronics.

Effects of the Encapsulating Resin on the Junction Temperature of the QFN16 and QFN32 Electronic Packages Subjected to Free Convection

ABSTRACT The junction temperature of the quad flat no-lead with 16 and 32 leads (QFN16 and QFN32) electronic packages subjected to free convection is highly affected by their encapsulating resins thermal conductivity. This study considers a variation of this conductivity between −80% and +100% of the average value measured on an industrial prototype by means of the Transient Plane Source method. The three dimensional numerical solution based on the control volume formulation shows that the thermal trend is of exponential type for these components but with different functions. The proposed relationships allow the calculation of the junction temperature of both QFN16 and QFN32 according to the power generated varying between 0.1 and 1W, and the inclinations relative to the horizontal plane in the range 0–90° (horizontal and vertical positions respectively). The law governing the influence of conductivity on the junction temperature shows that a more conductive resin does not significantly lower the junction temperature. However, for low conductivity values, the temperature can exceed the maximum recommended by the manufacturers, causing possible malfunction of the QFN and altering its technical performance that are directly related to its thermal state. In some cases, the device can be decommissioned.

Numerical and experimental study of free convection on wire-bonded QFN64b electronic package

Purpose The wire-bonded version of the quad flat non-lead with 64 leads (QFN64b) is increasingly integrated in modern arrangements, given its thermal and electrical characteristics suited for specific applications. Temperature control is thus essential for its proper operation, particularly when the heat exchange with the environment is done by natural convection. This work aims to consider a conventional assembly consisting of a large printed circuit board (PCB) on which is welded a QFN64b generating a power in the range 0.01-0.1 W. The PCB could be inclined at an angle varying between 0° and 90° (horizontal and vertical positions, respectively) according to the intended application. Design/methodology/approach The 3D numerical approach done by means of the finite volume method is complemented by thermal and electrical measurements for all the configurations numerically processed. The low deviations obtained between the calculations and the measurements validate the adopted model. These results complement recent work that considers the same assembly equipped with a tilted and low-powered QFN64 basic model subjected to free convection. Findings The surface temperature in any part of the assembly has been determined. The influence of the power generated by the device and the PCB’s inclination angle relative to the gravity field have been quantified. The work shows that the radiative heat transfer is negligible given the temperatures reached and that the thermal state of the considered assembly is different from the one equipped with the QFN64 basic model. The QFN’s temperature is lowered, while that of the PCB is increased. The temperature distribution is also different from that of assemblies equipped with other QFN models with and without wire-bonding. Originality/value The correlations proposed in this survey help optimize the thermal design of the QFN64b electronic package used in many engineering fields.

Natural convective heat transfer in the air-filled interstice between inclined concentric hemispheres: Application to thermoregulation in electronics

Purpose The main purpose of this work is to quantify the convective heat transfer occurring between two inclined and concentric hemispheres. Design/methodology/approach The inner one is an electronic assembly generating a constant heat flux during operation. The outer hemisphere is maintained isothermal at cold temperature. The interstitial space is air-filled. The base of the equipment can be inclined with respect to the horizontal plane by an angle ranging from 0° (horizontal position with dome faced upwards) to 180° (horizontal position with dome faced downwards). Findings Nusselt–Rayleigh correlations are proposed for several configurations obtained by varying the generated power and the base inclination. The large resulting Rayleigh number ranging between 2.4 × 105 and 1.7 × 107 allows using these new and original correlations in various engineering fields, such as electronics in the present work. The calculations are realized by means of a 3D numerical approach based on the finite volume method. Originality/value The geometry and the thermal boundary conditions considered in the present survey are suitable for applications in many engineering areas.

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

Purpose The purpose of this paper is to examine the details of the air mass flow and aerodynamical phenomena 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. Design/methodology/approach Several inlet velocities into the channel are considered, taking into account the possible local wind resources. Calculations corresponding to Reynolds number varying between 8×105 and 4×106 are made by means of the finite volume method and turbulence is treated with the realizable k-e model. The mesh consists of a fixed part associated to the contour of the channel, interfaced with a moving one linked to the turbine itself, equipped with nine partly filled wings. Findings The relative pressure and velocity fields are presented for various dynamic and static conditions. Calculation results clearly show that the vortex phenomena present in some cases are not a source of degradation of the wind turbine’s aerodynamical performances, given its location, intensity and rotation direction. Particular attention is devoted to the air mass flow and its distribution between the inlet and the outlet sections of the channel. Originality/value The present work provides technical information useful to consider the restoration and modernization of this installation whose architecture and technical performance are very interesting. This survey complements a previous one examining the aerodynamical phenomena occurring in a modified version of this assembly with a closed top channel.

Identification of the Forces in the Suspension System of a Race Car Using Artificial Neural Networks

The suspension system together with the chassis of the car play an important role in the performance of a race car. The knowledge of the forces that are transmitted through the car’s suspension system allows a better adjustment and optimization of various structural components. In this study, an identification method, with a neural network based methodology, was tested using experimental data in order to identify and quantify the horizontal and vertical forces in the wheel hub, which are transmitted to the triangle of the suspension and to the chassis of the car. The obtained results are promising and show that it is possible to use this methodology for real-time monitoring of horizontal and vertical forces acting on the triangle suspension of the formula student car.