On the Thermal Interaction Between an Isothermal Cylinder and Its Isothermal Enclosure for Cylinder Rayleigh Numbers of Order 104

2001 ◽  
Vol 123 (6) ◽  
pp. 1052-1061 ◽  
Author(s):  
D. T. Newport ◽  
T. M. Dalton ◽  
M. R. D. Davies ◽  
M. Whelan ◽  
C. Forno
Keyword(s):  
Nusselt Number ◽  
Electronic System ◽  
Electronic Systems ◽  
Thermal Interaction ◽  
Cubical Enclosure ◽  
System Temperature ◽  
Nusselt Number Distribution ◽  
Complex Fluid ◽  
Digital Moiré ◽  
Rayleigh Numbers

An experimental investigation is made of the thermal interaction between a horizontal isothermal cylinder centrally located in a water-cooled isothermal cubical enclosure. The study is restricted to laminar flow and cylinder Rayleigh numbers of order 104. The application of interest is the cooling of electronic systems. This field is currently lacking in techniques that can measure the complex fluid phenomena encountered in real systems. The paper therefore begins with an experimental review of interferometry to assess its applicability as a potential solution to this need. Based on this review, a real time Digital Moire´ Subtraction interferometer is used to measure temperature profiles, and local Nusselt number distributions in two regions of interest: the plume impingement on the ceiling of the enclosure, and the upper corner region of the enclosure. A Mach-Zehnder interferometer is used for the cylinder Nusselt number distribution. Results are compared both qualitatively and quantitatively with a numerical simulation run on a commercial CFD package widely used for electronic system temperature predictions. The paper gives considerable insight into the nature of the enclosure heat transfer and an indication of the accuracy of a widely used predictive code.

An Experimental Study of Free Corrective Heat Transfer in a Parallelogrammic Enclosure

1983 ◽  
Vol 105 (3) ◽  
pp. 433-439 ◽  
Author(s):  
N. Seki ◽  
S. Fukusako ◽  
A. Yamaguchi
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Nusselt Number ◽  
Correlation Equation ◽  
Transformer Oil ◽  
Experimental Measurements ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Prandtl Numbers ◽  
Rayleigh Numbers

Experimental measurements are presented for free convective heat transfer across a parallelogrammic enclosure with the various tilt angles of parallel upper and lower walls insulated. The experiments covered a range of Rayleigh numbers between 3.4 × 104 and 8.6 × 107, and Prandtl numbers between 0.70 and 480. Those also covered the tilt angles of the parallel insulated walls with respect to the horizontal, φ, of 0, ±25, ±45, ±60, and ±70 deg under an aspect ratio of H/W = 1.44. The fluids used were air, transformer oil, and water. It was found that the heat transfer coefficients for φ = −70 deg were decreased to be about 1/18 times those for φ = 0 deg. Experimental results are given as plots of the Nusselt number versus the Rayleigh number. A correlation equation is given for the Nusselt number, Nu, as a function of φ, Pr, and Ra.

Numerical simulations of Rayleigh–Bénard convection for Prandtl numbers between 10−1 and 104 and Rayleigh numbers between 105 and 109

2010 ◽  
Vol 662 ◽  
pp. 409-446 ◽  
Author(s):  
G. SILANO ◽  
K. R. SREENIVASAN ◽  
R. VERZICCO
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Numerical Simulations ◽  
Multiple Solutions ◽  
Large Scale ◽  
Prandtl Numbers ◽  
Rayleigh Benard Convection ◽  
Rayleigh Numbers ◽  
Rayleigh Benard

We summarize the results of an extensive campaign of direct numerical simulations of Rayleigh–Bénard convection at moderate and high Prandtl numbers (10−1 ≤ Pr ≤ 104) and moderate Rayleigh numbers (105 ≤ Ra ≤ 109). The computational domain is a cylindrical cell of aspect ratio Γ = 1/2, with the no-slip condition imposed on all boundaries. By scaling the numerical results, we find that the free-fall velocity should be multiplied by $1/\sqrt{{\it Pr}}$ in order to obtain a more appropriate representation of the large-scale velocity at high Pr. We investigate the Nusselt and the Reynolds number dependences on Ra and Pr, comparing the outcome with previous numerical and experimental results. Depending on Pr, we obtain different power laws of the Nusselt number with respect to Ra, ranging from Ra2/7 for Pr = 1 up to Ra0.31 for Pr = 103. The Nusselt number is independent of Pr. The Reynolds number scales as ${\it Re}\,{\sim}\,\sqrt{{\it Ra}}/{\it Pr}$, neglecting logarithmic corrections. We analyse the global and local features of viscous and thermal boundary layers and their scaling behaviours with respect to Ra and Pr, and with respect to the Reynolds and Péclet numbers. We find that the flow approaches a saturation state when Reynolds number decreases below the critical value, Res ≃ 40. The thermal-boundary-layer thickness increases slightly (instead of decreasing) when the Péclet number increases, because of the moderating influence of the viscous boundary layer. The simulated ranges of Ra and Pr contain steady, periodic and turbulent solutions. A rough estimate of the transition from the steady to the unsteady state is obtained by monitoring the time evolution of the system until it reaches stationary solutions. We find multiple solutions as long-term phenomena at Ra = 108 and Pr = 103, which, however, do not result in significantly different Nusselt numbers. One of these multiple solutions, even if stable over a long time interval, shows a break in the mid-plane symmetry of the temperature profile. We analyse the flow structures through the transitional phases by direct visualizations of the temperature and velocity fields. A wide variety of large-scale circulation and plume structures has been found. The single-roll circulation is characteristic only of the steady and periodic solutions. For other regimes at lower Pr, the mean flow generally consists of two opposite toroidal structures; at higher Pr, the flow is organized in the form of multi-jet structures, extending mostly in the vertical direction. At high Pr, plumes mainly detach from sheet-like structures. The signatures of different large-scale structures are generally well reflected in the data trends with respect to Ra, less in those with respect to Pr.

Donohue+: Developing performer-specific electronic improvisatory accompaniment for instrumental improvisation

2021 ◽  
Vol 26 (1) ◽  
pp. 129-139
Author(s):  
Sam Gillies ◽  
Maria Sappho Donohue
Keyword(s):  
Decision Making ◽  
Electronic System ◽  
Instrument Design ◽  
Electronic Systems ◽  
Musical Language ◽  
Live Performance ◽  
Collaborative Process ◽  
Creative Practice ◽  
Free Improvisation ◽  
Music Making

Electronic systems designed to improvise with a live instrumental performer are a constant mediation of musical language and artificial decision-making. Often these systems are designed to elicit a reaction in a very broad way, relying on segmenting and playing back audio material according to a fixed or mobile set of rules or analysis. As a result, such systems can produce an outcome that sounds generic across different improvisers, or restrict meaningful electroacoustic improvisation to those performers with a matching capacity for designing improvisatory electroacoustic processing. This article documents the development of an improvisatory electroacoustic instrument for pianist Maria Donohue as a collaborative process for music-making. The Donohue+ program is a bespoke electroacoustic improvisatory system designed to augment the performance capabilities of Maria, enabling her to achieve new possibilities in live performance. Through the process of development, Maria’s performative style, within the broader context of free improvisation, was analysed and used to design an interactive electronic system. The end result of this process is a meaningful augmentation of the piano in accordance with Maria’s creative practice, differing significantly from other improvising electroacoustic instruments she has previously experimented with. Through the process of development, Donohue+ identifies a practice for instrument design that engages not only with a performer’s musical materials but also with a broader free improvisation aesthetic.

scholarly journals CONSTRUCTAL DESIGN OF FINS IN COOLED CAVITIES BY NON-NEWTONIAN FLUIDS

2019 ◽  
Vol 18 (1) ◽  
pp. 85
Author(s):  
J. F. Bueno ◽  
A. R. S. Silva ◽  
T. A. Hirt ◽  
G. F. C. Bogo ◽  
F. S. F. Zinani ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Newtonian Fluids ◽  
Rheological Parameters ◽  
Flow Index ◽  
Pseudoplastic Fluid ◽  
High Reynolds ◽  
Energy Equations ◽  
Rayleigh Numbers

The present work investigates the Construtal Design of fins inserted in cavities submitted to mixed convection by non-Newtonian fluids. The objective is to obtain the optimum aspect ratio for the fin considering different flow conditions and variations in the rheological parameters of the fluid. The phenomena of flow and heat transfer are modeled by mass balance, momentum and energy equations, and by the generalized Newtonian liquid constitutive equation. The viscosity is modeled as that of a pseudoplastic fluid, using the Carreau function. The optimization problem consists in maximizing heat transfer from the fin using the average Nusselt number. The investigated project variable is the aspect ratio between the edges of the rectangular plane fin profile. The restrictions are the volume of the cavity and the fin. The results are obtained numerically using a finite volume code and a two-dimensional geometry, through exhaustive searching. The results show that the fin geometry influences the maximum Nusselt number mainly for the cases with high Reynolds and Rayleigh numbers, such as was shown in previous studies. The results show that the fin geometry influences the maximum Nusselt number mainly for the cases with high Reynolds and Rayleigh numbers, as was shown in previous studies. It was also found that the Nusselt number increases as the increase in flow intensity, represented by the parameter p, and that the result of the maximum Nusselt number does not change monotonically with the non-Newtonian dimensionless viscosity and with the flow index, showing that the pseudoplasticity of the fluid implies optimal configurations very different from those predicted for Newtonian fluids.

Electrochemical treatment of metal inserts for subsequent assembly injection molding of tight electronic systems

2018 ◽  
Vol 38 (7) ◽  
pp. 675-684 ◽  
Author(s):  
Tobias Kleffel ◽  
Dietmar Drummer
Keyword(s):  
Injection Molding ◽  
Electronic System ◽  
Electrochemical Treatment ◽  
Electronic Systems ◽  
Automotive Applications ◽  
Two Stage ◽  
Metal Insert

Abstract One method to produce electronic systems with high resilience is the encapsulation of metal inserts, for example, lead frames, using assembly injection molding. Such parts are exposed to different mediums, such as water and oil, which can infiltrate and damage the electronic system, especially in automotive applications. Hence, one challenge is to ensure the tightness. The research covered in this paper focuses on the assembly injection molding of tight electronic systems using microstructured metal inserts, manufactured by a two-stage electrochemical treatment. The effects of the electrochemical treatment on the tightness and the bond between metal and polymer of the electronic system are investigated. Furthermore, the influence of the electrochemical treatment on the surface and geometry of the metal insert is evaluated.

Blade Tip Heat Transfer and Aerodynamics in a Large Scale Turbine Cascade With Moving Endwall

2006 ◽  
Author(s):  
P. Palafox ◽  
M. L. G. Oldfield ◽  
P. T. Ireland ◽  
T. V. Jones ◽  
J. E. LaGraff
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Large Scale ◽  
Infrared Camera ◽  
Suction Side ◽  
Constant Heat Flux ◽  
Tip Clearance ◽  
Airfoil Surface ◽  
Nusselt Number Distribution ◽  
Blade Tip

High resolution Nusselt number (Nu) distributions were measured on the blade tip surface of a large, 1.0 meter-chord, low-speed cascade representative of a high-pressure turbine. Data was obtained at a Reynolds number of 4.0 × 105 based on exit velocity and blade axial chord. Tip clearance levels ranged from 0.56% to 1.68% design span or equally from 1% to 3% of blade chord. An infrared camera, looking through the hollow blade, made detailed temperature measurements on a constant heat flux tip surface. The relative motion between the endwall and the blade tip was simulated by a moving belt. The moving belt endwall significantly to shifts the region of high Nusselt number distribution and reduces the overall averaged Nusselt number on the tip surface by up to 13.3%. The addition of a suction side squealer tip significantly reduced local tip heat transfer and resulted in a 32% reduction in averaged Nusselt number. Analysis of pressure measurements on the blade airfoil surface and tip surface along with PIV velocity flow fields in the gap give an understanding of the heat transfer mechanism.

Numerical Simulation of Natural Convection Flow in a Cube With a Horizontal Heated Strip

2008 ◽  
Author(s):  
Esam M. Alawadhi
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Nusselt Number ◽  
High Temperature ◽  
Natural Convection ◽  
Vertical Wall ◽  
Convection Flow ◽  
Front Wall ◽  
Natural Convection Flow ◽  
Rayleigh Numbers

Natural convection flow in a cube with a heated strip is solved numerically. The heated strip is attached horizontally to the front wall and maintained at high temperature, while the entire opposite wall is maintained at low temperature. The heated strip simulates an array of electronic chips The Rayleigh numbers of 104, 105, and 106 are considered in the analysis and the heated strip is horizontally attached to the wall. The results indicate that the heat transfer strongly depends on the position of the heated strip. The maximum Nusselt number can be achieved if the heater is placed at the lower half of the vertical wall. Increasing the Rayleigh number significantly promotes heat transfer in the enclosure. Flow streamlines and temperature contours are presented, and the results are validated against published works.

Free Convection Thermal Interaction Between 2D Components Mounted on a Vertically Oriented PCB

2002 ◽  
Author(s):  
D. Newport ◽  
T. Dalton ◽  
M. Davies
Keyword(s):  
Boundary Layer ◽  
Effective Conductivity ◽  
Ball Grid Array ◽  
Velocity Fields ◽  
Two Dimensional ◽  
Thermal Interaction ◽  
Trade Off ◽  
Layer Flow ◽  
Digital Moiré ◽  
Temperature And Velocity Fields

In this paper, measurements are presented of the temperature and velocity fields about two PCBs, with an array of five equally spaced two dimensional ribs. The ribs are two dimensional approximations of the Super Ball Grid Array (SuperBGA) package from Amkor electronics. The temperature and Nusselt number distributions are measured using Digital Moire´ Subtraction Interferometry and PIV is used to measure the velocity field. The effect of substrate conductivity is examined, and the level of thermal interaction is quantified. It is found that substrate conductivity significantly alters the induced boundary layer flow and also the recirculating vortex structure external to it. It is also found that there is a trade-off between a downstream component being heated by the thermal energy of the plume from a lower component, and cooled by the kinetic energy of that plume. The spacing to length ratio, above which the cooling effect is greater, is three for components mounted on a board with a high effective conductivity (15 W/m K). The ratio is greater than three for PCBs with lower effective conductivities. Previous work in the literature indicates a ratio greater than four for components mounted flush with an adiabatic substrate.

Influence of Transverse Fins Attached to the Heated Wall of a Rayleigh-Be´nard Cavity

2004 ◽  
Author(s):  
Darren L. Hitt ◽  
Antonio Campo
Keyword(s):  
Thermal Conductivity ◽  
Nusselt Number ◽  
Numerical Simulations ◽  
Heat Transport ◽  
Local Heat ◽  
Heated Wall ◽  
Lower Plate ◽  
Maximum Heat ◽  
Rayleigh Numbers ◽  
Fin Spacing

In this article we examine the augmentation of classic Rayleigh-Be´nard convection by the addition of periodically-spaced tranverse fins attached to the heated, lower plate. The respective impacts of the fin size, the fin spacing and the thermal conductivity of the fin material are examined through numerical simulations for different laminar Rayleigh numbers and reported it terms of the Nusselt number. With the exception of very closely spaced fins, the heat transport is observed to exceed that of the idealized Rayleigh-Be´nard case. It is found that local heat transport maxima and minima do exist for specific fin spacings and that the maxima become more pronounced at higher Rayleigh numbers. For ‘small fins’ the fin spacing corresponding to maximum heat transport is such that the fin spacing is approximately equal to the enclosure height.

Modal equations for cellular convection

1975 ◽  
Vol 68 (4) ◽  
pp. 695-719 ◽  
Author(s):  
D. O. Gough ◽  
E. A. Spiegel ◽  
Juri Toomre
Keyword(s):  
Nusselt Number ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Qualitative Properties ◽  
The Mean ◽  
Flow Variables ◽  
Rayleigh Numbers ◽  
Very High ◽  
State Form

We expand the fluctuating flow variables of Boussinesq convection in the planform functions of linear theory. Our proposal is to consider a drastic truncation of this expansion as a possibly useful approximation scheme for studying cellular convection. With just one term included, we obtain a fairly simple set of equations which reproduces some of the qualitative properties of cellular convection and whose steady-state form has already been derived by Roberts (1966). This set of ‘modal equations’ is analysed at slightly supercritical and at very high Rayleigh numbers. In the latter regime the Nusselt number varies with Rayleigh number just as in the mean-field approximation with one horizontal scale when the boundaries are rigid. However, the Nusselt number now depends also on the Prandtl number in a way that seems compatible with experiment. The chief difficulty with the approach is the absence of a deductive scheme for deciding which planforms should be retained in the truncated expansion.

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