scholarly journals Modeling of Natural Convection in Electronic Enclosures

2005 ◽  
Vol 128 (2) ◽  
pp. 157-165 ◽  
Author(s):  
Peter M. Teertstra ◽  
M. Michael Yovanovich ◽  
J. Richard Culham
Keyword(s):  
Natural Convection ◽  
Numerical Data ◽  
Composite Model ◽  
Circuit Board ◽  
Flow Conditions ◽  
Transition Flow ◽  
Cfd Simulations ◽  
Wide Range ◽  
Using Data ◽  
Good Agreement

An analytical model is developed for natural convection from a single circuit board in a sealed electronic equipment enclosure. The circuit card is modeled as a vertical isothermal plate located at the center of an isothermal, cuboid shaped enclosure. A composite model is developed based on asymptotic solutions for three limiting cases: pure conduction, laminar boundary layer convection, and transition flow convection. The conduction shape factor and natural convection models are validated using data from CFD simulations for a wide range of enclosure geometries and flow conditions. The model is shown to be in good agreement, to within 10% RMS, with the numerical data for all test configurations.

scholarly journals High-resolution synchrotron diffraction study of porous buffer InP(001) layers

2014 ◽  
Vol 47 (5) ◽  
pp. 1614-1625 ◽  
Author(s):  
Andrey A. Lomov ◽  
Vasily I. Punegov ◽  
Dusan Nohavica ◽  
Mikhail A. Chuev ◽  
Alexander L. Vasiliev ◽  
...  
Keyword(s):  
Numerical Data ◽  
Dynamical Theory ◽  
Reciprocal Space ◽  
Scanning Electron Microscopy Data ◽  
Reciprocal Space Mapping ◽  
Porous Layers ◽  
Comprehensive Information ◽  
Wide Range ◽  
Microscopy Data ◽  
Good Agreement

X-ray reciprocal space mapping was used for quantitative investigation of porous layers in indium phosphide. A new theoretical model in the frame of the statistical dynamical theory for cylindrical pores was developed and applied for numerical data evaluation. The analysis of reciprocal space maps provided comprehensive information on a wide range of the porous layer parameters, for example, layer thickness and porosity, orientation, and correlation length of segmented pore structures. The results are in a good agreement with scanning electron microscopy data.

scholarly journals Thermal Examination of a Simplified Exhaust Tube-Heatshield Model

2018 ◽  
Vol 47 (3) ◽  
pp. 190-195 ◽  
Author(s):  
Balázs Vehovszky ◽  
Tamás Jakubík ◽  
Marcell Treszkai
Keyword(s):  
Natural Convection ◽  
Cross Flow ◽  
Exhaust System ◽  
Thermal Conditions ◽  
Forced Flow ◽  
Flow Conditions ◽  
Visualization Technique ◽  
Cfd Simulations ◽  
Critical Part ◽  
Parking Place

Exhaust system and its surrounding is a thermally highly critical part of a vehicle: during forced operation, hottest elements can reach 600 °C. The thermal conditions turn to even more critical if the forced flow leaves off – e.g. when the car stops at a highway parking place. In such a case not only the cooling effect of cross-flow disappears, but the natural convection starts to bring heat toward nearby elements – resulting potential overheating of concerned parts. A measurement setup for modelling such case was built, and different parameters were examined, which have influence on the heating of aluminium heatshield above the exhaust tube. Measurements were complemented by CFD simulations and flow visualization technique aiming the better understanding of evolving thermal and flow conditions.

scholarly journals Performance of WVSS-II hygrometers on the FAAM research aircraft

2015 ◽  
Vol 8 (3) ◽  
pp. 1617-1625 ◽  
Author(s):  
A. K. Vance ◽  
S. J. Abel ◽  
R. J. Cotton ◽  
A. M. Woolley
Keyword(s):  
Liquid Water ◽  
The Other ◽  
Optimal Conditions ◽  
Statistical Assessment ◽  
Free Data ◽  
Variable Nature ◽  
Wide Range ◽  
Research Aircraft ◽  
Using Data ◽  
Good Agreement

Abstract. We compare the performance of five hygrometers fitted to the Facility for Airborne Atmospheric Measurement's (FAAM) BAe 146-301 research aircraft using data from approximately 100 flights executed over the course of 2 years under a wide range of conditions. Bulk comparison of cloud free data show good agreement between chilled mirror hygrometers and a WVSS-II fed from a modified Rosemount inlet, but that a WVSS-II fed from the standard flush inlet appears to over-read compared to the other instruments, except at higher humidities. Statistical assessment of hygrometer performance in cloudy conditions is problematic due to the variable nature of clouds, so a number of case studies are used instead to investigate the performance of the hygrometers in sub-optimal conditions. It is found that the flush inlet is not susceptible to either liquid or solid water but that the Rosemount inlet has a significant susceptibility to liquid water and may also be susceptible to ice. In all conditions the WVSS-II responds much more rapidly than the chilled mirror devices, with the flush inlet-fed WVSS-II being more rapid than that connected to the Rosemount.

Numerical Simulations of Flow in Cerebral Aneurysms: Comparison of CFD Results and In Vivo MRI Measurements

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Vitaliy L. Rayz ◽  
Loic Boussel ◽  
Gabriel Acevedo-Bolton ◽  
Alastair J. Martin ◽  
William L. Young ◽  
...  
Keyword(s):  
Flow Fields ◽  
Patient Specific ◽  
Flow Ratio ◽  
Flow Conditions ◽  
Velocity Measurements ◽  
Cfd Simulations ◽  
Specific Flow ◽  
Inlet Flow ◽  
Good Agreement

Computational fluid dynamics (CFD) methods can be used to compute the velocity field in patient-specific vascular geometries for pulsatile physiological flow. Those simulations require geometric and hemodynamic boundary values. The purpose of this study is to demonstrate that CFD models constructed from patient-specific magnetic resonance (MR) angiography and velocimetry data predict flow fields that are in good agreement with in vivo measurements and therefore can provide valuable information for clinicians. The effect of the inlet flow rate conditions on calculated velocity fields was investigated. We assessed the internal consistency of our approach by comparing CFD predictions of the in-plane velocity field to the corresponding in vivo MR velocimetry measurements. Patient-specific surface models of four basilar artery aneurysms were constructed from contrast-enhanced MR angiography data. CFD simulations were carried out in those models using patient-specific flow conditions extracted from MR velocity measurements of flow in the inlet vessels. The simulation results computed for slices through the vasculature of interest were compared with in-plane velocity measurements acquired with phase-contrast MR imaging in vivo. The sensitivity of the flow fields to inlet flow ratio variations was assessed by simulating five different inlet flow scenarios for each of the basilar aneurysm models. In the majority of cases, altering the inlet flow ratio caused major changes in the flow fields predicted in the aneurysm. A good agreement was found between the flow fields measured in vivo using the in-plane MR velocimetry technique and those predicted with CFD simulations. The study serves to demonstrate the consistency and reliability of both MR imaging and numerical modeling methods. The results demonstrate the clinical relevance of computational models and suggest that realistic patient-specific flow conditions are required for numerical simulations of the flow in aneurysmal blood vessels.

Particle Resuspension in a Wall-Bounded Turbulent Flow

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
S. C. Fu ◽  
C. Y. H. Chao ◽  
R. M. C. So ◽  
W. T. Leung
Keyword(s):  
Angular Velocity ◽  
Uhlenbeck Process ◽  
Particle Resuspension ◽  
Air Stream ◽  
Safety And Health ◽  
Wide Range ◽  
Resuspension Rate ◽  
Mc Simulation ◽  
Using Data ◽  
Good Agreement

Resuspension is of common occurrence in a wide range of industrial and environmental processes. Excessive resuspension in these processes could have a severe impact on human safety and health. Therefore, it is necessary to develop a practical, yet reasonably accurate model to describe the resuspension phenomenon. It has been identified that rolling is the dominant mechanism for particle resuspension in the presence of an air stream, be it laminar or turbulent. Existing models predict the resuspension rate by regarding particles as being resuspended once they are set in motion; only a few of these models attempt to describe the full scenario, including rolling motion and the effect of turbulence. The objective of this paper is to propose a stochastic model to simulate the resuspension rate in the presence of a near-wall turbulent stream, and where the rolling mechanism is assumed to dominate the resuspension process. The fluctuating part of the angular velocity of a rolling particle is modeled by the Langevin equation (i.e., an Ornstein–Uhlenbeck process); thus, the overall angular velocity is modeled as a diffusion process. A free parameter of the proposed resuspension model is determined using data obtained from a Monte Carlo (MC) simulation of the problem. Once determined, the parameter is found to be universal for different materials and different sizes of particles tested. The modeling results obtained using this parameter are found to be in good agreement with experimental data, and the model performs better compared to other models.

scholarly journals NUMERICAL ANALYSIS OF THE NATURAL CONVECTION IN HORIZONTAL ANNULI AT LOW AND MODERATE Ra

2006 ◽  
Vol 5 (2) ◽  
pp. 58
Author(s):  
E. L. M. Padilla ◽  
R. Campregher ◽  
A. Silveira-Neto
Keyword(s):  
Natural Convection ◽  
Three Dimensional ◽  
Staggered Grid ◽  
Governing Equations ◽  
Concentric Cylinders ◽  
Wide Range ◽  
Horizontal Annuli ◽  
Rayleigh Numbers ◽  
The Heat Transfer Coefficient ◽  
Good Agreement

The natural convection at low and moderate Rayleigh numbers (Ra) incylindrical horizontal annuli with imposed temperatures in both surfaces isnumerically studied. This flow inside concentric cylinders classic configuration has a wide range of practical and technological applications, which justifies its growing studies efforts. In this work, the governing equations are discretized by the volume finite technique over a staggered grid, with second-order accuracy in space and time. The flow pattern is presented by several Rayleigh numbers, with an analysis of the heat transfer coefficient and flow properties. Furthermore, a three-dimensional field is shown at a moderate Ra number. The results showed a good agreement with the experimental data.

scholarly journals Experimental and numerical investigation of thermal and flow conditions inside a large pharmaceutical storage after the ventilation system failure

2021 ◽  
pp. 346-346
Author(s):  
Ilija Tabasevic ◽  
Rastko Jovanovic ◽  
Dragan Milanovic
Keyword(s):  
Temperature Distribution ◽  
Flow Field ◽  
Flow Rate ◽  
Ventilation System ◽  
Pharmaceutical Products ◽  
System Failure ◽  
Flow Conditions ◽  
Cfd Simulations ◽  
Depth Analysis ◽  
Good Agreement

Safe storage of pharmaceutical products is of great importance due to potential hazards for human health. The aim of this study was to assess the ability of pharmaceutical storage to recover design temperature during ventilation system recovery. The performed CFD simulations showed good agreement with experimental temperature measurements. Numerical results allowed in-depth analysis of flow field and temperature distribution inside the storage. It was discovered that the flow field is highly non-uniform, which consequently leads to an uneven temperature distribution of pallets with products. However, a high inlet mass flow rate ensured that all pallets reach the designed temperature.

Two-Phase Critical Flow under Diabatic Conditions

1969 ◽  
Vol 184 (3) ◽  
pp. 127-133
Author(s):  
A. E. Bergles ◽  
J. T. Kelly
Keyword(s):  
Experimental Investigation ◽  
Equilibrium Model ◽  
Small Diameter ◽  
Critical Flow ◽  
Subcooled Boiling ◽  
Flow Conditions ◽  
Two Phase ◽  
Wide Range ◽  
Good Agreement ◽  
Non Equilibrium

This paper summarizes an experimental investigation of steam-water critical flow in heated tubes. A wide range of data was taken for water at pressures below 100 lbf/in2 (abs.) in tubes of small diameter. It is demonstrated that critical flow conditions can occur in subcooled boiling at low exit subcoolings. At equilibrium qualities below about 0·04, the data differ significantly from adiabatic data for a similar exit geometry. The deviations can be explained in terms of the additional non-equilibrium effects present in heated flows. For higher qualities, the diabatic data are in good agreement with adiabatic data, and can be approximately predicted by a slip equilibrium model.

scholarly journals Structural and photometric properties of barred galaxies from the Auriga cosmological simulations

2019 ◽  
Vol 491 (2) ◽  
pp. 1800-1819 ◽  
Author(s):  
Guillermo Blázquez-Calero ◽  
Estrella Florido ◽  
Isabel Pérez ◽  
Almudena Zurita ◽  
Robert J J Grand ◽  
...  
Keyword(s):  
Cold Dark Matter ◽  
Structural Parameters ◽  
Broad Band ◽  
Numerical Data ◽  
Cosmological Simulations ◽  
Barred Galaxies ◽  
Secular Evolution ◽  
Cosmological Context ◽  
Wide Range ◽  
Good Agreement

ABSTRACT In this work we analyse the structural and photometric properties of 21 barred simulated galaxies from the Auriga Project. These consist of Milky Way-mass magnetohydrodynamical simulations in a Λ cold dark matter (ΛCDM) cosmological context. In order to compare with observations, we generate synthetic SDSS-like broad-band images from the numerical data at z = 0 with different inclinations (from face-on to edge-on). Ellipse fits are used to determine the bar lengths, and 2D bulge/disc/bar decompositions with galfit are also performed, modelling the bar component with the modified Ferrer profile. We find a wide range of bar sizes and luminosities in the sample, and their structural parameters are in good agreement with the observations. All bulges present low Sérsic indexes, and are classified as pseudobulges. In regard to the discs, the same breaks in the surface brightness profiles observed in real galaxies are found, and the radii at which these take place are in agreement with the observations. Also, from edge-on unsharp-masked images at z = 0, boxy or peanut-shaped (B/P) structures are clearly identified in the inner part of four bars, and also two more bars are found in buckling phase. The sizes of the B/P match fairly well with those obtained from observations. We thus conclude that the observed photometric and structural properties of galaxies with bars, which are the main drivers of secular evolution, can be developed in present state-of-the-art ΛCDM cosmological simulations.

Models and Experiments for Laminar Natural Convection From Heated Bodies in Enclosures

Volume 1 ◽  
2004 ◽  
Author(s):  
Peter M. Teertstra ◽  
M. Michael Yovanovich ◽  
J. Richard Culham
Keyword(s):  
Natural Convection ◽  
Analytical Study ◽  
Convection Heat Transfer ◽  
Transition Flow ◽  
Reduced Pressure ◽  
Heated Body ◽  
Wide Range ◽  
Diffusive Limit ◽  
Laminar Natural Convection ◽  
Transient Measurement

A combined experimental and analytical study of natural convection heat transfer in the enclosure formed between a convex shaped, isothermal heated body and its concave shaped, surrounding isothermal enclosure is presented. An experimental test program is conducted at atmospheric and reduced pressure conditions using a transient measurement technique for various enclosure configurations, including concentric cubes, cube-in-sphere, sphere-in-cube, and other geometries. Measurements are reported for a wide range of Rayleigh number, including the diffusive limit. An analytical modeling procedure is developed based on a composite solution of three asymptotic relationships, the conduction limit, the laminar boundary layer and transition flow convective limits. The composite model is in excellent agreement with the data, with an average RMS difference of 2–7% for all enclosure configurations and test conditions.

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