scholarly journals Convection regimes induced by local boundary heating in a liquid–gas system

2019 ◽  
Vol 873 ◽  
pp. 441-458 ◽  
Author(s):  
Victoria B. Bekezhanova ◽  
A. S. Ovcharova
Keyword(s):  
Gas Flow ◽  
Stokes Equations ◽  
Local Heating ◽  
Fluid Motion ◽  
Lower Boundary ◽  
Conjugate Problem ◽  
Temperature Fields ◽  
Layer System ◽  
Local Boundary ◽  
The Impact

In the framework of the complete formulation of the conjugate problem, the liquid–gas flow structure arising upon local heating using thermal sources is investigated numerically. The two-layer system is confined by solid impermeable walls. The Navier–Stokes equations in the Boussinesq approximation in the ‘streamfunction–vorticity’ variables are used to describe the media motion. The dynamic conditions at the interface are formulated in terms of the tangential and normal velocities, while the temperature conditions at the external boundaries of the system take into account the presence of local heaters. The influence of the number of heaters and heating modes on the dynamics and character of the appearing convective regimes is analysed. The steady and commutated heating modes for one and two heaters arranged at the lower boundary are investigated. The heating initiates convective and thermocapillary mechanisms causing the fluid motion. Transient regimes with the successive formation of two-vortex, quadruple-vortex and two-vortex flows are observed before the stabilization of the system in the uniform heating mode. A stable thermocapillary deflection appears at the interface above the heater. The commutated mode of heating entails oscillations of the interface with a change in the deflection form and the formation of travelling vortices in the fluids. The impact of particular mechanisms on the flow patterns is analysed. The paper presents typical distributions of the velocity and temperature fields in the system and the position of the interface for the considered cases.

Braking System Cooling Time Simulation

2003 ◽  
Author(s):  
Luiz Tobaldini Neto ◽  
Ramon Papa ◽  
Luis C. de Castro Santos
Keyword(s):  
Stokes Equations ◽  
Thermal Environment ◽  
Computational Cost ◽  
Calibration Procedure ◽  
Accurate Solution ◽  
Temperature Fields ◽  
Convection Flow ◽  
Time Interval ◽  
Braking System ◽  
The Impact

Aircraft braking pads are subject to an extremely severe thermal environment. During a typical landing the carbon brake pads can reach temperatures up to 700–800 K or even more. Between landings during the taxi and parking phase the brakes have to cool off back to their operational limits in a time interval consistent with the average operational time. In order to evaluate the impact of design modifications on the wheel mounting and fairings, without the need of extensive laboratory and flight campaigns, a CFD (Computational Fluid Dynamics) based methodology was developed. Due to the geometry complexity the need of a geometrically representative, but simplified model comes up, in order to capture the major features of the natural convection flow and temperature fields and can be used to evaluate the influence of design changes on the braking system cooling times. A calibration procedure is carried out, aiming a better representation of the transient phenomenon, using a thermal resistances setting up feature from the solver used. An example of the application of this methodology is presented. A computational grid of over 700,000 tetrahedral elements was constructed and the Navier-Stokes equations are solved using a commercial package (FLUENT). The computational cost for a time accurate solution demands the use of parallel processing in order to complete the analysis in a typical industrial environment timeframe. Comparison with both laboratory and flight data calibrate and validate the results of the computational model. This paper describes the details of the construction of the CFD model, the setting of the initial and boundary conditions and the comparison between measured and simulated parameters.

scholarly journals Modeling the conjugate problem of heat transfer at hot jet impingement onto a cooled surface

2021 ◽  
Vol 2119 (1) ◽  
pp. 012157
Author(s):  
V V Lukashov ◽  
V S Naumkin
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Flat Plate ◽  
Gas Flow ◽  
Jet Impingement ◽  
Conjugate Problem ◽  
Heat Fluxes ◽  
The Other ◽  
Local Maxima ◽  
The Impact

Abstract The paper solves the problem of thermal conductivity inside a flat plate under the impact of a hot jet of nitrogen impinging from one side and cooled by a gas flow from the other side. In this formulation of the problem, there may be local maxima and minima of the temperature inside the plate, caused by an uneven distribution of heat fluxes along the plate.

scholarly journals Construction of Exact Solution Describing Three-layer Flows with Evaporation in a Horizontal Channel

2021 ◽  
pp. 57-68
Author(s):  
Ekaterina V. Rezanova
Keyword(s):  
Exact Solution ◽  
Gas Flow ◽  
Stokes Equations ◽  
Silicone Oil ◽  
Boussinesq Approximation ◽  
Navier Stokes ◽  
Layer System ◽  
Soret And Dufour Effects ◽  
Navier Stokes Equations ◽  
Liquid Evaporation

The paper considers the flow in a three-layer system "liquid–liquid–gas" in a horizontal chan- nel with solid impermeable walls.The evaporation process at the thermocapillary interface of the liquid and gas is taken into account. The Soret and Dufour effects are taken into account in the upper layer filled with a gas-vapor mixture. The system of Navier-Stokes equations in the Boussinesq approximation is used as a mathematical model. A temperature regime is set on the channel walls. Liquid evaporation is modeled using the conditions at the liquid-gas interface. Exact solution of a special type describing the flow in a three-layer system is constructed. The velocity profiles are presented on the example of the "silicone oil–water–air" system for various values of gas flow rate, longitudinal temperature gradients at the system boundaries, thicknesses of liquid and gas-vapor layers

Cavity flows driven by buoyancy and shear

1972 ◽  
Vol 51 (2) ◽  
pp. 221-231 ◽  
Author(s):  
K. Torrance ◽  
R. Davis ◽  
K. Eike ◽  
P. Gill ◽  
D. Gutman ◽  
...  
Keyword(s):  
Numerical Solutions ◽  
Stokes Equations ◽  
Fluid Motion ◽  
Temperature Fields ◽  
Navier Stokes ◽  
Cavity Flows ◽  
Navier Stokes Equations ◽  
Moving Wall ◽  
Aspect Ratios ◽  
Range Of Values

Fluid motion driven by the combined effects of a moving wall and natura convection is examined for rectangular cavities with heightlwidth ratios of ½, 1 and 2. The Reynolds number and Prandtl number are held fixed at Re = 100 and Pr = 1; the Grashof number is varied over the range of values Gr = 0, ±104, ±106. Flow and temperature fields obtained from numerical solutions of the Navier-Stokes equations reveal a marked influence of buoyancy for the larger aspect ratios when Gr = ±106 and the dominance of buoyancy for all aspect ratios when Gr = ± 106. Results are compared with earlier work where possible and some observations are offered on the convergence of the numerical solutions.

Simulation of Flow, Heat and Mass Transfer in a Curing Oven

2006 ◽  
Author(s):  
Somesh Soni ◽  
Thomas S. Neeley ◽  
Jayathi Y. Murthy
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Thermal Performance ◽  
Performance Index ◽  
Gas Flow ◽  
Temperature Fields ◽  
Thermal Mass ◽  
Air Temperatures ◽  
Flow Heat ◽  
The Impact

Flow, heat and mass transfer in a paint curing oven are studied numerically with a view to improving the energy efficiency of the oven and to control pollution. Painted products traverse the paint curing oven at a constant rate and in a fixed trajectory, and are heated by hot air jets which control the part temperature to ensure paint curing. Steady simulations are performed to compute the air flow and temperature fields. Computed air temperatures match experimentally measured values to an accuracy of 19% (temperatures calculated relative to the room temperature). Assuming thermal equilibrium between the painted part and the local gas flow, positiondependent smoke release rates due to paint curing are computed from the part temperature using experimentally measured cure rates. Smoke is modeled as a gas-phase species in a dilute mixture with air and its concentration and distribution in the oven are computed. The thermal behavior of the oven is captured in a parameter called the thermal performance index. The exhaust air mass flux is shown to have large impact on this index. Smoke loss to the outside environment is computed to quantify the degree of pollution. The impact of air seals on the thermal performance index and smoke release to the environment are quantified. Finally the effect of the thermal mass of the parts is considered and the convective and radiative effects are studied.

scholarly journals Calculation of gas flow rates in concentrated fire vortices

2019 ◽  
pp. 108-114
Author(s):  
A. G. Obukhov ◽  
L. I. Maksimov
Keyword(s):  
Gas Flow ◽  
Stokes Equations ◽  
Local Heating ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Initial Boundary ◽  
Initial Boundary Value Problem ◽  
Approximate Solutions ◽  
Navier Stokes ◽  
Heat Conducting

The article presents the results of numerical simulation of the generation of free fire vortices in the laboratory without the use of special twisting devices. A. Yu. Varaksin, the corresponding member of the Russian Academy of Sciences, in his experimental studies has described the principal possibility of physical modeling of the occurrence of concentrated fire vortices.  In the model of a compressible continuous medium for the complete system of Navier — Stokes equations, an initial-boundary value problem has been proposed that describes complex three-dimensional unsteady flows of a viscous compressible heat-conducting gas in ascending swirling heat flows. We has constructed approximate solutions of the complete Navier — Stokes system of equations and has determined velocity characteristics of threedimensional unsteady gas flows initiated by local heating of the underlying surface by nineteen heat sources, using explicit difference schemes and the proposed initial-boundary conditions.  

scholarly journals Darcy-Benard double diffusive Marangoni convection in a composite layer system with constant heat source along with non uniform temperature gradients

2021 ◽  
Vol 17 (1) ◽  
pp. 7-15
Author(s):  
N Manjunatha ◽  
R Sumithra ◽  
R K Vanishree
Keyword(s):  
Marangoni Number ◽  
Marangoni Convection ◽  
Composite Layer ◽  
Lower Boundary ◽  
Temperature Gradients ◽  
Layer System ◽  
Constant Heat ◽  
The Impact ◽  
Double Diffusive ◽  
Diffusivity Ratio

The problem of Benard double diffusive Marangoni convection is investigated in a horizontally infinite composite layer system enclosed by adiabatic boundaries for Darcy model. This composite layer is subjected to three temperature gradients with constant heat sources in both the layers. The lower boundary of the porous region is rigid and upper boundary of the fluid region is free with Marangoni effects. The Eigenvalue problem of a system of ordinary differential equations is solved in closed form for the Thermal Marangoni number, which happens to be the Eigen value. The three different temperature profiles considered are linear, parabolic and inverted parabolic profiles with the corresponding thermal Marangoni numbers are obtained. The impact of the porous parameter, modified internal Rayleigh number, solute Marangoni number, solute diffusivity ratio and the diffusivity ratio on Darcy-Benard double diffusive Marangoni convection are investigated in detail.

scholarly journals A Model for the Thermal Behaviour of an Offshore Cable Installed in a J-Tube

Proceedings ◽  
2020 ◽  
Vol 58 (1) ◽  
pp. 31
Author(s):  
Jeremy Arancio ◽  
Ahmed Ould El Moctar ◽  
Minh Nguyen Tuan ◽  
Faradj Tayat ◽  
Jean-Philippe Roques
Keyword(s):  
Sensitivity Analysis ◽  
Numerical Model ◽  
Thermal Behaviour ◽  
Energy Production ◽  
Power Transmission ◽  
Temperature Fields ◽  
Sobol Indices ◽  
Lumped Element ◽  
Thermal Phenomena ◽  
The Impact

In the race for energy production, supplier companies are concerned by the thermal rating of offshore cables installed in a J-tube, not covered by IEC 60287 standards, and are now looking for solutions to optimize this type of system. This paper presents a numerical model capable of calculating temperature fields of a power transmission cable installed in a J-tube, based on the lumped element method. This model is validated against the existing literature. A sensitivity analysis performed using Sobol indices is then presented in order to understand the impact of the different parameters involved in the heating of the cable. This analysis provides an understanding of the thermal phenomena in the J-tube and paves the way for potential technical and economic solutions to increase the ampacity of offshore cables installed in a J-tube.

scholarly journals The High-Rate Sealed MRPC to Promote Pollutant Exchange in Gas Gaps: Status on the Development and Observations

2021 ◽  
Vol 11 (11) ◽  
pp. 4722
Author(s):  
Botan Wang ◽  
Xiaolong Chen ◽  
Yi Wang ◽  
Dong Han ◽  
Baohong Guo ◽  
...  
Keyword(s):  
Gas Flow ◽  
High Rate ◽  
Stable Operation ◽  
Beam Test ◽  
High Luminosity ◽  
Rate Test ◽  
3D Printed ◽  
Resistive Plate Chambers ◽  
The Impact ◽  
Current Behavior

This work reports the latest observations on the behavior of two Multigap Resistive Plate Chambers (MRPC) under wide high-luminosity exposures, which motivate the development and in-beam test of the sealed MRPC prototype assembled with low-resistive glass. The operation currently being monitored, together with previous simulation results, shows the impact of gas pollution caused by avalanches in gas gaps, and the necessity to shrink the gas-streaming volume. With the lateral edge of the detector sealed by a 3D-printed frame, a reduced gas-streaming volume of ~170 mL has been achieved for a direct gas flow to the active area. A high-rate test of the sealed MRPC prototype shows that, ensuring a 97% efficiency and 70 ps time resolution, the sealed design results in a stable operation current behavior at a counting rate of 3–5 kHz/cm2. The sealed MRPC will become a potential solution for future high luminosity applications.

Numerical Integration of the Navier-Stokes Equations for a Disk Rotating in a Housing

1985 ◽  
Vol 40 (8) ◽  
pp. 789-799 ◽  
Author(s):  
A. F. Borghesani
Keyword(s):  
Boundary Layer ◽  
Cylindrical Cavity ◽  
Boundary Layer Thickness ◽  
Stokes Equations ◽  
Fluid Motion ◽  
Rotating Disk ◽  
Infinite Medium ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Viscous Torque

The Navier-Stokes equations for the fluid motion induced by a disk rotating inside a cylindrical cavity have been integrated for several values of the boundary layer thickness d. The equivalence of such a device to a rotating disk immersed in an infinite medium has been shown in the limit as d → 0. From that solution and taking into account edge effect corrections an equation for the viscous torque acting on the disk has been derived, which depends only on d. Moreover, these results justify the use of a rotating disk to perform accurate viscosity measurements.

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