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Thermal Boundary Conditions (thermal + boundary_condition)

Distribution by Scientific Domains

Engineering	80%

Selected Abstracts

DNS of turbulent heat transfer in a channel flow with a varying streamwise thermal boundary condition

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2006
Yohji Seki
Abstract Direct numerical simulation (DNS) was performed for the turbulent heat transfer in a channel flow. In the present study, the effect of the thermal boundary condition was examined. DNS was carried out for varying streamwise thermal boundary conditions (Re, = 180) with Pr = 0.71 to obtain statistical mean temperatures, temperature variances, budget terms, and time scale ratios. The results obtained indicate that the time scale ratio varies along the stream direction. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(4): 265,278, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20114 [source]

A simulation of the non-isothermal resin transfer molding process

POLYMER ENGINEERING & SCIENCE, Issue 12 2000
Vincenza Antonucci
A simulation of the non-isothermal resin transfer molding manufacturing process accounting for both the filling and the consolidation stage has been developed. The flow of an exothermally reactive resin through a porous medium has been analyzed with reference to the Darcy law, allowing for the chemorheological properties of the reacting resin. Thermal profile calculations have been extended to a three phase domain, namely the mold, the dry preform and the filled preform. The mold has been included in order to evaluate the thermal inertial effects. The energy balance equation includes the reaction term together with the conductive and convective terms, and particular attention has been devoted to setting the thermal boundary condition at the flow front surface. The moving boundary condition has been derived by a jump equation. The simulation performance has been tested by comparing the predicted temperature profiles with experimental data from literature. Further numerical analysis assessed the relevance of using the jump equation at the flow front position for both filling time and thermal profile determination. [source]

Effects of Viscous Dissipation on Heat Transfer between an Array of Long Circular Cylinders and Power Law Fluids

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2007
R. P. Chhabra
Abstract The free surface model has been combined with the equations of motion and of thermal energy to investigate the role of viscous dissipation on heat transfer between banks of long cylinders and power law (shear-thinning and shear-thickening) fluids. The equations of motion cast in the stream function/vorticity formulation have been solved numerically using a second-order accurate finite difference method to obtain extensive information on the behaviour of local and surface-averaged Nusselt numbers over a range of Reynolds numbers 1 , 500, for a wide range of power law indices (0.4 , n , 2.0), Brinkman numbers (0 , Br , 5) and Prandtl numbers (Pr = 1, 1000) at two representative solid volume fractions corresponding to the porosities of e = 0.4 and 0.9. Two different thermal boundary conditions are considered at the cylinder surface: constant temperature (CT) and constant heat flux (CHF). The results presented herein provide a fundamental knowledge about the influence of viscous dissipation on the heat transfer characteristics. The results reported herein further show that the effect of Brinkman number on heat transfer is strongly conditioned by the thermal boundary condition, Prandtl number and the power law index. On a combiné le modèle de surface libre aux équations de mouvement et de transfert de chaleur afin d'étudier le rôle de la dissipation visqueuse sur le transfert de chaleur entre des rangées de cylindres longs pour des fluides de loi de puissance (rhéofluidifiants et rhéoépaississants). Les équations de mouvement formulées en fonction de courant/vorticité ont été résolues numériquement à l'aide d'une méthode de différences finies du second ordre, afin d'obtenir des informations détaillées sur le comportement des nombres de Nusselt locaux et moyennés en surface pour une gamme de nombres de Reynolds compris entre 1 et 500, une large gamme d'indices de loi de puissance (0,4 , n , 2,0), de nombres de Brinkman (0 , Br , 5) et de nombres de Prandtl (Pr = 1,1000) à deux fractions de volume de solides correspondant à une porosité de e = 0,4 et 0,9. Deux conditions aux limites thermiques ont été considérées à la surface du cylindre: la température constante (CT) et le flux de chaleur constant (CHF). Les résultats présentés permettent de rendre compte de l'influence de la dissipation visqueuse sur les caractéristiques du transfert de chaleur et l'effet du nombre de Brinkman sur le transfert de chaleur qui est fortement influencé par la condition aux limites thermique, le nombre de Prandtl et l'indice de loi de puissance. [source]

Temperature drop analysis of the thruster in a space cryogenic environment

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2007
Ze-Juan Xiao
Abstract Based on the conservation of energy, a coupling heat-transfer physical model and a set of mathematical equations are put forward to calculate the main components of the thruster, including the capillary injection tube, the aggregate organ, the injection plate, and the bracket when they are exposed to a space cryogenic environment. The typical temperature drop course of a 10N monopropellant thruster has been calculated by this computational model. The calculation results agree well with test data in a vacuum cryogenic simulation experiment performed on the ground. The temperature of the injection tube provides the thermal boundary conditions for the propellant temperature drop calculation while flowing through it. This provided the criterion to judge whether the propellant freezes or not. The upper stage has no air conditioning, so the injection tube is a weak link for the cryogenic reliability work of the thruster. This is considered one of the most important areas of the whole for reliability research. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(2): 85,95, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20144 [source]

DNS of turbulent heat transfer in a channel flow with a varying streamwise thermal boundary condition

Reverse computation of forced convection heat transfer for optimal control of thermal boundary conditions

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2004
Kazunari Momose
Abstract A reverse computation based on adjoint formulation of forced convection heat transfer is proposed to obtain the optimal thermal boundary conditions for heat transfer characteristics; for example, a total heat transfer rate or a temperature at a specific location. In the reverse analysis via adjoint formulation, the heat flow is reversed in both time and space. Thus, using the numerical solution of the adjoint problem, we can inversely predict the boundary condition effects on the heat transfer characteristics. As a result, we can obtain the optimal thermal boundary conditions in both time and space to control the heat transfer at any given time. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(3): 161,174, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20002 [source]

Consistent coupling of beam and shell models for thermo-elastic analysis

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 14 2004
K. S. Chavan
Abstract In this paper, the finite element formulation of a transition element for consistent coupling between shell and beam finite element models of thin-walled beam-like structures in thermo-elastic problems is presented. Thin-walled beam-like structures modelled only with beam elements cannot be used to study local stress concentrations or to provide local mechanical or thermal boundary conditions. For this purpose, the structure has to be modelled using shell elements. However, computations using shell elements are a lot more expensive as compared to beam elements. The finite element model can be more efficient when the shell elements are used only in regions where the local effects are to be studied or local boundary conditions have to be provided. The remaining part of the structure can be modelled with beam elements. To couple these two models (i.e. shell and beam models) at transitional cross-sections, transition elements are derived here for thermo-elastic problems. The formulation encloses large displacement and rotational behaviour, which is important in case of thin-walled beam-like structures. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Inverse design of directional solidification processes in the presence of a strong external magnetic field

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2001
Rajiv Sampath
Abstract A computational method for the design of directional alloy solidification processes is addressed such that a desired growth velocity ,f under stable growth conditions is achieved. An externally imposed magnetic field is introduced to facilitate the design process and to reduce macrosegregation by the damping of melt flow. The design problem is posed as a functional optimization problem. The unknowns of the design problem are the thermal boundary conditions. The cost functional is taken as the square of the L2 norm of an expression representing the deviation of the freezing interface thermal conditions from the conditions corresponding to local thermodynamic equilibrium. The adjoint method for the inverse design of continuum processes is adopted in this work. A continuum adjoint system is derived to calculate the adjoint temperature, concentration, velocity and electric potential fields such that the gradient of the L2 cost functional can be expressed analytically. The cost functional minimization process is realized by the conjugate gradient method via the FE solutions of the continuum direct, sensitivity and adjoint problems. The developed formulation is demonstrated with an example of designing the boundary thermal fluxes for the directional growth of a germanium melt with dopant impurities in the presence of an externally applied magnetic field. The design is shown to achieve a stable interface growth at a prescribed desired growth rate. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Level-set based numerical simulation of a migrating and dissolving liquid drop in a cylindrical cavity

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2004
Edmondo Bassano
Abstract In the present paper the dissolution of a binary liquid drop having a miscibility gap and migrating due to thermo-solutal capillary convection in a cylindrical cavity is studied numerically. The interest in studying this problem is twofold. From a side, in the absence of gravity, capillary migration is one of the main physical mechanisms to set into motion dispersed liquid phases and from the other side, phase equilibria of multi-component liquid systems, ubiquitous in applications, often exhibit a miscibility gap. The drop capillary migration is due to an imposed temperature gradient between the cavity top and bottom walls. The drop dissolution is due to the fact that initial composition and volume values, and thermal boundary conditions are only compatible with a final single phase equilibrium state. In order to study the drop migration along the cavity and the coupling with dissolution, a previously developed planar two-dimensional code is extended to treat axis-symmetric geometries. The code is based on a finite volume formulation. A level-set technique is used for describing the dynamics of the interface separating the different phases and for mollifying the interface discontinuities between them. The level-set related tools of redistancing and off-interface extension are used to enhance code resolution in the critical interface region. Migration speeds and volume variations are determined for different drop radii. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Second-law analysis and optimization of microchannel flows subjected to different thermal boundary conditions

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2005
Kuan Chen
Abstract Entropy generation and transfer in microchannel flows were calculated and analyzed for different thermal boundary conditions. Due to the small flow cross-sectional area, fluid temperature variation in the lateral direction was neglected and a laterally lumped model was developed and used in the first- and second-law analyses. Since the Peclet numbers of microchannel flows are typically low, heat conduction in the flow direction was taken into consideration. Computed fluid temperature and entropy generation rate were cast into dimensionless forms, thus can be applied to different fluids and channels of different sizes and configurations. Local entropy generation rate was found to be only dependent upon the temperature gradient in the flow direction. The optimization results of microchannel flows exchanging heat with their surroundings indicate the optimal fluid temperature distribution is a linear one. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Effects of Viscous Dissipation on Heat Transfer between an Array of Long Circular Cylinders and Power Law Fluids

Dynamisch-thermisches CFD-Verfahren mit angepaßter Regelungsmethode

BAUPHYSIK, Issue 1 2007
Tobias Zitzmann Dipl.-Ing. (FH)
Zur Reduktion des Zeitaufwands von dynamisch-thermischen Langzeitsimulationen mit CFD-Programmen wurde in kürzlich veröffentlichten Studien eine neuartige Freeze-Flow Methode vorgestellt. Diese basiert auf der periodischen Umschaltung zwischen der volldynamischen Lösung aller Gleichungen und der ausschließlichen Lösung der Enthalpie-Gleichungen (eingefrorene Luftströmung). Dieser Artikel beschreibt eine neue, angepaßte Regelung für diese Umschaltung, wodurch eine zusätzliche Reduzierung der Simulationszeit erzielt wird. In Tests an Modellen für die mechanische und freie Lüftung sowie der freien Konvektion im geschlossenen Raum für feste und zeitveränderliche thermische Randbedingungen wurde im Vergleich zur ununterbrochenen volldynamischen Simulation eine Simulationszeiteinsparung von bis zu 93% erreicht. Dynamic thermal CFD approach using an adaptive control method. Previously published studies have presented a novel freeze-flow method for reducing CPU requirements of long-term dynamic thermal simulations using CFD programs. This works by intermittently switching between solution of the full dynamic equations and solution of the enthalpy equation only (frozen flow). This paper describes a new automated control method for this switching strategy and shows an additional decrease in simulation time. In tests with models for mechanical and natural ventilation and for free convection in a sealed room with constant and time varying thermal boundary conditions, a simulation time reduction of up to 93% was achieved when compared to a continuous fully dynamic simulation. [source]