Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
3
1
2011
TRANSIENT CONJUGATED UPWARD AND DOWNWARD MIXED CONVECTION IN A PARTIALLY HEATED THICK PIPE
1-14
Abdeslam
Omara
Université des Frères Mentouri Constantine 1, Département de Physique, Constantine, Algeria
Said
Abboudi
Laboratoire Interdisciplinaire Carnot de Bourgogne, ICB UMR 6303 CNRS, Université
Bourgogne Franche Comté (UBFC), UTBM, site de Sévenans 90010 Belfort cedex, France
Transient conjugated downward and upward laminar mixed-convection heat transfer in a vertical pipe, partially submitted to a constant heat flux, has been investigated computationally. The governing Navier-Stokes and energy equations were solved by a code developed using the finite volume method and Boussinesq's assumptions. Solutions were obtained for (Pr, Re, Gr) = (5,100, 5 × 105), wall-to-fluid conductivity ratio K = 10, 50, and 100, and pipe thickness-to-diameter ratios Δ = 0.05 and 0.25. From a parametric study, transient distribution of the normalized interfacial heat flux and of the friction coefficient ratio as a function of the axial coordinates as well as transient evolution of the vector velocities were obtained and the effect of K and Δ investigated. It was found that the magnitude and the extent of upstream and downstream heating increase monotonically with an increase of Δ or K. In turn, this heat flux redistribution significantly affects the friction coefficient ratio and velocity field in the downstream and upstream adiabatic sections for the downward and upward mixed-convection cases.
NUMERICAL SIMULATION OF HEAT AND MASS TRANSFER BETWEEN HETEROGENEOUS FLOW AND AN OBSTACLE
15-30
T. V.
Ershova
Institute of High Temperatures of the Russian Academy of Science, Moscow, Russia, 127412
D. S.
Mikhatulin
Institute of High Temperatures of the Russian Academy of Science, Moscow, Russia, 127412
Dmitry L.
Reviznikov
Moscow Aviation Institute, Volokolamskoe Shosse 4, 125993 Moscow, Russia; Dorodnicyn Computing Centre, Federal Research Center "Computer Science and Control" of Russian Academy of Sciences, 44, b. 2, Vavilov st., Moscow, 119333, Russia
Andrey V.
Sposobin
Moscow Aviation Institute, Volokolamskoe Shosse 4, 125993 Moscow, Russia
Vladimir V.
Vinnikov
Moscow Aviation Institute (State Technical University), Moscow, Russia
This paper describes the problems of numerical simulation of supersonic gas-particle flow over blunt bodies. A complex mathematical model is proposed, coupling gas flow in the shock layer, particle advection in the carrying phase, and heat- mass transfer in the body that is being destroyed. The Eulerian description fits best for the gas phase, and the Lagrangian description is most suitable for the dispersed phase. Particle dynamics is fully handled via the discrete-element method. The result is a numerical simulation of the thermoerosive destruction of a circular cylinder in two-phase flow. The authors present an analysis of multiple factors, such as interparticle collisions in a flow, particle reflection from a streamlined surface, dispersed admixture feedback on the carrier phase, and the influence of changing body geometry due to mass entrainment on two-phase shock layer parameters.
VISUALIZATION OF HEAT TRANSFER IN UNSTEADY LAMINAR FLOWS
31-47
Michel F. M.
Speetjens
Energy Technology, Mechanical Engineering, Eindhoven University of Technology
Anton A.
van Steenhoven
Faculty of Mechanical Engineering, Energy Technology Section, Den Dolech 2, 5600MB, Eindhoven, The Netherlands
Heat transfer in fluid flows traditionally is examined in terms of temperature fields and heat-transfer coefficients. However, heat transfer may alternatively be considered as the transport of thermal energy by the total convective-conductive heat flux in a way analogous to the transport of fluid by the flow field1. The paths followed by the total heat flux are the thermal counterpart to fluid trajectories and facilitate heat-transfer visualization in a similar manner as flow visualization. This has great potential for applications in which insight into the heat fluxes throughout the entire configuration is essential (e.g., cooling systems, heat exchangers). To date, this concept has been restricted primarily to steady flows; generalization to unsteady flows is a very recent development and depends on representation of heat transfer as the "motion" of a virtual "fluid" subject to continuity. The present study expands on this generalization and demonstrates its application for thermal analyses by way of examples. Furthermore, a fundamental analogy between fluid motion and heat transfer is addressed that may pave the way to future heat-transfer studies by well-established geometrical methods from laminar-mixing studies.
PREDICTION OF TURBULENT HEAT TRANSFER IN RADIALLY OUTWARD FLOW IN A TWISTED-TAPE INSERTED TUBE ROTATING IN ORTHOGONAL MODE
49-61
Brijkishore
Soni
Mechanical Engineering Department, Indian Institute of Technology Bombay
Anil W.
Date
Department Mechanical Engineering, Indian Institute of Technology, Bombay
This paper presents numerically computed pressure-drop and heat-transfer characteristics of turbulent developing flow in a tube rotating in orthogonal mode. The tube is fitted with a twisted tape. The flow is radially outward. Numerical predictions are obtained by solving three-dimensional elliptic transport equations in a tube with a length-to-diameter ratio of 14.5. Turbulence effects are captured through use of 8 high-Reynolds-number form of the k − ε model. It is assumed that the tube is at axially and peripherally constant wall temperature and that the tape is perfectly conducting. Numerical predictions are obtained for both clockwise and counter-clockwise tape twist with respect to the direction of the tube axis. Axial variations of the apparent friction factor and of the Nusselt number are presented for air (Pr = 0.7) for 10, 000 < Re < 50, 000, twist ratio 3 ≤ Y ≤ ∞, rotation number 0 ≤ Ro ≤ 0.15, and buoyancy parameter 0 ≤ ΒΔT ≤ 0.30.
SELF-SUSTAINED OSCILLATIONS AND BIFURCATIONS OF MIXED CONVECTION IN A MULTIPLE VENTILATED ENCLOSURE
63-72
Ming
Zhao
University of Shanghai for Science and Technology
M.
Yang
University of Shanghai for Science and Technology, Shanghai, China
Mei
Lu
School of Energy and Power Engineering, University of Shanghai for Science and Technology, 516 Jun Gong Road, Shanghai, 200093, P. R. China
Yuwen
Zhang
University of Missouri, Columbia, MO 65201, USA
A numerical study is made of the self-sustained oscillations and bifurcations of mixed convection in a two-dimensional multiple ventilated enclosure. These two mechanisms of buoyancy [Richardson number (Ri) is a measure] and forcing by the inlet flow [Reynolds number (Re) is a measure] lead to complex interaction. The results are obtained for a range of the Richardson number from 0 to 20 at Pr = 0.701, and the Reynolds number is given in a range of 1000-2500. The results show that depending on the values of Re and Ri, the flow inside the enclosure may be steady, periodic, nonperiodic, or turbulent; and the velocity and temperature fields may show an asymmetric structure for certain combinations of the control parameters, even though the boundary conditions are steady and symmetric. Further, certain features of nonlinear dynamical systems such as bifurcation, self-sustained oscillations are also seen. The simulation results also show that when the inlet flow angle θ (θ) equals 70° (proved to be the most unstable among four given values of θ) the enclosure loses its stability at Re = 1500, Ri = 0, and Re = 1000, Ri = 0.5; transforms into periodic oscillatory flow via the steady symmetry breaking Hopf bifurcation; and becomes nonperiodic-unstable at Re = 2000
COMBINED EFFECTS OF RADIATION AND NATURAL CONVECTION IN A SQUARE CAVITY SUBMITTED TO CROSS GRADIENTS OF TEMPERATURE: CASE OF PARTIAL HEATING AND COOLING
73-87
R.
El Ayachi
Sultan Moulay Slimane University, Faculty of Sciences and Technologies, Department of Physics, Laboratory of Flows and Transfers Modelling (LAMET), B.P. 523, Beni-Mellal 23000, Morocco
Abdelghani
Raji
Sultan Moulay Slimane university, Faculty of Sciences and Technologies, Physics Department, UFR of Sciences and Engineering of Materials, Team of Flows and Transfers Modelling (EMET), B.P. 523, Béni-Mellal, Morocco
Mohammed
Hasnaoui
Cadi Ayyad University, Faculty of Sciences Semlalia, Physics Department, UFR TMF, Laboratory of Fluid Mechanics and Energetics (LMFE), B.P. 2390, Marrakech, Morocco
A.
Abdelbaki
Cadi Ayyad University, Faculty of Sciences Semlalia, Department of Physics, Laboratory of Fluid Mechanics and Energetics (LMFE), Unit affiliated to CNRST (URAC, 27), B.P. 2390, Marrakech, Morocco
Mohamed
Naimi
Faculty of Sciences and Technologies, Physics Department, Laboratory of Flows and Transfers Modeling (LAMET), Sultan Moulay Slimane University, B.P. 523, Beni-Mellal, Morocco
The present paper reports numerical results of natural convection and surface radiation within a square cavity filled with air and discretely heated and cooled from the four walls. In this study, the bottom active wall is at higher temperature than that of the top active wall. The remaining portions of the horizontal walls are considered adiabatic. The parameters governing the problem are the emissivity of the walls (0 ≤ ε ≤ 1), the relative lengths of the active elements (0.1 ≤ B = h'/H' = l'/L ≤ 0.9), and the Rayleigh number (104 ≤ Ra ≤ 3 × 106). The effect of these parameters on heat transfer and fluid flow within the cavity is examined. Results of the study are presented and compared to the case of pure natural convection for various typical combinations of the governing parameters in terms of flow and temperature patterns, average convective, radiative, and total Nusselt numbers. The heatlines visualization technique, which is a useful means for understanding the mechanism of heat flow, is employed to exhibit the direction and intensity of heat flux in the cavity.