Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
3
2
2011
NATURAL CONVECTION IN A HORIZONTAL ANNULUS WITH AN INNER HEAT-GENERATING SOLID SQUARE CYLINDER AND AN OUTER ISOTHERMAL CIRCULAR BOUNDARY
89-102
A.
Shaija
Department of Mechanical Engineering, National Institute of Technology Calicut, Kerala -676001, India
G.S.V.L.
Narasimham
Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India
A numerical study of two-dimensional conjugate natural convection flow and heat transfer in a horizontal annulus, formed between an inner heat-generating solid square cylinder placed concentrically inside an isothermal circular cylinder is performed. Numerical solutions of the Boussinesq equations and the solid energy equation in primitive variables are obtained on a nonstaggered (collocated) grid with a pressure correction method. Results for the dimensionless maximum solid temperature, average solid temperature, average inner boundary temperature, and average Nusselt number are obtained for the heat-generation and outer-radius−based Grashof number ranging from 104 to 109, for solid-to-fluid thermal conductivity ratio of 1, 10, 50, and 100, and aspect ratio values of 0.2 and 0.4, with air as the working medium. The streamlines and isotherms show that refraction of isotherms occurs at the solid-fluid interface. The degree of refraction is found to be higher for higher thermal conductivity ratios. Because in steady state all the heat generated is to be transferred to the outer cold boundary irrespective of the thermal conductivity ratio, the average Nusselt number is not sensitive to the thermal conductivity ratio, while the local Nusselt numbers are found to be sensitive to solid-to-fluid thermal conductivity ratio. The maximum temperature depends on the solid thermal conductivity, and hence, its determination requires the solution of the conjugate problem. The results are expected to be useful in the design of thermal systems such as spent nuclear fuel casks and underground transmission cables.
SOME EXACT SOLUTIONS OF COUPLE STRESS FLUIDS
103-109
S.
Islam
Department of Mathematics, COMSATS Institute of Information Technology, Chakshazad Park Road, Islamabad, Pakistan
Murad
Ullah
Islamia College Peshawar (Charted University), Peshawar, NWFP, Pakistan
Akhtar
Hussain
Department of Mathematics, COMSATS Institute of Information Technology, Chakshazad Park Road, Islamabad, Pakistan
Abdul Majeed
Siddiqui
Department of Mathematics, Pennsylvania State University, York Campus, 1031 Edgecomb Avenue, York, PA 17403, USA
In this paper, we investigated theoretically the flow of an incompressible 2D couple stress fluid. Here, we considered the flows for which the stream function is given by ψ = y + f(x) eky, where k is a real constant and f(x) is a function to be determined.We obtained the exact expressions for the stream function and thus the velocity and pressure for different values of k and for the different values of viscosities.
EFFECT OF A PERIODIC HEATING TEMPERATURE ON DOUBLE-DIFFUSIVE CONVECTION IN A POROUS SQUARE ENCLOSURE SUBMITTED TO CROSS GRADIENTS OF TEMPERATURE AND CONCENTRATION
111-122
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
B.
Abourida
Ibn Zohr University, Ecole Nationale des Sciences Appliquґees, ENSA, Agadir, 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
Numerical results of 2D double-diffusive natural convection in a square porous cavity submitted to cross gradients of temperature and concentration are presented in this study. The temperature of the lower horizontal surface (hot temperature) is varied sinusoidally with time, while that of the opposite surface (cold temperature) is maintained constant. The vertical walls are maintained at uniform but different concentrations. The parameters governing the problem are the amplitude of the variable temperature (0 ≤ a ≤ 1), its period (0.01 ≤ τ ≤ 1), the Lewis number (0.1 ≤ Le ≤ 10), and the thermal Rayleigh number (50 ≤ Ra ≤ 250). The ratio of the buoyancy forces was maintained at a constant value equal to 0.1 (case of dominating thermal buoyancy forces). The effects of these parameters on the flow intensity and heat and mass transfers are studied. The results obtained show that the heat transfer, the mass transfer, and the flow intensity could be significantly enhanced, with respect to the case of a constant heating temperature, by a proper choice of the parameters related to the periodic heating.
MICROPOLAR FLUID FLOW IN A STRAIGHT CIRCULAR CYLINDER PERFORMING LONGITUDINAL AND TORSIONAL OSCILLATIONS
123-131
J. V. Ramana
Murthy
Department of Mathematics, National Institute of Technology, Warangal-506 004, A.P., India
N. K.
Bahali
Department of Mathematics, National Institute of Technology
The flow of micropolar fluid inside a circular cylinder that is subjected to longitudinal and torsional oscillations with different frequencies is investigated. Analytical expressions for the velocity components and microrotation components are obtained in terms of modified Bessel's functions. The drag force acting on the wall of the cylinder is derived. It is observed that as the micropolarity of the fluid increases, drag decreases.
THE METHOD OF LINES FOR RECONSTRUCTING A MOVING BOUNDARY IN ONE-DIMENSIONAL HEAT CONDUCTION PROBLEM
133-143
Ting
Wei
School of Mathematics and Statistics, Lanzhou University
Ji-Chuan
Liu
China University of Mining and Technology
In this paper, we use a method of lines to determine a moving boundary from Cauchy data in a one-dimensional heat conduction problem. This problem is ill-posed; thus, a quasi-reversibility regularization method is applied to obtain a stable numerical solution. Numerical experiments for several examples show that the proposed method is effective and stable.
LIQUID FILMS FALLING ON HORIZONTAL PLAIN CYLINDERS: PART 1-EXPERIMENTAL AND NUMERICAL STUDY OF FLOW BEHAVIOR
145-156
Farial
Jafar
Victoria University
Graham
Thorpe
Centre for Environmental Safety and Risk Engineering College of Engineering and Science, Victoria University, Melbourne, Australia 8001
Ozden F.
Turan
School of Engineering and Science, Faculty of Health, Engineering and Science, Victoria University
In this paper, an experimental and numerical investigation of liquid film falling over three horizontal plain cylinders is presented. The flow Reynolds number range studied is 50−2000, rendering the flow laminar. Numerical predictions are obtained using FLUENT, a proprietary computational fluid dynamic (CFD) code, for the 2D and 3D configurations of the three cylinders. In the numerical predictions, the mathematical approach is based on the volume of fluid (VOF) method to account for the fluid's two phases, namely, air and water. The primary objective of the present study was to carry out experiments to validate the numerical code. It was found that increasing the Reynolds number resulted in the flow mode changing from droplet, to jet, to sheet mode. The numerical analyses accurately predicted the Reynolds numbers at which these transitions occur. The flow mode is also related to the separation distance between the horizontal cylinders. The flow mode tends to be droplet at large separation, whereas it tends to be jet and sheet modes at small separations. The distances between adjacent columns of droplets and the adjacent jet decrease with increasing Reynolds number and cylinder diameter, a phenomenon also captured by the numerical analyses. No effects of hysteresis were observed on the spacing of the columns of droplets and jets as the Reynolds number was increased and decreased. The frequency at which droplets fell from all of the cylinders increased when the distance between the water feeder and the cylinder increased, and this effect exhibited hysteresis as the flow rate was successively increased and decreased.
PARAMETRIC STUDY OF THE PRESSURE CHARACTERISTIC CURVE IN A BOILING CHANNEL
157-168
E. Manavela
Chiapero
Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim
M.
Fernandino
Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim
C. A.
Dorao
Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim
The main objective of this work is to understand the behavior of the pressure drop of a boiling fluid along a heated pipe as a function of the mass flux. The steady-state plot of the pressure drop against the mass flux of a heated boiling channel with subcooled liquid at the inlet is widely used for pressure drop and thermal oscillations simulations. The influence of several important parameters, such as the heat applied, the inlet pressure, and the inlet temperature, is analyzed. As the inlet pressure goes down, the steepness of the negative slope of the static curve increases. The inlet temperature has a very important role in this plot, showing that the negative slope of the curve gets steeper as the subcooling increases. Although the amount of heat applied to the test section is found to have no influence on the shape of the static curve, the axial distribution of the heat along the heated section plays a very important role in the steepness of the negative slope of the steady-state pressure drop versus mass flux plot.