Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
9
6
2017
EFFECT OF FLUID YIELD STRESS ON FREE CONVECTION FROM AN ISOTHERMAL CYLINDER ADJACENT TO AN ADIABATIC WALL
483-511
A. K.
Baranwal
Department of Chemical Engineering, Indian Institute of Technology, Kanpur 208016, India
Rajenda P.
Chhabra
Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur, U.P.208016, India
Laminar natural convection heat transfer from a horizontal isothermal cylinder immersed in a Bingham fluid situated
above or below an adiabatic wall has been studied over ranges of parameters, Rayleigh numbers (10 ≤ Ra ≤ 105), Prandtl numbers (10 ≤ Pr ≤ 100), and Bingham numbers (0.1 ≤ Bn ≤ 103) for cylinder-to-wall gaps |H/D| = 0.05,
0.1, 0.3, 0.7, 1.1, and 1.5. Detailed flow and temperature fields are analyzed in terms of the streamlines, isotherms, and the yield surfaces. At the next level, these results are discussed in terms of the local and average Nusselt number. For sufficiently large values of the Bingham number, the average Nusselt number reaches its asymptotic value commensurate with the conduction limit. The average Nusselt number increases with the Rayleigh number and |H/D|, while the Bingham number has an adverse influence with reference to the behavior in Newtonian fluids otherwise under identical conditions. The limiting value of the Bingham number (Bnmax) increases with the increasing Rayleigh number. With reference to the case of an unconfined cylinder, the confining adiabatic wall has an adverse influence on the overall heat transfer. Simple predictive expressions are developed which can be used to estimate the values of the average Nusselt number and the limiting Bingham number in a new application.
STUDY OF NATURAL CONVECTION WITH A STABILIZED FINITE ELEMENT FORMULATION
513-527
Marcos
Curi
CEFET/RJ – UnED Itaguaí, Rodovia Mário Covas, Lote J2, Quadra J, Rio de Janeiro, P.O. Box
23812-101, Brazil
Paulo Augusto Berquó
De Sampaio
Nuclear Engineering Institute – CNEN, P.O. Box 68550, Rio de Janeiro, RJ 21945-970, Brazil
Milton Alves
Gonçalves Junior
Center for Parallel Computations, Federal University of Rio de Janeiro, P.O. Box 68516, Rio de Janeiro, RJ 21945-970, Brazil
In this work we study two cases of natural convection using a second-order finite element formulation stabilized
by local time-steps. The pressure, velocity, and temperature fields are determined from procedures that use the mass
conservation law, the Navier-Stokes equations, and the convection-diffusion energy equation, employing a second-order scheme. A Taylor-Galerkin methodology is first applied to determine the pressure field at each time step, in a process that combines the continuity equation and the Navier-Stokes equations. Once the pressure field has been determined, the velocity and temperature fields are solved by another second-order time-accurate procedure on momentum and energy equations. A least-squares minimization procedure from the previous residuals leads to a set of discretized
equations for temperature and velocity fields. The finite element method is naturally stabilized by the process, where
local time-steps, chosen according to the time scales of convection-diffusion of momentum and energy, play the role
of stabilization parameters. Results are given for quasi-incompressible viscous flows and heat transfer for transient
and steady states for two-dimensional free convection in a square cavity and from a hot horizontal cylinder utilizing
the described method. Numerical investigations were carried out for the Rayleigh number range 104 ≤ Ra ≤ 108. Excellent agreement with previously published experimental and computational results has been obtained.
COMPARISON OF PERFORMANCE OF DIFFERENT MULTIPHASE MODELS IN PREDICTING STRATIFIED FLOW
529-539
Santosh Kumar
Senapati
Mechanical Engineering Department, National Institute of Technology, Raipur (CG) 492010,
India
Satish Kumar
Dewangan
NIT Raipur (CG) - INDIA
Stratified flow is one of the important multiphase flow patterns found in the petroleum industries, nuclear industries, chemical industries, etc. The key feature of this flow pattern is the presence of interface(s) separating the phases. The interface evolves with space and time. It is also subjected to the force of surface tension along with other intermolecular forces. Thus, it is necessary to capture the interface(s) of stratified flow in order to predict the characteristics of such flows. The complex nature of stratified flow essentially demands for the use of multiphase computational fluid dynamics for predicting them. The multiphase model, which is employed for the analysis, must be able to properly capture the evolving interface. The level-set method (LSM), volume of fluid method (VOF), etc., are popular methods used for this purpose. The combination of these two methods is known as the coupled level set and volume of fluid (CLSVOF), which is also becoming popular for the prediction of a stratified flow pattern. Another multiphase model, called the multifluid VOF (MVOF) model, is available in the recent versions of ANSYS Fluent, which has been developed with the aim that this would overcome the limitations of VOF. Thus, the present study aims at comparing the performance of three multiphase models, namely, CLSVOF, VOF, and MVOF, available in ANSYS Fluent (Version 15) with the experimental data of Elseth (Elseth, G., An experimental study of oil/water flow in horizontal pipes, PhD thesis, Norwegian University of Science and Technology, 2000) for the analysis of stratified flow.
NUMERICAL INVESTIGATION OF HEAT TRANSFER ON TWO GROOVED CYLINDERS IN A TANDEM ARRANGEMENT
541-547
Omar
Ladjedel
Laboratoire d'aérohydrodynamique naval, Département de Génie Maritime, Mechanical
Engineering Faculty, USTO Oran, 31000, Algeria
Lahouari
Adjlout
Laboratoire d'Aéro-Hydrodynamique Naval, Département de Génie Maritime,
Université des Sciences et de la Technologie d'Oran Mohamed Boudiaf,
USTO-MB, Oran, Algérie
Tayeb
Yahiaoui
Laboratoire d’Aéronautique et Systèmes Propulsive, Université des Sciences et de la
Technologie d’Oran - Mohamed-Boudiaf, Algeria
Omar
Imine
Laboratoire d'Aéronautique et Systèmes Propulsifs, Département de Génie
Mécanique, Université des Sciences et de la Technologie d'Oran Mohamed
Boudiaf, USTO-MB, Oran, Algérie
Ondrej
Sikula
Brno University of Technology, Faculty of Civil Engineering, Brno, Czech Republic
In this paper, a CFD investigation of the heat transfer on two grooved cylinders is investigated with L/D = 4.2 and Reynolds number of 2 × 104. Two cases are performed, smooth-smooth cylinders (case 1) and grooved-grooved cylinders (case 2). Two longitudinal grooves are placed on the external surface at 90 and 270 deg. Each cylinder has two grooves on the external surface of the cylinder. The steady-state Reynolds-averaged Navier-Stokes equations are solved using a finite volume method, where k-ω SST turbulence model is used to produce a closed system of solvable equations. The tandem cylinders' geometry simulations are performed at steady conditions. An adapted grid using static pressure,
pressure coefficient, and velocity gradient, and furthermore, a second-order upwind scheme, were used. The obtained results show that the numerical predictions are in good agreement with the experimental measurements. The local
Nusselt number distributions for all cylinders are described. The influence of the grooved cylinder on the heat transfer is well exhibited.
COMPARATIVE STUDY OF FLUID FLOW AND HEAT TRANSFER IN RECTANGULAR AND WAVY MICROCHANNEL
549-565
Satish Kumar
Dewangan
NIT Raipur (CG) - INDIA
Shobha Lata
Sinha
Mechanical Engineering Department, National Institute of Technology–Raipur (CG), India
492010
Prateek Kumar
Gupta
Mechanical Engineering Department, National Institute of Technology–Raipur (CG), India
492010
A comparative study of steady, laminar, single-phase flow of nanofluid through a rectangular microchannel and wavy
microchannel heat exchanger of equal dimensions has been carried out. The effect on three important variables (i.e., heat transfer coefficient, pumping power, and friction factor) have been analyzed by considering the effect of four parameters (i.e., effect of flow rate, effect of nanofluid concentration, effect of amplitude of wavy surface, and effect of wave length of wavy surfaces). Numerical simulation has been validated with the experimental work of Lee and Mudawar (Lee, J. and Mudawar, I., Assessment of the effectiveness of nanofluids for single and multiphase heat transfer in micro channel, Int. J. Heat Mass Transfer, vol. 50, pp. 452–463, 2007). It is concluded that, with an increase in the amplitude of a wavy surface, the heat transfer coefficient increases. Results show that the wavy channel performed better than the plane rectangular microchannel in terms of the rise in heat transfer coefficient but is costly due to the pump power requirement.
THE INVESTIGATION OF THE HEAT TRANSFER CHARACTERISTICS OF A CROSS-FLOW PULSATING JET IN A FORCED FLOW
567-582
Unal
Akdag
Aksaray University Mechanical Eng. Dept. 68100, Aksaray/Turkey
Selma
Akcay
Department of Mechanical Engineering, Aksaray University, 68100 Aksaray, Turkey
Dogan
Demiral
Department of Mechanical Engineering, Aksaray University, 68100 Aksaray, Turkey
In the present study, the effect of a transversely pulsating jet on heat transfer performance over a flat plate is investigated experimentally and numerically. A secondary mass flux by the transverse pulsating jet to the main flow from the front end of the plate with constant heat flux is added. It enhances the heat transfer by placing a periodically changing film layer between the plate and the forced flow on the plate. In the investigations, the Reynolds number in the main stream (or the blowing ratio) and the frequency and amplitude of the pulsating jet are changed while the geometry and Prandtl number remain constant for all cases, and the effect of these parameters on the heat transfer performance is analyzed. The experimental studies are performed at four different blowing ratios for six different frequencies and four different amplitudes, and they are evaluated with respect to heat transfer. In addition, the problem is modeled numerically using control-volume-based commercial code. To explain the heat transfer mechanism, instantaneous velocity and
temperature profiles are obtained. The results reveal that the pulsating jet is effective in all plate surfaces and that the heat transfer performance increases with increases in both the Womersley number (W0) and the dimensionless amplitude (A0) at a high blowing ratio (M). The obtained results are presented as a function of dimensionless parameters, which are the primary factors affecting the heat performance on the flat plate.
INDEX VOLUME 9, 2017
583-588