Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
6
1
2014
NUMERICAL STUDY OF NANOFLUID HEAT TRANSFER ENHANCEMENT WITH MIXING THERMAL CONDUCTIVITY MODELS
1-12
10.1615/ComputThermalScien.2013006287
Amarin
Tongkratoke
Faculty of Science and Engineering, Kasetsart University, Chalermphrakiat Sakon Nakhon Province Campus, Sakon Nakhon 47000 Thailand
Anchasa
Pramuanjaroenkij
Faculty of Science and Engineering, Kasetsart University, Chalermphrakiat Sakon Nakhon Province Campus, Sakon Nakhon 47000 Thailand
Apichart
Chaengbamrung
Department of Mechanical Engineering, Kasetsart University, Bangkok, 10900, Thailand
Sadik
Kakac
Department of Mechanical Engineering,TOBB University of Economics and Technology, Ankara-Turkey; and LIPING CAO, Westinghouse Electric Company, LLC, PA; and Department of Mechanical Engineering, University of Miami, Florida - USA
nanofluid
laminar flow
heat transfer enhancement
single-phase model
mixing model
Nanofluids have shown the possibility of enhancing heat transfer performance above its base fluids. This work presents a numerical study that analyzes the nanofluid heat transfer enhancement using different theoretical models; i.e., the effective thermal conductivity and effective viscosity models. The Maxwell, Brownian motion, and Yu and Choi models were considered as the effective thermal conductivity models and these models were used and mixed alternately in the simulation domain, referred to as mixing models. The Al2O3−water nanofluid was chosen in this study and assumed to flow under a laminar, fully developed flow condition through a rectangular pipe such as in a circuit application. The governing equations, written in terms of the primitive variables, were solved through an in-house program using the finite-volume method and the semi-implicit method for pressure linked equations (SIMPLE) algorithm. From the study, the mixing models using Yu and Choi model coupled with Maxwell and Brownian models at the wall boundaries combined with the viscosity model from Maiga provided the numerical results closer to the experimental results from Zeinali Heris and co-workers at volume fractions of 0.01, 0.02, and 0.03%, as well as those of the base fluid. Therefore, by increasing the nanoparticle amounts, volume fraction, effective viscosity, and effective thermal conductivity at the wall region could be increased and enhancements of 0.01, 0.02, and 0.03% volume fractions were 21, 29, and 36% increasing from the base fluid, respectively. This work can strongly support the literature in which the volume fraction, effective viscosity, and effective thermal conductivity can enhance the heat transfer performance in nanofluid flows not only with the single-phase model considered but also with the mixing models examined.
A FIXED-GRID BASED MIXTURE MODEL FOR PULSED LASER PHASE CHANGE PROCESS
13-26
10.1615/ComputThermalScien.2014007841
Satya Prakash
Kar
School of Mechanical Sciences, Indian Institute of Technology Bhubaneswar, Odisha-751 013, India
Prasanjeet
Rath
School of Mechanical Sciences, Indian Institute of Technology Bhubaneswar, Odisha-751 013, India
fixed-grid
laser melting
mixture
solid-liquid interface
transient
axisymmetric
A two-dimensional, transient, axisymmetric model is developed to study the transport phenomena in a laser melting problem under a single laser pulse as well as repetitive laser pulse. The model is based on one-phase continuum mixture theory and fixed-grid technique. The model incorporates natural convection in the melt pool and radiation and convection heat losses from the irradiated surface. The complicated phase front evolution is captured implicitly by calculating the liquid volume fraction based on latent heat content at each control volume. An iterative update procedure is developed to update the liquid volume fraction at each control volume. A comparative study between the effect of natural convection and diffusion on the position and shape of the solid-liquid interface is made. It is found that natural convection does not play any significant role under the present condition in deciding the width and depth of the melt pool. The melt depth and melt radius predicted using the proposed model is compared with the available results and a good agreement is found. The model is further explored to investigate the effect of natural convection on the position and shape of the molten pool under the repetitive laser pulse.
MHD FORCED CONVECTION FLOW OF A NANOFLUID ADJACENT TO A NON-ISOTHERMAL WEDGE
27-39
10.1615/ComputThermalScien.2014005800
Ali J.
Chamkha
Department of Mechanical Engineering, Prince Sultan Endowment for Energy and
Environment, Prince Mohammad Bin Fahd University, Al-Khobar 31952, Kingdom of Saudi
Arabia; RAK Research and Innovation Center, American University of Ras Al Khaimah, United Arab Emirates, 10021
Ahmed M.
Rashad
Department of Mathematics, Aswan University, Faculty of Science, Aswan, 81528, Egypt
forced convection
magnetohydrodynamics
wedge
nanofluid
thermophoresis
A boundary-layer analysis is presented for the magnetohydrodynamic (MHD) forced convection flow of a nanofluid adjacent to a non-isothermal wedge. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The governing partial differential equations are transformed into a set of non-similar equations and solved numerically by an efficient implicit, iterative, finite-difference method. Comparisons with previously published work are performed and excellent agreement is obtained. A parametric study of the physical parameters is conducted and a representative set of numerical results for the velocity, temperature, and nanoparticles volume fraction profiles as well as the local skin-friction coefficient and local Nusselt and Sherwood numbers are illustrated graphically to show interesting features of the solutions.
BOOK REVIEW: ROTATING THERMAL FLOWS IN NATURAL AND INDUSTRIAL PROCESSES
41-42
10.1615/ComputThermalScien.2014010121
John
Reizes
School of Mechanical and Manufacturing Engineering, UNSW-Sydney, Sydney 2052, Australia
PREFACE: SPECIAL SECTION ON TRANSPORT PHENOMENA
45
10.1615/ComputThermalScien.2014010287
Christos
Spitas
Delft University of Technology, The Netherlands
THERMOHYDRODYNAMIC ANALYSIS OF A JOURNAL BEARING WITH A MICROGROOVE ON THE SHAFT
47-57
10.1615/ComputThermalScien.2014005894
Samuel
Cupillard
Hydro-Quebec Research Institute, Varennes, QC, Canada
Michel J.
Cervantes
Lulea University of Technology, Division of Fluid Mechanics, Lulea SE-971 87, Sweden; Water Power Laboratory, Norwegian University of Science and Technology, Trondheim, Norway
S.
Glavatskih
Machine Design, KTH Royal Institute of Technology, 10044 Stockholm, Sweden Department of Mechanical Construction and Production, Ghent University, B-9000 Ghent, Belgium
CFD
journal bearing
microgroove motion
grid update
thermal effects
In this study, thermohydrodynamic performance of a journal bearing with a microgroove created on the shaft is analyzed. A plain journal bearing is modeled using a computational fluid dynamics (CFD) software package. Navier-Stokes and energy equations are solved. The rotor-stator interaction is treated by using a computational grid deformation technique. The goal is to examine the pressure/temperature distribution in the bearing film. Results are presented in terms of typical bearing parameters as well as flow patterns. Results are also compared to the bearing with a smooth shaft. The effect induced by a microgroove on pressure distribution is explained for different bearing configurations, eccentricities, and microgroove depths. It is shown that the microgroove produces a local drop in pressure which, averaged over one revolution, decreases the load carrying capacity. The load carrying capacity is further decreased by using deeper microgrooves. With thermal effects considered, the microgroove carries more cold lubricant into the warmest regions of the bearing. This effect, more pronounced with deeper microgrooves, is due to a global flow recirculation inside the microgroove, which improves mixing.
THE MATHEMATICAL MODELING OF THERMOCHEMICAL PROCESS OF A TWO-STAGE DOWNDRAFT GASIFICATION
59-68
10.1615/ComputThermalScien.2014005664
Kitipong
Jaojaruek
Energy Research Laboratory of Mechanical Engineering (ERLoME), Faculty of Engineering KPS, Kasetsart University, Kamphaeng Saen (KPS) Campus, Nakon Pathom, 73140 Thailand
gasification finite computation
temperature profile in gasifier
heat transfer in packed bed
feedstock consumption prediction in gasifier
experiment uncertainty
This work developed a mathematical model to predict the temperature profile in the pyrolysis zone, and the feedstock feed rate of the KU-KPS two-stage downdraft gasification process using wood chips as feedstock. The obtained temperature profile is an important input parameter to calculate the gas composition of volatile gas in the pyrolysis zone of the gasification process. The feedstock feed rate is also useful to evaluate the gas generation rate, thermal efficiency, and gas composition in producer gas of gasification. Thermochemical concepts were applied to derive the energy and mass balance equations composed of chemical, kinetic, and three modes of heat transfer; conduction, convection, and radiation. The feedstock was treated as a porous medium. The equations were solved by the implicit finite difference method on the node of 200 and conversion criteria of 10−6. Experiments were also conducted to validate the model results. The validation results showed that the maximum temperature deviation between model and experiment was 62° C at the combustion temperature of 790° C while for the feedstock feed rate it had a deviation of 0.94 kg/h at the rate of 14.7 kg/h. The experimental uncertainty was also analyzed based on a 95% level of confidence. The total experimental uncertainties of temperature and feedstock feed rate were 72° C and 0.95 kg/h, respectively.
NUMERICAL INVESTIGATION OF COOLING CHARACTERISTICS FOR FINE MIST COOLING OF HIGH TEMPERATURE MATERIAL
69-78
10.1615/ComputThermalScien.2014005831
Tsuyoshi
Yamamoto
Department of Chemical Engineering, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan
Takuya
Kuwahara
Department of Chemical Engineering, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan
Kakeru
Yoshino
Department of Chemical Engineering, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan
Koichi
Nakaso
Kyushu University, Motooka 744, Nishi-ku, Fukuoka 819-0395, Japan
Takahisa
Yamamoto
Department of Mechanical Engineering, Gifu National College Technology
mist cooling
fine mist
high heat flux
numerical simulation
Mist cooling is a technology to cool high temperature surfaces using an evaporative latent heat associated with the vaporization of atomized droplets. It has higher cooling capacity than the conventional cooling techniques such as forced convection, as it takes advantage of relatively large values of evaporative latent heat. In this paper, fine mist cooling as a high heat removal technology has been applied to the cooling of a high temperature work material. A threedimensional numerical simulation has been developed in order to investigate the behavior of fine mist particles, flow of gas phase and temperature of work material. Model predictions show that water droplets hardly evaporate in the gas phase of the analytical domain; approximately 45% of fine mist particles flow out of the analytical domain and approximately 55% of fine mist particles collide on the work material. 10%−20% of collided water droplets evaporate on the work material and 80%−90% of collided water droplets stay on the work material under steadystate condition. Collision of fine mist particles on the work material has a high frequency in the central part of the device and the collision frequency of fine mist particles decreases with an increasing distance from the center of the work material. As a result, the surface temperature of the work material is comparatively low in the central part of the work material due to the evaporative latent heat of fine mist particles and becomes higher toward the outside of the work material.
HEAT TRANSFER IN A VISCOELASTIC ORIFICE FLOW AT LOW TO MODERATE REYNOLDS NUMBERS
79-90
10.1615/ComputThermalScien.2014006371
Takahiro
Tsukahara
Tokyo University of Science
T.
Kawase
Department of Mechanical Engineering, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba278-8510, Japan
Yasuo
Kawaguchi
Department of Mechanical Engineering, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba 278-8510, Japan
direct numerical simulation
drag reduction
Giesekus model
heat transfer
non-Newtonian fluid
orifice
Toms effect
turbulence
viscoelasticity
Direct numerical simulations of heat transfer in channel flows of a viscoelastic fluid with an immersed periodic rectangular orifice were carried out to investigate the statistics of the velocity and thermal fields. The friction Weissenberg number of the viscoelastic fluid was set at 20 and the Prandtl number was given as either 1.0 or 2.0. In the present flow configuration, the reduction rates of the drag factor and the Nusselt number were ranged in the percent drag reduction DR% = −90%−20% and the percent heat-transfer reduction HTR% = 0%−50%, respectively. The variations observed in the Reynolds-number dependencies of DR%, HTR%, and the separated flow behind the orifice were analyzed. Consequently, the viscoelasticity was found to affect the orifice flow and its heat transfer most significantly in the transitional regime, since it suppressed the turbulent transition and/or the Kelvin-Helmholtz instability of the separated shear layer emanating from the orifice edge.