Begell House Inc.
Journal of Enhanced Heat Transfer
JEH(T)
1065-5131
25
4-5
2018
PREFACE: ADVANCES IN COMPUTATIONAL HEAT TRANSFER (CHT-17)
v-vi
Oronzio
Manca
Dipartimento di Ingegneria Industriale e dell'Informazione, Università degli
Studi della Campania "Luigi Vanvitelli," Aversa (CE), Italy
Yogesh
Jaluria
Department of Mechanical and Aerospace Engineering Rutgers-New Brunswick, The State University of New Jersey Piscataway, NJ 08854, USA
NUMERICAL INVESTIGATION OF WAVY MICROCHANNELS WITH RECTANGULAR CROSS SECTION
293-313
P. M. Mithun
Krishna
Department of Aerospace Engineering, Indian Institute of Space Science and
Technology, Thiruvananthapuram, India, 695547
M.
Deepu
Department of Aerospace Engineering, Indian Institute of Space Science and
Technology, Thiruvananthapuram, Kerala, India, 695547
S. R.
Shine
Department of Aerospace Engineering, Indian Institute of Space Science and
Technology, Trivandrum – 695547, Kerala, India
Computational results are presented that describe thermo-hydrodynamic behavior of wavy microchannels of various geometric configurations. The configurations have been obtained by changing the geometric parameters such as relative waviness and aspect ratio for a constant hydraulic diameter of 400 μ;m. A 3D, steady, laminar conjugate model is developed and validated against available experimental data. A comparative study on wavy and straight channels has been conducted. Fluid flow and heat transfer characteristics have been studied for distinct configurations of wavy channel and it is found that the thermo-hydrodynamic behavior of fluid flow strongly depends on relative
waviness and aspect ratio. The increased heat transfer and pressure drop are due to the occurrence of vortices that develop within the channel. Variation of local Nusselt number has been analyzed and found to follow similar trend for different aspect ratios. A performance parameter known as channel effectiveness has been used to analyze the combined effect of heat transfer and pressure drop. Results
show that higher waviness channels with an aspect ratio of 1 can be recommended for obtaining higher effectiveness.
ANALYSIS OF NATURAL CONVECTION OF Cu AND TiO2 NANOFLUIDS INSIDE NONCONVENTIONAL ENCLOSURES
315-332
Sahar A.
Abbood
Department of Energy Sciences, Lund University, P.O. Box 118, Lund, SE-22100, Sweden
Jin
Wang
Department of Energy Sciences, Lund University,
P.O. Box 118, Lund SE-22100, Sweden
Zan
Wu
Department of Energy Sciences, Lund University, P.O. Box 118, Lund, SE-22100, Sweden
Bengt
Sunden
Division of Heat Transfer, Department of Energy Sciences, Lund University, P.O. Box 118,
SE-22100, Lund, Sweden
Steady-state laminar natural convection of Cu and TiO2 nanofluids inside different enclosures is numerically investigated. Natural convection is concerned due to a temperature difference between the hot and cold surfaces. The Boussinesq approximation is used to form the governing equations, and the commercial software package ANSYS FLUENT version 14.0 is used to numerically solve the governing equations. The temperature profiles and flow patterns at different Rayleigh numbers, such as 104, 105, and 106, are studied and compared for different curved geometries that are 1/8, 2/8, and 3/8 of the height of the enclosure. Heat transfer coefficients are presented for enclosures with
different nanofluid concentrations. The nanoparticles enhance the heat transfer, and the heat transfer enhancement increases with increasing nanoparticle concentrations. A new curved enclosure is suggested to augment heat transfer.
FULLY DEVELOPED CONVECTION HEAT TRANSFER IN OPEN-CELL FOAMS
333-346
Marcello
Iasiello
Dipartimento di Ingegneria Industriale, Università degli studi di Napoli Federico II, P.le Tecchio 80, 80125, Napoli, Italy
Salvatore
Cunsolo
Dipartimento di Ingegneria Industriale, Università degli Studi di Napoli Federico II, Napoli, Italy; LaMCos, INSA-Lyon, UMR CNRS 5259, Villeurbanne, France
Nicola
Bianco
Dipartimento di Ingegneria Industriale, Università degli studi di Napoli Federico II, P.le Tecchio 80, 80125, Napoli, Italy
Wilson K. S.
Chiu
Department of Mechanical Engineering, University of Connecticut, 191 Auditorium Road, Storrs, CT, 06269-3139, USA
Vincenzo
Naso
Dipartimento di Ingegneria Industriale, Università degli studi di Napoli Federico II, P.le Tecchio 80, 80125, Napoli, Italy
Convection heat transfer in open-cell foams mainly occurs under thermally developed conditions for both uniform temperature and heat flux boundary conditions at the solid/fluid interface, since few cells are in the entrance region. Therefore, convection heat transfer needs to be thoroughly studied in order to allow reliable predictions of foam performance. A numerical analysis of fully developed
laminar convection in open-cell foams at a pore scale is presented in this paper. The geometry of the cell is chosen making reference to Kelvin's tetrakaidecahedron foam model. The finite-element-based commercial code COMSOL Multiphysics (COMSOL Inc., Burlington, MA, USA) is employed in building up the numerical grid and solving the problem for different porosities and Reynolds numbers. The local velocity and local interfacial convective heat transfer coefficient in a cell in the thermal fully developed region are predicted. The results highlight the dependence of velocity on
foam porosity and the effect of porosity on flow separation. They also exhibit a periodical behavior of the local convection heat transfer through the cell affected by the porosity and Reynolds number. Finally, cell-averaged heat transfer coefficients and average Nusselt numbers are presented, which highlight the effects due to scale changes.
NUMERICAL INVESTIGATION OF HEAT-TRANSFER ENHANCEMENT IN A DIMPLED DIVERGING MICROCHANNEL WITH AL2O3–WATER NANOFLUID
347-365
S. L.
Nandakrishnan
Department of Aerospace Engineering, Indian Institute of Space Science and Technology,
Trivandrum – 695547, Kerala, India
M.
Deepu
Department of Aerospace Engineering, Indian Institute of Space Science and
Technology, Trivandrum – 695547, Kerala, India
S. R.
Shine
Department of Aerospace Engineering, Indian Institute of Space Science and
Technology, Trivandrum – 695547, Kerala, India
Recent interest in high heat-flux removal applications in micropower devices and electronic cooling applications have contributed to the development of heat-transfer enhancement techniques in microchannels. Passive enhancement methods have been widely used by researchers to improve microchannel
heat-transfer characteristics. The incorporation of multiple enhancement methods in microchannel heat sinks has proven to be advantageous in high heat-flux removal systems. The present study focuses on the application of improved heat-transfer properties of Al2O3–water nanofluids when used in conjunction with a diverging microchannel with a staggered dimpled surface to improve
overall heat-transfer characteristics. We analyzed three-dimensional laminar incompressible internal convection flow field in a diverging microchannel with heat transfer from a dimpled surface using the SIMPLE algorithm with a second-order upwind scheme in a finite volume solver. We performed
extensive computations to reveal thermohydraulic performance aspects of dimpled diverging microchannels for various heat- and mass-flux conditions. Our study was extended to analyze performance augmentation that is achieved when Al2O3–water nanofluids are used in such channels.
UNSTEADY MAGNETOHYDRODYNAMIC CHANNEL FLOW WITH HALL AND ION-SLIP EFFECTS: THE INTEGRAL TRANSFORM SOLUTION PROCEDURE
367-386
Bruno N. M.
da Silva
Post-Graduate Program of Mechanical Engineering, UFRN, Natal-RN, Brazil
Gustavo E.
Assad
Federal Institute of Technology, IF/PB, João Pessoa-PB, Brazil
João A.
de Lima
Renewable Energy Engineering Department, UFPB/CEAR, João Pessoa-PB
Brazil
This paper deals with the generalized integral transform solution procedure to the unsteady magneto-convection problem of an electrically conducting Newtonian fluid within a parallel-plate channel, in which Hall and ion-slip effects are taken into account. It is considered that the magnetic
Reynolds number is small, i.e., the flow-induced magnetic fields are not strong enough to modify the applied transversal magnetic field. To cover a broader range of problems, temperature-dependent transport properties, time-dependent pressure gradient, inflow perpendicular to the plates (porous plates), and Couette flow are also considered in the mathematical formulation. Results are illustrated
and compared to the main numerical results from the literature for the related velocity and temperature
potentials as function of the main governing parameters, namely, Hartmann, suction/injection, transport properties, and electron and ion-slip parameters. In order to illustrate the consistency of the Generalized Integral Transform Technique (GITT) and its use for benchmarking purposes in the magneto fluid dynamics area, convergence analyses are carried out for the main potentials.
COMPUTATIONAL FLUID DYNAMICS MODELING OF DEVELOPING FORCED LAMINAR CONVECTION FLOW OF AL2O3–WATER NANOFLUID IN A TWO-DIMENSIONAL RECTANGULAR SECTION CHANNEL
387-398
Vincenzo
Bianco
Dipartimento di Ingegneria Meccanica, Energetica, Gestionale e dei Trasporti, Università degli Studi di Genova, Via All'Opera Pia 15/A, 16145 Genova, Italy
Annalisa
Marchitto
University of Genoa–DIME/TEC, Division of Thermal Energy and
Environmental Conditioning, Via All'Opera Pia 15/A, 16145 Genova, Italy
Federico
Scarpa
University of Genoa, DIME/TEC, Division of Thermal Energy and Environmental Conditioning Via All'Opera Pia 15 A, 16145 Genoa, Italy
Luca A.
Tagliafico
University of Genoa–DIME/TEC, Division of Thermal Energy and
Environmental Conditioning, Via All'Opera Pia 15/A, 16145 Genova, Italy
We propose a numerical analysis of developing forced laminar convection flow of Al2O3–water
nanofluid within a two-dimensional rectangular section channel, heated on the top wall with a constant heat flux of 1000 W/m2. The problem is replicated with the finite-element method using Comsol Multiphysics commercial software. Different cases are simulated with Reynolds numbers of 250–1000 and concentrations between 0% and 6% for particle dimensions of 20 and 40 nm. The
analysis demonstrates that nanofluids provide better cooling performance with respect to base fluid. We found an increase in average Nusselt number of ~16% for dp = 20 nm and concentration of 6%, whereas an average enhancement of 13% was detected when the particle dimension was 40 nm.
On the contrary, a relevant increase in pressure drop occurred when nanofluids were considered.
THE EFFECTS OF POROSITY AND MASS-TO-THERMAL DRIVE RATIO ON AIDING AND OPPOSING CONVECTION IN POROUS ENCLOSURES
399-419
Marcelo J. S.
de Lemos
Departamento de Energia – IEME, Instituto Tecnológico de Aeronáutica – ITA,12228-900 São José dos Campos SP, Brazil
Paulo H.S.
Carvalho
Departamento de Energia − IEME, Instituto Tecnológico de Aeronáutica - ITA
12228-900 - São José dos Campos - SP, Brazil
This work presents a study on double-diffusive free convection in a porous square cavity saturated with a Newtonian fluid under laminar flow simulated with the thermal equilibrium model. Transport equations are discretized using the control-volume method and the system of algebraic equations is relaxed via the SIMPLE algorithm. The effect of Ram and porosity on average Nusselt and Sherwood values was investigated. Results show that as Ram increases, both Nusselt and Sherwood numbers increase, indicating enhancement of heat and mass transfer across the cavity. Further, when the Lewis number is increased while keeping the same thermal properties, reduction of mass diffusivity further enhances flow recirculation for aiding flows (N = 1) within the cavity, which leads to a further increase in Nuω and Shω. When varying the buoyancy ratio N from aiding (N > 0) to opposing flow (N < 0), simulations indicate that when both drives are of equal strength, minimum values for Nusselt and Sherwood occur for N = −1, regardless of Ram. For larger values of |N|, aiding drives will promote fluid rotation in the clockwise direction, for the gradients of T and C applied here, whereas for opposing flows, the fluid rotates in the counterclockwise direction for opposed conditions at the lateral walls. Porosity and thermal conductivity ratio also affect Nuω and Shω.
FLUID FLOW AND HEAT TRANSFER CHARACTERISTICS PAST TWO TANDEM ELLIPTIC CYLINDERS: A NUMERICAL STUDY
421-441
Soumya
Sunakraneni
Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai - 600036, India
Vivek
Puliyeri
Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai - 600036, India
K. Arul
Prakash
Fluid Mechanics Laboratory Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai 600036, India
In this paper, fluid flow and heat transfer characteristics are analyzed numerically for fluid flow past two elliptic cylinders arranged in a tandem manner. The numerical computation was performed using an in-house code based on the SUPG - FEM algorithm. Isothermal boundary condition is
imposed on the surface of both the elliptic cylinders. Parametric studies are carried out by varying the axis ratio of the elliptic cylinders (AR = 0.5, 0.8, and 1.0) and distance between the two cylinders (L/D = 1.5, 2.0, 2.5, 3.5, and 5.0) for different Reynolds numbers (Re = 50, 100, 150, and 200). Parameters such as pressure coefficient, drag coefficient, lift coefficient, Strouhal number, and
Nusselt number are calculated for all the cases. It is observed that the critical spacing ratio (distance
between the cylinders at which the mean drag coefficient shows a sharp increase) of the cylinders shifts toward a lower value at Re = 200 for AR = 0.5 and 0.8. It is also found that for both the cylinders, convective heat transfer increases for elliptic cylinders with lower axis ratio (AR = 0.5 and 0.8). Finally, correlations are derived for mean drag coefficient and average Nusselt number as a function of Reynolds number, spacing ratio, and axis ratio.
EFFECT OF ASPECT RATIO AND ARRANGEMENT OF SURFACE-MOUNTED CIRCULAR CYLINDERS ON HEAT TRANSFER CHARACTERISTICS
443-463
Hemant
Naik
Department of Mechanical Engineering,
Indian Institute of Technology Madras, Chennai, 600036, India
Shaligram
Tiwari
Department of Mechanical Engineering, Indian Institute of Technology Madras Chennai, India,
600036
The flow and heat transfer characteristics over three rows of circular cylinders mounted on a flat plate have been studied numerically using the commercial software ANSYS Fluent version 15.0. The present three-dimensional investigations aim to determine the effect of the aspect ratio of surface-mounted circular cylinders on heat transfer enhancement and fluid flow characteristics. Both inline
and staggered arrangements of cylinders have been considered for Reynolds numbers ranging from 1000 to 4000. The flow field and heat transfer characteristics are studied using streamline plots and temperature contours in various planes. Enhancement in heat transfer is quantified in terms
of span-averaged and overall Nusselt number (Nu). Variations in the perimeter-averaged Nu along the height of a cylinder and of height-averaged Nu around the cylinders are presented. The combined effects of heat transfer and pressure drop are expressed in terms of the thermal performance factor (JF) and are evaluated for different cylinder heights and inflow velocities.