Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
8
1
2016
NUMERICAL PREDICTION OF THE MEAN TEMPERATURE OF THE VAPOR FILM IN FILM BOILING HEAT TRANSFER
1-10
A.
Abanades
ETSII/Universidad Politécnica de Madrid, J. Gutiérrez Abascal, 2-28006 Madrid, Spain
Ruben
Arevalo
Mechanical Engineering Department, UNET, San Cristobal 5001, Venezuela
L.
Rebollo
ETSII/Universidad Politécnica de Madrid, J. Gutiérrez Abascal, 2-28006 Madrid, Spain
The phase change heat (hfg) plays a fundamental role in the description of the film boiling phenomena and, therefore, is
included in most of the correlation to evaluate film boiling heat transfer coefficients. The Jakob number (Ja) is used to
establish the ratio between hfg and the sensible heat required to heat the vapor formed from the saturation temperature of the surroundings to the temperature on the solid-fluid interface. In the most accepted correlations, the enthalpy increase in the fluid is described with a scaling factor of hfg based on a fraction of Ja. In literature, this fraction varies from 0.34 to 0.95. In this paper, a numerical prediction of the mean temperature of the vapor film and this fraction were done based on computational fluid dynamic (CFD) calculation. Our analysis of the vapor film temperature shows that this Ja
fraction is of the order of 0.4, with a small dependency of the emissivity and Prandtl number.
A MATHEMATICAL MODEL FOR SOLIDIFICATION OF BINARY EUTECTIC SYSTEM INCLUDING RELAXATION TIME
11-30
Sarita
Yadav
Department of Mathematical Sciences, Indian Institute of Technology (BHU), Varanasi-
221005, India
Subrahmanayam
Upadhyay
DST-CIMS, Banaras Hindu University, Varanasi-221005, Uttar Pradesh, India
Kabindra Nath
Rai
Department of Mathematical Sciences, Indian Institute of Technology (BHU), Varanasi- 22005, Uttar Pradesh, India; DST-CIMS, Banaras Hindu University,Varanasi-22005, Uttar Pradesh, India
In this paper we have developed the time relaxation model for solidification of a binary eutectic system. In this model, we have considered the melt of a binary eutectic composite filled in a container; the flat probe is kept inside the container.
The surface temperature of the flat probe decreases linearly with time. The solidification process occurs in three stages
and, whole region is divided into solid, mushy, and liquid regions. The heat released in the mushy region is considered as discontinuous heat generation. The solid fraction present in the mushy region is characterized in two different ways: (i) when the solid fraction depends on distance and (ii) when the solid fraction depends on temperature. To solve this model we have developed the Legendre wavelets spectral Galerkin method. The whole analysis is presented in a dimensionless form and the results thus obtained are discussed in detail.
SIMULATION OF NATURAL CONVECTION OF NANOFLUIDS AT HIGH RAYLEIGH NUMBERS: A TWO-COMPONENT LATTICE BOLTZMANN STUDY
31-47
Mehdi
Hosseini Abadshapoori
Center of Excellence in Energy Conversion (CEEC), Mechanical Engineering Department,
Sharif University of Technology, P.O. Box: 11155-9567, Tehran, Iran
Mohammad Hassan
Saidi
Center of Excellence in Energy Conversion (CEEC), School of Mechanical Engineering, Sharif
University of Technology, P.O. Box 11155-9567, Tehran, Iran
In this research, the effect of using nanoparticles on the Nusselt number in the natural convection at high Rayleigh
numbers has been investigated. A two-component multiple relaxation times lattice Boltzmann code has been developed
to investigate the natural convection of nanofluids in a 2D square enclosure. Three main forces, namely, buoyancy, drag,
and Brownian forces are included to consider the interactions of the components. The potential force is also added to the model for the interactions among nanoparticles. The effects of Ra number, volume fraction of nanoparticles (φ), and size of nanoparticles (λ) have been investigated for two nanofluids (CuO-water and TiO2-water). Five different volume fractions (0.01−0.05) have been simulated while the Rayleigh number has been selected among 106, 107, 108, and 109.
Four different sizes, namely, 10, 30, 60, and 80 nm have been used for the nanoparticles. Results reveal that Nusselt
number increases with the increase of φ. However, it is shown that adding nanoparticles also increases viscosity which reduces the positive effect of nanoparticles on the Nu number. Results also show that an increase in the λ results in the decrease in the Nusselt number. The method is shown to have good capability of simulating nanofluids in natural convection at high Rayleigh numbers considering the effect of nanoparticles.
TWO-DIMENSIONAL BOUNDARY VALUE PROBLEM FOR SYMMETRIC EQUATION OF ANOMALOUS DIFFUSION
49-55
Tetiana
Kirichok
Sumy State University, Sumy, 40007, Ukraine
Marina
Synah
Sumy State University, Sumy, 40007, Ukraine; NetCracker Technology, Sumy, 40000, Ukraine
Dmytro
Kushnir
Sumy State University, Sumy, 40007, Ukraine
In this paper, we propose a new numerical-analytical method of solving the boundary value problem for a symmetric
equation of anomalous diffusion in a bounded 2D-region. The fundamental solutions of diffusion equations in the plane
of Laplace transform are found as an auxiliary problem. With the help of the fundamental solutions, the boundary
value problem is reduced to a singular integral equation of the first kind, which is solved numerically by successive
approximations. The calculation results in the circular domain are presented.
AN ADAPTIVE FINITE ELEMENT METHOD WITH DYNAMIC LES FOR TURBULENT REACTIVE FLOWS
57-71
Jiajia
Waters
Los Alamos National Laboratory, T-3 Fluid Dynamics and Solid Mechanics
David
Carrington
Los Alamos National Laboratory, T-3 Fluid Dynamics and Solid Mechanics
Darrell W.
Pepper
NCACM, Department of Mechanical Engineering, University of Nevada Las Vegas, Las Vegas, NV 89154, USA
A Vreman dynamic subgrid scale (SGS) large eddy simulation (LES) model is implemented in a predictor-corrector split
h-adaptive finite element method (FEM) for modeling combustion. The use of h-adaptation provides a measurement of the actual error in the discretization, and can adjust spatial accuracy to control the error. By utilizing the dynamic model, laminar or turbulent flow can be automatically calculated. In this study, we try to validate this Vreman SGS LES model in just the fluid dynamics system by assuming all species are air and all results are compared with experimental data and RANS k − ω model. The model is tested by solving an 18° ramp at a Mach number of 2.25 as well as unsteady turbulent flow over a backward-facing step. The high Mach number ramp demonstrates the ability of the model to capture shocks and shock-wave/boundary layer interactions. In the high Reynolds number backward-facing step, large eddies are resolved without the requirement of a fine mesh, in contrast to DNS, although it is finer than a RANS model would require. The reattachment length and instantaneous flow results compare well with published simulations and experimental data.
EFFECT OF PRANDTL NUMBER ON FREE CONVECTION IN NEWTONIAN AND POWER-LAW FLUIDS FROM A CYLINDER ADJACENT TO AN ADIABATIC WALL
73-98
A. K.
Baranwal
Department of Chemical Engineering, Indian Institute of Technology, Kanpur 208016, India
S. A.
Patel
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
Steady two-dimensional natural convection heat transfer from a horizontal cylinder situated above or beneath an adiabatic
wall is numerically studied. The governing differential equations have been solved over wide ranges of dimensionless
parameters, namely, Grashof number (10 ≤ Gr ≤ 104), Prandtl number (5 ≤ Pr ≤ 100) and power-law index (0.2 ≤ n ≤ 1), for a range of gaps between the cylinder and the adiabatic wall, ΙH/DΙ = 0.05, 0.2, 0.5, 0.9, 1.1, 1.5, 3, and 5. Limited results were also obtained for large values of (H/D) ≥ 3000 to approach the unconfined cylinder limit. Detailed discussion of the momentum and heat transfer phenomena is presented in terms of the streamlines, velocity
field, isotherms, and the Nusselt number. The effect of the Prandtl number is more pronounced when the cylinder is
close to the wall and this effect gradually diminishes as the gap increases. The average Nusselt number shows a positive dependence on the values of the Grashof and Prandtl numbers. With reference to the value of the Nusselt number for an unconfined cylinder, the presence of the adiabatic wall, above or below the cylinder, has an adverse influence on heat transfer. Indeed, the influence of the wall persists up to large values of the gap between the wall and the cylinder. The present results on the average Nusselt number have been reconciled in the form of a single correlation for the both top and bottom confinements.
THE CHARACTERISTICS OF LOCAL MECHANICAL ENERGY DISSIPATION IN THE FIN SIDE OF A CIRCULAR TUBE BANK FIN HEAT EXCHANGER
99-116
Mei
Su
Key Laboratory of Railway Vehicle Thermal Engineering (Lanzhou Jiaotong University),
Ministry of Education of People's Republic of China, China
Liang-Bi
Wang
School of Mechanical Engineering, Lanzhou Jiaotong University, Lanzhou, Gansu 730070, PR China; Key Laboratory of Railway Vehicle Thermal Engineering of MOE, Lanzhou Jiaotong University, Lanzhou,
Gansu 730070, PR China
The mechanical energy dissipation characteristics in the fin side channel of a circular tube bank fin heat exchanger
and their relations with the convective heat transfer characteristics on the fin surfaces are studied numerically. Most mechanical energy is dissipated in the regions near the surface and beside the tubes (having an arc angle from 0° to 138° relating to the upstream direction). In these regions the local heat transfer coefficient is large. The distribution of the span-volume-average mechanical energy dissipation has a trend roughly similar to the distribution of the span-average heat transfer coefficient. Downstream the mechanical energy dissipation has less efficiency to enhance heat transfer. The dimensionless span-volume-average mechanical energy dissipation φrms and span-average Euler Number Eurms do not closely correspond. The change of Eurms reflects that the static pressure energy may change into mechanical energy.