Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
4
3
2012
DIFFERENTIAL TRANSFORMATION METHOD FOR SOLVING THE NONLINEAR HEAT TRANSFER EQUATION WITH A VARIABLE SPECIFIC HEAT COEFFICIENT
183-191
Mohsen
Torabi
Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong
Hessameddin
Yaghoobi
Faculty of Mechanical Engineering, Semnan University, Semnan; Young Researchers and Elite Club, Central Tehran Branch, Islamic Azad University, Tehran, Iran
In this paper, the nonlinear heat transfer equation is investigated by considering a variable specific heat coefficient. The calculations are carried out by using the differential transformation method (DTM), which is a seminumerical analytical solution technique. Using the DTM, the nonlinear constrained governing equations are reduced to recurrence relations and related initial conditions are transformed into a set of algebraic equations. The principle of differential transformation is briefly introduced, and is then applied to the aforementioned equation. The solutions are subsequently solved by a process of inverse transformation. The current results are then compared with those derived from the established Fehlberg fourth-fifth order Runge-Kutta method in order to verify the accuracy of the proposed method. Accordingly, several illustrative numerical computations are given to demonstrate the effectiveness of the present method. The findings reveal that the DTM can achieve accurate results in predicting the solution of such problems.
EDGE EFFECT ON PHONON TRANSPORT IN SUSPENDED AND SUPPORTED GRAPHENE NANORIBBONS
193-199
Masanari
Kimura
Department of Aeronautics and Astronautics, Kyushu University, 744 Motooka, Fukuoka 8190395, Japan
Takafumi
Matsuzaki
Department of Aeronautics and Astronautics, Kyushu University, 744 Motooka, Fukuoka 8190395, Japan
Koji
Takahashi
Department of Aeronautics and Astronautics, Kyushu University, Motooka 744, Nishi-Ku, Fukuoka 819-0395, Japan; International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Motooka
744, Nishi-Ku, Fukuoka 819-0395, Japan
Heat conduction in a graphene nanoribbon (GNR) is investigated using nonequilibrium molecular dynamics simulation. GNR shows an intriguing dependence of thermal conductivity on its width, length, and edge shape. For example, thermal conductivity of thin armchair GNR is about three times lower than that of zigzag GNR due to the strong phonon scattering at the armchair edge. The substrate interaction is another critical issue for phonon transport. GNR supported on a substrate is analyzed by using the Lennard-Jones potential, and the thermal conductivity of a zigzag ribbon is found to decrease significantly due to phonon scattering by the substrate. However, under the same conditions, that of armchair ribbon is not affected by the substrate or even increases. This phenomenon is caused by the suppression of edge-localized flexural phonons of armchair GNR, which triggers their smaller thermal conductivity than the zigzag one. This anomalous edge-substrate combined effect on thermal transport in supported GNR is discussed.
DOUBLE DIFFUSION MIXED CONVECTION IN AN AXISYMMETRIC STAGNATION FLOW OF A NANOFLUID OVER A VERTICAL CYLINDER
201-211
M. Modather M.
Abdou
Department of Mathematics, Faculty of Science Aswan, South Valley University, Aswan, Egypt; Department of Mathematics, College of Science and Humanity Studies, Salman Bin AbdulAziz University, Al-Kharj, KSA
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
The effect of double diffusion on mixed convection of a viscous incompressible in an axisymmetric stagnation flow of nanofluid past a vertical cylinder with constant or variable thermal wall condition is analyzed. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The governing equations are transformed into dimensionless form using the stream function and suitable variables. The transformed equations are then solved numerically using the Runge-Kutta numerical integration procedure in conjunction with the shooting technique. 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 friction factor, and the local Nusselt and Sherwood numbers, are illustrated graphically to show interesting features of the solutions.
PREFACE: ASIAN SYMPOSIUM ON COMPUTATIONAL HEAT TRANSFER AND FLUID FLOW-2011 (ASCHT-11)
215
Kazuhiko
Suga
Department of Mechanical Engineering, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku,
Sakai, Osaka 599-8531, Japan
Masahiko
Shibahara
Department of Mechanical Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, JAPAN
NUMERICAL SIMULATION FOR A FLOW AROUND BODY EJECTION USING AN AXISYMMETRIC UNSTRUCTURED MOVING GRID METHOD
217-223
Masashi
Yamakawa
Department of Mechanical and System Engineering, Kyoto Institute of Technology, Kyoto, Japan
Daiki
Takekawa
Department of Mechanical and System Engineering, Kyoto Institute of Technology, Kyoto, Japan
Kenichi
Matsuno
Department of Mechanical and System Engineering, Kyoto Institute of Technology, Kyoto, Japan
Shinichi
Asao
Department of Mechanical Engineering, College of Industrial Technology, Hyogo, Japan
An unstructured moving-grid finite volume method is developed for an axisymmetric grid system. In this paper, the method is applied to a body ejection problem. When a body is ejected through a cylinder, complicated motion of the body and complicated flow phenomena occur. It shows that the body is separated from the cylinder. Thus, in the case of a body fitted coordinate system, computational elements should be created and eliminated according to the motion of the body. Furthermore by ejection of the body, two separated physical spaces between the inside of the cylinder and the outside of the cylinder are combined in an instant. Then, to capture a sudden change of flow at the point, it is necessary to generate a valid mesh around it. In this paper, a new method is constructed satisfying the geometric conservation law perfectly.
NUMERICAL STUDY OF PYROLYSIS GAS FLOW AND HEAT TRANSFER INSIDE AN ABLATOR
225-242
Naoya
Hirata
Department of Aeronautics and Astronautics, Kyushu University, Fukuoka, Japan
Sohey
Nozawa
Research and Education Center of Carbon Resources, Kyushu University, Fukuoka, Japan
Y.
Takahashi
Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan
H.
Kihara
Department of Aeronautics and Astranautics, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan
Ken-ichi
Abe
Department of Aeronautics and Astronautics, Kyushu University, Motooka, Nishi-ku, Fukuoka 819-0395
A numerical simulation of a lightweight ablator in an arc-heated flow was carried out. Thermal response analysis of the ablator was coupled with thermochemical nonequilibrium analysis of an arc jet around the ablator. In the thermal response analysis, the pyrolysis gas flow inside the ablator was calculated in detail by solving the conservation equations. Phenomena such as heat conduction, pyrolysis of resin, surface reactions, and recession were also considered in the simulation. Furthermore, in order to evaluate the injection of the ablation gas (pyrolysis gas and carbonaceous gas generated by the surface reactions) from the ablator surface into the outer flow field, a computational fluid dynamics code was extended by including further chemical species besides those in the previous study. This also allowed the simulations for wider-range flow conditions such as a nitrogen flow and airflow. The simulation was conducted for flow conditions of a 20 kW arc−heated nitrogen flow and a 750 kW arc−heated airflow. The results from the former simulation were compared with the experimental data and the computational results using other models. This comparison showed that the effect of the pyrolysis gas flow on the thermal response was significant, and thus the detailed analysis considering the multidimensional pyrolysis gas flow led to a considerable improvement of the predictive performance.
A NUMERICAL ANALYSIS OF POWER EFFICIENCY OF WIND ROTOR SYSTEMS IN A PARALLEL MATRIX
243-262
Jia-Shiuan
Feng
Department of Mechanical Engineering, National Chiao Tung University, HsinChu 30010, Taiwan
Chin-Lien
Tseng
EAK Engineer Consultants & Technology CO., LTD, Taipei 10655, Taiwan
Chiun-Hsun
Chen
Department of Mechanical Engineering, National Chiao Tung University, HsinChu 30010, Taiwan
This research employs the computational fluid dynamics (CFD) software Fluent to analyze the flow fields around two-blade Savonius wind rotors and their corresponding performances. It utilizes the moving mesh method to simulate the rotating wind rotors in both 2D and 3D transient systems. The study is divided into two topics: a study of a single Savonius wind rotor and a study of a parallel matrix system. The simulation results show that the performance of the wind rotor in the atmosphere is lower than that inside the wind tunnel due to the effect of wind tunnel walls. In the 2D simulation results of the parallel matrix system, the best power coefficient (cp) can be obtained with a phase-angle difference of 90 deg, which is 2.05 times of that of a single wind rotor. The improved performance from the parallel matrix system is due to the positive interaction between the Savonius wind rotors, and the flow fluctuation has a major contribution to the positive interaction. However, this effect is strongly influenced by the change in wind direction. When the wind direction is 45 deg, the cp of the parallel matrix system becomes almost the same or even lower than that of a single rotor. The maximum cp in the parallel matrix system according to the 3D simulation is ~1.45 times that of a single Savonius wind rotor. The ratio of 2D to 3D cp is 1.28 in the single Savonius wind rotor condition and 1.83 in the parallel matrix system.
THE ROLE OF HELIUM/ARGON GAS FLOW IN A GLASS FIBER DRAWING FURNACE
263-270
Kyoungjin
Kim
Department of Mechanical System Engineering, Kumoh National Institute of Technology,
61 Daehak-ro, Gumi, Gyeongbuk 39177, Korea
Ho Sang
Kwak
Department of Mechanical System Engineering, Kumoh National Institute of Technology,
61 Daehak-ro, Gumi, Gyeongbuk 39177, Korea
Dongjoo
Kim
Department of Mechanical Engineering, Kumoh National Institute of Technology, 1 Yangho, Gumi, Gyeongbuk 730-701, Korea
A glass fiber drawing process in optical fiber manufacturing is numerically modeled and simulated in order to appreciate the effects of inert working gas supplied around the silica preform and glass fiber. The iterative computational scheme is employed between the one-dimensional model for prediction of the preform neck-down profile and the two-dimensional thermo-fluid analysis, which includes the radiative heating of the preform and convective heat transport of the working gas in a simplified geometry of the glass fiber drawing furnace. By testing the gas composition of helium and argon in the working gas supply, its effects on the preform heating conditions and draw tension are found to be insignificant. However, when the helium usage is high, the cooling rate of the glass fiber after being drawn from the softened preform is considerably increased, which results in a shorter post-heater length of the furnace required for the solidification of the glass fiber before leaving the furnace.
NUMERICAL STUDY OF CONJUGATE HEAT TRANSFER IN PIN-FIN CHANNELS BASED ON LARGE-EDDY SIMULATION DATA
271-282
Yutaka
Oda
Kansai University, 3-3-35, Yamate-cho, Suita, Osaka 564-8680, Japan
Kenichiro
Takeishi
Department of Mechanical Engineering, Osaka University; 2-1, Yamadaoka, Suita, Osaka 5650871, Japan; Tokushima Bunri University, 1314-1, Shido, Sanuki, Kagawa 769-2193, Japan
Yoshiaki
Miyake
Guidance & Propulsion Division, Aerospace Systems, Mitsubishi Heavy Industries, Ltd.; 1200, Higashitanaka, Komaki, Aichi 485-8561, Japan
Precedent mass transfer experiments and the corresponding large-eddy simulation (LES) by Oda et al. (Proc. 14th Intl. Heat Transfer Conf, IHTC14-23191, Washington, D.C., USA, Aug. 8−13, 2010) and Takeishi et al. (ASME Paper GT2012-69625, 2012) revealed that an inclined pin-fin channel with a wavy endwall shows better "endwall" heat transfer than that with a flat endwall with less or comparable pressure loss, as long as the pin-fin surface was treated as thermally adiabatic. Therefore, in this study, a conjugate heat transfer problem in the pin-fin channels was solved numerically to evaluate the overall heat transfer performance including heat transfer from the pin-fin surface. To this end, an LES-based conjugate heat transfer analysis was newly proposed, which utilizes time-mean velocity and turbulent statistics obtained by preliminary LES to estimate the eddy thermal diffusivity for thermal Reynolds-averaged Navier−Stokes (RANS) analysis to solve the conjugate heat transfer problem. This method has an advantage over conventional RANS-based methods when the time-mean flow field is difficult to predict due to the complex turbulent flows, e.g., massively separated flows in pin-fin channels. By applying the method to the inclined pin-fin channel with a flat or wavy endwall, it is clarified that the wavy endwall shows a clearly better overall heat transfer rate than the flat endwall when the Biot number is of the order of10−1, which represents a typical condition to cool combustor liners of jet engines.