Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
3
6
2011
A NEW METHOD TO SPECIFY THE OUTLET BOUNDARY CONDITION OF FLUID FLOW IN THE CHANNEL FORMED BY TUBE BANK FINS
445-459
Zhi-Min
Lin
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
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
Quan-Fu
Gao
Department of Mechanical Engineering, Lanzhou Jiaotong University, Lanzhou, Gansu 730070 P. R. China
The numerical treatment of the boundary conditions (BCs) in the computational domain is of paramount importance. In the passages formed by tube bank fins, a recirculation flow may occur at the outflow boundary. One of the conventional approaches to prescribe this kind BCs is to extend the computational domain far from the domain of interest, thus it waste the computing resource and lacks in a proper physical basis; while the convective boundary condition is somewhat difficult to implement and also lacks in a proper physical basis for elliptic-type problem. To find a more reasonable implement, firstly, the present study illustrates the quantitative similarities of the velocity components on those cross sections located at the periodic counterparts of the outflow boundary in the passages formed by the multi-row tube bank fins, and then a new method to specify the outlet flow BCs is introduced based on the quantitative similarities. If the proposed method is used, the simulation domain does not need to be extended and the possible recirculation flow at the outlet can be specified. The reliability of the proposed method is tested through comparing numerical results with experimental ones. The numerical results using the proposed and the conventional methods are also compared. The results show that the proposed method is feasible and can obtain reliable averaged characteristics with acceptable discrepancy.
THREE-DIMENSIONAL ANALYSIS OF LARGE SHELL-AND-TUBE HEAT EXCHANGERS AT HIGH TEMPERATURES
461-481
Masato
Handa
Hitachi, Ltd., Hitachi Research Laboratory, 832-2 Horiguchi, Hitachinaka-shi, Ibaraki-ken 312-0034, Japan
Kenji
Yamamoto
Hitachi, Ltd., Hitachi Research Laboratory, 832-2 Horiguchi, Hitachinaka-shi, Ibaraki-ken 312-0034, Japan
Yoshio
Shimogori
Babcock-Hitachi, K. K. Kure Division, 6-9 Takara-machi, Kure-shi, Hiroshima-ken, 737-8508 Japan
The distributed resistance approach has been extended to obtain surface temperature distributions around the tubes in large shell-and-tube heat exchangers at high temperatures. The tube side is discretized in a different manner while following the existing shell-side models of flow resistance, convective heat transfer, and turbulence. The tube side is divided into small straight parts and they are further discretized in their circumferential directions as well as in their axial ones. To reduce the computational time and memory, convective and radiative heat fluxes are not calculated directly on each discretized surface; rather, each of them is calculated on the representative surface in which the discretized surfaces are lumped differently depending on convection or radiation. The discrete transfer method (DTM) is adopted to calculate radiation. To implement DTM properly a new algorithm of ray tracing is developed. For the example application, the heat recovery area in a coal fired boiler is taken. As the emissivity of the heat exchanger at high temperatures increases, a large increased temperature variation around the tube is observed. The simulated results of the global heat absorption and local temperature distributions exhibit good agreement with the measured data. The paths of the radiation beams onto the tube are investigated and the influence range of radiation is clarified. The treatment of the influence range in a past numerical study of a utility boiler is also discussed.
INFLUENCE OF BOILER SWING RATE ON DYNAMICS OF THERMAL AND FLOW CHARACTERISTICS IN WATER CIRCULATION BOILERS
483-500
Mohamed A.
Habib
Mechanical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia
I.
Al-Zaharnah
Mechanical Engineering Department, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
T.
Ayinde
Mechanical Engineering Department, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
S.
Al-Anizi
Consulting Services Department, Saudi Aramco, Dhahran, Saudi Arabia
Y.
Al-Awwad
Consulting Services Department, Saudi Aramco, Dhahran, Saudi Arabia
Tube overheating may cause tube failure resulting in an unscheduled boiler shutdown that may interrupt plant operation. The impact of this problem is not only due to the cost of replacing defective parts but also due to the frequent need of system shutdown and the possible imminent safety hazards. This paper provides an investigation of the influence of rapid rise in steam flow rate (swing rate) on the thermal and flow characteristics of the riser tubes in natural circulation water tube boilers. A thermal model for the prediction of possible tube overheating was developed. The developed model incorporates a nonlinear state space dynamic model which captures the important physical interactions of the main variables of steam generation in drum boilers. The system under consideration includes the drum, the riser, and downcomer as its major components. A numerical scheme for the solution of the governing differential equations was established. The dynamic response of the system's state variables due to rapid rises in steam flow rate was investigated. The results show that the rapid rise in the steam flow rate results in decrease in the pressure and an initial increase in the steam quality which is followed by a decrease in the steam quality. The riser temperature increases partly due to the increase in the steam temperature and partly due to the dynamic influence resulting from a decrease in the heat transfer coefficient. The present calculations of the water level in the drum provide good comparison with those in the literature.
DSMC SCHEME TO STUDY THE NONLINEAR BOLTZMANN TRANSPORT EQUATION FOR PHONONS
503-510
Yusuke
Masao
Department of Mechanical Engineering and Science, Graduate School of Engineering, Kyoto University, Kyoto, 606-8501, Japan
Mitsuhiro
Matsumoto
Department of Mechanical Engineering and Science, Graduate School of Engineering, Kyoto University, Kyoto, 606-8501, Japan ; Advanced Research Institute of Fluid Science and Engineering, Graduate School of Engineering, Kyoto University, Kyoto, 606-8530,
A DSMC (direct simulation Monte Carlo) scheme is a method to solve a nonlinear Boltzmann transport equation (BTE) and widely used for analysis of rarefied gas dynamics. We adopt this scheme to study phonon dynamics in analogous with rarefied gas. Phonons are one of the dominant energy carriers in solid materials. Although heat conduction is generally described by the Fourier rule, this fails when spatial scale of the system becomes smaller. In this case, heat conduction should be described by the BTE which is often treated with the relaxation time approximation. However, our previous work with molecular dynamics (MD) simulation suggested that this has some limitations that couplings among phonons are not considered directly. We have developed a simulation code based on the DSMC scheme for analysis of phonon dynamics and carried out two test calculations. In the first case, we simulated the phonon dynamics in a large nonequilibrium situation. Relaxation behaviors similar to MD results were observed. In the second case, we simulated phonon dynamics at equilibrium to calculate the relaxation time, which is an input parameter in the relaxation time approximation. Thus the proposed DSMC scheme is a promising method for micro-scale heat conduction in solids.
NUMERICAL STUDY OF A TRANSITIONAL NATURAL VENTILATION FLOW DRIVEN BY A LINE SOURCE PLUME WITH VARIED REYNOLDS AND PRANDTL NUMBERS
511-519
Tae
Hattori
School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Australia
Steven W.
Armfield
School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney, NSW 2006, Australia
Michael P.
Kirkpatrick
School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, NSW 2006, Australia
Shigenao
Maruyama
Institute of Fluid Science, Tohoku University Katahira 2-1 -1, Aoba-ku Sendai, 980-8577 Japan
Atsuki
Komiya
Institute of Fluid Science, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan
The effects of the parameters, Reynolds number, Re, and Prandtl number, Pr, on natural ventilation flow in the transitional regime, with a line heat flux source, are investigated using two-dimensional direct numerical simulations. Results have been obtained for Re and Pr in the ranges, 5.0 × 105 ≤ Re ≤ 1.58 × 106 and 0.7 ≤ Pr ≤ 70. Flows with constant heat flux,q ∼ Re2/Pr, at Re2/Pr = 3.57 × 1010 and 3.57 × 1011 are studied in detail. The results obtained in this study provide a good illustration of the effect of Re and Pr on flow turbulence and the fully-developed flow characteristics. In particular, the Pr dependent variation in the turbulence intensity in the upper buoyant layer, and in the plume volume flux, have been shown to increase with reducing Re2/Pr.
SIMULTANEOUS CONTROL OF FRICTION DRAG REDUCTION AND HEAT TRANSFER AUGMENTATION BY TRAVELING WAVE-LIKE BLOWING/SUCTION
521-530
Kosuke
Higashi
Department of Mechanical Engineering, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama 223-8522,Japan
Hiroya
Mamori
Department of Mechanical Engineering, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama 223-8522,Japan; Department of Mechanical Systems Engineering Tokyo University of Agriculture and Technology 2-24-16 Koganei City Naka Town Tokyo; Tokyo University of Science,6-3-1 Niijuku, Katsushika-ku, Tokyo, 125-8585, Japan
Koji
Fukagata
Department of Mechanical Engineering, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama 223-8522,Japan
The possibility of simultaneous control of skin-friction drag reduction and heat transfer augmentation by traveling wave-like blowing/suction is explored for laminar channel flow. In addition to the constant temperature difference condition, uniform heat generation is considered for the temperature field so that the boundary condition similar to that in a velocity field holds. Friction drag reduction and heat transfer augmentation are simultaneously achieved when the wave travels in the upstream direction. The global phases of streamwise velocity and temperature fluctuations are found to oppose each other, which eventually leads to dissimilarity between the friction drag and heat transfer. Direct numerical simulation confirms that this dissimilar control effect also can be obtained in a turbulent channel flow.
OUTFLOW BOUNDARY CONDITION IN THE FINITE-VOLUME METHOD FOR UNSTEADY-STATE FLUID FLOW COMPUTATION WITH VARIABLE DENSITY
531-537
Yohsuke
Matsushita
Research and Education Center of Carbon Resources, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan
This paper presents the outflow boundary condition for unsteady-state fluid flow computations with variable density as part of the semi-implicit method for pressure-linked equations (SIMPLE) calculation in the finite-volume method. In the SIMPLE algorithm, there is no built-in numerical procedure to calculate the velocities at an outflow boundary. The outflow boundary condition is meant to satisfy the mass flow rate between the inflow and outflow boundary conditions and the sum of all transient terms over the entire computational domain. When the proposed outflow boundary condition for unsteady-state computations is applied to a thermal fluid flow calculation, stable, robust, and highly accurate mass conservation is obtained compared with that obtained for steady-state calculations. Therefore, the proposed outflow boundary condition is expected to have wide applicability in unsteady-state fluid flow computations with variable density, such as in combustion calculations.