共查询到20条相似文献,搜索用时 46 毫秒
1.
Sun-Ae Moon Tae-Gu Lee Jin-Huek Hur Ki-Moo Heo Hoseon Yoo Seung-Jae Moon Jae-Heon Lee 《Heat and Mass Transfer》2008,44(11):1345-1353
In this paper, the averaged reentering rates of the densely built cooling towers, which form banks on the building roof in
Seoul, Korea have been predicted by a numerical method according to various summer wind conditions and roof wall types. The
averaged reentering rates of all the cooling towers are compared according to two wall types to study the effect of the intake
outdoor air louver on the reentering rates. Consequently, two findings are drawn as follows. (1) With a curtain wall, the
averaged reentering rates of the total cooling towers against the west and the south wind at ν = 5 m/s are 13.3 and 24.4%, respectively. Therefore, it is strongly needed to find a method to reduce the reentering of the
discharged air from the cooling towers. (2) In the case of a louver wall, the averaged reentering rates of the cooling towers
with the west and south wind at ν = 5 m/s are 2.5 and 9.74%, respectively, which have been estimated to be lower than those of the curtain wall. Therefore,
the louver wall can be suitably adopted to reduce the reentering of the discharged air from the cooling towers in the present
study. 相似文献
2.
Curvature sensitive nonlinear turbulence model 总被引:2,自引:0,他引:2
By modifying the Rodi assumption to take account of the influence of flow curvature, a new curvature modified algebraic stress
model (CMASM) is developed from the second moment closure in the generalized curvilinear coordinate system. And the explicit
form of the ASM, a new curvature modified nonlineark-ε model (CMNKE), is derived in the orthogonal curvilinear coordinate system. This new nonlineark-ε model is further validated by a numerical simulation of a two-dimensional U-type turnaround duct flow. The results show that
the CMNKE can effectively capture the main characteristic of this curvature flow and simulate the damping effect of the shear
stress by a convex curvature and the enhancing effect by a concave curvature. So, this model is a rational and effective simplification
to the second moment closure.
The project supported by the National Natural Science Foundation of China (19725208) and the National Climbing project of
China 相似文献
3.
A. F. Polyakov D. L. Reviznikov Shen Qing Tang Jinrong Wei Shuru 《Acta Mechanica Sinica》2001,17(3):245-250
Heat and mass transfer of a porous permeable wall in a high temperature gas dynamical flow is considered. Numerical simulation
is conducted on the ground of the conjugate mathematical model which includes filtration and heat transfer equations in a
porous body and boundary layer equations on its surface. Such an approach enables one to take into account complex interaction
between heat and mass transfer in the gasdynamical flow and in the structure subjected to this flow. The main attention is
given to the impact of the intraporous heat transfer intensity on the transpiration cooling efficiency.
The project supported by the National Natural Science Foundation of China (19889209) and Russian Foundation for Basic Research
(97-02-16943) 相似文献
4.
This article presents recent progresses in turbulence modeling in the Unit for Turbulence Simulation in the Department of
Engineering Mechanics at Tsinghua University. The main contents include: compact Non-Linear Eddy-Viscosity Model (NLEVM) based
on the second-moment closure, near-wall low-Re non-linear eddy-viscosity model and curvature sensitive turbulence model. The models have been validated in a wide range
of complex flow test cases and the calculated results show that the present models exhibited overall good performance.
The project supported by the National Natural Science Foundation of China (10232020), the National Key Basic Research Special
Fund of China (2001CB409600) and the National High-Tech Development Program (2002AA311240) 相似文献
5.
In this paper, with the aid of superimposing technique and the Pseudo Traction Method (PTM), the interaction problem between
an interface macrocrack and parallel microcracks in the process zone in bimaterial anisotropic solids is reduced to a system
of integral equations. After the integral equations are solved numerically, a conservation law among three kinds ofJ-integrals is obtained which are induced from the interface macrocrack tip, the microcrack and the remote field, respectively.
This conservation law reveals that the microcrack shielding effect in such materials could be considered as the redistribution
of the remoteJ-integral.
The project supported by the National Natural Science Foundation of China, and the Doctorate Foundation of Xi'an Jiaotong
University 相似文献
6.
Performance improvements of cross flow cooling towers in variable wet bulb temperature were performed. A conventional mathematical model is used to predict desiccant wheel effect on the performance of cooling tower. It is found that by using optimum parameters of desiccant wheel, the inlet air wet bulb temperature into the cooling tower would decrease more than 6 °C and outlet water temperature would decrease more than 4 °C. 相似文献
7.
The flow near a wall suddenly set in motion for a viscoelastic fluid with the generalized Oldroyd-B model is studied. The
fractional calculus approach is used in the constitutive relationship of fluid model. Exact analytical solutions of velocity
and stress are obtained by using the discrete Laplace transform of the sequential fractional derivative and the Fox H-function. The obtained results indicate that some well known solutions for the Newtonian fluid, the generalized second grade
fluid as well as the ordinary Oldroyd-B fluid, as limiting cases, are included in our solutions.
The project supported by the National Natural Science Foundation of China (10272067), the Doctoral Program Foundation of the
Education Ministry of China (20030422046), the Natural Science Foundation of Shandong Province, China (Y2006A14) and the Research
Foundation of Shandong University at Weihai.
The English text was polished by Keren Wang. 相似文献
8.
This paper extends symbolic dynamics to general cases. Some chaotic properties and applications of the general symbolic dynamics (∑(X),σ) and its special cases are discussed, where X is a separable metric space. 相似文献
9.
The stability of convective motion, generated by a lateral temperature difference across a vertical slot, is studied numerically
over a range ofGr=5000 to 1.5 × 105,Pr=0.01 to 10, andA=8,16 and 20. Various cellular flow structures and temperature patterns are illustrated. Several branches of solutions characterized
by different numbers of the cells in the flow patterns as well as by both steady and unsteady multicellular patterns are found
for low-Prandtl-number fluid in the vertical slot. Meanwhile, the behaviors of the temperature variation and heat transfer
are also discussed.
The project supported by the National Natural Science Foundation of China (59776011) and by the Returnee from Abroad Funding
of Academia Sinica. 相似文献
10.
Application of the principles of the fluidization is made for cooling towers. The performance on a smaller size Fluidized Bed Cooling Tower (FBCT) is found to be encouraging. Hence a larger size FBCT is designed and the performance is found to be equally good. The pressure drop encountered in FBCT is comparable to that of conventional cooling towers. The packing height in FBCT reduces considerably because of fluidization. A table is provided to show that the throughput of the FBCT is greater than that of conventional cooling towers.
Nomenclature L water flow rate, kg per hour/m2 - K overall enthalpy transfer coefficient, kg per hour/m2 - V active tower volume, m3/m2 plan area - T i cold water temp. deg. C - i i enthalpy of the air at the interface, Kcal/kg - G airflow rate, kg per hour/m2 - a area of water interface, m2/m3 - H st static height of packing - T 2 hot water temp. deg. C - i g enthalpy of air, Kcal/kg 相似文献
Der Einfluß der Größe auf die Leistung eines Wirbelschicht-Kühlturms
Zusammenfassung Das Prinzip der Fluidisierung wird für Kühltürme eingesetzt. Die Leistung eines Wirbelschicht-Kühlturms mit geringer Größe ist als ermutigend angesehen worden. Deshalb wurde ein größerer Wirbelschicht-Kühlturm entwickelt, dessen Leistung ebenso gut eingestuft wurde. Der Druckverlust, der in einem Wirbelschicht-Kühlturm auftritt, ist mit dem Druckverlust in einem konventionellen Kühlturm vergleichbar. Die Packungshöhe in einem Wirbelschicht-Kühlturm verringert sich aufgrund der Fluidisierung wesentlich. In einer Tabelle wird gezeigt, daß die Durchflußleistung eines Wirbelschicht-Kühlturms erheblich größer ist, als bei konventionellen Kühltürmen.
Nomenclature L water flow rate, kg per hour/m2 - K overall enthalpy transfer coefficient, kg per hour/m2 - V active tower volume, m3/m2 plan area - T i cold water temp. deg. C - i i enthalpy of the air at the interface, Kcal/kg - G airflow rate, kg per hour/m2 - a area of water interface, m2/m3 - H st static height of packing - T 2 hot water temp. deg. C - i g enthalpy of air, Kcal/kg 相似文献
11.
The combined effects of void size and void shape on the void growth are studied by using the classical spectrum method. An infinite solid containing an isolated prolate spheroidal void is considered to depict the void shape effect and the Fleck-Hutchinson phenomenological strain gradient plasticity theory is employed to capture the size effects. It is found that the combined effects of void size and void shape are mainly controlled by the remote stress triaxiality. Based on this, a new size-dependent void growth model similar to the Rice-Tracey model is proposed and an important conclusion about the size-dependent void growth is drawn: the growth rate of the void with radius smaller than a critical radius rc may be ignored. It is interesting that rc is a material constant independent of the initial void shape and the remote stress triaxiality.The project supported by the National Natural Science Foundation of China (A10102006) and the New Century Excellent Talents in Universities of China. The English text was polished by Keren Wang. 相似文献
12.
This paper is concerned with a numerical solution of hyperbolic cooling tower shell, a class of full nonlinear problems in solid mechanics of considerable interest in engineering applications. In this analysis, the post-buckling analysis of cooling tower shell with discrete fixed support and under the action of wind loads and dead load is studied. The influences of ring-stiffener on instability load are also discussed. In addition, a new solution procedure for nonlinear problems which is the combination of load increment iteration with modified R-C are- length method is suggested. Finally, some conclusions having important significance for practice engineering are given.The Project Supported by National Natural Science Foundation of China. 相似文献
13.
This paper presents an elasto-viscoplastic consistent tangent operator (CTO) based boundary element formulation, and application
for calculation of path-domain independentJ integrals (extension of the classicalJ integrals) in nonlinear crack analysis. When viscoplastic deformation happens, the effective stresses around the crack tip
in the nonlinear region is allowed to exceed the loading surface, and the pure plastic theory is not suitable for this situation.
The concept of consistency employed in the solution of increment viscoplastic problem, plays a crucial role in preserving
the quadratic rate asymptotic convergence of iteractive schemes based on Newton's method. Therefore, this paper investigates
the viscoplastic crack problem, and presents an implicit viscoplastic algorithm using the CTO concept in a boundary element
framework for path-domain independentJ integrals. Applications are presented with two numerical examples for viscoplastic crack problems andJ integrals.
The project supported by National Natural Science Foundation of China (9713008) and Zhejiang Natural Science Foundation Special
Funds No. RC.9601 相似文献
14.
A finite element model for numerical simulation of thermo-mechanical frictional contact problems 总被引:2,自引:0,他引:2
Two kinds of variational principles for numerical simulation of heat transfer and contact analysis are respectively presented.
A finite element model for numerical simulation of the thermal contact problems is developed with a pressure dependent heat
transfer constitutive model across the contact surface. The numerical algorithm for the finite element analysis of the thermomechanical
contact problems is thus developed. Numerical examples are computed and the results demonstrate the validity of the model
and algorithm developed.
The project supported by the National Key Basic Research Special Foundation (G1999032805), the National Natural Science Foundation
of China (50178016, 10225212) and the Foundation for University Key Teacher by the Ministry of Education of China 相似文献
15.
The inverse heat conduction problem (IHCP) is a severely ill-posed problem in the sense that the solution ( if it exists) does not depend continuously on the data. But now the results on inverse heat conduction problem are mainly devoted to the standard inverse heat conduction problem. Some optimal error bounds in a Sobolev space of regularized approximation solutions for a sideways parabolic equation, i. e. , a non-standard inverse heat conduction problem with convection term which appears in some applied subject are given. 相似文献
16.
Adhesive contact model between an elastic cylinder and an elastic half space is studied in the present paper, in which an external pulling force is acted on the above cylinder with an arbitrary direction and the contact width is assumed to be asymmetric with respect to the structure. Solutions to the asymmetric model are obtained and the effect of the asymmetric contact width on the whole pulling process is mainly discussed. It is found that the smaller the absolute value of Dundurs' parameter 13 or the larger the pulling angle O, the more reasonable the symmetric model would be to approximate the asymmetric one. 相似文献
17.
A theoretical solution is presented for the convective heat transfer of Giesekus viscoelastic fluid in pipes and channels,
under fully developed thermal and hydrodynamic flow conditions, for an imposed constant heat flux at the wall. The fluid properties
are taken as constant and axial conduction is negligible. The effect of Weissenberg number (We), mobility parameter (α) and Brinkman number (Br) on the temperature profile and Nusselt number are investigated. The results emphasize the significant effect of viscous
dissipation and fluid elasticity on the Nusselt number in all circumstances. For wall cooling and the Brinkman number exceeds
a critical value (Br
1), the heat generated by viscous dissipation overcomes the heat removed at the wall and fluid heats up longitudinally. Fluid
elasticity shifts this critical Brinkman number to higher values. 相似文献
18.
Liang Zaichao 《Acta Mechanica Sinica》1996,12(4):289-295
In the present paper the coherent structures in the outer region of turbulent boundary layer were investigated experimentally
and analytically. From the observation of the flow field over smooth wall, rough wall and sand wave wall, it was found that
the direct effect of wall on the flow structure can reachy
+1≈100, and both lateral and vertical vortices exist in the outer region, but the coherent structures in the outer region are
mainly the formation, development and decay of the large-scale lateral vortices. By experimental and dynamical analysis, some
influence factors and their relations associated with the dynamical process of lateral vortices were deduced.
The project supported by the National Natural Science Foundation of China 相似文献
19.
Multiphase fluid dynamics and transport processes of low capillary number cavitating flows 总被引:1,自引:0,他引:1
Wei Shyy 《Acta Mechanica Sinica》2009,25(2):161-172
To better understand the multiphase fluid dynamics and associated transport processes of cavitating flows at the capillary number of 0.74 and 0.54, and to validate the numerical results, a combined computational and experimental investigation of flows around a hydrofoil is studied based on flow visualizations and time-resolved interface movement. The computational model is based on a modified RNG k-ε model as turbulence closure, along with a vapor-liquid mass transfer model for treating the cavitation process. Overall, favorable agreement between the numerical and experimental results is observed. It is shown that the cavi- tation structure depends on the interaction of the water-vapor mixture and the vapor among the whole cavitation stage, the interface between the vapor and the two-phase mixture exhibits substantial unsteadiness. And, the adverse motion of the interface relates to pressure and velocity fluctuations inside the cavity. In particular, the velocity in the vapor region is lower than that in the two-phase region. 相似文献
20.
Y. Zhang C. Zheng Y Liu L. Shao · C. Gou School of Mechanical Vehicular Engineering Beijing Institute of Technology Beijing China Y.Liu School of Mechanical-Electronic Automobile Engineering Beijing University of Civil Engineering Architecture Beijing China 《Acta Mechanica Sinica》2009,25(2):205-210
This paper presents two exact explicit solutions for the three dimensional dual-phase lag (DLP) heat conduction equation, during the derivation of which the method of trial and error and the authors' previous experiences are utilized. To the authors' knowledge, most solutions of 2D or 3D DPL models available in the literature are obtained by numerical methods, and there are few exact solutions up to now. The exact solutions in this paper can be used as benchmarks to validate numerical solutions and to develop numerical schemes, grid generation methods and so forth. In addition, they are of theoretical significance since they correspond to physically possible situations. The main goal of this paper is to obtain some possible exact explicit solutions of the dual-phase lag heat conduction equation as the benchmark solutions for computational heat transfer, rather than specific solutions for some given initial and boundary conditions. Therefore, the initial and boundary conditions are indeterminate before derivation and can be deduced from the solutions afterwards. Actually, all solutions given in this paper can be easily proven by substituting them into the governing equation. 相似文献