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This paper deals with the experimental and theoretical investigation of the influence of an electric field on the heat transfer
rate during stable film boiling of the electrically insulating fluid FC-72. In particular the case of stable saturated film
boiling from a horizontal plate is studied. The experiments show that the heat transfer rate increases ±50 when an electric
field of 27.3 kV/cm is applied. A new correlation for the heat transfer rate in the presence of an electric field based on
the heat transfer model of Klimenko is derived in this paper. Therefore the behavior of the liquid-vapor interface is studied
in more detail. This study shows that the electric field has a two fold effect on the interface. On the one hand the distance
between adjacent bubbles decreases and on the other hand the bubbles elongate in the presence of the electric field. The new
correlation is in good agreement with the experiments.
Received on 20 October 1998 相似文献
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Summary A boundary layer problem of a nonnewtonian fluid flow with fluid injection on a semi-infinite flat plate whose surface moves
with a constant velocity in the opposite direction to that of the uniform mainstream is analyzed. Concluding similarity equations
are solved numerically to show the dependence of the problem to the velocity ratio λ of the plate to uniform flow and to the
injection velocity parameter C. The critical values of λ and C for each nonnewtonian power-law index n are obtained, and their significance in drag reduction is discussed.
Received 26 August 1997; accepted for publication 21 October 1998 相似文献
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Rafael Cortell 《Theoretical and Computational Fluid Dynamics》2007,21(6):435-446
In this paper, a numerical analysis of the momentum and heat transfer of an incompressible fluid past a parallel moving sheet
based on composite reference velocity U is carried out. A single set of equations has been formulated for both momentum and thermal boundary layer problems containing
the following parameters: r the ratio of the free stream velocity to the composite reference velocity, σ (Prandtl number) the ratio of the momentum diffusivity
of the fluid to its thermal diffusivity, and E
c
(E
ck
) (Eckert number). The present study has been carried out in the domain 0 ≤ r ≤ 1. It is found that the direction of the wall shear changes in such an interval and an increase of the parameter r yields an increase in temperature.
相似文献
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The cooperative motion of a fluid and a parabolic tank is modeled. Use is made of a discrete model based on the Hamilton–Ostrogradsky
principle for an arbitrary body of revolution and a non-Cartesian parametrization of the domain occupied by the fluid. A set
of coordinate functions satisfying kinematic boundary conditions and solvability conditions is set up. The discrete model
is used to study the transients in the system. It is shown that the model adequately describes the nonlinear dynamic properties
of the system 相似文献
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Jet impingement boiling is very efficient in cooling of hot surfaces as a part of the impinging liquid evaporates. Several
studies have been carried out to measure and correlate the heat transfer to impinging jets as a function of global parameters
such as jet subcooling, jet velocity, nozzle size and distance to the surface, etc. If physically based mechanistic models
are to be developed, studies on the fundamentals of two-phase dynamics near the hot surface are required. In the present study
the vapor–liquid structures underneath a subcooled (20 K) planar (1 mm × 9 mm) water jet, impinging the heated plate vertically
with a velocity of 0.4 m/s, were analyzed by means of a miniaturized optical probe. It has a tip diameter of app. 1.5 μm and
is moved toward the plate by a micrometer device. The temperature controlled experimental technique enabled steady-state experiments
in all boiling regimes. The optical probe data provides information about the void fraction, the contact frequencies and the
distribution of the vapor and liquid contact times as a function of the distance to the surface. The measured contact frequencies
range from 40 Hz at the onset of nucleate boiling to nearly 20,000 Hz at the end of the transition boiling regime. Due to
condensation in the subcooled jet vapor disappears at a distance to the surface of app. 1.2 mm in nucleate boiling. This vapor
layer becomes smaller with increasing wall superheat. In film boiling a vapor film thickness of 8 ± 2 μm was found. 相似文献
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Nonlinear Dynamics - In this work, the combination of the 0–1 test for chaos and approximate entropy is applied to a newly established mechanical model instead of the Lyapunov exponent... 相似文献
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L. A. Barmina 《Fluid Dynamics》1973,8(1):1-5
A solution is given for the plane nonstationary motion of an arbitary deformable contour in the potential flow of an ideal incompressible fluid. The problem was solved by conformal mapping. A simple formula is obtained for the force acting on a small size contour.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 4–8, January–February, 1973.The author is grateful to L. I. Sedov and Yu. L. Yakimov for formulating the problem and supervising the research. 相似文献
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A. A. Zaitsev 《Fluid Dynamics》1966,1(1):69-71
The Taylor instability develops in a parallel flows when the body force acts in the direction from the heavier fluid toward the lighter [1]. It has been suggested that an increase in flow vorticity may have a stabilizing influence on the Taylor instability [2]. In studying the hydrodynamic stability of a viscous film on a body in a flow of a low-viscosity fluid [3], the author noted some stabilization of the Taylor instability with increase in Reynolds number, and suggested that cases of complete stabilization of the flow with respect to two-dimensional disturbances are possible with some increase in Reynolds number. In the present investigation, calculations revealed cases in which with increase in Reynolds number the Taylor instability goes over into a Helmholtz instability, which increases with increase in Reynolds number, and also cases in which the Taylor instability completely disappears at some value of the Reynolds number before a Helmholtz instability has developed, i.e., cases of complete stabilization of the flow with respect to two-dimensional disturbances as a result of an increase in Reynolds number. 相似文献
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V. L. Sennitskii 《Journal of Applied Mechanics and Technical Physics》1990,31(2):266-272
Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 111–118, March–April, 1990. 相似文献
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In this paper, the results of a series of experimental tests on single- and multi-droplet boiling systems are presented and
discussed. The main objectives of the present study are: a) to investigate experimentally the effect of the boiling onset
on the evaporation rate of water droplets; b) to measure the evolution of the solid surface temperature during evaporation;
c) to examine the possibility of improving spray cooling efficiencies. The behavior of small water droplets (from 10 to 50 μl)
gently deposited on hot, non-porous surfaces is observed. The evaporation of multi-droplet arrays (50 and 100 μl) under the
same conditions of the single-droplet tests is analyzed. In particular, the conditions which determine the onset of nucleate
and film boiling are stressed out. In the experimental tests, the interaction of different materials with several multi-droplet
systems is monitored by infrared thermography. The spray cooling efficiency is related to the solid temperature decrease as
a function of the water mass flux. In the present study, the effect of varying the droplet volume and the mass flux is also
analyzed and discussed. The results on the droplets evaporation time and on the solid surface transient temperature distribution
are also compared with the data obtained by the same authors during the analysis of droplet evaporation in total absence of
nucleate and film boiling. In order to analyze the different behavior of the evaporating droplet as a function of the solid
surface thermal conductivity, evaporative transients on aluminum, stainless steel and macor (a glass-like, low-conductivity
material) are considered.
Received on 20 February 1998 相似文献
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Hitoshi Fujimoto Yosuke Oku Tomohiro Ogihara Hirohiko Takuda 《International Journal of Multiphase Flow》2010
The collision of single water droplets with a hot Inconel 625 alloy surface was investigated by a two-directional flash photography technique using two digital still cameras and three flash units. The experiments were conducted under the following conditions: the pre-impact diameters of the droplets ranged from 0.53 to 0.60 mm, the impact velocities ranged from 1.7 m/s to 4.1 m/s, and the solid surface temperatures ranged from 170 °C to 500 °C. When a droplet impacted onto the solid at a temperature of 170 °C, weak boiling was observed at the liquid/solid interface. At temperatures of 200 or 300 °C, numerous vapor bubbles were formed. Numerous secondary droplets then jetted upward from the deforming droplet due to the blowout of the vapor bubbles into the atmosphere. No secondary droplets were observed for a surface temperature of 500 °C at the low-impact Weber numbers (∼30) associated with the impact inertia of the droplets. Experiments using 2.5-mm-diameter droplets were also conducted. The dimensionless collision behaviors of large and small droplets were compared under the same Weber number conditions. At temperatures of less than or equal to 300 °C, the blowout of vapor bubbles occurred at early stages for a large droplet. At a surface temperature of 500 °C, the two dimensionless deformation behaviors of the droplets were very similar to each other. 相似文献
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The force acting on a spherical particle in a nonuniformly heated magnetizable fluid is calculated in the case in which the permeability of the particle material depends arbitrarily on temperature and the strength of the magnetic field, and the permeability of the fluid on temperature. In calculating the force the difference between the thermal conductivities of the particle material and the fluid and, as distinct from [6], the distortion of the applied magnetic field due to the presence of a temperature gradient are taken into account. Accordingly, the expression for the force differs from that obtained in [6]. It is shown that the expression obtained for the force is correct up to terms of the order of a certain power of a small parameter — the ratio of the particle size to the characteristic interval of variation of the parameters (temperature, strength of magnetic field, etc.). A condition determining the value of this power is derived.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 76–83, March–April, 1989. 相似文献
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