共查询到20条相似文献,搜索用时 31 毫秒
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The jet boiling heat transfer of a bar water–CuO particle suspensions (nanofluids) jet impingement on a large flat surface
was experimentally investigated. The experimental results were compared with those from water. The quantificational effects
of the nanoparticles concentration and the flow conditions on the nucleate boiling heat transfer and the critical heat flux
(CHF) were investigated. The experimental data showed that the jet boiling heat transfer for the water–CuO nanofluid is significantly
different from those for water. The nanofluids have poor nucleate boiling heat transfer compared with the base fluid due to
that a very thin nanoparticle sorption layer was formed on the heated surface. The CHF for the nanofluid increased compared
with that of water. The reasons were that the solid–liquid contact angle decreased due to a very thin sorption layer on the
heated surface and the jet and agitating effect of the nanoparticles on the subfilm layer enhance supply of liquid to the
surface. 相似文献
3.
B. P. Avksentyuk V. V. Ovchinnikov 《Journal of Applied Mechanics and Technical Physics》1999,40(6):1070-1076
A physical model for explosive boiling of drops is presented. Loss of stability of the liquid-vapor interface results in occurrence
of evaporation fronts. Their propagation in a metastable liquid is determined by the vapor recoil momentum. Detachment of
drops from the interface is due to thermocapillary forces. The validity of the model is supported by comparison of calculations
with experimental data.
Kutateladze Institute of Thermal Physics, Siberian Division, Russian Academy of Science, Novosibirsk 630090. Translated from
Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 83–91, November–December, 1999. 相似文献
4.
This paper presents an experimental study of microscopic explosive boiling introduced by a pulsed laser. The violent explosive
boiling was observed in the liquid film, and the vapor bubbles together with liquid droplets were expelled from the platinum
film. It is found that the apparent bubble nucleation temperature is a strong function of the heating rate. The pressure signal
appears as continuous oscillation and is intensified as laser power density increases. 相似文献
5.
V. A. Bykov E. F. Gryaznov V. N. Okhitin 《Journal of Applied Mechanics and Technical Physics》2009,50(3):406-412
The process of projection of a layer of an ideal liquid enclosed into a cylindrical elastoplastic shell by products of instantaneous
detonation of a high explosive charge is studied numerically in a two-dimensional plane formulation. The processes of shell
fracture and liquid exhaustion through the resultant slots are considered. Numerical results are analyzed, and analytical
relations for angular distributions of radial velocity and mass of the liquid escaping through the slots are derived.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 3, pp. 56–63, May–June, 2009. 相似文献
6.
In this work a simplified calculation method taking into account the effect of mass transport on the heat transfer coefficient
(HTC) during boiling of multicomponent mixture has been elaborated. The calculation results were compared with own experimental
data for ternary system methanol–isopropanol–water and Grigoriev data [1] (acetone–methanol–water). The experiments were performed in different hydrodynamic conditions such as: pool boiling and
liquid evaporation at the free surface of the falling film. The experimental data covered wide range of heat fluxes from 6
to 30 kW/m2 in the case of liquid evaporation from the falling film and from 30 to 240 kW/m2 for pool boiling. The analysis of the results indicates that the mass transfer resistance in the liquid phase caused a significant
reduction of experimental value HTC in comparison to so-called ideal HTC. 相似文献
7.
P. I. Golubnichii G. S. Kalyuzhnyi S. D. Korchikov 《Journal of Applied Mechanics and Technical Physics》1984,25(1):7-9
Sound generation by a laser beam within a liquid, related to liquid boiling at absorption centers, has been studied relatively little. Acoustic effects upon liquid boiling in a laser beam were first reported in [1]. A change in the index of refraction of a liquid has been observed under the action of acoustical radiation of microbubbles formed on absorbing particles in the zone irradiated by a laser beam [2–4]. However direct measurements of acoustical radiation from a set of microbubbles uniformly distributed over the volume of laser beam-liquid interaction has yet to be performed, to the authors' knowledge. The present study is a preliminary report of results of an experimental study of this class of opticoacoustical phenomena.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 9–12, January–February, 1984.In conclusion, the authors consider it their pleasant duty to thank G. A. Askar'yan for evaluating the study and S. V. Luk'yanov for assistance in measuring the particle size distribution. 相似文献
8.
The inception process of nucleation in explosive boiling systems is theoretically investigated. With the effect of pulse heating
or sudden cooling, the temperature distribution near the surface during explosive boiling is calculated. The liquid near the
wall can maintain a stable layer induced by strong attractive force, and there exists maximum supersaturation beyond this
stable layer. As the surface temperature and temperature gradient are high enough, the critical distance of maximum supersaturation
can be larger than the radius of critical bubble, and the homogeneous nucleation will dominate the inception boiling process.
For explosive boiling induced by pulse heating, homogeneous nucleation forms after a short time; while homogeneous nucleation
can dominate the initial explosive boiling induced by sudden cooling. 相似文献
9.
An experimental study was carried out to investigate the effects of heat transfer surface orientation and the solid–liquid
contact angle on the boiling heat transfer and critical heat flux (CHF) in water pool boiling using a smooth heat-transfer
surface under atmospheric pressure. The orientation angle was ranged from 0° (up-facing horizontal position) to 180° (down-facing
horizontal position) with a pace of 45°. The three kinds of heat transfer surfaces having different solid–liquid contact angles
were the normal surface with a contact angle of 55°, the hydrophilic surface with a contact angle of 30° and the superhydrophilic
surface with a contact angle of 0°. The experimental results indicate that orientation and contact angle have complex, coupling
effects on heat transfer and CHF. A predicting correlation for the CHF which takes the effects of both orientation and contact
angle into account is established. The predicting correlation agrees reasonably well with the experimental data. 相似文献
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11.
Yu. D. Varlamov Yu. P. Meshcheryakov M. P. Predtechenskii S. I. Lezhnin S. N. Ul’yankin 《Journal of Applied Mechanics and Technical Physics》2007,48(2):213-220
Explosive boiling of liquids on film heaters under the action of pulsed heat fluxes q = 108–109
W/m
2 is considered. A technique of stroboscopic visualization of boiling stages with a time resolution of 100 nsec is used. Numerous
scenarios of evolution of explosive boiling are demonstrated. Conditions of the thermal effect (magnitude of the heat flux,
duration and repetition frequency of heat pulses) are found, which ensure single and repeated boiling, intermittent boiling,
and boiling with formation of complicated multi-bubble structures. It is noted that homogeneous nucleation is a dominating
mechanism of incipience of examined liquids for q > 108
W/m
2.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 81–89, March–April, 2007. 相似文献
12.
A three-dimensional bubble-tracking model of subcooled nucleate boiling flow in a vertical channel at low-pressure conditions
is proposed with specific application to the case of boiling in an annulus with a central heating rod. Vapour is distributed
in the liquid in the form of individually tracked bubbles. The overall behaviour of the liquid–vapour system results from
motion, interaction, coalescence and boiling mechanisms prescribed mostly at the level of bubbles. Bubbles are nucleated at
nucleation sites randomly distributed over the heated surface. After nucleation, bubbles slide on the heated wall, detach
and then migrate into the lower-temperature region away from the heated surface, where they condense. The proposed model was
applied to experiments on subcooled boiling from Purdue University (USA). Experimental and calculated void fraction radial
profiles at different axial locations are compared. 相似文献
13.
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
14.
A model of kinetics of phase transitions in a substance in a metastable state is proposed, where the probability of extensive
nucleation owing to homogeneous mechanisms is rather large; the model is an alternative to Kolmogorov’s model. The use of
this model is demonstrated to offer analytical solutions that describe both the crystallization processes with similar densities
of the liquid and solid phases and, for instance, the kinetics of nucleation and growth of bubbles in surface boiling. Solutions
obtained by Kolmogorov’s model and by the present model coincide at the initial stage of the process where the volume fraction
of the new phase is small.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 75–80, March–April, 2007. 相似文献
15.
Andrea Luke 《Heat and Mass Transfer》2009,45(7):909-917
The processes of the phase change in boiling occur at the solid–liquid interface by heat transfer from a solid heating surface
to the boiling liquid. The characteristic features of the heating surfaces are therefore of great interest to optimize the
design of evaporators. The microstructure with all its peaks and cavities influences directly the wetting and rewetting conditions
of the heated surface by the boiling liquid and hence bubble formation and heat transfer. The roughness structures of different
evaporator copper tubes with 8 or 25 mm diameter are characterized quantitatively with regard to the cavities offered to nucleation.
The surfaces of the heating elements are sandblasted by different means resulting in a stochastic microstructure. The surfaces
are investigated by a three-dimensional contactless roughness measurement technique combining the stylus technique with the
near field acoustic microscopy. The method opens the possibility to obtain results according to standard for practical applications
and additionally delivers detailed information about the three-dimensional shape of each cavity within the surface investigated.
The analysis of the microstructure implies the total number of cavities, their local and size distribution calculated by the
method of the envelope area. The results of the surface analysis are linked to those of heat transfer and bubble formation
discussed in a contribution by Kotthoff and Gorenflo. 相似文献
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17.
A. P. Zhuk 《International Applied Mechanics》2007,43(7):726-733
The effect of radiation force on a drop of liquid in an acoustic field is examined. It is established that the force depends
on the ratio of the densities of the liquid and the drop and on their adiabatic elastic moduli
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Translated from Prikladnaya Mekhanika, Vol. 43, No. 7, pp. 26–34, July 2007. 相似文献
18.
Molecular dynamics simulation of annular flow boiling in a nanochannel is numerically investigated. In this research, an annular
flow model is developed to predict the superheated flow boiling heat transfer characteristics in a nanochannel. To characterize
the forced annular boiling flow in a nanochannel, an external driving force
F?\textext \overrightarrow {F}_{\text{ext}} ranging from 1 to 12 PN (PN = pico newton) is applied along the flow direction to inlet fluid particles during the simulation.
Based on an annular flow model analysis, it is found that saturation condition and superheat degree have great influences
on the liquid–vapor interface. Also, the results show that due to the relatively strong influence of the surface tension in
small channels, the interface between the liquid film and the vapor core is fairly smooth, and the mean velocity along the
stream-wise direction does not change anymore. Also, it is found that the heat flux values depend on the boundary conditions.
Finally, the Green–Kubo formula is used to calculate the thermal conductivity of liquid Argon. The simulations predict thermal
conductivity of liquid Argon quite well. 相似文献
19.
A new expression for the radiation force function – which is the radiation force per unit energy density and unit cross-sectional surface area – for spheres in a stationary (or standing) and quasi-stationary wave is obtained based on the far-field acoustic scattering field. The radiation force function formulation has been simplified mathematically and improved into a more general form. Numerical results are presented for rigid and elastic spheres, air bubbles in water as well as liquid drops in air to illustrate the theory. It is demonstrated that expressions for the radiation force functions obtained from the far-field derivation approach are equivalent to those obtained from the near-field-based derivation. 相似文献
20.
S. P. Aktershev V. V. Ovchinnikov 《Journal of Applied Mechanics and Technical Physics》2008,49(2):194-200
Steady propagation of the boundary of a vapor cavity in a layer of a metastable liquid along the heater surface is considered.
The temperature and velocity of interface propagation are determined from the equations of conservation of mass, momentum,
and energy in the neighborhood of the stagnation point of the vapor cavity and the condition of stability of steady motion
of the interface. It is shown that a solution of these equations exists only if the liquid is heated above a threshold value.
The calculated velocity of interface motion and the threshold value of temperature are in reasonable agreement with available
experimental data for various liquids within wide ranges of saturation pressures and temperatures of the superheated liquid.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 2, pp. 47–55, March–April, 2008. 相似文献