共查询到20条相似文献,搜索用时 31 毫秒
1.
The near-wall transport characteristics, inclusive of mass transfer coefficient and wall shear stress, which have a great
effect on gas–liquid two-phase flow induced internal corrosion of low alloy pipelines in vertical upward oil and gas mixing
transport, have been both mechanistically and experimentally investigated in this paper. Based on the analyses on the hydrodynamic
characteristics of an upward slug unit, the mass transfer in the near wall can be divided into four zones, Taylor bubble nose
zone, falling liquid film zone, Taylor bubble wake zone and the remaining liquid slug zone; the wall shear stress can be divided
into two zones, the positive wall shear stress zone associated with the falling liquid film and the negative wall shear stress
zone associated with the liquid slug. Based on the conventional mass transfer and wall shear stress characteristics formulas
of single phase liquid full-pipe turbulent flow, corrected normalized mass transfer coefficient formula and wall shear stress
formula are proposed. The
calculated results are in good agreement with the experimental data. The shear stress and the mass transfer coefficient in
the near wall zone are increased with the increase of superficial gas velocity and decreased with the increase of superficial
liquid velocity. The mass transfer coefficients in the falling liquid film zone and the wake zone of leading Taylor bubble
are lager than those in the Taylor bubble nose zone and the remaining liquid slug zone, and the wall shear stress associated
falling liquid film is larger than that associated the liquid slug. The mass transfer coefficient is within 10−3 m/s, and the wall shear stress below 103 Pa. It can be concluded that the alternate wall shear stress due to upward gas–liquid slug flow is considered to be the major
cause of the corrosion production film fatigue cracking. 相似文献
2.
This paper presents experimental investigations on Freon R141b flow boiling in rectangular microchannel heat sinks. The main
aim is to provide an appropriate working fluid for microchannel flow boiling to meet the cooling demand of high power electronic
devices. The microchannel heat sink used in this work contains 50 parallel channels, with a 60 × 200 (W × H) μm cross-section. The flow boiling heat transfer experiments are performed with R141b over mass velocities ranging from
400 to 980 kg/(m2 s) and heat flux from 40 to 700 kW/m2, and the outlet pressure satisfying the atmospheric condition. The fluid flow-rate, fluid inlet/outlet temperature, wall
temperature, and pressure drop are measured. The results indicate that the mean heat transfer coefficient of R141b flow boiling
in present microchannel heat sinks depends heavily on mass velocity and heat flux and can be predicted by Kandlikar’s correlation
(Heat Transf Eng 25(3):86–93, 2004). The two-phase pressure drop keeps increasing as mass velocity and exit vapor quality rise. 相似文献
3.
V.E. Nakoryakov O.N. Kashinsky A.P. Burdukov V.P. Odnoral 《International Journal of Multiphase Flow》1981,7(1):63-81
The results of two-phase flow structure measurements in an upward gas-liquid flow in a 86.4 mm i.d. tube by the electrochemical and conductivity techniques are presented. Measurements were made in bubble and slug flow regimes at liquid flow rates ranging from 0.2 to 2 m/s.The flow instability and ambiguity in a bubble regime at low velocities is shown to exist. Great discrepancy between measured wall shear stress values and those predicted by the Lockhart-Martinelli model are due to the nonuniform distribution of gas over the tube cross section. Measurements of intensity of wall shear stress and liquid velocity fluctuations in a two-phase flow are presented. 相似文献
4.
Stereoscopic micro particle image velocimetry 总被引:1,自引:0,他引:1
A stereoscopic micro-PIV (stereo-μPIV) system for the simultaneous measurement of all three components of the velocity vector in a measurement plane (2D–3C) in a closed microchannel has been developed and first test measurements were performed on the 3D laminar flow in a T-shaped micromixer. Stereomicroscopy is used to capture PIV images of the flow in a microchannel from two different angles. Stereoscopic viewing is achieved by the use of a large diameter stereo objective lens with two off-axis beam paths. Additional floating lenses in the beam paths in the microscope body allow a magnification up to 23×. The stereo-PIV images are captured simultaneously by two CCD cameras. Due to the very small confinement, a standard calibration procedure for the stereoscopic imaging by means of a calibration target is not feasible, and therefore stereo-μPIV measurements in closed microchannels require a calibration based on the self-calibration of the tracer particle images. In order to include the effects of different refractive indices (of the fluid in the microchannel, the entrance window and the surrounding air) a three-media-model is included in the triangulation procedure of the self-calibration. Test measurement in both an aligned and a tilted channel serve as an accuracy assessment of the proposed method. This shows that the stereo-μPIV results have an RMS error of less than 10% of the expected value of the in-plane velocity component. First measurements in the mixing region of a T-shaped micromixer at Re = 120 show that 3D flow in a microchannel with dimensions of 800 × 200 μm2 can be measured with a spatial resolution of 44 × 44 × 15 μm3. The stationary flow in the 200 μm deep channel was scanned in multiple planes at 22 μm separation, providing a full 3D measurement of the averaged velocity distribution in the mixing region of the T-mixer. A limitation is that this approach requires a stereo-objective that typically has a low NA (0.14–0.28) and large depth-of-focus as opposed to high NA lenses (up to 0.95 without immersion) for standard μPIV. 相似文献
5.
The Characterization of the effects of surface wettability and geometry on pressure drop of slug flow in isothermal horizontal
microchannels is investigated for circular and square channels with hydraulic diameter (D
h
) of 700 μm. Flow visualization is employed to characterize the bubble in slug flow established in microchannels of various
surface wettabilities. Pressure drop increases with decrease in surface wettability, while the channel geometry influences
slug frequency. It is observed that the gas–liquid contact line in advancing and receding interfaces of bubble change with
surface wettability in slug flows. Flow resistance, where capillary force is important, is estimated using Laplace–Young equation
considering the change of dynamic contact angles of bubble. The experimental study also demonstrates that the liquid film
presence elucidates the pressure drop variation of slug flows at various surface wettabilities due to diminishing capillary
effect. 相似文献
6.
A. P. Alkhimov V. F. Kosarev A. N. Papyrin 《Journal of Applied Mechanics and Technical Physics》1998,39(2):318-323
We present results of an experimental study of the specific features of the gas-dynamic formation of coatings from metallic
powders (dp<50 μm) on substrates of various materials depending on the particle velocity (200–1200m/sec), the jet temperature (300–700K), and other parameters. Results of a prospecting study of the implementation of the methods of particle acceleration in supersonic
(M=2.0–3.0) rectangular nozzles are described. The rate of bond formation in a cold particle-cold substrate contact occurring
in gas-dynamic spraying is estimated within the framework of the concepts applied in analysis of gas-dynamic spraying.
Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated
from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 2, pp. 182–188, March–Apil, 1998. 相似文献
7.
The rapid development of two-phase microfluidic devices has triggered the demand for a detailed understanding of the flow characteristics inside microchannel heat sinks to advance the cooling process of micro-electronics. The present study focuses on the experimental investigation of pressure drop characteristics and flow visualization of a two-phase flow in a silicon microchannel heat sink. The microchannel heat sink consists of a rectangular silicon chip in which 45 rectangular microchannels were chemically etched with a depth of 276 μm, width of 225 μm, and a length of 16 mm. Experiments are carried out for mass fluxes ranging from 341 to 531 kg/m2 s and heat fluxes from 60.4 to 130.6 kW/m2 using FC-72 as the working fluid. Bubble growth and flow regimes are observed using high speed visualization. Three major flow regimes are identified: bubbly, slug, and annular. The frictional two-phase pressure drop increases with exit quality for a constant mass flux. An assessment of various pressure drop correlations reported in the literature is conducted for validation. A new general correlation is developed to predict the two-phase pressure drop in microchannel heat sinks for five different refrigerants. The experimental pressure drops for laminar-liquid laminar-vapor and laminar-liquid turbulent-vapor flow conditions are predicted by the new correlation with mean absolute errors of 10.4% and 14.5%, respectively. 相似文献
8.
V. K. Kedrinskii M. N. Davydov 《Journal of Applied Mechanics and Technical Physics》2010,51(4):529-537
Based on the full mathematical model of a viscous magma melt flow ascending in the gravity field behind a decompression wave
front, an unsteady two-dimensional axisymmetric problem of the melt state dynamics at the initial stage of an explosive volcanic
eruption and specific features of the flow in the vicinity of the channel wall for the cases of stationary and dynamically
increasing viscosity are studied. The evolution of the boundary layer is numerically analyzed for a constant melt viscosity
equal to μ = 10
3
, 10
5
, and 10
7
Pa · sec. It is demonstrated that a boundary layer is formed on the wall of the channel with a radius of 100 m as the melt viscosity is changed in the range of 10
3
–10
5
Pa · sec, and the boundary layer thickness increases from 2 to 15 m. As the magma viscosity increases to 10
7
Pa · sec, the boundary layer chokes the major part of the channel, thus, locking the flow in the vicinity of the axis of symmetry
of the channel almost over the entire channel length. Substantial changes in the flow structure caused by dynamically increasing
viscosity are demonstrated by an example of the melt in the channel with a radius of 10 m. By the time t = 1.1 sec, the boundary layer thickness in the channel cross section at a height of approximately 1000 m reaches almost 8 m, the boundary layer acquires the shape similar to a “diaphragm,” penetrates inward the channel by 200 m (with the mass velocity ranging from 0 to 15 m/sec), and locks the flow in a zone with a radius of approximately 2 m around the axis of symmetry of the channel. 相似文献
9.
The effect of the impact velocity and shape of the head of a rigid shell of caliber 20mm on the depth of its penetration into a thick obstacle made of mild low-carbon steel for impact velocities of up to 600m/sec is studied experimentally. Experimental relations between the penetration depth and the impact velocity are obtained for
shells with conical and semispherical heads. It is found that for a penetration depth equal to 1 or 2 calibers, the penetration
resistance does not depend on the head shape and is characterized by an average stress equal to 2.98GPa.
Institute of Experimental Physics, Sarov 607190. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No.
1, pp. 38–40, January–February, 2000. 相似文献
10.
G. I. Rastorguev S. I. Snisarenko 《Journal of Applied Mechanics and Technical Physics》2009,50(1):155-162
A problem of determining elastic and viscous characteristics of composite materials, necessary and sufficient for choosing
physical relations in solving problems of impact loading with low impact velocities (up to 200 m/sec) and unsteady deformation in the range of strain rates within 10
2
sec−1
for multilayer beams, plates, and shells, is considered.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 1, pp. 187–196, January–February, 2009. 相似文献
11.
In relation to the development of the interfacial area transport equation, local flow measurements of vertical downward air–water flows in a pipe with an inner diameter of 50.8 mm were performed at three axial locations of z/D=6.50, 34.0, and 66.5 as well as ten radial locations from r/R=0 to r/R=0.9 using a multi-sensor probe. In the experiment, the superficial liquid velocity and the void fraction ranged from –0.620 m/s to –2.49 m/s and from 0.21% to 8.4%, respectively. The dependence of the interfacial area transport on the liquid velocity, void fraction, and bubble size is discussed in detail. 相似文献
12.
V. G. Bazhenov A. M. Bragov V. L. Kotov 《Journal of Applied Mechanics and Technical Physics》2009,50(6):1011-1019
The parameters of the Grigoryan soil model are determined using an experimental-computational method previously proposed and
the results of reversed experiments on penetration of projectiles with flat and hemispherical heads at impact velocities of
50–450 m/sec in sandy soil. It is shown that the quasistationary dependences of the resistance force on impact velocity obtained in the
reversed experiment can be used to solve problems of deep penetration of projectile in soil with an error not exceeding the
measurement error. 相似文献
13.
基于液滴或气泡的多相微流控是近年来微流控技术中快速发展的重要分支之一.本文利用高速显微摄影技术和数字图像处理技术对T型微通道反应器内气液两相流动机制及影响因素进行实验研究.实验采用添加表面活性剂的海藻酸钠水溶液作为液相,空气作为气相.研究T型微通道反应器内气液两相流型的转变过程,并根据微通道内气泡的生成频率和生成气泡的长径比对气泡流进行分类.研究发现当前的进料方式下,可以观测到气泡流和分层流2种流型,且依据气泡生成频率和微通道内气泡的长径比可将气泡流划分为分散气泡流、短弹状气泡流和长弹状气泡流3种类型,并基于受力分析确定3种气泡流的形成机制分别为剪切机制、剪切-挤压机制和挤压机制.考察不同液相黏度和表面张力系数对不同类型气泡流范围的影响规律.结果表明:液相黏度相较于表面张力系数而言,对气泡流生成范围影响更大.给出不同类型气泡流流型转变条件的无量纲关系式,实现微通道生成微气泡过程的可控操作. 相似文献
14.
The challenges that microchannel flow boiling technology faces are the lack of understanding of underlying mechanisms of heat transfer during various flow boiling regimes and a dearth of analytical models that can predict heat transfer. This paper aims to understand flow boiling heat transfer mechanisms by analyzing results obtained by synchronously captured high-speed flow visualizations with local, transient temperature data. Using Inverse Heat Conduction Problem (IHCP) solution methodology, the transient wetted surface heat flux and temperature as well as heat transfer coefficient are calculated. These are then correlated with the visual data. Experiments are performed on a single microchannel embedded with fast response temperature sensors located (630 µm) below the wetted surface. The height, width and length of the microchannel are 0.42 mm, 2.54 mm and 25.4 mm respectively. De-ionized, de-gassed water is used as the working fluid. Two heat fluxes are tested at each of the mass fluxes of 182 kg/(m2s) and 380 kg/(m2s). Because of vapor confinement, slug flow is observed for the tested conditions. The present study provides detailed insights into the effect of various events such as passage of vapor slug, 3-phase contact line, partial-dry-out and liquid slug on transient heat transfer coefficient. Transient heat transfer coefficient peaks when thin film evaporation mechanism is prevalent. The peak value is influenced by the distance of bubble incipience as well as downstream events obstructing the flow. Heat transfer coefficient during the passage of liquid slug and 3-phase contact line were relatively lower for the tested experimental conditions. 相似文献
15.
Immiscible viscous liquid–liquid two-phase flow patterns and pressure drop characteristics in a circular microchannel have been investigated. Water and silicone oil with a dynamic viscosity of 863 mPa s were injected into a fused silica microchannel with an inner diameter of 250 μm. As the microchannel was initially filled with the silicone oil, an oil film was found to always form and remain on the microchannel wall. Different flow patterns were observed and classified over a wide range of water and oil flow rates. A flow pattern map is presented in terms of Re, Ca, and We numbers. Two-phase pressure drop data have also been collected and analyzed to develop a simple correlation for slug, annular and annular-droplet flow patterns in terms of superficial water and oil velocities. 相似文献
16.
In this work, we measured 14 horizontal velocity profiles along the vertical direction of a rectangular microchannel with
aspect ratio α = h/w = 0.35 (h is the height of the channel and w is the width of the channel) using microPIV at Re = 1.8 and 3.6. The experimental velocity profiles are compared with the full 3D theoretical solution, and also with a Poiseuille
parabolic profile. It is shown that the experimental velocity profiles in the horizontal and vertical planes are in agreement
with the theoretical profiles, except for the planes close to the wall. The discrepancies between the experimental data and
3D theoretical results in the center vertical plane are less than 3.6%. But the deviations between experimental data and Poiseuille’s
results approaches 5%. It indicates that 2D Poiseuille profile is no longer a perfect theoretical approximation since α = 0.35. The experiments also reveal that, very near the hydrophilic wall (z = 0.5–1 μm), the measured velocities are significantly larger than the theoretical velocity based on the no-slip assumption.
A proper discussion on some physical effects influencing the near wall velocity measurement is given. 相似文献
17.
Concerning to the non-stationary Navier–Stokes flow with a nonzero constant velocity at infinity, just a few results have
been obtained, while most of the results are for the flow with the zero velocity at infinity. The temporal stability of stationary
solutions for the Navier–Stokes flow with a nonzero constant velocity at infinity has been studied by Enomoto and Shibata
(J Math Fluid Mech 7:339–367, 2005), in L
p
spaces for p ≥ 3. In this article, we first extend their result to the case
\frac32 < p{\frac{3}{2} < p} by modifying the method in Bae and Jin (J Math Fluid Mech 10:423–433, 2008) that was used to obtain weighted estimates for the Navier–Stokes flow with the zero velocity at infinity. Then, by using
our generalized temporal estimates we obtain the weighted stability of stationary solutions for the Navier–Stokes flow with
a nonzero velocity at infinity. 相似文献
18.
A model is developed for the analysis of mass transfer during isothermal absorption in a vertical gas-liquid slug flow at
large Reynolds numbers with liquid plugs containing small bubbles. Simple formulas for mass flux from the N-th unit cell of gas-liquid slug flow and for total mass flux from N unit cells are derived. In the limiting case the derived formulas for mass transfer during gas absorption in a slug flow
with liquid plugs containing small bubbles recover the derived expressions for mass transfer in slug flow without small bubbles
in the liquid plugs. Using the developed model recommendations concerning the design of the absorber operating in a slug flow
regime are suggested.
Received on 28 July 1997 相似文献
19.
Buoyant flow is analysed for a vertical fluid saturated porous layer bounded by an isothermal plane and an isoflux plane in
the case of a fully developed flow with a parallel velocity field. The effects of viscous dissipation and pressure work are
taken into account in the framework of the Oberbeck–Boussinesq approximation scheme and of the Darcy flow model. Momentum
and energy balances are combined in a dimensionless nonlinear ordinary differential equation solved numerically by a Runge–Kutta
method. Both cases of upward pressure force (upward driven flows) and of downward pressure force (downward driven flows) are examined. The thermal behaviour for upward driven flows and downward driven flows is quite different. For upward driven
flows, the combined effects of viscous dissipation and pressure work may produce a net cooling of the fluid even in the case
of a positive heat input from the isoflux wall. For downward driven flows, viscous dissipation and pressure work yield a net
heating of the fluid. A general reflection on the roles played by the effects of viscous dissipation and pressure work with
respect to the Oberbeck–Boussinesq approximation is proposed. 相似文献
20.
A. Marshall P. Venkateswaran D. Noble J. Seitzman T. Lieuwen 《Experiments in fluids》2011,51(3):611-620
Experimental turbulent combustion studies require systems that can simulate the turbulence intensities [u′/U
0 ~ 20–30% (Koutmos and McGuirk in Exp Fluids 7(5):344–354, 1989)] and operating conditions of real systems. Furthermore, it is important to have systems where turbulence intensity can be
varied independently of mean flow velocity, as quantities such as turbulent flame speed and turbulent flame brush thickness
exhibit complex and not yet fully understood dependencies upon both U
0 and u′. Finally, high pressure operation in a highly pre-heated environment requires systems that can be sealed, withstand high
gas temperatures, and have remotely variable turbulence intensity that does not require system shut down and disassembly.
This paper describes the development and characterization of a variable turbulence generation system for turbulent combustion
studies. The system is capable of a wide range of turbulence intensities (10–30%) and turbulent Reynolds numbers (140–2,200)
over a range of flow velocities. An important aspect of this system is the ability to vary the turbulence intensity remotely,
without changing the mean flow velocity. This system is similar to the turbulence generators described by Videto and Santavicca
(Combust Sci Technol 76(1):159–164, 1991) and Coppola and Gomez (Exp Therm Fluid Sci 33(7):1037–1048, 2009), where variable blockage ratio slots are located upstream of a contoured nozzle. Vortical structures from the slots impinge
on the walls of the contoured nozzle to produce fine-scale turbulence. The flow field was characterized for two nozzle diameters
using three-component Laser Doppler velocimetry (LDV) and hotwire anemometry for mean flow velocities from 4 to 50 m/s. This
paper describes the key design features of the system, as well as the variation of mean and RMS velocity, integral length
scales, and spectra with nozzle diameter, flow velocity, and turbulence generator blockage ratio. 相似文献