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1.
The liquid–metal magneto-hydrodynamic (LMMHD) facility at the Bhabha Atomic Research Centre (Mumbai) has a two-phase mercury–nitrogen
flow system which is currently used for various studies related to void-fraction, flow, pressure, slip-ratio, of the flow
system. Non-invasive measurements of steady-state void-fraction profiles has been carried out by a 60 mCi Cesium-137 gamma-ray
source and a NaI(Tl) detector mounted on a trolley. The reconstructed cross-sectional void-fraction profiles were in the riser
section of the LMMHD loop, and in this process radial tomographic methods were used, e.g. least-squares and chord-segment-inversion
(CSI). The present work investigates the possible uncertainties in the profiles thus measured. A simple statistical model
has been developed for the CSI algorithm due to the inherent “square nature” of the data matrix. The inherent Poisson error
has been also investigated in this exercise.
Received: 1 December 1997/Accepted: 30 May 1998 相似文献
2.
Andréas Redl Marie Hélène Morel Joëlle Bonicel Stéphane Guilbert Bruno Vergnes 《Rheologica Acta》1999,38(4):311-320
The rheological behaviour of a gluten plasticized with glycerol has been studied in oscillatory shear. The mixing operation
in a Haake batch mixer leads to a maximum torque for a level of specific energy (500–600 kJ/kg) and temperature (50–60 °C)
quite independent of mixing conditions (rotor speed, mixing time, filling ratio). The gluten/glycerol dough behaves as a classical
gluten/water dough, with a storage modulus higher than the loss modulus over the frequency range under study. A temperature
increase induces a decrease of moduli, but the material is not thermorheologically simple. Glycerol has a plasticizing effect,
which can be classically described by an exponential dependence. Mixing conditions influence the viscoelastic properties of
the material, mainly through the specific mechanical energy input (to 2000 kJ/kg) and temperature increase (to 80 °C). Above
50 °C, specific mechanical energy highly increases the complex modulus. The aggregation of proteins, as evidenced by size-exclusion
chromatography measurements, occurs later as the dough temperature reaches 70 °C. The nature of network interactions and the
respective influence of hydrophobic and disulphide contribution is discussed. A general expression is proposed for describing
the viscous behaviour of a gluten/glycerol mix, which could seem simplistic for such a complex rheological behaviour, but
would remain sufficient for modelling the flow behaviour in a twin screw extruder.
Received: 24 November 1997 Accepted: 28 April 1999 相似文献
3.
M. D. Brodetsky A. M. Kharitonov E. Krause A. A. Pavlov S. B. Nikiforov A. M. Shevchenko 《Experiments in fluids》2000,29(6):592-604
The leeside vortex structures on delta wings with sharp leading edges were studied for supersonic flow at the Institute of
Theoretical and Applied Mechanics of the Russian Academy of Sciences in Novosibirsk. The experiments were carried out with
three wings with sweep angles of χ=68°, 73°, and 78° and parabolic profiles in the 0.6 × 0.6 m2 test section of the blow-down wind tunnel T-313 of the institute. The test conditions were varied from Mach numbers M=2 to 4, unit Reynolds numbers from Re
l=26 × 106 to 56 × 106 m−1, and angles of attack from α=0° to 22°. The results of the investigations revealed that for certain flow conditions shocks
are formed above, below, and between the primary vortices. The experimental data were accurate enough to detect the onset
of secondary and tertiary separation as well as other boundaries. The various flow regimes discussed in the literature were
extended in several cases. The major findings are reported.
Received: 6 September 1999/Accepted: 24 January 2000 相似文献
4.
An experimental study is presented for water droplet impingement on a liquid surface. The impaction process was recorded
using a high-speed digital camera at 1,000 frames/s. The initial droplet diameter was fixed at 3.1 mm ± 0.1 mm, and all experiments
were performed in atmospheric air. The impact velocity was varied from 0.36 m/s to 2.2 m/s thus varying the impact Weber number
from 5.5 to 206. The impacted liquid surface consisted of two fluids, namely water and methoxy-nonafluorobutane, C4F9OCH3 (HFE7100). The depth of the water and HFE7100 pool was varied from 2 mm to 25 mm. The collision dynamics of water in the
HFE7100 pool was observed to be drastically different from that observed for the water droplet impingement on a water pool.
The critical impact Weber number for jet breakup was found to be independent of liquid depth. Water–HFE7100 impact resulted
in no jet breakup over the range of velocities studied. Therefore, no critical impact Weber number can be defined for water–HFE7100
impact.
Received: 27 June 2001/Accepted: 29 November 2001 相似文献
5.
The convective heat transfer from a cylinder to a humid air stream flowing normal to the cylinder was investigated experimentally
at atmospheric pressure over a range of variables which is relevant to the use of hot‐wire anemometry: air temperatures between
30 °C and 70 °C and velocities between 12 and 37 m/s. For molar fractions of water vapour up to 0.27, the heat transfer increased
with increasing humidity. The ratio of heat transfer rates in humid air and dry air is a unique function of the molar fraction
of water vapour, independent of the air temperature and flow velocity.
Received: 28 November 1996/Accepted: 5 July 1997 相似文献
6.
Measurements of two-components of velocity in the wake of a square cylinder using a hot-wire anemometer are reported. Two
Reynolds numbers, namely 8700 and 17,625, have been considered. The measurements were carried out in a low-speed, low-turbulence
wind tunnel. Benchmark experiments at much lower Reynolds numbers show good agreement between the present experiments and
published results. At higher Reynolds numbers, the experimental data reveal anticipated trends in terms of wake recovery and
turbulence decay. Both velocity and velocity fluctuations show symmetry about the wake axis. The experimental data have been
compared with the large eddy simulation (LES) calculation reported by Wang et al. [University of Illinois at Urbana – Champaign
(1996) Report CFD 96-03] and LDV measurements of Lyn et al. [J Fluid Mech (1995) 304: 285–319]. The agreement among the three
sets is generally acceptable in terms of the time-averaged velocity components, but not the velocity fluctuations. The turbulence
fluctuations in the present experiments are seen to be lower than in the referred work. The differences have been traced to
factors such as the aspect ratio, blockage ratio and upstream turbulence. Experiments with increased upstream turbulence did
show a reduction in the discrepancy between the present experiments and the published data. An assessment of the experimental
data in terms of physical mechanisms revealed that (a) streamwise normal stresses were correlated with the vortex centers,
and (b) the turbulence kinetic energy profiles are similar to the turbulence shear stress. Spectral analysis of the velocity
signals was carried out in the present work. Energy transfer from the mean flow to the streamwise velocity fluctuation was
confirmed in the near wake. A redistribution of the kinetic energy between the streamwise and transverse components of velocity
over a longer distance downstream was subsequently observed.
Received: 17 May 1999/Accepted: 29 December 1999 相似文献
7.
María Soledad Barral Isabel Lizaso María Eugenia Muñoz Antonio Santamaría 《Rheologica Acta》2001,40(2):193-195
In this work we investigate the gel formation of EVA/recycled motor oil systems as a route to obtain synthetic binders which
could be used instead of natural bitumen, as well as mixed with natural bitumen to modify adequately its viscoelastic response.
The EVA copolymer studied in this work has a vinyl acetate content of 18 wt% and solutions of EVA/motor oil have been prepared
up to a concentration of 50 wt%. Dynamic viscoelastic frequency sweeps between 10−2 Hz and 102 Hz have shown that above 3 wt%, at 25 °C, EVA/motor oil systems form gels. It has been possible to define an elastic equilibrium
modulus, Ge, for each gel. The dependence of Ge on concentration has been compared with that of PVC/DOP and SBS/oil gels on the basis of the De Gennes model. Thermal stability
of EVA/motor oil gels has also been analyzed, indicating that for the highest polymer concentrations gel point is above 80 °C.
Received: 23 December 1999 Accepted: 13 June 2000 相似文献
8.
A laser-induced fluorescence (LIF) technique is described to measure vertical concentration profiles of gases in the aqueous
mass boundary layer at a free water surface. The technique uses an acid-base reaction of the fluorescence indicator fluorescein
at the water surface to visualize the concentration profiles. The technique is capable of measuring two-dimensional vertical
concentration profiles at a rate of 200 frames/s and a spatial resolution of 16 μm. The mass boundary layer at a free surface
is characterized by significant fluctuations. Direct surface renewal is observed. The mean profiles also support rather surface
renewal models than turbulent diffusion models.
Received: 21 May 1997/Accepted: 18 December 1997 相似文献
9.
Planar images of Rayleigh scattering and laser-induced predissociative OH-fluorescence (OH-LIPF) have been obtained simultaneously
in turbulent premixed jet flames on a single-shot basis. The geometric structure of temperature and OH isocontours were extracted
for fractal analysis. A power-law fractal behavior can be identified in the ensemble-averaged flame length measure. It was
found that the inner and outer cut-off scales of OH contours are larger than those of the iso-temperature contours; while
the OH images show comparatively smaller fractal dimensions. The joint-pdf ’s between flame temperature and OH LIPF signals
at different heights are also derived to evaluate the flame stretch effect on local flame structure. Comparison of image pairs
near the extinction limit suggests that Rayleigh thermometry is more adequate to characterize the fine-scale flame front wrinkling
in highly stretched turbulent premixed flames.
Received: 12 September 1997/Accepted: 19 May 1998 相似文献
10.
Critical heat flux (CHF) has been measured in saturated forced convective boiling with a wall jet on a rectangular heated
surface of 40 and 80 mm in length and 20 mm in width. The jet velocity is varied from 3 to 15 m/s, and the system pressure
is 0.1, 0.2, and 0.4 MPa for R113. It is found that the existing correlation for saturation condition can be applied to the
CHF at high and low ρl/ρg values (e.g. water and R22), but hardly to the CHF at medium ρl/ρg values (e.g. R113 at 0.2 and 0.4 MPa). A revised correlation is proposed to predict most of the CHF data within an accuracy
of ±25%.
Received on 26 April 1999 相似文献
11.
T. M. Healy A. A. Fontaine J. T. Ellis S. P. Walton A. P. Yoganathan 《Experiments in fluids》1998,25(5-6):512-518
In this work, a flow visualization experiment was performed to elucidate features of the retrograde hinge flow through a
5 : 1 scaled model of the Medtronic Parallel bileaflet heart valve. It was hypothesized that this model would provide detailed
flow information facilitating identification of flow structures associated with thrombus formation in this valve. The experimental
protocol was designed to ensure fluid dynamic similarity between the model and prototype heart valves. Flow was visualized
using dye injection. The detailed flow structures observed showed the hinge’s inflow channel was the most suspect region for
thrombus formation. Here a complex helical structure was observed.
Received: 27 October 1997/Accepted: 1 May 1998 相似文献
12.
Gerald Henry Meeten 《Rheologica Acta》2001,40(3):279-288
Experiments are described in which a constant force F squeezed a fluid, either between two parallel circular plates, or between a plate and convex spherical lens. Newtonian fluids
obeyed the relation of Stefan (1874) for plates, and the relation of Adams et al. (1994) for plate and lens. The non-Newtonian
yield stress fluids Brylcreem, Laponite and Sephadex were squeezed between plates of various diameter D to attain a stationary separation h. Only for separations greater than h
* (which depended on the fluid) did Brylcreem and Laponite obey the relation F/D
3 ∝ h
−1 of Scott (1931) and give a yield stress in agreement with the vane method. For Sephadex the dependence of F/D
3 on h disagreed with Scott's relation, but varied as h
−5/2 for h > 0.6 mm and h
−3/2 for h < 0.6 mm. On rotating one plate in its plane the yield stress fluids at a fixed F suffered a marked decrease of h. This, and the existence of h
*, are discussed in terms of the soft glassy material model of Sollich et al. (1997) and Sollich (1998). Brylcreem and Laponite
were squeezed between a plate and lenses of various curvature and their yield stress obtained using the relation of Adams
et al. (1994) was compared with measurements by plate-plate squeeze-flow and vane methods.
Received: 12 April 2000 Accepted: 26 October 2000 相似文献
13.
Experiments are presented on the surge effect induced by cylindrical bodies piercing a free surface at constant velocity.
The study covers the following ranges: 0.1 < Froude2 < 7.3, 0.7 < Weber < 89, 46 < Reynolds < 6000; with the Goucher number (Go) evolving between 1.8 and 4.5. Free-surface profiles are compared with those issued from a boundary element method (BEM)
simulation based on potential theory and axisymmetric flow configuration. The free-surface deformation is accurately predicted
by the BEM approach for Reynolds numbers (Re) higher than 500. However, for Re less than about 200, computed results underestimate the interface elevation, except on the axis of symmetry, where they remain
accurate. Finally, the magnitudes of the interface deformation predicted by the numerical simulation are provided over a wide
range of Goucher numbers (0.001 < Go < 50) both for hemispherical and conical tips. Implications of these results for phase detection probes are discussed.
Received: 18 December 2000/Accepted: 25 January 2001 相似文献
14.
Flow visualization is an important tool for investigating turbulent flow, and, specifically, for characterizing low-speed
streaks in the boundary layer. The span-wise spatial characteristics of these streaks are commonly extracted by human visual
inspection, which is time consuming and subject to human errors and biases. Attempts to develop automatic methods have relied
exclusively on spectral techniques, using mostly the autocorrelation or its Fourier transform, the spatial spectrum. However,
the autocorrelation tends to get flattened with the amount of data analyzed and has been reported to provide biased estimates.
Furthermore, it estimates only the mean spacing and does not provide a direct measure of its distribution. In this paper,
an alternative automatic method is developed based on edge detection, and is applied to thermal images obtained by infrared
thermography of a heated wall exposed to a turbulent flow. The method presented yields not only the spacing between the low-speed
streaks but also their width and separation. The analysis indicates that the spacing (120 ± 52 wall units) is divided almost
evenly between the width (65 ± 33 wall units) and the separation (55 ± 40 wall units) between the streaks, and that the width
and separation are statistically independent. We also present a statistical model for the data, and demonstrate that when
the spatial parameters of the streaks are so widely distributed, the spectral methods are not reliable.
Received: 19 December 2000/Accepted: 26 January 2001 相似文献
15.
Critical heat flux (CHF) during forced convective subcooled boiling with a plane jet has been yet made insufficient except
for saturation condition when comparing CHF with impinging jet system including multiple jets. The present experiment has
measured the CHF with plane jet on a rectangular heated surface of 40, 60, and 80 mm in length and 10 and 20 mm in width.
Subcooled liquid being supplied through the plane jet with a different thickness of 1 and 2 mm, covers the heated surface
where rigorous boiling takes place. The experiment varies a jet velocity from 3 to 15 m/s, a subcooling from 0 to 60 K, and
system pressure at 0.1 MPa for water and at 1.5 to 3.0 MPa for R22. It is found that the existing correlation for saturation
can be applied to the CHF of water, but hardly to the CHF of R22 in spite of saturation condition. After the effects of jet
velocity and subcooling on the CHF can be elucidated, a new correlation including the effect of subcooling is proposed to
predict most of the CHF data within an accuracy of ±20 percent. This correlation for saturated condition is found to interestingly
agree with that theoretically derived by applying the Katto and Haramura criterion to this system.
Received on 8 January 1997 相似文献
16.
This paper reports an experimental study of free convection heat transfer from rectangular fin-arrays on a horizontal base.
An experimental set-up was constructed and calibrated, 15 sets of fin-arrays and a base plate without fins were tested in
atmosphere. Fin height was varied from 6 mm to 26 mm, fin spacing was varied from 6.2 mm to 83 mm. The base-to-ambient temperature
difference was also varied independently and systematically with the power supply to heater ranging from 8 W to 50 W. Fin
length and fin thicknesses were fixed at 100 mm and 3 mm, respectively. The experimental program was conducted so as to clearly
delineate the separate roles of fin height, fin spacing and base-to-ambient temperature difference. It was found that for
a given base-to-ambient temperature difference the convection heat transfer rate from fin-arrays takes on a maximum value
as a function of fin spacing and fin height. For a given base-to-ambient temperature difference the enhancement of the convection
heat transfer rate of fin-arrays relative to that for base plate without fins is strongly dependent on the fin spacing to
fin height ratio and number of fins. A correlation was also presented relating the convection heat transfer rate of fin-arrays
relative to that for base plate without fins with the relevant non-dimensional parameters.
Received on 7 August 1997 相似文献
17.
M. Khalilian M. Navidbakhsh M. Rezazadeh Valojerdi M. Chizari P. Eftekhari Yazdi 《Experimental Mechanics》2011,51(2):175-182
The unfertilized oocyte is surrounded by a spherical layer called the zona pellucida (ZP). The physical hardness of this layer
plays a crucial role in fertilization and it is largely unknown because of the lack of appropriate measuring and modeling
methods. Recently, considerable biomedical attentions have concentrated on determination of the mechanical properties of oocytes
as a single cell. In order to investigate the biophysical characteristics of mammalian oocytes, a change in the elasticity
of human ZP has been quantitatively evaluated before and after fertilization. Young’s modulus of ZP of metaphase-II (MII)
and pronuclear (PN) stages have been estimated using two different protocols of the micropipette aspiration, step-by-step
and continuous increase in pressure, in combination with proportional theoretical models. Experimental results clearly demonstrated
that after fertilization the mean Young’s modulus of the ZP calculated from the step-by-step aspiration test (MII: 7.34 ± 1.36
kPa vs PN: 13.18 ± 1.17 kPa.) and continuous aspiration test (MII: 2.41 ± 0.75 kPa vs. PN: 4.43 ± 1.66 kPa) significantly
increased, (p < 0.05). Mathematical Evaluation of the results shows that although the results of the two methods are different but both
confirm that the hardening of ZP will increase following fertilization. As can be seen, different experimental methods can
influence the choice of the models and this in turn will lead the mechanical properties to be found. 相似文献
18.
Heat transfer characteristics to laminar pulsating pipe flow under different conditions of Reynolds number and pulsation
frequency were experimentally investigated. The tube wall of uniform heat flux condition was considered. Reynolds number was
varied from 780 to 1987 while the frequency of pulsation ranged from 1 to 29.5 Hz. The results showed that the relative mean
Nusselt number is strongly affected by pulsation frequency while it is slightly affected by Reynolds number. The results showed
enhancements in the relative mean Nusselt number. In the frequency range of 1–4 Hz, an enhancement up to 30% (at Reynolds
number of 1366 and pulsation frequency of 1.4 Hz) was obtained. In the frequency range of 17–25 Hz, an enhancement up to 9%
(at Reynolds number of 1366 and pulsation frequency of 17.5 Hz) was indicated. The rate of enhancement of the relative mean
Nusselt number decreased as pulsation frequency increased or as Reynolds number increased. A reduction in relative mean Nusselt
number occurred outside these ranges of pulsation frequencies. A reduction in relative mean Nusselt number up to 40% for pulsation
frequency range of 4.1–17 Hz and a reduction up to 20% for pulsation frequency range of 25–29.5 Hz for Reynolds numbers range
of 780–1987 were considered. This reduction is directly proportional to the pulsation frequency. Empirical dimensionless equations
have been developed for the relative mean Nusselt number that related to Reynolds number (750 < Re < 2000) and the dimensionless
frequency (3<Ω<18) with about 10% rms.
Received on 16 May 2000 / Published online: 29 November 2001 相似文献
19.
Comparative evaluation of three heat transfer enhancement strategies in a grooved channel 总被引:1,自引:0,他引:1
Results of a comparative evaluation of three heat transfer enhancement strategies for forced convection cooling of a parallel
plate channel populated with heated blocks, representing electronic components mounted on printed circuit boards, are reported.
Heat transfer in the reference geometry, the asymmetrically heated parallel plate channel, is compared with that for the basic
grooved channel, and the same geometry enhanced by cylinders and vanes placed above the downstream edge of each heated block.
In addition to conventional heat transfer and pressure drop measurements, holographic interferometry combined with high-speed
cinematography was used to visualize the unsteady temperature fields in the self-sustained oscillatory flow. The locations
of increased heat transfer within one channel periodicity depend on the enhancement technique applied, and were identified
by analyzing the unsteady temperature distributions visualized by holographic interferometry. This approach allowed gaining
insight into the mechanisms responsible for heat transfer enhancement. Experiments were conducted at moderate flow velocities
in the laminar, transitional and turbulent flow regimes. Reynolds numbers were varied in the range Re = 200–6500, corresponding
to flow velocities from 0.076 to 2.36 m/s. Flow oscillations were first observed between Re = 1050 and 1320 for the basic
grooved channel, and around Re = 350 and 450 for the grooved channels equipped with cylinders and vanes, respectively. At
Reynolds numbers above the onset of oscillations and in the transitional flow regime, heat transfer rates in the investigated
grooved channels exceeded the performance of the reference geometry, the asymmetrically heated parallel plate channel. Heat
transfer in the grooved channels enhanced with cylinders and vanes showed an increase by a factor of 1.2–1.8 and 1.5–3.5,
respectively, when compared to data obtained for the basic grooved channel; however, the accompanying pressure drop penalties
also increased significantly.
Received on 5 April 2001 相似文献
20.
V. Bertola 《Experiments in fluids》2002,32(4):481-486
Single-fiber optical probes were used to investigate the time-averaged structure of gas–liquid horizontal flow through a
sharp-edged sudden area contraction. The probes allowed to measure the local void fraction distribution over several cross
sections of a pipe having an inner diameter of 0.08 m upstream and 0.06 m downstream of the sudden contraction. The water
mass flow rate was 3 kg/s, while the gas fraction of the volume flow ranged from 0.2 to 0.8. The local void fraction was plotted
as a function of its two spatial coordinates, so that a representation of the time-averaged gas distribution over the cross
section could be obtained. The contraction was shown to considerably alter the distribution of the phases, so that the correlations
for straight pipes appear no longer suitable.
Received: 27 August 2001 / Accepted: 19 November 2001 相似文献