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1.
This paper presents an experimental and theoretical investigation of drying of moist slab, cylinder and spherical products
to study dimensionless moisture content distributions and their comparisons. Experimental study includes the measurement of
the moisture content distributions of slab and cylindrical carrot, slab and cylindrical pumpkin and spherical blueberry during
drying at various temperatures (e.g., 30, 40, 50 and 60°C) at specific constant velocity (U = 1 m/s) and the relative humidity φ = 30%. In theoretical analysis, two moisture transfer models are used to determine drying process parameters (e.g., drying
coefficient and lag factor) and moisture transfer parameters (e.g., moisture diffusivity and moisture transfer coefficient),
and to calculate the dimensionless moisture content distributions. The calculated results are then compared with the experimental
moisture data. A considerably high agreement is obtained between the calculations and experimental measurements for the cases
considered. The effective diffusivity values were evaluated between 0.741 × 10−5 and 5.981 × 10−5 m2/h for slab products, 0.818 × 10−5 and 6.287 × 10−5 m2/h for cylindrical products and 1.213 × 10−7 and 7.589 × 10−7 m2/h spherical products using the Model-I and 0.316 × 10−5–5.072 × 10−5 m2/h for slab products, 0.580 × 10−5–9.587 × 10−5 m2/h for cylindrical products and 1.408 × 10−7–13.913 × 10−7 m2/h spherical products using the Model-II. 相似文献
2.
The passage of solid spheres through a liquid–liquid interface was experimentally investigated using a high-speed video and
PIV (particle image velocimetry) system. Experiments were conducted in a square Plexiglas column of 0.1 m. The Newtonian Emkarox
(HV45 50 and 65% wt) aqueous solutions were employed for the dense phase, while different silicone oils of different viscosity
ranging from 10 to 100 mPa s were used as light phase. Experimental results quantitatively reveal the effect of the sphere’s
size, interfacial tension and viscosity of both phases on the retaining time and the height of the liquid entrained behind
the sphere. These data were combined with our previous results concerning the passage of a rising bubble through a liquid–liquid
interface in order to propose a general relationship for the interface breakthrough for the wide range of Mo
1/Mo
2 ∈ [2 × 10−5–5 × 104] and Re
1/Re
2 ∈ [2 × 10−3–5 × 102]. 相似文献
3.
G. H. Keetels W. Kramer H. J. H. Clercx G. J. F. van Heijst 《Theoretical and Computational Fluid Dynamics》2011,25(5):293-300
Recently, numerical studies revealed two different scaling regimes of the peak enstrophy Z and palinstrophy P during the collision of a dipole with a no-slip wall [Clercx and van Heijst, Phys. Rev. E 65, 066305, 2002]: Z μ Re0.8{Z\propto{\rm Re}^{0.8}} and P μ Re2.25{P\propto {\rm Re}^{2.25}} for 5 × 102 ≤ Re ≤ 2 × 104 and Z μ Re0.5{Z\propto{\rm Re}^{0.5}} and P μ Re1.5{P\propto{\rm Re}^{1.5}} for Re ≥ 2 × 104 (with Re based on the velocity and size of the dipole). A critical Reynolds number Re
c
(here, Rec ? 2×104{{\rm Re}_c\approx 2\times 10^4}) is identified below which the interaction time of the dipole with the boundary layer depends on the kinematic viscosity
ν. The oscillating plate as a boundary-layer problem can then be used to mimick the vortex-wall interaction and the following
scaling relations are obtained: Z μ Re3/4, P μ Re9/4{Z\propto{\rm Re}^{3/4}, P\propto {\rm Re}^{9/4}} , and dP/dt μ Re11/4{\propto {\rm Re}^{11/4}} in agreement with the numerically obtained scaling laws. For Re ≥ Re
c
the interaction time of the dipole with the boundary layer becomes independent of the kinematic viscosity and, applying flat-plate
boundary-layer theory, this yields: Z μ Re1/2{Z\propto{\rm Re}^{1/2}} and P μ Re3/2{P\propto {\rm Re}^{3/2}}. 相似文献
4.
The profile and excitation mechanism of vacuum-ultraviolet radiation emitted from shock wave is investigated in a shock tube.
For shock wave in argon, the rdiation is due to resonant transition excited by argon-argon collision in the shock front with
excitation cross section coefficientS
*=1.0×10−17 cm2·ev−1 and activation energyE
*=11.4 ev. For shock wave in air the radition is emitted from a very thin shock layer in which the mechanism ofX
1∑→b
1∑ of N2 is excited with excitation cross sectionQ=2×10−16cm2 and activation energyE
*=12.1 ev.
Institute of Mechanics, Academia Sinica 相似文献
5.
In this article, an optical method to control the break-up of high-speed liquid jets is proposed. The method consists of focusing the light of a pulsed laser source into the jet behaving as a waveguide. Experiments were performed with the help of a Q-switched frequency doubled Nd:Yag laser (=532 nm). The jet diameter was 48 µm and jet velocities from 100 to 200 m/s. To study the laser-induced water jet break-up, observations of the jet coupled with the high power laser were performed for variable coupling and jet velocity conditions. Experimentally determined wavelength and growth rate of the laser-generated disturbance were also compared with the ones predicted by linear stability theory of free jets. 相似文献
6.
The mechanism of precursor ionization ahead of strong shock waves has been studied in a low density shock tube. The experimental
results are illustrated with Arrhenius plots with kink points dividing them into two parts with apparent activation energy
ratio 1:2, namely with the values 7.7 eV and 15.3 eV, and varying with first and third power of the density respectively.
A model is proposed to interpret the facts where the process taking place in the precursor region, is a two step photo ionization
accompanied with the drift flow effect of the gas relative to the shock wave or the ionization recombination effect according
to whether the shock speed and initial density are low enough. The product of the A-A collision excitation cross section coefficientS
* multiplied by the radiation cross sectionQ
* of ArgonS
*×Q
*=1×10−36 (cm4eV−1) and the three body recombination coefficient of Argon at room temperaturek
ra
=1×10−24 (cm−6s−1).
The project supported by the National Natural Science Foundation of China 相似文献
7.
Yi Wu Hangfeng Wang Zhaohui Liu Jing Li Liqi Zhang Chuguang Zheng 《Acta Mechanica Sinica》2006,22(2):99-108
Particle-laden flows in a horizontal channel were investigated by means of a two-phase particle image velocimetry (PIV) technique.
Experiments were performed at a Reynolds number of 6 826 and the flow is seeded with polythene beads of two sizes, 60 μm and 110 μm. One was slightly smaller than and the other was larger than the Kolmogorov length scale. The particle loadings were relatively
low, with mass loading ratio ranging from 5×10−4 to 4×10−2 and volume fractions from 6×10−7 to 4.8×10−5, respectively. The results show that the presence of particles can dramatically modify the turbulence even under the lowest
mass loading ratio of 5×10−4. The mean flow is attenuated and decreased with increasing particle size and mass loading. The turbulence intensities are
enhanced in all the cases concerned. With the increase of the mass loading, the intensities vary in a complicated manner in
the case of small particles, indicating complicated particle-turbulence interactions; whereas they increase monotonously in
the case of large particles. The particle velocities and concentrations are also given. The particles lag behind the fluid
in the center region but lead in the wall region, and this trend is more prominent for the large particles. The streamwise
particle fluctuations are larger than the gas fluctuations for both sizes of particles, however their varying trend with the
mass loadings is not so clear. The wall-normal fluctuations increase with increasing mass loadings. They are smaller in the
60 μm particle case but larger in the 110 μm particle case than those of the gas phase. It seems that the small particles follow the fluid motion to certain extent while
the larger particles are more likely dominated by their own inertia. Finally, remarkable non-uniform distributions of particle
concentration are observed, especially for the large particles. The inertia of particles is proved to be very important for
the turbulence modification and particles behaviors and thus should be considered in horizontal channels.
The project supported by the National Natural Science Foundation of China (50276021), and Program for New Century Excellent
Talents in University, Ministry of Education (NCET-04-0708) The English text was polished by Yunming Chen. 相似文献
8.
Localized arc filament plasma actuators (LAFPAs) have been developed and used at The Gas Dynamics and Turbulence Laboratory
for the purpose of controlling high-speed and high Reynolds number jets. The ability of LAFPAs for use in both subsonic and
supersonic jets has been explored, and experiments to date have shown that these actuators have significant potential for
mixing enhancement and noise control applications. While it has been established that the actuators manipulate instabilities
of the jet, the exact nature of how the actuation couples to the flow is still unclear. All of the results previously reported
have been based on a nozzle extension that has an azimuthal groove of 1 mm width and 0.5 mm depth along the inner surface
approximately 1 mm upstream of nozzle extension exit. The ring groove was initially added to shield the plasma arcs from the
high-momentum flow. However, the effect of the ring groove on the actuation mechanism is not known. To explore this effect,
a new nozzle extension is designed, which relocates the actuators to the nozzle extension face and eliminates the ring groove.
Schlieren images, particle image velocimetry and acoustic results of a Mach 0.9 jet of Reynolds number ~6.1 × 105 show similar trends and magnitudes with and without a ring groove. Thus, it is concluded that the ring groove does not play
a primary role in the LAFPAs’ control mechanism. Furthermore, the effect of the duty cycle of the actuator input pulse on
the LAFPAs’ control authority is investigated. The results show that the minimum duty cycle that provides complete plasma
formation has the largest control over the jet. 相似文献
9.
In order to evaluate characteristics of the liquid film flow and their influences on heat and mass transfer, measurements
of the instantaneous film thickness using a capacitance method and observation of film breakdown are performed. Experimental
results are reported in the paper. Experiments are carried out at Re = 250–10000, T
in = 20–50°C and three axial positions of vertically falling liquid films for film thickness measurements. Instantaneous surface
waveshapes are given by the interpretation of the test data using the cubic spline method. The correlation of the mean film
thickness versus the film Reynolds number is also given by fitting the test data. It is revealed that the surface wave has
nonlinear behavior. Observation of film breakdown is performed at Re = 1.40 × 103–1.75 × 104 and T
in = 85–95°C. From experimental results, the correlation of the film breakdown criterion can be obtained as follows: Bd = 1.567 × 10−6
Re
1.183 相似文献
10.
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
11.
The near-field instability of variable property jets of air, CO2, and He, issued into the ambient air, has been investigated experimentally within normal gravity and microgravity fields.
The density ratio to the ambient air is unity for air jets, more than unity (1.53) for CO2 jets, and less than unity (0.14) for He jets, respectively. The ratio of kinematic viscosity to the ambient air is unity
for air jets, less than unity for CO2 jets (0.53), and more than unity for He jets (7.75), respectively. The jet velocity is varied from 0.4 to 1.8 m/s and then
the jet Reynolds number varies from 60 for Helium jet to 2,000 for CO2 jet, while the Richardson number varies from negative to positive values. The motion of the jet is visualized using a laser
tomographic method and recorded by a high-speed digital video camera with 250 frames/s. The result shows that the instability
of the jet is intensified when Re > 800 while it is weakened at Re < 800 at the microgravity field, indicating that the viscosity plays an important role in weakening the instability. Under
a normal gravity field, the buoyancy also becomes important. In order to quantify the instability criteria, the quantity of
the instability is introduced, which consists of the Kelvin–Helmholtz instability, buoyancy effect and viscous effect. When
the ratio of the sum of Kelvin–Helmholtz and buoyancy forces to viscous force exceeds a certain value, around 12 in the present
study, the jet becomes unstable even when Re < 800. These results reveal that the instability of variable property jets is influenced by the Kelvin–Helmholtz instability,
the viscous effect and the buoyancy effect. 相似文献
12.
A computational fluid dynamics (CFD) model is used to investigate the hydrodynamics of a gas–solid fluidized bed with two vertical jets. Sand particles with a density of 2660 kg/m3 and a diameter of 5.0 × 10?4 m are employed as the solid phase. Numerical computation is carried out in a 0.57 m × 1.00 m two-dimensional bed using a commercial CFD code, CFX 4.4, together with user-defined Fortran subroutines. The applicability of the CFD model is validated by predicting the bed pressure drop in a bubbling fluidized bed, and the jet detachment time and equivalent bubble diameter in a fluidized bed with a single jet. Subsequently, the model is used to explore the hydrodynamics of two vertical jets in a fluidized bed. The computational results reveal three flow patterns, isolated, merged and transitional jets, depending on the nozzle separation distance and jet gas velocity and influencing significantly the solid circulation pattern. The jet penetration depth is found to increase with increasing jet gas velocity, and can be predicted reasonably well by the correlations of Hong et al. (2003) for isolated jets and of Yang and Keairns (1979) for interacting jets. 相似文献
13.
The injection of a liquid jet into a crossing Mach 6 air flow is investigated. Experiments were conducted on a sharp leading
edge flat plate with flush mounted injectors. Water jets were introduced through different nozzle shapes at relevant jet-to-air
momentum–flux ratios. Sufficient temporal resolution to capture small scale effects was obtained by high-speed recording,
while directional illumination allowed variation in field of view. Shock pattern and flow topology were visualized by Schlieren-technique.
Correlations are proposed on relating water jet penetration height and lateral extension with the injection ratio and orifice
diameter for circular injector jets. Penetration height and lateral extension are compared for different injector shapes at
relevant jet-to-air momentum–flux ratios showing that penetration height and lateral extension decrease and increase, respectively,
with injector’s aspect ratio. Probability density function analysis has shown that the mixing of the jet with the crossflow
is completed at a distance of x/d
j
~ 40, independent of the momentum–flux ratio. Mean velocity profiles related with the liquid jet have been extracted by means
of an ensemble correlation PIV algorithm. Finally, frequency analyses of the jet breakup and fluctuating shock pattern are
performed using a Fast Fourier algorithm and characteristic Strouhal numbers of St = 0.18 for the liquid jet breakup and of St = 0.011 for the separation shock fluctuation are obtained. 相似文献
14.
Based on the mass transfer theory, a new mass transfer model of ion-exchange process on zeolite under liquid film diffusion
control is established, and the kinetic curves and the mass transfer coefficients of –K+ ion-exchange under different conditions were systemically determined using the shallow-bed experimental method. The results
showed that the –K+ ion-exchange rates and transfer coefficients are directly proportional to solution flow rate and temperature, and inversely
proportional to solution viscosity and the size of zeolite granules. It also showed that the transfer coefficient is not influenced
by the ion concentrations. For a large ranges of operational conditions including temperatures (10 − 75°C), flow rates (0.031 m s−1 −0.26 m s−1), liquid viscosities (1.002 × 10−3 N s m−2 − 4.44 × 10−3 N s m−2), and zeolite granular sizes (0.2 − 1.45 mm), the average mass transfer coefficients calculated by the model agree with the
experimental results very well. 相似文献
15.
Grant England Peter A. M. Kalt Graham J. Nathan Richard M. Kelso 《Experiments in fluids》2010,48(1):69-80
The triangular oscillating jet nozzle generates a triangular jet partially confined within an axi-symmetric chamber to produce
a large scale flow oscillation that has application in thermal processes. Particle image velocimetry and oscillation frequency
measurements were conducted to investigate the influence of the jet fluid to ambient fluid density ratio on the resulting
oscillating flow. The investigation was conducted with a jet momentum flux of 0.06 kg m s−2 (Re = 7.3−47.2 × 103) and density ratios ranging from 0.2 to 5.0. The initial spread and decay of the emerging jet was found to depend upon the
density ratio but in a more complex way than does an unconfined jet. Both the spread and decay are strongly influenced by
the instantaneous angle of jet deflection, with greater deflection leading to increased spreading and decay of the jet. Decreasing
the density ratio below unity results in a rapid decrease in the deflection angle, while increasing the density ratio above
unity results in an increase in the deflection angle, albeit with less sensitivity. The frequency of oscillation was also
shown to depend on the density ratio with an increase in the density ratio causing a decrease in the dominant oscillation
frequency. 相似文献
16.
The effects of solid particles on the flow structure in the near field region of a coaxial water jet are investigated non-intrusively
using molecular tagging velocimetry. Glass beads of 240 μm and specific gravity SG of 2.46 are used at three volume loadings
of γv=0.03, 0.06, and 0.09% in the central water jet with a Reynolds number of 4.1×104. Measurements are acquired for four annular to central jet velocity ratios in the range 0.11≤ U
o/U
i≤1.15 at downstream distances up to six inner jet diameters and the results are analyzed for the effects of solid particles
on the characteristics of flow. It is found that the addition of particles does not affect the mean fluid velocity profile
in this region. The results also indicate a small and moderate enhancement of axial turbulent velocity and radial gradients
of velocity fluctuations, respectively, due to the presence of particles. 相似文献
17.
The mixing length theory is employed to simulate the fully developed turbulent heat transfer in annular-sector ducts with
five apex angles (θ0=18,20,24,30,40∘) and four radius ratios (R
o/R
i=2,3,4,5). The Reynolds number range is 104105. The numerical results agree well with an available correlation which was obtained in following parameter range: θ0=18,20,24,30,40∘, R
o/R
i=4 and Re=1045×104. The present work demonstrates that the application range of the correlation can be much extended. Apart from the mixing
length theory, the kɛ model with wall function and the Reynolds stress model are also employed. None of the friction factor results predicted
by the three models agrees well with the test data. For the heat transfer prediction the mixing length theory seems the best
for the cases studied.
Received on 17 July 2000 / Published online: 29 November 2001 相似文献
18.
The flow and heat transfer in an inclined and horizontal rectangular duct with a heated plate longitudinally mounted in the
middle of cross section was experimentally investigated. The heated plate and rectangular duct were both made of highly conductive
materials, and the heated plate was subjected to a uniform heat flux. The heat transfer processes through the test section
were under various operating conditions: Pr ≈ 0.7, inclination angle ϕ = −60° to +60°, Reynolds number Re = 334–1,911, Grashof number Gr = 5.26 × 102–5.78 × 106. The experimental results showed that the average Nusselt number in the entrance region was 1.6–2 times as large as that
in the fully developed region. The average Nusselt numbers and pressure drops increased with the Reynolds number. The average
Nusselt numbers and pressure drops decreased with an increase in the inclination angle from −60° to +60° when the Reynolds
number was less than 1,500. But when the Reynolds number increased to over about 1,800, the heat transfer coefficients and
pressure drops were independent of inclination angles. 相似文献
19.
Understanding the radiation embrittlement of reactor pressure vessel (RPV) steels is required to be able to operate safely
a nuclear power plant or to extend its lifetime. The mechanical properties degradation is partly due to the clustering of
solute under irradiation. To gain knowledge about the clustering process, a Fe−1.1 Mn−0.7 Ni (at.%) alloy was irradiated in
a test reactor at two fluxes of 0.15 and 9 ×1017 n
E > 1MeV
.m − 2.s − 1 and at increasing doses from 0.18 to 1.3 ×1024 n
E > 1MeV
.m − 2 at 300°C. Atom probe tomography (APT) experiments revealed that the irradiation promotes the formation in the α iron matrix of Mn/Mn and/or Ni/Ni pair correlations at low dose and Mn–Ni enriched clusters at high dose. These clusters
dissolve partially after a thermal treatment at 400°C. Based on a comparison with thermodynamic calculations, we show that
the solute clustering under irradiation can just result from an induced mechanism. 相似文献
20.
V. G. Pimshtein 《Fluid Dynamics》2002,37(2):204-212
The results of a comparative investigation of the influence of high-intensity sound (sound pressure level at the nozzle edge L=165 dB) on the expansion of turbulent helium and air jets are given. The jets and sound waves were visualized by means of the direct schlieren method using a spark light source with an exposure of 2·10-7 s. It is shown that the helium jet expands much faster than an air jet with the same dynamic pressure. 相似文献