Dispersed phase droplet behavior research is very important for the design and scaling up of extraction columns. Recently, the droplet velocities at high holdup were found to be uniform, which means ...the conventional concept of forward mixing needs correction. The drop size distribution only influences the mass transfer coefficients and not the residence time distribution of droplets. In this work, an improved dynamic combined model considering the influence of drop size distribution has been developed, by which the axial mixing can be easily evaluated using a one-dimension search. A typical experimental system of 30% tributyl phosphate (TBP) (in kerosene)-nitric acid–water with interfacial tension of 0.00995
N/m was used to investigate the mass transfer performances in a coalescence-dispersion pulsed-sieve-plate extraction column (CDPSEC) with 150
mm in diameter. The two-point dynamic method was used to obtain the stimulus–response curves. With these results, the axial mixing in the CDPSEC was evaluated. The calculated results showed that the response curves could be predicted by the dynamic combined model with a deviation less than 0.001. This model has marked advantages over previous models in literature because of its accuracy, simple boundary conditions, and single parameter optimization.
Various methods have been proposed to evaluate hydrophobicity of silicone rubber used for sheds of polymeric insulators. CIGRE WG D1.14 has proposed Dynamic Drop Test (DDT) method to evaluate the ...hydrophobicity changes of the materials. In this paper, we measured static contact angle, hydrophobicity class in spray method, and drop velocity of water droplets, in order to observe the change in hydrophobicity of silicone rubber surface suffered to local arc discharge at DDT. Because of the hydrophobicity decreases due to the local arc discharge, the water droplet changes from a spherical to a water film. In particular, changes of initial state in hydrophobicity can be observed by measuring the drop velocity of water droplets. And the correlation was confirmed with the cumulative charge of local arc discharge. Therefore, the water drop velocity was effective for the evaluation of hydrophobicity change.
Distributions of the drop size and velocity in an asymmetric impinging jet are investigated by injecting water and a sodium carbonate (Na
2
CO
3
) solution, which simulates the mixing process in ...impinging jet sprays of liquid oxidizer and liquid fuel for liquid propellants. The liquid sheet formed from the impinging jet is visualized and the drop size distributions are obtained by using image processing for the visualized images. The drop size distribution of the asymmetric impinging jets is fitted to the Rosin-Rammler distribution function. The obtained drop size distributions according to the azimuth angle in the impinging jet are compared with the theoretical predictions of previous research. The experimental results of the drop size distributions are located between the two curves obtained from the theoretical predictions by treating each jet in the asymmetric impinging jets as an independent wall-impinging jet. PIV images using a double-exposure method were processed to obtain the drop velocity vector in the impinging jets. Whether the drops shedding from the edge of the asymmetric impinging jets occurs radially or tangentially is also investigated from the PIV results.
A phase Doppler interferometry (PDI) system was used to characterize the water sprays produced by four residential fire sprinklers. Four pendent sprinklers with
K-factors ranging from 7.2×10
−5
m
3
s
...−1
kPa
−0.5 (3.0
gal
min
−1
psig
−0.5) to 1.35×10
−4
m
3
s
−1
kPa
−0.5 (5.6
gal
min
−1
psig
−0.5) were investigated. The measurements include characteristic size (arithmetic mean diameter, volume mean diameter, Sauter mean diameter), mean velocity (axial and radial components), and liquid volume flux. The effect of water pressure on drop size was also investigated. The mean drop size (flux-averaged volume diameter,
D
30
) was found to be proportional to
P
−1/3 over the range 93
kPa⩽P⩽200
kPa.
The results of phase Doppler interferometry (PDI) and particle image velocimetry (PIV) measurements to characterize the water sprays produced by fire sprinklers are presented. The large size of the ...water drops produced by fire sprinklers, and the relatively large coverage area of the spray, present significant challenges when attempting to characterize these sprays. These difficulties are especially relevant when using PDI because large drops and large coverage areas may result in attenuation of the transmitting laser beams. For the fire sprinkler investigated, it was determined that attenuation of the laser beam resulted in over-counting of drops due to burst splitting, a situation in which the Doppler signals from single drops are misinterpreted as being due to multiple drops. This effect was minimized by carefully choosing the operating conditions of the PDI processing electronics. PIV measurements provide velocity profiles that can be used as input for fire dynamics simulations to predict the effect of sprinkler sprays on fires. The results from the PIV measurements show good agreement with the velocity measurements obtained from PDI in the core of the spray, but poorer agreement along the sprinkler axis. The discrepancy was attributed to recirculation zones present in the experimental facility and possible biasing of the PIV measurements towards the larger drops.
This study has been undertaken to clarify the motion of condensate drops under drowise condensation. It is difficult to clarify the behavior of the condensate drops on the condensing surface, because ...of their constantly changing weight and shape. Therefore, in the air, the behavior of a water drop with a constant weight on an inclined unwet surface was investigated using a video tape recorder. The velocity and width of a water drop were measured against the moving distance. The velocity and width of a tailless water drop were nearly constant. Moreover, in a tailed water drop, the tail was broken at some distance. The limit velocity and width of the hindmost edge were obtained both experimentally and theoretically.
The raindrop size distribution (DSD) quantifies the microstructure of rainfall and is critical to studying precipitation processes. We present a method to improve the accuracy of DSD measurements ...from Parsivel (particle size and velocity) disdrometers, using a two-dimensional video disdrometer (2DVD) as a reference instrument. Parsivel disdrometers bin raindrops into velocity and equivolume diameter classes, but may misestimate the number of drops per class. In our correction method, drop velocities are corrected with reference to theoretical models of terminal drop velocity. We define a filter for raw disdrometer measurements to remove particles that are unlikely to be plausible raindrops. Drop concentrations are corrected such that on average the Parsivel concentrations match those recorded by a 2DVD. The correction can be trained on and applied to data from both generations of OTT Parsivel disdrometers, and indeed any disdrometer in general. The method was applied to data collected during field campaigns in Mediterranean France for a network of first- and second-generation Parsivel disdrometers, and on a first-generation Parsivel in Payerne, Switzerland. We compared the moments of the resulting DSDs to those of a collocated 2DVD, and the resulting DSD-derived rain rates to collocated rain gauges. The correction improved the accuracy of the moments of the Parsivel DSDs, and in the majority of cases the rain rate match with collocated rain gauges was improved. In addition, the correction was shown to be similar for two different climatologies, suggesting its general applicability.
The impact of vertical downdraft on rain attenuation estimation from rain rate measurements has been studied. The rain rate ( R ) and specific attenuation (γ) are derived from rain drop size ...distributions (DSD) by considering the widely accepted Gunn-Kinzer (G-K) relationship between drop size and drop fall velocity that is valid for stagnant air. In the real atmosphere, drops are carried with the vertical wind draft, and the actual fall velocity of the raindrops deviates from the G-K formulation. The ITU-R estimated rain attenuation values, based on DSDs, which are mostly valid for temperate regions, can deviate from actual rain attenuation measurements in tropical regions, especially at higher rain rates when downdraft is prominent. The present study uses disdrometer measurements of DSD, optical rain gauge measurements of rain rates, and Ku-band rain attenuation data over an earth-space path at a tropical location Kolkata (22°34′ N, 88°29′ E) to show that vertical downdrafts impact the rain attenuation estimation from rain rate measurements. At the present location, an overall representative vertical downdraft of 2 m/s needs to be considered to match the experimental attenuation measurements with the estimated values using the modified γ- R relationship in the ITU-R model.
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