An improved dropwise condensation heat transfer model modified from previous models is proposed in this paper. The critical radius for onset of droplet condensation is determined in the preceding ...paper (Part I), leading to a more accurate determination of droplet nucleation density and the coalescence radius in this paper (Part II). Effects of subcooling, contact angle, thickness and thermal conductivity of the coating layer on droplet nucleation density, condensation heat flux, and critical condensation heat transfer rate for onset of droplet condensation are illustrated. The predicted droplet nucleation density and dropwise condensation heat flux are shown in excellent agreement with existing experimental data.
Differences in atmospheric environments can have a significant impact on microphysical processes of precipitation. Dominant warm (cold) rain processes in East Asia (southern Great Plains of the ...United States) are implied by a large (small or constant) gradient of reflectivity at low levels in vertical reflectivity profiles. Long-term ground observations using two-dimensional video disdrometers were conducted in the southern Korean Peninsula (KOR) and Norman, Oklahoma, United States (OKL). Raindrop size distributions (RSD) and their moments in the two regions were analyzed in the framework of scaling normalized RSDs. Results show that the concentrations of small (big) raindrops were higher (smaller) in KOR than in OKL. KOR RSDs were also found to be characterized by relatively high characteristic number concentrations
N
0
'
and small characteristic diameters
D
m
'
when compared to OKL RSDs. The
N
0
'
increases with increasing
D
m
'
in both KOR and OKL at lower Z with the opposite trend at higher Z. In addition, OKL RSDs with
D
m
'
>
2.5
mm
indicate the existence of an equilibrium between coalescence and breakup processes. Rainfall estimation relationships between the rain rate R and radar variables were retrieved from scattering simulations at S-, C-, and X-band wavelengths. KOR RSDs showed relatively small horizontal reflectivity and specific differential phase shift at the same R and same wavelength when compared to OKL RSDs. The regional dependency was significant due to the different microphysical process in KOR and OKL. The specific attenuation of KOR was, however, similar to that of OKL only at S band, indicating an advantage of using specific attenuation in S band in rainfall estimation.
Spin Torque—Generated Magnetic Droplet Solitons Mohseni, S. M.; Sani, S. R.; Persson, J. ...
Science (American Association for the Advancement of Science),
03/2013, Volume:
339, Issue:
6125
Journal Article
Peer reviewed
Dissipative solitons have been reported in a wide range of nonlinear systems, but the observation of their magnetic analog has been experimentally challenging. Using spin transfer torque underneath a ...nanocontact on a magnetic thin film with perpendicular magnetic anisotropy (PMA), we have observed the generation of dissipative magnetic droplet solitons and report on their rich dynamical properties. Micromagnetic simulations identify a wide range of automodulation frequencies, including droplet oscillatory motion, droplet "spinning," and droplet "breather" states. The droplet can be controlled by using both current and magnetic fields and is expected to have applications in spintronics, magnonics, and PMA-based domain-wall devices.
•Design a new type of aeration impact sprinkler (two-phase flow).•Compare the drop size distribution of single-phase flow and two-phase flow Impact sprinkler at different low pressure.•Compare the ...cumulative volume curve of both sprinkler at different distance and different pressure.•Compare the frequency distribution of AIS and IS at a different distance, drop diameter and at a different velocity.•Compare the velocity of different size of droplets at a different distance from sprinkler with low pressure.•Compare the kinetic energy of both sprinklers to reduce the soil and crop damage problems.
Impact sprinkler (20PY2 IS) outlet is a single-phase water flow, and the aeration impact sprinkler (20PY2 AIS) outlet is gas-liquid two-phase flow. The jet dispersing principle of AIS is somewhat different from conventional sprinklers and has advantages and the ability to working well at the low-pressure condition. The experimental study on the droplet size distribution of IS and AIS was carried out by the volume-weighted method to analyze the mean diameter (Dv), median diameter(D50), water droplets frequency distribution, and the cumulative frequency at different distances from sprinklers. Similarly, the velocity of the drop was measured by Laser Precipitation Monitor (LPM) and statically analyzed by using a number-weighted method. The results showed that both the drop diameters Dv and D50 increased with the distance from the sprinkler nozzle but decreased with an increase in the working pressure. Similarly, droplet frequency distribution at a diameter < 3.5 mm of both sprinklers increased with the working pressure. The quantity of larger droplets decreased with an increase in working pressure, and this trend amplified with an increase in the distance from the sprinkler nozzle. Under low-pressure (0.15 MPa, 0.2 MPa, and 0.25 MPa) and the absence of wind conditions, the droplet distribution of the AIS was more uniform and constant than the IS. The droplet's frequency distribution of AIS and IS nozzles was conformed to a logarithmic normal distribution. With the distance from the sprinkler increasing, the slope of the droplet cumulative frequency curve decreased gradually. Under the same pressure and at similar distances from the nozzle, the (D50) of the 20PY2IS was less than the 20PY2AIS, and the functional relationship between median diameter, working pressure, and distance from the sprinkler was established. When the pressure was set at 0.15 MPa and 10 m away from the sprinkler, the droplet's median diameter was 6% higher under AIS than under IS. At the working pressure of 0.25 MPa, the frequency distribution of water droplets under both nozzles was higher, and water droplets are more frequent for a different distance from a sprinkler. Droplet velocity was improved with the decreasing droplet diameter, but due to low pressure, there was not significantly influenced in velocity. The results may deliver a basis for additional efficient exploration of the AIS.
Quantifying the influence of rain in LiDAR performance Filgueira, A.; González-Jorge, H.; Lagüela, S. ...
Measurement : journal of the International Measurement Confederation,
January 2017, 2017-01-00, 20170101, Volume:
95
Journal Article
Peer reviewed
•Methodology to evaluate the relationship between LiDAR performance under rainy weather.•LiDAR intensity decreases with rain increasing. Pavement is the less affected material.•LiDAR detected points ...decrease with rain increasing.
LiDAR systems emerge as one of the key systems for autonomous vehicles. The present work quantifies the influence of rain in different LiDAR parameters: range, intensity, and number of detected points. Six areas with different target materials are used for the study. Range measurements appear stable even under important rain affectation. The variations are always lower than 20cm. These variations come from the experimental procedure (averaging of points detected from a surface) and not from the instabilities in the LiDAR detection with rain. The detected LiDAR intensity and the sampled points attenuate with the increasing of rain intensity. Drop size distribution is assumed constant along the study area. The highest decrease in the number of points appears for pavement. However, the intensity returned from pavement is not specially influenced by rain. The rest of the materials show similar trend in the intensity and the number of detected points.
Optical disdrometers can be used to estimate rainfall erosivity; however, the relative accuracy of different disdrometers is unclear. This study compared three types of optical laser-based ...disdrometers to quantify differences in measured rainfall characteristics and to develop correction factors for kinetic energy (KE). Two identical PWS100 (Campbell Scientific), one Laser Precipitation Monitor (Thies Clima) and a first-generation Parsivel (OTT) were collocated with a weighing rain gauge (OTT Pluvio
2
) at a site in Austria. All disdrometers underestimated total rainfall compared to the rain gauge with relative biases from 2% to 29%. Differences in drop size distribution and velocity resulted in different KE estimates. By applying a linear regression to the KE-intensity relationship of each disdrometer, a correction factor for KE between the disdrometers was developed. This factor ranged from 1.15 to 1.36 and allowed comparison of KE between different disdrometer types despite differences in measured drop size and velocity.
Abstract
This study investigates the microphysical parameters and shapes of droplet size distributions (DSDs) along three aircraft traverses of developing convective clouds during Cloud Aerosol ...Interactions and Precipitation Enhancement EXperiment (CAIPEEX) 2015 at a sampling frequency of 25 Hz. The droplet number concentration (
N
c
, cm
−3
), and liquid water content (LWC, gm
−3
) present steep gradients within a few tens of meters’ zones near the cloud edges and relatively gentle gradients in the strong updraft zones. Sometimes, the horizontal
LWC
distribution resembles a trapezoid-like shape with steep LWC and
N
c
gradients near the cloud edges. The LWC maximums (LWC
max
) are lower than the adiabatic LWC, but the high adiabatic fractions in the cloud core indicate low dilution. High LWC/LWC
max
, largest droplets, and narrow and similarly-shaped DSDs are found in the regions of high updrafts. Zones of low LWC/LWC
max
are found close to the cloud edges, where DSDs are highly diverse, containing both large and small droplets. Finally, we analyze the mixing diagrams.
Significant in-phase turbulent fluctuations in LWC and
N
c
were found. The effective radii change slightly across cloud updraft zones but decrease at the low LWC/LWC
max
ratio zone close to cloud edges. The spectra of LWC and
N
c
obey Kolmogorov -5/3 turbulence law. The radii of the correlation of LWC and
N
c
in updraft zones are of several tens of meters. Filaments up to 120-175 m in size are also noticed.
Collisional drop breakup is one of the important processes during evolution of the rain drops and leads to modified shape of the drop size distribution (DSD), which is a primary parameter in rain ...retrieval in remote sensing techniques. Though several experimental and observational studies have been performed in the recent past on this aspect, the impact of the same in natural rain, particularly in orographic rain, is still poorly represented. The present study aims to examine and identify the rain conditions in which collisional drop breakup is prominent and is capable of modifying the shape of DSD in orographic rain over north-eastern India. The 2-min averaged DSDs from four hilly locations are studied in both stratiform and convective rain types separately using ground-based DSD measurements. Even though drop breakup in intense to moderate rain seemed to be in notable percentage (0.2% - 11.2%), the low intensity rain also showed a considerable break-up signature (2.5% - 9%), depending upon the locations. The overall results showed that collisional breakup was more prominent in convective rain (1%–11%) than in stratiform rain (4%–5%), however, breakup is also seen primarily during stratiform rain in two of the locations. The Z-R coefficients are found to be significantly different for the break-up and non-break up cases. For breakup cases, both convective and stratiform rainfall shows an increase in intercept parameter for all locations. For stratiform rain types, the coefficient a and b ranged from 307.6 to 321.4 (167.1–178.7) and 1.27–1.37 (1.31–1.34) for rain with break-up (without break-up), respectively. In the case of convective rain, the coefficients were found to be in the range of 377.5–654.7 (270.4–641.3) and 1.28–1.42 (1.14–1.31) with break-up (without break-up), respectively. The results suggest that collisional breakup is an important process in orographic rain over North-Eastern India and it has to be taken care of, while studying rainfall over these regions, particularly in conventional radar derived quantitative precipitation estimates (QPE).
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•Collisional drop breakup in orographic rain has been explored in four tropical Indian locations.•Breakup occurs mainly in convective rain at two locations, while the other two show notable breakup in stratiform rain.•Occurrence of equilibrium DSD registered highest in low rain intensity for all locations.•The Z-R coefficient “A” was consistently higher across all locations and rain types in situations involving collisional drop breakup in comparison to scenarios with no breakup.
This paper investigates the primary atomization of airblasted liquid sheet using detailed numerical simulations. The atomization of liquid sheet under airblasting conditions involve complex ...mechanisms and a thorough understanding is necessary. A planar pre-filming airblast atomization configuration have been chosen to study the breakup of liquid sheet/film injected on a solid flat plate. We have investigated an operating point directly relevant for high altitude relight condition of the aircraft. This configuration has been chosen based on the experimental investigation of Gepperth et al. S. Gepperth, A. Müller, R. Koch, H.-J. Bauer, Ligament and droplet characteristics in pre-filming airblast atomization, Proceedings of the ICLASS, 12th Triennial International Conference on Liquid Atomization and Spray Systems, September 2-6, Heidelberg, Germany, 2012 for the airblast atomization. The numerical simulations have been performed using in-house Navier–Stokes solver that uses consistent mass and momentum flux computation technique. The purpose of this work is to provide a comprehensive database and analyses of the airblast atomization of liquid sheet. This include studies on the effect of velocity profile on the atomization characteristics, occurrence of secondary atomization and drop coalescence, and extraction of near-field atomization characteristics. The qualitative analyses of the results from the simulations showed that there are two major atomization mechanisms of liquid film breakup — sheet/bag breakup and ligament breakup. The drop diameter and velocity distributions computed from the simulations was found to be of the same order of magnitude although under-predicting the experimental data. Based on the atomized drop data, both the secondary atomization and drop coalescence have been observed to occur in the simulations. The quantitative analyses of the near-field liquid ligaments results revealed the lengths of these ligaments are of the same order of magnitude as the experimental data while an under-prediction in the ligament velocity has been observed. Finally, an excellent agreement between simulations and experimental data has been found for the Sauter Mean Diameter (SMD) of the atomized droplets.
•Hybrid treatment of liquid/gas multiphase interface using moment of fluid (MOF) and level set frameworks.•Novel study of the effect of inlet velocity profile for liquid fuel and air investigated.•Two prominent atomization mechanisms found — sheet breakup and ligament breakup.•Identified the presence and occurrence of secondary atomization and drop coalescence.•Novel study to extract near-field ligament data that agrees satisfactorily with experimental measurements.
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