scholarly journals Lifting of Tribocharged Grains by Martian Winds

2021 ◽  
Vol 2 (6) ◽  
pp. 238
Author(s):  
Maximilian Kruss ◽  
Tim Salzmann ◽  
Eric Parteli ◽  
Felix Jungmann ◽  
Jens Teiser ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Electric Fields ◽  
Wind Shear ◽  
Particle Surface ◽  
Shear Velocity ◽  
Sand Transport ◽  
Particle Collisions ◽  
Surface Charges ◽  
Martian Soil ◽  
Open Question

Abstract It is a long-standing open question whether electrification of wind-blown sand due to tribocharging—the generation of electric charges on the surface of sand grains by particle–particle collisions—could affect rates of sand transport occurrence on Mars substantially. While previous wind tunnel experiments and numerical simulations addressed how particle trajectories may be affected by external electric fields, the effect of sand electrification remains uncertain. Here we show, by means of wind tunnel simulations under air pressure of 20 mbar, that the presence of electric charges on the particle surface can reduce the minimal threshold wind shear velocity for the initiation of sand transport, u *ft, significantly. In our experiments, we considered different samples, a model system of glass beads as well as a Martian soil analog, and different scenarios of triboelectrification. Furthermore, we present a model to explain the values of u *ft obtained in the wind tunnel that is based on inhomogeneously distributed surface charges. Our results imply that particle transport that subsides, once the wind shear velocity has fallen below the threshold for sustained transport, can more easily be restarted on Mars than previously thought.

scholarly journals Aeolian Ripple Migration and Associated Creep Transport Rates

Geosciences ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 389 ◽  
Author(s):  
Sherman ◽  
Zhang ◽  
Martin ◽  
Ellis ◽  
Kok ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Field Experiments ◽  
Shear Velocity ◽  
Original Data ◽  
Sand Transport ◽  
Total Transport ◽  
Original Field ◽  
Ripple Migration ◽  
Using Data ◽  
And Migration

Wind-formed ripples are distinctive features of many sandy aeolian environments, and their development and migration are basic responses to sand transport via saltation. Using data from the literature and from original field experiments, we presented empirical models linking dimensionless migration rates, urgd (ur is the ripple migration speed, g is the gravity acceleration, and d is the grain diameter) with dimensionless shear velocity, u*/u*t (u* is shear velocity and u*t is fluid threshold shear velocity). Data from previous studies provided 34 usable cases from four wind tunnel experiments and 93 cases from two field experiments. Original data comprising 68 cases were obtained from sites in Ceará, Brazil (26) and California, USA (42), using combinations of sonic anemometry, sand traps, photogrammetry, and laser distance sensors and particle counters. The results supported earlier findings of distinctively different relationships between urgd and u*/u*t for wind tunnel and field data. With our data, we could also estimate the contribution of creep transport associated with ripple migration to total transport rates. We calculated ripple-creep transport for 1 ≤ u*/u*t ≤ 2.5 and found that this accounted for about 3.6% (standard deviation = 2.3%) of total transport.

scholarly journals BLOWN SAND ON BEACHES

1982 ◽  
Vol 1 (18) ◽  
pp. 73
Author(s):  
Susumu Kubota ◽  
Kiyoshi Horikawa ◽  
Shintaro Hotta
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
Vertical Distribution ◽  
Shear Velocity ◽  
Wind Tunnel Experiment ◽  
Transport Rate ◽  
Sand Transport ◽  
Sand Transport Rate ◽  
Empirical Coefficients ◽  
The Vertical Distribution

The blown sand transport rate and the vertical and shore-normal distributions of the wind speed were measured simultaneously on a windy beach. The sand transport rate was measured with conventional total quantity-type traps and with a large trap in the form of a trench. The vertical distribution of the wind speed was measured using an ultrasonic anemometer array consisting of six meters. The distribution of wind speed at a height of 1 m in a section normal to the shoreline was measured with five ultrasonic anemometers. A logarithmic law for the vertical distribution of the wind speed was satisfied, and the wind speed in the section normal to the shoreline was almost constant. The Kawamura and Bagnold formulae were found to predict well the sand transport rate. The trench trap and conventional traps gave empirical coefficients of 1.5 and 1.0, respectively, for the sand transport rate averaged over a section normal to the shoreline. The lower value determined with the conventional traps (1.0) is attributed to their inefficiency compared with the trench trap. In order to obtain data at high shear velocities, a wind tunnel experiment was carried out. This experiment showed that both the Kawamura and Bagnold formulae were valid in the range between 60 to 300 cm/s in the wind shear velocity. The empirical coefficient in the laboratory experiments was 1.0: the difference between the field result with the trench trap and the wind tunnel experiment is attributed to the fluctuations in natural wind.

Electric-Field Induced Formation of Superconducting Granular Balls

2002 ◽  
Vol 16 (17n18) ◽  
pp. 2529-2535
Author(s):  
R. Tao ◽  
X. Xu ◽  
Y. C. Lan
Keyword(s):  
Surface Energy ◽  
Electric Field ◽  
Liquid Nitrogen ◽  
Applied Electric Field ◽  
Strong Electric Field ◽  
Particle Surface ◽  
Cooper Pairs ◽  
Surface Charges

When a strong electric field is applied to a suspension of micron-sized high T c superconducting particles in liquid nitrogen, the particles quickly aggregate together to form millimeter-size balls. The balls are sturdy, surviving constant heavy collisions with the electrodes, while they hold over 106 particles each. The phenomenon is a result of interaction between Cooper pairs and the strong electric field. The strong electric field induces surface charges on the particle surface. When the applied electric field is strong enough, Cooper pairs near the surface are depleted, leading to a positive surface energy. The minimization of this surface energy leads to the aggregation of particles to form balls.

scholarly journals Aeolian mass flux characterization: uncertainties from a wind-tunnel perspective and implications for field studies

2014 ◽  
Author(s):  
Ate Poortinga ◽  
Joep GS Keijsers ◽  
Jerry Maroulis ◽  
Saskia M. Visser
Keyword(s):  
Wind Tunnel ◽  
Mass Flux ◽  
Shear Velocity ◽  
Field Studies ◽  
Sediment Traps ◽  
Sediment Flux ◽  
Cumulative Probability ◽  
Surface Moisture ◽  
The North ◽  
Specific Configuration

Aeolian sediment traps are widely used to estimate the total volume of wind-driven sediment transport, but also to study the vertical mass distribution of a saltating sand cloud. The reliability of sediment flux estimations from this data are dependent upon the specific configuration of the measurement compartments and the analysis approach used. In this study, we analyse the uncertainty of these measurements by investigating the vertical cumulative probability distribution and relative sediment flux derived from both wind-tunnel and field studies. Three existing datasets were used in combination with a newly acquired meteorological dataset, which was collected in combination with sediment fluxes from six different events, using three customized catchers at one of the beaches of Ameland in the north of The Netherlands. Fast-temporal data collected in a wind-tunnel shows that eq has a scattered pattern between impact and fluid threshold, but increases linearly with shear velocities above the fluid threshold. For finer sediment fractions, a larger portion of the sediment was transported closer to the surface compared to coarser sediment fractions. It was also shown that errors originating from the the distribution of the sampling compartments, specifically the location of the lowest sediment trap relative to the surface, can be identified using the relative sediment flux. In the field, surface conditions such as surface moisture, surface crusts or frozen surfaces have a more pronounced, but localized effect, than shear velocity. Uncertainty in aeolian mass flux estimates can be reduced by placing multiple compartments in closer proximity to the surface.

scholarly journals Surface Tracking of MgO/Epoxy Nanocomposites: Effect of Surface Hydrophobicity

2019 ◽  
Vol 9 (3) ◽  
pp. 413 ◽  
Author(s):  
Zhaoliang Xing ◽  
Chong Zhang ◽  
Xiangnan Hu ◽  
Panhui Guo ◽  
Jingyuan Zhang ◽  
...  
Keyword(s):  
Contact Angle ◽  
Electric Fields ◽  
Surface Hydrophobicity ◽  
Surface Charges ◽  
Surface Tracking ◽  
Surface Contact ◽  
Surface Contact Angle ◽  
Tracking Behavior ◽  
Composite Samples ◽  
Reduced Surface

Surface tracking has been one of the challenges for outdoor organic insulations, in electronic and electrical devices. In this paper, surface tracking behavior of nano-MgO/epoxy composite samples were measured according to the standard IEC 60112. Improved tracking resistance was obtained in nanocomposites with an 18.75% uplift in the comparative tracking index, and a decrease of 58.20% in the surface ablation area at a fixed 425 V. It was observed that the tracking resistance and surface hydrophobicity shared the same tendency—both, the comparative tracking index and surface contact angle increased with an increase of the nanofiller content. Samples with better hydrophobicity exhibited a higher tracking resistance. It could be the case that the conductive pathway of contamination was harder to form, as a result there were fewer discharging processes. With the development of surface tracking, the surface contact angle abruptly decreased, at first, and tended to be constant, which was also accomplished with the failure of samples. In addition, reduced surface resistivity was also found in the nanocomposites, which was beneficial for releasing surface charges and inhibiting distortions in the electric fields.

Aeolian sand transport over gobi with different gravel coverages under limited sand supply: A mobile wind tunnel investigation

2013 ◽  
Vol 11 ◽  
pp. 67-74 ◽  
Author(s):  
Lihai Tan ◽  
Weimin Zhang ◽  
Jianjun Qu ◽  
Kecun Zhang ◽  
Zhishan An ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Sand Transport ◽  
Aeolian Sand ◽  
Aeolian Sand Transport ◽  
Sand Supply

Surface displacements and surface charges on Ba2CuWO6 and Ba2Cu0.5Zn0.5WO6 ceramics induced by local electric fields investigated with scanning-probe microscopy

2007 ◽  
Vol 22 (1) ◽  
pp. 193-200
Author(s):  
Ralf-Peter Herber ◽  
Gerold A. Schneider
Keyword(s):  
Electric Fields ◽  
Ferroelectric Properties ◽  
Piezoresponse Force Microscopy ◽  
Ferroelectric Material ◽  
Relaxor Ferroelectrics ◽  
Surface Charges ◽  
Kelvin Probe ◽  
Force Microscopy ◽  
Atomic Force ◽  
Surface Displacements

Ba2CuWO6 (BCW) was first synthesized in the mid 1960s, and it was predicted to be a ferroelectric material with a very high Curie temperature of 1200 °C [N. Venevtsev and A.G. Kapyshev: New ferroelectrics. Proc. Int. Meet. Ferroelectr.1, 261 (1966)]. Since then, crystallographic studies were performed on the compound with the result that its crystal structure is centrosymmetric. Thus for principal reason, BCW cannot be ferroelectric. That obvious contradiction was examined in this study. Disk-shaped ceramic samples of BCW and Ba2Cu0.5Zn0.5WO6 (BCZW) were prepared. Because of the low electrical resistivity of the ceramics, it was not possible to perform a typical polariszation hysteresis loop for characterization of ferroelectric properties. Scanning electron microscopy investigations strongly suggest that the reason for the conductivity is found in the impurities/precipitations within the microstructure of the samples. With atomic force microscopy (AFM) in piezoresponse force microscopy (PFM) mode, it is possible to characterize local piezoelectricity by imaging the ferroelectric domains. Neither BCW nor BCZW showed any domain structure. Nevertheless, when local electric fields were applied to the surfaces of the ceramics topographic displacements, imaged with AFM, and surface charges, imaged with Kelvin probe force microscopy (KFM) and PFM, were measured and remained stable on the surface for the time of the experiment. Therefore BCW and BCZW are considered to be electrets and possibly relaxor ferroelectrics.

Electrohydrodynamic Kelvin-Helmholtz Instability of Two Rotating Dielectric Fluids

1998 ◽  
Vol 53 (1-2) ◽  
pp. 17-26
Author(s):  
Mohamed Fahmy El-Sayed
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Applied Electric Field ◽  
Rotation Frequency ◽  
Short Wave ◽  
Surface Charges ◽  
Rotation Surface ◽  
Dielectric Fluids ◽  
Fluid Velocities ◽  
Conditions Of Stability

Abstract A linear stability analysis of a novel electrohydrodynamic Kelvin-Helmholtz system consisting of the superposition of two uniformly rotating dielectric media is presented. The characteristic equation for such an arrangement is derived, which in turn yields a stability criterion for velocity differences of disturbances at a given rotation frequency. The conditions of stability for long and short wave perturbations are obtained, and their dependence on rotation, surface tension and applied electric field is discussed. Limiting cases for vanishing fluid velocities, rotation frequency, and applied electric field are also discussed. Under suitable limits, results of previous works are recovered. A detailed analysis for tangential and normal applied electric fields, in the presence and absence of surface charges, is carried out.

Sign in / Sign up

Export Citation Format

Share Document