On the ?inertial? time in instability of materials with non-monotone yield stress

AbstractNegative refraction of acoustic waves is demonstrated through underwater experiments conducted at ultrasonic frequencies on a 3D locally resonant acoustic metafluid made of soft porous silicone-rubber micro-beads suspended in a yield-stress fluid. By measuring the refracted angle of the acoustic beam transmitted through this metafluid shaped as a prism, we determine the acoustic index to water according to Snell’s law. These experimental data are then compared with an excellent agreement to calculations performed in the framework of Multiple Scattering Theory showing that the emergence of negative refraction depends on the volume fraction $$\Phi$$ Φ of the resonant micro-beads. For diluted metafluid ($$\Phi =3\%$$ Φ = 3 % ), only positive refraction occurs whereas negative refraction is demonstrated over a broad frequency band with concentrated metafluid ($$\Phi =17\%$$ Φ = 17 % ).

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Use of Concentric Hele-Shaw Cell for the Study of Displacement Flow and Interface Tracking in Primary Cementing

Energies ◽

10.3390/en14010051 ◽

2020 ◽

Vol 14 (1) ◽

pp. 51

Author(s):

Amir Taheri ◽

Jan David Ytrehus ◽

Bjørnar Lund ◽

Malin Torsæter

Keyword(s):

Yield Stress ◽

Drilling Fluid ◽

Co2 Storage ◽

Main Idea ◽

Real Field ◽

Interface Tracking ◽

Pressure Gradients ◽

Cell Geometry ◽

Primary Cementing ◽

Hele Shaw Cell

We present our new designed concentric Hele-Shaw cell geometry with dynamic similarity to a real field wellbore annulus during primary cementing, and then, the results of displacement flow of Newtonian and yield-stress non-Newtonian fluids in it are described. The displacement stability and efficiency, the effect of back, front, and side boundaries on displacement, bypassing pockets of displaced yield-stress fluid in displacing fluid, and the behavior of pressure gradients in the cell are investigated. Applications of intermediate buoyant particles with different sizes and densities intermediate between those of successively pumped fluids for tracking the interface between the two displaced and displacing fluids are examined. The main idea is to upgrade this concentric Hele-Shaw cell geometry later to an eccentric one and check the possibility of tracking the interface between successive fluids pumped in the cell. Successful results help us track the interface between drilling fluid and spacer/cement during primary cementing in wells penetrating a CO2 storage reservoir and decreasing the risk of CO2 leakage from them.

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Investigation of Thick-Film-Paste Rheology and Film Material for Pattern Transfer Printing (PTP) Technology

Coatings ◽

10.3390/coatings11010108 ◽

2021 ◽

Vol 11 (1) ◽

pp. 108

Author(s):

Adrian Adrian ◽

Dominik Rudolph ◽

Jan Lossen ◽

Norbert Willenbacher

Keyword(s):

Solar Cell ◽

Aspect Ratio ◽

Yield Stress ◽

Laser Power ◽

Light Transmission ◽

Pattern Transfer ◽

Volatile Components ◽

Film Material ◽

Transfer Printing ◽

Power Threshold

Steady cost pressure in silicon solar cell production leads to a continuous reduction of silver consumption per cell. Pattern Transfer Printing (PTP) technology enables to reduce silver consumption by depositing smaller front electrodes on solar cells. Here, we aim at a better understanding of the laser deposition process. The aspect ratio of printed lines improved with increasing paste yield stress but was lower than the theoretical aspect ratio for a given trench geometry, suggesting that line spreading was caused by the pressure that was due to the vaporization of volatile paste components and a yield stress reduction that was due to local paste heating. A low laser power threshold, mandatory to fabricate narrow electrodes with a high aspect ratio and low amount of debris, could be achieved using pastes with low boiling temperature of volatile components and poor wetting between paste and film. The material with the lowest light transmission exhibited the lowest laser power threshold. We attribute this to the weaker adhesion to the paste and a better alignment with the laser focal plane. Our results provide valuable guidelines for paste and film material design aimed at narrower electrodes, with a higher aspect ratio to be obtained at an even lower laser power threshold in PTP-based solar cell metallization.

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