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Abstract

Electroflotation is used in the water treatment industry for the recovery of suspended particles. In this study the bubble formation and release of hydrogen bubbles generated electrolytically from a platinum cathode was investigated. Previously, it was found that both the growth rate and detachment diameter increased with increasing wire diameter. Conversely, current density had little effect on the released bubble size. It was also found that the detached bubbles rapidly increased in volume as they rose through the liquid as a result of decreasing hydrostatic pressure and high levels of dissolved hydrogen gas in the surrounding liquid. The experimental system was computationally modelled using a Lagrangian-Eulerian Discrete Particle approach. It was revealed that desorption of gaseous solutes from the electrolyte solution, other than hydrogen, may have a significant impact on the diameter variation of the formed bubbles. The simulation confirmed that liquid circulation, either forced or induced by the rising bubble plume, influences both the hydrogen supersaturation (concentration) in the neighbourhood of the electrode and the size of the resulting bubbles.

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Authors and Affiliations

Shahjahan K. A. Sarkar
Piotr M. Machniewski
Geoffrey M. Evans
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Abstract

To reduce the sediment transport capacity, shear stress needs to be reduced as well. The article describes work that has been done to find a way to make these reductions possible. The theoretical study and the approach proposed allowed us to obtain a general equation that determines conditions and calculates the most important parameters which support the reduction of shear stress. This describes the mechanism that erodes soils by free surface water flow.
In a similar vein, we have shown that adding a short non-prismatic channel to the entrance of a prismatic channel, which has the same geometric shape, is a very powerful way to reduce shear stress. With the idea of reducing shear stress, we have shown that the water-surface profile type plays a key role and must therefore be included in future reflections on reducing the importance of shear stress.
Additionally, the notion of efficiency was introduced that allows to evaluate the expected gain after the reduction of shear stress and adding a short non-prismatic channel.
The laws of similarity applied to free surface flows allowed us to obtain an equation with several equivalence scales and compare different geometric shapes in terms of their efficiency in the reduction of shear stress.
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Bibliography

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HADDAD S., BOUHADEF M. 2018. Contribution to runoff erosion of earthen channels. Polish Journal of Soil Science. Vol. 51. No. 2 p. 313–325. DOI 10.17951/pjss.2018.51.2.313.
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Authors and Affiliations

Samir Haddad
1 2
ORCID: ORCID

  1. Houari Boumediène University of Sciences and Technology, Faculty of Civil Engineering. LEGHYD Laboratory, BP 32 Bab Ezzouar, 16111 Algiers, Algeria
  2. Akli Mohand Oulhadj University of Bouira, Rue Frères Boussendalah, 10000 Bouira, Algeria
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Abstract

In the presented work Egorov’s approach (adding a source term to the ω-equation in the k-! model, which mimics the damping of turbulence close to a solid wall) was implemented in on the subclass of shear stress transport models. Hence, turbulence damping is available for all shear stress transport type models, including hybrid models that are based on the ω-equation. It is shown that turbulence damping improves the prediction of the axial velocity profile not only for Reynolds-averaged Navier–Stokes simulation but also for detached eddy simulation and delayed detached eddy simulation models. Furthermore, it leads to a more realistic estimation of the pressure drop and, hence, to a more correct prediction of the liquid level. In this paper, simulation results for four different turbulence models are presented and validated by comparison with experimental data. Furthermore, the influence of the magnitude of the damping factor on the pressure drop in the channel is investigated for a variety of different gas-to-liquid flow rate ratios. These investigations show that higher gas-to-liquid flow rate ratios require higher damping factors to correctly predict the pressure drop. In the end, advice is formulated on how an appropriate damping factor can be determined for a specific test case.
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Bibliography

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Authors and Affiliations

Jiri Polansky
1
Sonja Schmelter
2

  1. Czech Technical University in Prague, Jugoslávských partyzánu 1580/3, 160 00 Prague 6 – Dejvice, Czech Republic
  2. Physikalisch-Technische Bundesanstalt (PTB), Abbestraße 2-12, D-10587 Berlin-Charlottenburg, Germany
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Abstract

The subflorescence and efflorescence phenomena are widely acknowledged as the major causes of permanent damage to fresco wall paintings. They are related to the occurrence of cycles of dry/wet conditions inside the walls. Therefore, it is essential to identify the presence of water on the decorated surfaces and inside the walls.

Nondestructive testing in industrial applications have confirmed that active infrared thermography with continuous timed images acquisition can improve the outcomes of thermal analysis aimed to moisture identification. In spite of that, in cultural heritage investigations these techniques have not been yet used extensively on a regular basis. This paper illustrates an application of these principles in order to evaluate the decay of fresco mural paintings in a medieval chapel located in North−West of Italy. One important feature of this study is the use of a robotic system called aIRview that can be utilized to automatically acquire and process thermal images. Multiple accurate thermal views of the inside walls of the building have been produced in a survey that lasted several days. Signal processing algorithms based on Fast Fourier Transform analysis have been applied to the acquired data in order to formulate trustworthy hypotheses about the deterioration mechanisms.

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Authors and Affiliations

G. Cadelano
P. Bison
A. Bortolin
G. Ferrarini
F. Peron
M. Girotto
M. Volinia

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