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Non-prismatic channels for reducing shear stress

Haddad Samir

Journal of Water and Land Development

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2022

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no. 52

87--94

EN

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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Remont konserwatorski kamiennej rzeźby na elewacji frontowej Teatru im. Juliusza Słowackiego w Krakowie

Siudut Janusz, Karczmarczyk Stanisław, Maślak Mariusz

Inżynieria i Budownictwo

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2022

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R. 78, nr 9-10

416--420

PL

Zaprezentowano i przedyskutowano przyczyny oderwania się fragmentu kamiennej rzeźby będącej personifikacją Komedii od ściany elewacji frontowej budynku Teatru im. Juliusza Słowackiego w Krakowie. Pokazano sposób rekonstrukcji tej rzeźby oraz zastosowaną w praktyce technikę jej zabezpieczenia przed szkodliwymi wpływami atmosferycznymi.

EN

The reasons for the detachment of a fragment of a stone sculpture, which is the personification of Comedy, from the front elevation wall of the Juliusz Słowacki Theater in Cracow are presented and discussed in detail. The methods of reconstructing this sculpture are shown as well, and also the techniques used in practice to protect it against harmful atmospheric influences.

3

A study of bubble-particle interactions in a column flotation process

Cheng G., Shi C., Yan X., Zhang Z., Xu H., Lu Y.

Physicochemical Problems of Mineral Processing

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2017

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Vol. 53, iss. 1

17--33

EN

Bubble-particle interactions play an important role in flotation. This study examines the behaviour of bubble clusters in a turbulent flotation cell. Particularly, the bubble-particle interaction characteristics in flotation are investigated. The bubble size in a flotation column was measured using an Olympus i-SPEED 3 high-speed camera. Relationships between the circulating volume, bubble size and bubble terminal velocity were discussed. Probabilities of collision, attachment, detachment and acquisition between bubbles and particles in different circulating volumes were calculated based on the flotation kinetic theory. Using the extended Derjaguin–Landau–Verwey–Overbeek (EDLVO) theory, the relationship between the potential energy and distance in bubble-particle interaction was analysed. The results demonstrated that as the circulating volume increased, the bubble size and velocity decreased. When the circulating volume increased from 0.253 to 0.495 m3/h, the bubble diameter decreased from 511 to 462 μm, and the corresponding bubble velocity decreased from 43.1 to 37.5 mm/s. When the circulating volume remained constant as the particle size increased, probabilities of collision, attachment, detachment and acquisition increased. When the particle size remained constant as the circulating volume increased, these probabilities also increased. At a constant circulating volume as the particle size increased, the absolute value of the total potential energy between the particle and bubble increased. When the distance between the bubble and particle was 30 nm, the energy barrier appeared.

4

Modelling and measurement of bubble formation and growth in electroflotation processes

Sarkar S. K., Machniewski P.M., Evans G.M.

Chemical and Process Engineering

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2013

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Vol. 34, nr 3

327--336

EN

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.