Bubble Dynamics in a Narrow Gap Flow under the Influence of Pressure Gradient and Shear Flow

Reinke, Peter; Ahlrichs, Jan; Beckmann, Tom; Schmidt, Marcus

doi:10.3390/fluids5040208

Cited by 3 publications

(12 citation statements)

References 24 publications

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“…The experimental set-up is a further development of the Couette flow apparatus that was presented originally by Reinke et al [24] consisting of a cylinder 1 located inside housing with a cylindrical cavity 2. The housing is made of polymethyl methacrylate (PMMA), precision-machined and polished, providing the best optical quality.…”

Section: Methodsmentioning

confidence: 99%

“…The cavity encloses the cylinder completely; thus, the clearance at top and bottom of the cylinder give space for a cross-flow, from the pressure maximum towards the pressure minimum which are caused by the circumferential flow, creating a three-dimensional flow structure. In addition to the original design [24], the cavity 2 is mounted on a linear traversing guide 4 which assures precise positioning in relation to the cylinder 1 and control of the minimum fluid film thickness between 1 and 2. The dynamic variation of the film thickness is achieved by means of an actuator 5 and a rocker mechanism 6.…”

Section: Methodsmentioning

confidence: 99%

“…The total air content is calculated based on an oxygen-to-air ratio of 21%. Due to the real operating conditions of the experiment that are described in detail in [24] which include a natural eccentricity and the elasticity, the resulting minimal film thickness is corrected according to Equation (1):…”

Section: Fluid and Dissolved Gasmentioning

confidence: 99%

“…Figure 4 displays the data of the present, further developed set-up versus the data of the original set-up [24] at steady state when the cylinder 1 rotates with constant angular speed ω 1 .…”

Section: Main Parameters and Elasticitymentioning

confidence: 99%

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High-Speed Digital Photography of Gaseous Cavitation in a Narrow Gap Flow

Reinke¹,

Ahlrichs²,

Beckmann³

et al. 2022

Fluids

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The research of cavitation in narrow gap flows, e.g., lubrication films in journal bearings or squeeze film dampers, is a challenging task due to spatial restrictions combined with a high time-resolution. Typically, the lubrication film thickness is in the range of a few microns and the characteristic time for bubble generation and collapse is less than a few milliseconds. The authors have developed a journal bearing model experiment, which is designed according to similarity laws providing fully similar flow conditions to real journal flows while offering ideal access to the flow by means of optical measurement equipment. This work presents the high-speed photography of bubble evolution and transportation in a Stokes-type flow under the influence of shear and a strong pressure gradient which are typical for lubricant films. A paramount feature of the experiment is the dynamic variation (increase/decrease) of the minimum film thickness which triggers the onset of cavitation in narrow gap flows. Results presented in the work on hand include the time-resolved data of the gas release rate and the transient expansion of gas bubbles. Both parameters are necessary to set up numerical models for the computation of two-phase flows.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Fluid and Dissolved Gasmentioning

confidence: 99%

Section: Main Parameters and Elasticitymentioning

confidence: 99%

See 2 more Smart Citations

High-Speed Digital Photography of Gaseous Cavitation in a Narrow Gap Flow

Reinke¹,

Ahlrichs²,

Beckmann³

et al. 2022

Fluids

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“…In addition, at the higher gas flow rate, bubbles coalesce more at a higher gas fraction [9]. However, the high pressure gradient in the chamber can force the deformation of bubbles and in turn contributes to the breakup of large bubbles [52]. Furthermore, the improved solubility of CO 2 at the high pressure may influence the bubble generation.…”

Section: Dependence Of Bubble Sizes On Gas Flow Rate Pressure Of the ...mentioning

confidence: 99%

Effects of Gas Type, Oil, Salts and Detergent on Formation and Stability of Air and Carbon Dioxide Bubbles Produced by Using a Nanobubble Generator

et al. 2023

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Recent developments in ultrafine bubble generation have opened up new possibilities for applications in various fields. Herein, we investigated how substances in water affect the size distribution and stability of microbubbles generated by a common nanobubble generator. By combining light scattering techniques with optical microscopy and high-speed imaging, we were able to track the evolution of microbubbles over time during and after bubble generation. Our results showed that air injection generated a higher number of microbubbles (<10 μm) than CO2 injection. Increasing detergent concentration led to a rapid increase in the number of microbubbles generated by both air and CO2 injection and the intensity signal detected by dynamic light scattering (DLS) slightly increased. This suggested that surface-active molecules may inhibit the growth and coalescence of bubbles. In contrast, we found that salts (NaCl and Na2CO3) in water did not significantly affect the number or size distribution of bubbles. Interestingly, the presence of oil in water increased the intensity signal and we observed that the bubbles were coated with an oil layer. This may contribute to the stability of bubbles. Overall, our study sheds light on the effects of common impurities on bubble generation and provides insights for analyzing dispersed bubbles in bulk.

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Experimental Identification of the Void Fraction in a Large Hydrodynamic Offset Halves Bearing

Engels,

Wettmarshausen,

Stottrop

et al. 2024

Lubricants

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A common approach to optimising hydrodynamic journal bearings for power loss is to reduce the lubricant supply and direct the oil to specific bearing areas where it is needed to guarantee safe operation. This requires information on the processes in the gap and the surrounding pocket areas for both pre-design and simulation. In this paper, a system consisting of a total of eight cameras is used to determine the void fraction in deep grooves outside the lubricant film. The void fraction in the lubrication gap is determined using a novel method for the evaluation of two proximity measurements. While the variation of the deep groove void fraction is realised by a special oil supply and radially adjustable deep groove elements, the gap void fraction is adjusted by the oil supply in the lube oil pockets at the pad leading edges. On the one hand, the experimental investigations show that the void fraction of the deep groove areas has hardly any influence on the general operating behaviour. On the other hand, the void fraction in the lubrication gap can be measured quantitatively for the first time, and the operating point-dependent gas fractions can be visualised. It is also shown that gaseous cavitation is the main mechanism in partially filled regions of the lubrication gap.

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Bubble Dynamics in a Narrow Gap Flow under the Influence of Pressure Gradient and Shear Flow

Cited by 3 publications

References 24 publications

High-Speed Digital Photography of Gaseous Cavitation in a Narrow Gap Flow

High-Speed Digital Photography of Gaseous Cavitation in a Narrow Gap Flow

Effects of Gas Type, Oil, Salts and Detergent on Formation and Stability of Air and Carbon Dioxide Bubbles Produced by Using a Nanobubble Generator

Experimental Identification of the Void Fraction in a Large Hydrodynamic Offset Halves Bearing

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