Investigations of static and dynamic interactions between bubbles and X-hot-film probes

Abstract

Very few investigations of bubbly two-phase flows have used X-hot-film probes for the measurement of the turbulence field in the continuous phase. Therefore the interactions between the sensors of the X probe and the bubbles are not well known and thus can lead to errors in the determination of turbulence parameters. To gain understanding of the interaction, investigations of static and dynamic bubble-sensor interactions were carried out. In the static investigations a probe that is moved through stagnant water interacts with a bubble that is fixed to a small nozzle. These experiments help us to understand signals for situations in which the liquid and the bubble move with the same speed. In this case, the so-called post-signal occurring at the exit of the sensor penetration through the bubble is caused by the deformation of the bubble surface by the sensor and its prongs rather than by the flow field. In the dynamic investigations the probe is fixed in a vertical flow and it interacts with single bubbles of a bubble stream, as is the case in any two-phase flow situation. A bubble-probe interaction map is proposed that classifies the behaviour into four different modes of interaction. In both series of measurements, various parameters characterizing bubble signals were determined. A synchronized video system is used for visual investigations of deformations of the bubble surface. The results will be used for the future development of a so-called bubble elimination algorithm that is used for filtering the bubble signals out of the two-phase signal.

Hot-film anemometry in bubbly flow I: bubble–probe interaction

“…5 displays image sequences for these three types. These classes correspond to the results of Serizawa et al (1983) and Benk et al (2001), though these authors found a fourth interaction type, namely glancing bubbles. As it is not possible to strictly discriminate between glancing and bouncing hits, we merged these two types.…”

“…These images show that the bubbles are strongly deformed during the interaction. Even when a bubble has already left the probe, shape deformations can be present, see also Benk et al (2001). These surface oscillations, which originate from the bubble-probe interaction, are sometimes very strong.…”

Study of kerosene–water two‐phase flow characteristics in vertical and inclined pipes

“…The images given by Rensen et al [31] illustrated that there was a variety of shapes of the signals for the bouncing and splitting bubbles contrasting to the common shape for penetrating bubbles. The video images produced by Benk et al [30] showed that the bubbles were strongly deformed during the interaction with the probe and it became difficult to identify the start and the end of the bubble signal accurately. The dual optical probes for liquid-liquid flow applications were developed by Hamad et al [32] The probe geometry was optimised by studying the signal from the drop-probe interaction.…”

“…The drop–probe interaction, which depends on the direction of the drop velocity, may cause more uncertainty for measurements in an inclined pipe due to the change in the flow structure from almost one‐dimensional to three‐dimensional in the inclined pipe. The drop–probe interaction was studied by Benk et al and Rensen et al using a high speed camera to follow the drop movement during the penetration process. They classified bubble–probe interaction into three types: penetrating, splitting and bouncing.…”

Parametric effects of bubble-microcantilever impacts in a confined channel

“…While the terminology differs, all three studies observed bubbles that grazed the probe, wrapped around and bounced off, split, or were penetrated by the probe while remaining intact. Benk et al, 9 who looked at x-wire probes, observed an additional type of collision outcome in which the initial bubble was split into multiple small fragments for large ͑D Ն 3 mm͒, high-speed ͑U bubble Ն 1.8 m / s͒ bubbles ͑We= 124͒. Other studies considered the effects of bubble impacts and deformation on their rise velocity in liquids.…”