Schlieren-based simultaneous mapping of bubble dynamics and temperature gradients in nucleate flow boiling regime: Effect of flow rates and degree of subcooling

Sinha, Gulshan Kumar; Mahimkar, Saylee; Srivastava, Atul

doi:10.1016/j.expthermflusci.2019.02.018

Cited by 36 publications

(6 citation statements)

References 38 publications

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“…The observed asymmetry in the microlayer profile may be explained through the dynamic changes in the shape of the vapour bubble. After the initial growth period, the vapour bubble changes its shape from hemispherical to round (Sinha, Mahimkar & Srivastava 2019;. In the context of the present experiments, bubble shape and upstream microlayer radius have been plotted in figure 8.…”

Section: Dynamics Of Microlayer and Vapour Bubblementioning

confidence: 99%

Microlayer dynamics during the growth process of a single vapour bubble under subcooled flow boiling conditions

2021

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The phenomena of microlayer formation and its dynamic characteristics during the nucleate pool boiling regime have been widely investigated in the past. However, experimental works on real-time microlayer dynamics during nucleate flow boiling conditions are highly scarce. The present work is an attempt to address this lacuna and is concerned with developing a fundamental understanding of microlayer dynamics during the growth process of a single vapour bubble under nucleate flow boiling conditions. Boiling experiments have been conducted under subcooled conditions in a vertical rectangular channel with water as the working fluid. Thin-film interferometry combined with high-speed cinematography have been adopted to simultaneously capture the dynamic behaviour of the microlayer along with the bubble growth process. Transients associated with the microlayer have been recorded in the form of interferometric fringe patterns, which clearly reveal the evolution of the microlayer beneath the growing vapour bubble, the movement of the triple contact line and the growth of the dryspot region during the bubble growth process. While symmetric growth of the microlayer was confirmed in the early growth phase, the bulk flow-induced bubble deformation rendered asymmetry to its profile during the later stages of the bubble growth process. The recorded fringe patterns have been quantitatively analysed to obtain microlayer thickness profiles at different stages of the bubble growth process. For Re = 3600, the maximum thickness of the almost wedge-shaped microlayer was obtained as δ ~ 3.5 μm for a vapour bubble of diameter 1.6 mm. Similarly, for Re = 6000, a maximum microlayer thickness of δ ~ 2.5 μm was obtained for a bubble of diameter 1.1 mm.

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Section: Dynamics Of Microlayer and Vapour Bubblementioning

confidence: 99%

Microlayer dynamics during the growth process of a single vapour bubble under subcooled flow boiling conditions

2021

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“…HT2332 was a high precision, high stability, low noise linear programmable DC power supply with independent three-channel output. 2 bit D/A converter to control output voltage and current By using the interference principle of coherent light, schlieren images featured the change of flow field of the zone to be measured as light and dark stripes on the optical screen, thus capturing the transparent flow field which is otherwise difficult to observe [17]- [19]. The high-speed shooting system consists of a Z-shaped reflective schlieren and a Fastec Imaging IL5 high-speed camera, which had full HD frame rates 1000 fps.…”

Section: Observation Platform Of the Ionic Windmentioning

confidence: 99%

Influencing Factors of Flow Field of Ionic Wind Induced by Corona Discharge in a Multi-Needle-to-Net Electrode Structure Under Direct-Current Voltage

Song

Wang

et al. 2019

IEEE Access

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The morphologies and velocity of ionic wind induced by direct-current (DC) corona discharge were experimentally measured. DC voltage was applied to short air gaps of high-voltage electrode-needle electrode and grounding electrode-net electrode to generate coronas, so as to allow the generation of ionic wind induced by corona discharge. The purpose of the study is to optimise the multi-needle-to-net electrode structure to improve the velocity of the ionic wind and keep it in a relatively stable state. For this purpose, the influences of various parameters on the velocity of the ionic wind were explored. The research results showed that the side length of meshes and the distribution mode of needles significantly affected the velocity of the ionic wind. The maximum velocity of the ionic wind, when the side length of meshes was 0.85 mm was 3 and 1.28 times those when the side lengths of the meshes were 2 and 0.425 mm, respectively. This indicated that there was an optimal side length that can maximise the velocity of the ionic wind. Increasing the number of needles and optimising the distribution mode of needles can effectively improve the velocity, that is, the improvement of the number and distribution uniformity of needles was conducive to increase the velocity of the ionic wind. Increasing the voltage amplitude can increase the velocity of the ionic wind, however, it was possible that noise was significant and in this case, the corresponding voltage cannot be considered as the working voltage of the ionic wind generator.INDEX TERMS Corna diacharge, gap discharge, schlieren technique, multi-needle-to-net electrode.

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“…Bubble dynamic such as bubble growth, detachment, and sliding can be attributed to the improved flow boiling heat transfer. The sliding of the bubbles disturbs the thermal and velocity boundary layers, increasing heat transfer between the refrigerant and the heated wall [48] , [49] . The video images show that the ultrasonic field significantly alters the sliding trajectories of bubbles.…”

Section: Resultsmentioning

confidence: 99%

Experimental investigation on flow boiling bubble motion under ultrasonic field in vertical minichannel by using bubble tracking algorithm

Xiao

Zhang

2023

Ultrasonics Sonochemistry

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Schlieren-based simultaneous mapping of bubble dynamics and temperature gradients in nucleate flow boiling regime: Effect of flow rates and degree of subcooling

Cited by 36 publications

References 38 publications

Microlayer dynamics during the growth process of a single vapour bubble under subcooled flow boiling conditions

Microlayer dynamics during the growth process of a single vapour bubble under subcooled flow boiling conditions

Influencing Factors of Flow Field of Ionic Wind Induced by Corona Discharge in a Multi-Needle-to-Net Electrode Structure Under Direct-Current Voltage

Experimental investigation on flow boiling bubble motion under ultrasonic field in vertical minichannel by using bubble tracking algorithm

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