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Experimental investigation of heat transport in homogeneous bubbly flow
- Source :
- Journal of Fluid Mechanics, Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 845, pp.226-244. ⟨10.1017/jfm.2018.213⟩, Journal of fluid mechanics, 845, 226-244. Cambridge University Press
- Publication Year :
- 2018
- Publisher :
- HAL CCSD, 2018.
-
Abstract
- We present results on the global and local characterisation of heat transport in homogeneous bubbly flow. Experimental measurements were performed with and without the injection of $\sim 2.5$ mm diameter bubbles (corresponding to $Re_b \approx 600$) in a rectangular water column heated from one side and cooled from the other. The gas volume fraction $\alpha$ was varied in the range $0\% - 5\%$, and the Rayleigh number $Ra_H$ in the range $4.0 \times 10^9 - 1.2 \times 10^{11}$. We find that the global heat transfer is enhanced up to 20 times due to bubble injection. Interestingly, for bubbly flow, for our lowest concentration $\alpha = 0.5\% $ onwards, the Nusselt number $\overline{Nu}$ is nearly independent of $Ra_H$, and depends solely on the gas volume fraction~$\alpha$. We observe the scaling $\overline{Nu} \propto \alpha^{0.45}$, which is suggestive of a diffusive transport mechanism. Through local temperature measurements, we show that the bubbles induce a huge increase in the strength of liquid temperature fluctuations, e.g. by a factor of 200 for $\alpha = 0.9\%$. Further, we compare the power spectra of the temperature fluctuations for the single- and two-phase cases. In the single-phase cases, most of the spectral power of the temperature fluctuations is concentrated in the large-scale rolls. However, with the injection of bubbles, we observe intense fluctuations over a wide range of scales, extending up to very high frequencies. Thus, while in the single-phase flow the thermal boundary layers control the heat transport, once the bubbles are injected, the bubble-induced liquid agitation governs the process from a very small bubble concentration onwards.<br />Comment: Journal of Fluid Mechanics (accepted)
- Subjects :
- Materials science
Gas/liquid flows
Bubble
UT-Hybrid-D
Mixing (process engineering)
FOS: Physical sciences
Settore ING-IND/06
gas/liquid flows
multiphase and particle-laden flows
01 natural sciences
010305 fluids & plasmas
Physics::Fluid Dynamics
symbols.namesake
[CHIM.GENI]Chemical Sciences/Chemical engineering
Multiphase and particle-laden flows
0103 physical sciences
Thermal
Heat transfer
Génie chimique
[SPI.GPROC]Engineering Sciences [physics]/Chemical and Process Engineering
Génie des procédés
010306 general physics
Bubbly flows
Natural convection
Mechanical Engineering
Fluid Dynamics (physics.flu-dyn)
Reynolds number
Physics - Fluid Dynamics
Rayleigh number
Mechanics
Condensed Matter Physics
Nusselt number
Mechanics of Materials
symbols
Experiments
Bubble column
Subjects
Details
- Language :
- English
- ISSN :
- 00221120 and 14697645
- Database :
- OpenAIRE
- Journal :
- Journal of Fluid Mechanics, Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 845, pp.226-244. ⟨10.1017/jfm.2018.213⟩, Journal of fluid mechanics, 845, 226-244. Cambridge University Press
- Accession number :
- edsair.doi.dedup.....92698dd6204dfff5d42b377a43d6415c