Experimental investigation of heat transport in inhomogeneous bubbly flow

• Published in: Chemical engineering science Vol. 198; pp. 260 - 267
• Main Authors: Gvozdić, Biljana, Dung, On-Yu, Alméras, Elise, van Gils, Dennis P.M., Lohse, Detlef, Huisman, Sander G., Sun, Chao
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 28.04.2019; Elsevier
• Subjects: Bubble column; Bubbly flows; Chemical and Process Engineering; Chemical engineering; Chemical Sciences; Engineering Sciences; Experiments; Heat transfer; Bubbly flows; Experiments; Heat transfer; Bubble column
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2018.09.040

•Heat transfer enhancement increases with increasing gas volume fraction α.•Inhomogeneous bubbly flow enhances the heat transfer more than the homogeneous bubble injection for α < 4%.•For α > 4% interaction of mixing mechanisms reduces the heat transfer enhancement. In this work we study the heat transport in inhomogeneous bubbly flow. The experiments were performed in a rectangular bubble column heated from one side wall and cooled from the other, with millimetric bubbles introduced through one half of the injection section (close to the hot wall or close to the cold wall). We characterise the global heat transport while varying two parameters: the gas volume fraction α=0.4–5.1%, and the Rayleigh number RaH=4×109-2.2×1010. As captured by imaging and characterised using Laser Doppler Anemometry (LDA), different flow regimes occur with increasing gas flow rates. In the generated inhomogeneous bubbly flow there are three main contributions to the mixing: (i) transport by the buoyancy driven recirculation, (ii) bubble induced turbulence (BIT) and (iii) shear-induced turbulence (SIT). The strength of these contributions and their interplay depends on the gas volume fraction which is reflected in the measured heat transport enhancement. We compare our results with the findings for heat transport in homogeneous bubbly flow from Gvozdić et al. (2018). We find that for the lower gas volume fractions (α<4%), inhomogeneous bubbly injection results in better heat transport due to induced large-scale circulation. In contrast, for α>4%, when the contribution of SIT becomes stronger, but so does the competition between all three contributions, the homogeneous injection is more efficient.