Thermal Damping in Bubbly Flows

• Main Authors: Hsien-Chun Chang, 張賢俊
• Other Authors: Yi-Chun Wang
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/845669

碩士 === 國立成功大學 === 機械工程學系碩博士班 === 90 === One-dimensional bubbly flows through converging-diverging nozzles are investigated using a two-fluid model. Effects associated with both translational and radial relative motions between bubbles and liquid are incorporated. Calculation of a subsonic case is performed first and shows good agreement with experiments. The model is then applied to critical (or choked) flow situations studied previously by Muir and Eichhorn (1963). In their experiments, Muir and Eichhorn found larger critical pressure ratios (which are defined as the ratio of the pressure in the throat to that in the reservoir under choked conditions) and flow rates than homogeneous flow theory. They measured significant slip between phases which, therefore, was speculated to be responsible for these discrepancies. It is demonstrated in this paper that the phase relative velocity and mass flow rates can be predicted reasonably well (within the experimental uncertainly) using the present model, however, can not fully compensate the critical pressure ratio. Other important features of the critical flows are also explored, including the formation of compression shock waves present in the divergent part of the nozzle. Our computations show that the pressure ratio across the shocks agree very well with the Hugoniot relation established by Thang and Davis (1981). We also examine the sensitivity of the flow field to the value the effective viscosity employed in the Rayleigh-Plesset equation. In order to describe the effects of heat diffusion during the variation of bubble volume, we modify the Rayleigh-Plesset equation to in corporate the thermal damping into the present model. Both the subsonic flows and the supersonic flows are revisited. Results obtained show that the flashing instability of the bubbly flows can be stabilized by the thermal damping effects.