Abstract
The energy dissipation rate is a crucial parameter for system control and turbulence modeling but is difficult to quantify in gas–liquid two-phase flows. Little relevant information is available, especially in horizontal pipe flows. Based on the consideration that the bubble characteristics in a stable bubbly flow are a reflection of flow turbulence, the bubble shape and bubble size spectrum are investigated in a 10-m-long horizontal rectangular pipe by means of high-speed imaging and graphic processing techniques. The bubble size spectra indicate a critical length scale, deemed to be the Hinze scale, and the spectral shape is related to turbulent fragmentation and, thus, enables calculation of the turbulence dissipation rate. After careful validation of the approach for estimating the turbulence dissipation rate, an empirical prediction equation is proposed based on the present tested flow conditions, reflecting the effects of both the pipe flow velocity and the gas flow rate. Such information is useful for the modeling of turbulent two-phase flows.
Highlights
Two-phase flows are commonly encountered in industrial processes such as chemical reactors, hydrotransport, and biomedical treatment.1–4 For gas–liquid pipe flows, because of the coexistence of and interaction between the gas and liquid phases, the flow dynamics are complex, and failure in monitoring and controlling the flow conditions can cause severe consequences
New experiments were conducted in a rectangular pipe, to enable an analysis of the energy dissipation rate ε of the bubbly pipe flow for different flow conditions
Flow imaging observations were performed in a horizontal rectangular pipe, and the bubble size spectra were obtained under different background pipe flow velocities and gas flow rates
Summary
Two-phase flows are commonly encountered in industrial processes such as chemical reactors, hydrotransport, and biomedical treatment. For gas–liquid pipe flows, because of the coexistence of and interaction between the gas and liquid phases, the flow dynamics are complex, and failure in monitoring and controlling the flow conditions can cause severe consequences. For gas–liquid pipe flows, because of the coexistence of and interaction between the gas and liquid phases, the flow dynamics are complex, and failure in monitoring and controlling the flow conditions can cause severe consequences. Among the most commonly used parameters for turbulence characterization, the energy dissipation rate ε is crucial. It determines the energy loss caused by the viscous forces in the turbulent flow and has been used in a variety of k-ε turbulence models in computational fluid dynamics to simulate the development of turbulence along the pipeline.. New experiments were conducted in a rectangular pipe, to enable an analysis of the energy dissipation rate ε of the bubbly pipe flow for different flow conditions. The finding is useful for a better description of the flow field and choice of two-equation turbulence models in numerical simulations
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