Dynamic Two-Phase Flows - Models and Applications to Flexible Risers. Severe slugging revisited
Ole Jorgen Nydal1
1NTNU - Norwegian University of Science and Technology
Abstract: Severe slugging in pipelines with gas-liquid two phase flows is a well known phenomenon. It is a large scale flow instability, where the gas compressibility causes alternating gas-liquid flows. Prediction of severe slugging in flow-line riser systems, where the liquid can fill the riser followed by a violent blowout, was a strong motivation for the development of the OLGA flow simulator in the early 80’s. Although the physics of the phenomenon is quite well defined, the diversity of gas-liquid flow dynamics is so large that flow simulators often fail to accurately reproduce field and laboratory observations. Some experiences on severe slugging from the NTNU MultiphaseFlow Laboratory is reviewed, including experimental observations and prediction methods.
Nonlinear waves and transfer processes in liquid film flow
1Institute of Thermophysics SB RAS
Abstract: Results of theoretical and experimental study of nonlinear waves and transfer processes in the falling liquid films and rivulets are presented. Theoretical modeling was mainly carried out based on the integral Kapitza-Shkadov method, valid in the case of moderate Reynolds numbers. Experimental investigations of wave formation in a wide range of wave parameters were performed applying the superimposed periodic oscillations, as well as the single local impacts. Spatial distributions of local thickness of the wave film were determined by the method of laser induced fluorescence, and instantaneous velocity fields were measured by Particle Image Velocimetry. Theoretical and experimental data on propagation of two-dimensional periodic stationary waves and three-dimensional stationary solitons on a vertically falling liquid film are presented. The mechanisms of intensification of heat and mass transfer processes by the nonlinear waves for the cases of film condensation and evaporation or desorption from the falling liquid films are described. The influence of turbulent gas flow on wave generation in the liquid film at different orientations of average velocity vectors of the phases relative to each other and direction of gravity is shown, including the case of non-parallel movement of liquid and gas. The structure of interface in the annular gas-liquid flow is described; the mechanisms of droplet entrainment from the crests of large waves are shown. The three-dimensional regular waves on the straight rivulets flowing down a vertical plane or over the lower outer surface of an inclined tube were studied theoretically and experimentally. The effect of wettability and other parameters on the flow structure is shown.
Modelling requirements for CFD calculations of spray dryers
Abstract: Spray dryers are being used in many industrial areas for converting a liquid suspension or solution into a dry powder. Essential for further processing or use are the properties of the powder which are of course determined by the operational conditions for spray dryers. The particle-laden flow in a spray dryer is very complex and numerous transport processes and physical effect influence droplet motion and drying history, eventually affecting the powder properties. Most dryers are operated in a co-current configuration where both hot air and liquid spray are injected from the top of the dryer and the powder product is extracted at the bottom.
Challenges for Gas Hydrates in Multiphase Flow Systems
Amadeu K. Sum1
1Colorado School of Mines
Abstract: Gas hydrates are crystalline structures formed from the hydrogen-bonding of water molecules to enclose light gases, such as, methane, ethane, propane, carbon dioxide, hydrogen sulfide, nitrogen. They are prevalent in the production of hydrocarbon fluids, such as oil and gas. It is typically very costly to prevent and remediate gas hydrate in flowlines. As such, there is significant interest to develop strategies for the management of hydrates, meaning that hydrates are not completely avoid from forming, but a risk base approach is employed so that the chances of hydrate blockages from forming is minimized. For this strategy to work, a good understanding of hydrate formation and accumulation in multiphase flow is needed, in particular in terms of fundamental processes for hydrate nucleation, growth, agglomeration, deposition, and plugging. The presentation will highlight the multidisciplinary and multiscale approach for developing the engineering of gas hydrates in flow assurance.
Heat Transfer During Boiling and Condensation in Microchannels
Júlio César Passos1
1Universidade Federal de Santa Catarina
Abstract: An increase in the surface area to volume ratio is the main motivation for the industrial development of compact and small heat exchangers. This keynote is structured with an introduction revisiting the main characteristics of two-phase flow inside single or multiple parallel microchannels, including the visualization of the flow and, in particular, the scale effects on the relative forces during flow boiling in microchannels. This is followed by a description of the deviation from the transition lines of the flow maps and some differences with regard to the dryout regime and the onset of nucleate boiling are considered through a comparison between experimental results obtained at LEPTEN (UFSC) and those published in the literature. The second part of this keynote focuses on the convective condensation inside multiple parallel microchannels. A brief review of the literature is presented, including numerical analysis of the effect of the geometrical forms of the cross section on the liquid-vapor interface configuration during the convective condensation inside a single channel. Recent results were obtained at LEPTEN (UFSC) during the condensation of R-134a inside multiple parallel microchannels, where the channel surfaces were cooled using Peltier coolers. Finally, an experimental approach using heat flux transducers during the condensation inside a commercial multiport extruded (MPE) is described and some of the difficulties associated with the experimental studies are detailed.