Computational Modeling of Boiling Flow Regime Maps
Bernard Geurts & Hans Kuerten
For the design of evaporator tubes used in various types of conventional power plants, medium-size boilers and waste incinerators, knowledge of flow pattern change under the influence of external heating is of utmost importance to warrant safe operation. The production of steam in evaporator tubes accelerates the remaining liquid and causes topology changes of vapor-liquid interfaces along the pipe. In boiling, the so-colled two-phase flow regime changes in flow direction and heat transfer and pressure drop depend much on the flow regime present. The intended main results of this project of this project is a multi-scale numerical method to determine flow pattern maps, validated using experimental data at operation conditions. In all commercial codes that are presently used for the prediction of phase-transitional flows, the internal structure of the interface between the two phases is not modeled and correlations for inter-phase mass and heat transfer are implemented. In this project we propose to develop a numerical method based on a multi-scale approach. On the large, macroscopic, scale a combination of single-phase methods for the two separate phases and an interface tracking method will be developed in the context of Open FOAM. On the smaller scales turbulence modeling and a diffuse interface model will be incorporated to accurately represent all dynamical scales of relevance. The proposed research will produce a validated, reliable and versatile prediction tool as well as a set of practical flow pattern maps for heated two-phase flows. In this way, we will be able to design higher safety preventing wall superheating in each and every flow regime and predicting deposition rates in boiling multiphase flow.
Temperature contour plot and velocity field of a evaporating rising bubble in a vertical channel. In order to capture the thin thermal boundary layer that we can see aroud the top and the shoulders of the bubble we need a really high resolution mesh is needed. Beneath the bubble we have a region of lower superheat caused by the latent heat necessary for the evaporation process.
3D rising bubble on a grid 160 ×320 ×160 with the corresponding veloc- ity field (arrows) on a plane passing through the centre of mass of the bubble: (a) t = 1 ; (b) t = 3 . One velocity vector in each 10 grid points is shown. The magnitude of the velocity is shown on the background.