Eulerian: Wall Boiling
This tutorial validates the wall boiling model in Simcenter STAR-CCM+ against experimental void and temperature data for high-pressure forced convective boiling.
The 1967 paper of Bartolomei [971] provides 13 cases. The first case at 45 bar is of particular interest as it provides wall superheat data, and is the focus of this tutorial. Although the agreement between prediction and experiment is adequate rather than good, the same models can be used to obtain reasonable predictions for void in many of the further 29 cases spanning 30-150 bar given in the 1982 paper [972].
The geometry that is used is a Bartolomei boiling tube, where subcooled water flows upward through a 2 meter tall vertical pipe. The pressure at the outlet is 45 bar. Heat is applied uniformly at the pipe wall.
The basic geometry is a tube of 15.4-mm diameter and heated length of 2 m. To allow some flow development between the inlet and the heated section, a short unheated leader has been added. Similarly so that the outlet conditions in this developing flow do not influence the end of the heated section, a short trailer has also been added.
The conditions are defined as follows:
Length |
L |
2 m |
Equivalent Diameter |
D |
0.0154 m |
Heat Flux |
q |
570000 W/m2 |
Mass Flux |
G |
900 kg/m2 |
Inlet Temperature |
470.63 K |
|
System Pressure |
45.0 bar |
Boiling starts when the wall temperature exceeds the water saturation temperature. This point is called the point of Inception of Boiling (IB) and small bubbles start to appear near the wall. When the degree of subcooling decreases, downstream of the point of IB, the volume fraction of the steam begins to grow. This point in the tube is called the point of Net Vapor Generation (NVG). Further downstream from the NVG point, the volume fraction of the steam continues to grow at an increasing rate and the bubbles start to detach from the wall and move into the liquid. As this detaching occurs, some of the bubbles condense, enhancing the heat transfer to the water. The mixture of steam and water exits at the top of the tube.
An axisymmetric, two-dimensional volume mesh of the Bartolomei boiling tube is provided, as shown below.
