Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

3 Publications

Evolution of the structure of a gas-liquid two-phase flow in a large vertical pipe

Prasser, H.-M.; Beyer, M.; Carl, H.; Gregor, S.; Lucas, D.; Pietruske, H.; Schütz, P.; Weiss, F.-P.

Experimental results on the evolution of the radial gas fraction profiles, gas velocity profiles and bubble size distributions in a gas-liquid two-phase flow along a large vertical pipe of 194 mm inner diameter are presented. The tests were performed at the TOPFLOW facility in Rossendorf, where two wire-mesh sensors were used to measure sequences of two-dimensional distributions of local instantaneous gas fraction within the complete pipe cross-section with a lateral resolution of 3 mm and a sampling frequency of 2500 Hz. This data is the basis for a fast flow visualization and for the calculation of the mentioned profiles. The gas fraction profiles were obtained by averaging the sequences over time, velocities were measured by cross-correlation of the signals of the two sensors, which were located on a short (63 mm) distance behind each other. The high resolution of the mesh sensors allows to identify regions of connected measuring points in the data array, which are filled with the gas phase. This method was used to obtain the bubble size distributions.
In the experiments, the superficial velocities ranged from 0.04 to 8 m/s for the gas phase and from 0.04 to 1.6 m/s for the liquid. In this way, the experiments cover the range from bubbly to churn turbulent flow regimes. The evolution of the flow structure was studied by varying the distance between the gas injection and the sensor position. This distance was changed by the help of a so-called variable gas injection set-up. It consists of 6 gas injection units, each of them equipped with three rings of orifices in the pipe wall for the gas injection. These rings are fed with the gas phase from ring chambers, which can be individually controlled by valves. The middle ring has orifices of 4 mm diameter, while the upper and the lower rings have nozzles of 1 mm diameter. In this way, 18 different inlet lengths and two different gas injection geometries can be chosen. The latter allows to vary the initial bubble diameter at identical superficial velocities. The test setup is designed for steam-water operation at up to 7 MPa saturation pressure as well, which will be performed later. The paper presents the results of air-water tests.
A special data evaluation technique allows to study the evolution of radial gas fraction profiles that are decomposed according to bubble size classes. In this way, the behavior of bubbles of different diameter can be observed, which experience different non-drag forces depending on their diameter. A parallel test section of 52.3 mm inner diameter allows the study of scaling effects.

Keywords: Gas-liquid flow; two-phase flow; wire-mesh sensor; flow structure; bubble size; gas fraction; vertical pipe flow

  • Lecture (Conference)
    Eleventh International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH 11), 02.-06.10.2005, Avignon, France
  • Contribution to proceedings
    Eleventh International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH 11), 02.-06.10.2005, Avignon, France, paper 399.
  • Nuclear Engineering and Design 237(2007), 1848-1861