Test section loop
This facility part was erected already during the construction of TOPFLOW in 2002. The loop is used for the investigation of two-phase flows in vertical pipes. Thereby the liquid phase (water) is pumped from a separation tank (steam drum) by a centrifugal pump into the test sections. The injection of the gas phase is realized by special gas sparger modules. After the tests the mixture returns into the steam drum and is separated there. The excess gas is blow off. The test section loop is designed for air water and for steam water flows. It can be operated up to 7 MPa. The air is supplied by a pressurized air controlling station with 6 parallel legs up to a maximum norm volume flow of 900 m³/h. The steam is generated by a forced circulation boiler with electrical heating that provides a maximum of 1.4 kg/s saturated steam. The water circulation in the loop is limited to 50 kg/s.
Sectional view of the vertical test section DN200, started in the basement (left hand side) up to the wire-mesh sensor level (right hand side)
At the moment 2 test sections with nominal diameter of DN50 and DN200 are installed in the loop. In both pipes can be observed upward directed co-current flows. Additional in the DN50 pipe downward flows and counter current flows are possible. An important task during the investigation of two phase flows is the measurement of the flow characteristics. For this purpose two systems are applied on the TOPFLOW facility. On the DN200 pipe wire-mesh sensors are installed that measure the electrical conductivity of the fluid. Therefore a wire-mesh is fixed over the pipe cross section and the phase status is measured at the crossing points.
The 2nd system is a fast X-ray tomograph (ROFEX) that is mounted on the DN50 test section. In opposite to the wire-mesh sensors this system works without influence to the flow. Further information about working principle of the X-ray scanner is available with the link above. Both systems measure the phase status at two successive levels. In this way gas velocities can be calculated by cross-correlation or bubble tracing methods. Additional the data of the first measurement level (in flow direction) is used to calculate void fraction and bubble size distributions.
Beside the investigation of developed flows the analysis of flow evolution from the gas injection level to the mixture outlet is of scientific interest. On TOPFLOW two methods are applied for the measurement of the necessary data: On the DN200 pipe the wire-mesh sensors are fixed on top. To provide different inlet length, 8 gas injection modules (wall injection) are distributed along the tube. On the other side the ROFEX scanner is mounted at a linear traversing system that allows the investigation of user-defined positions also with a constant gas injection at the bottom of the test section.
Instead of the DN50 Ti-pipe transparent test sections made from PMMA or PVC clear were operated, so that parallel to the X-ray measurement optical observation was possible.
In the last 15 years both vertical test sections were applied basically for generic investigation of gas-water-flows. The provided data was used for the model development and validation for flow simulation software. For this purpose flow pattern was analyzed in smooth vertical pipes, started with fine bubble flow up to annular flow. Furthermore, series of measurements were run with flow observation around an obstacle (half-moon and ring shaped) that induces more complex flows. Currently, the influence of two-phase flows on the propagation of ultrasound is being investigated within the framework of a partnership with the company Sick.