ADIABATIC AIR-WATER UPFLOW IN A LARGE DIAMETER PIPE: EXPERIMENTS VS. PREDICTIONS OF PRESSURE DROP
Due to its complexity and ubiquity, liquid-gas two-phase flow is a challenging research topic for the oil and gas, process, and power industries. Accurate prediction of the pressure drop in the outlet piping of a thermosiphon reboiler is necessary to determine the flow circulation rate. Moreover, the presence of slug flow in these long vertical pipes can often lead to pressure pulsations and vibrations. Thermosiphon outlet piping is typically classified as large pipe, with flow characterized by increased turbulence, distorted bubble interfaces and bubble breakup, and formation of small bubbles in comparison to flow in small pipes. Furthermore, in a large pipe, slug bubbles are not able to span the entire pipe diameter. Because the majority of gas-liquid flow studies concern pipes of small diameter, HTRI constructed a transparent air-water flow loop (127-mm diameter, ~6-m square) at our Research & Technology Center. Using quantitative measurements and visual observations, we improved our understanding of pressure drop, void fraction, and flow regimes for adiabatic vertical upflow, horizontal flow, and vertical downflow inside large pipes. In this study, we compare and critique predictions of two-phase analytical models and commercial CFD simulations with the experimental results for vertical upflow. Of particular commercial interest is the evolution of the flow from the developing region at the start of the vertical pipe to the more developed region at the end of the pipe.