Experimental results show that for very viscous solution, the scaled film thickness can be as large as 0.45. In this section, we attempt to determine a minimum tube length required for the different flow patterns to be fully developed for two-phase flows under microgravity conditions. The microgravity experiments must be designed to overcome the restrictions in space and distance due to a limited amount of space available aboard the KC-135 aircraft. To our knowledge, no prior work reported in the literature can provide conclusive experimental evidences or estimates of the minimum required length for the flow development section. In this study, we conducted five sets of experiments using the test section consists of six sets of conductance probes, 15.24 cm apart.
Air enters the test section as a jet stream through a small annulus tube.
Liquid enters from the side of the test section and flows along the annulus gap as a laminar film before mixing with the gas. The chosen inlet geometry was designed to promote the annular flow condition at the entrance since it is the preferred pattern in this investigation. We analyzed the film thickness traces collected at the six conductance probes to determine the required development. Our strategy in this study is to focus mainly on the time traces collected at probe 5 and 6 in annular flow conditions. If the flow is fully developed, the characteristics of the wave profiles such as the mean film thickness, hmean, and the maximum wave amplitude, hmax, should be independent of the distance Z .