Statistical characteristics of free falling water film

Flow of gravitationally falling thin liquid films over the outer cylindrical surfaces with or without concurrent steam flow has always been a fundamental problem of major importance at applied thermal hydraulics, especially, on thermal hydraulic phenomena that occur after a large or small break LOCA such as the rewetting of the overheated fuel elements by a top spraying ECCS and CCFL during reflux condensation. In this study an experimental apparatus has been set up, so as to thoroughly collect liquid films data at low Reynolds numbers by means of needle contact probes. Although this technique is not widely adopted, it is reliable and accurate as other probing techniques and it has the major advantage that it can provide direct measurements of the film characteristics as no calibration is needed. The probes' axial movement is controlled by the use of two step motors capable of 2.5 μm resolution. Step motors are directly connected with a computer that undertakes all the acquisition tasks and thus provides a fully automated measurement procedure. Measurements are performed within the liquid inception region where no surface wave formation is expected and at a proper longitudinal distance from the liquid entrance where the two-wave system would be well developed.