Triple simultaneous and partially co-located annular flow film measurement with total internal reflection method, X-Ray attenuation and conductivity film sensor

Experimental characterization of thin liquid films in annular flow regime is central in many engineering applications, ranging from chemical industry to refrigeration systems, and in particular to cooling and safety thermal analysis of nuclear boiling water reactors and for validation of system codes as well as Computational Fluid Dynamics (CFD) codes. However, characterization of thin films in annular flow is absolutely not trivial, given the flow turbulence and the high non-linearity of the free-surface behaviour. Particularly, film thickness and wave characteristics are very challenging to be measured, with many correlations from the literature showing substantial offsets in predicting the same quantities under seemingly close boundary conditions. In this paper, results of a simultaneous measurement of vertical upward annular flow film in an adiabatic test section is presented using three different techniques. These consist in: a) total internal reflection method (TIRM), providing highly resolved local thickness measurements; b) X-Ray attenuation method, providing interfacial topology and void fraction that can be converted into film thickness information; and c) a conductivity film sensor providing high speed measurements of film thickness and wave information with a spatial resolution of 2 mm. By performing independent calibrations, the three techniques are cross-validated within the corresponding uncertainties. To the authors’ knowledge, this is the first time that the three measurement techniques for film thickness are combined, thus constituting a unique benchmark. The three techniques complement each other and provide highly reliable measurements of annular flows, which are also compared to existing correlations available in the open literature.