A widely used device for continuous contacting in microdevices is the Falling Film Micro Reactor (FFMR). The liquid films that are formed in the channels of a FFMR are quite stable and have a typical thickness of less than 100 mu m. In the present work, a mu-PIV system was used for measuring velocity profiles and for estimating the local liquid film thickness in three open inclined microchannels (with width of 1200, 600 and 300 mu m). The film thickness measurements were utilized for reconstructing the shape of the interface, while the effect of various fluid parameters (e.g. physical properties, flow rate) as well as geometrical characteristics of the conduit and the inclination angle of the microchannels, on the geometrical characteristics of the liquid phase has been also experimentally investigated. As the correlations that are valid in the macroscale are generally not applicable in the microscale, the aim of the present study is to develop a means for predicting the geometrical characteristics (i.e liquid film thickness, shape of the gas/liquid interface) of the liquid phase, as well as its mean residence time Generalized correlations for predicting film thickness and meniscus shape are proposed (accuracy +/- 15%) while, by combining these correlations an estimation of the mean residence time can be also made. (C) 2013 Elsevier Ltd. All rights reserved.