The increased attention towards continuous processes in, e.g. reaction or crystallization has put emphasis towards gas-liquid two-phase flow and especially towards slug flow. The segmentation leads to narrow residence time distributions under laminar flow conditions enabling the implementation of kinetically slow processes. Furthermore, mixing inside slugs is ensured without introduction of additional mixing devices. However, such internal mixing is affected by the slug length itself and its distribution formed during slug formation. Therefore, for uniform process conditions inside the slugs, they need to be as homogeneous as possible in length identifying slug formation as one of the crucial steps towards the design of slug flow reactors/crystallizers. In this study, the performance of slug flow with focus on slug lengths' homogeneity is quantified by evaluating characteristic values of a slug length distribution. For that, an automated image based quantification method is developed. Various inlet conditions, including the air supply and the geometry of mixer, are investigated regarding their influence on slug length distribution. Different mixer materials are compared such that finally an improved setup towards homogeneity of slug flow is defined. (C) 2019 Elsevier Ltd. All rights reserved.