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[en] The present work reports an numerical study of a turbulent natural convection flow resulting from the interaction of a thermal plume with a thermosiphon flow. in this paper we expose results of the numerical study related to the heating source position. We study particularly the effects of the vertical source canal spacing on the flow structure. A comparative study is presented for different configurations. This study is based on CFD fluent code results concerning the average field. These results are compared with experimental results
[en] Highlights: • Development of an analytical model for assessing the well-mixing length of a tracer in a duct airflow. • Validation on data from in situ experiments. • Model simplification for proposing correlations more suitable for the industrial issue. - Abstract: The aim of this study is to propose an analytical model for assessing the well-mixing length of a tracer in a ventilation duct. The first part of the article is devoted to describe an experimental bench developed for validating the proposed model. This bench allows to follow the evolution of a tracer injected at a source point in the center of a duct by using an original optical measurement technique. In a second part, an analytical model for the spatial evolution of a tracer concentration in a circular duct is developed, taking into account an eddy viscosity model. The difficulty for applying this model to industrial cases led us to propose a simplified version that can be used for a non-dimensional distance greater than 20 diameters. The latter was then inverted in order to access to two criteria: the coefficient of variation in the duct section and the difference between the local measured concentration and the expected homogeneous concentration. Each one has its interest depending on whether a global information on the duct section or a local information (on the axis for example) at a given distance is required.