Using a cold hydraulic facility, we determine the convective mass transfer coefficients : local and global, from the surface of a flat plate segment impinging by axisymetrical circular jets coming through inline holes and pipe injectors from a plenum facing the plate. After the impact, the fluid is extracted from the confined space located between the plate and the plenum by means of exhausts whose influence we intend to examine : number and location. We show that transfers are increased by 5% when the extraction occurs by four exhausts and not by only one. As for the exhaust location (height), it clearly appears that the parameter is more significant since the local and global mass transfer increase can reach 15% when we move away the exhausts from the injection plane of the plenum. The comparison of the two configurations, with holes and pipe injectors, points out that the second one has an advantage over the first one which can be materialized by a mass transfer increase of 17%. A dynamic wall study, based on measurements of local friction and fluid direction gives a realistic view of flow structures and allows us to explain in a satisfying way the transfer evolution obtained.