Particle image velocimetry (PIV) was applied to characterize the flow field in a vertically oriented cold wall reactor, which is used for the catalytic chemical vapor deposition (CCVD) of carbon nanotubes (CNTs). Quantitative information about the radial and axial profiles of the velocity components has been obtained and on their basis, actual volumetric flow rates, gas temperatures, the jet Reynolds number, the working regime as well as the residence time curves and the minimum impingement time of the feed flow into the substrate surface at different operation conditions were estimated. The reliability of the PIV measurements has been assessed with respect to the effect of the thermophoretic force, being partially compromised at defined regions attached to the substrate surface. (C) 2012 Elsevier B.V. All rights reserved.