Fluid flow, heat and mass transfer of liquid steel in a trough type tundish were physically and mathematically simulated using a water model. Flow structures were determined through particle image velocimetry (PIV) techniques. Under isothermal conditions fluid flow approaches that of a plug pattern. Non-isothermal conditions provoked long recirculating flows along the vessel and makes the flow to departure form the plug pattern. Buoyancy forces increased fluid velocities close to the bath surface and enhanced convection mass transfer of a tracer injected in the flow and the flotation of solid particles. Measured fluid velocity fields maintained an acceptable good agreement with mathematical simulations under isothermal and non-isothermal conditions. (C) 2003 Elsevier Science Ltd. All rights reserved.