This paper reports the results of a numerical study on the transient removal of a contaminant from a two!dimensional enclosure with one inlet and one outlet[ The in~uence of buoyancy forces due to thermal and concentration gradients\ contaminant di}usivity\ inlet velocity and outlet disposition over the cleaning!time are studied[ The governing equations of the laminar ~ow "continuity\ momentum\ energy and contaminant concentration# are solved by means of the SIMPLEC algorithm[ Several simulations of the same test case have been made\ using two numerical schemes ] PLDS and SMART\ in order to determinate which one provides better performances[ For isothermal situations\ the time required to remove the contaminant is studied parametrically as a function of the outlet position and the governing dimensionless numbers "Reynolds number\ Schmidt number and solutal Rayleigh number#\ while the e}ect of horizontal temperature di}erences is studied in several situations in which it plays an important role[ Buoyancy forces are found to have a strong in~uence over the ~ows and\ in consequence\ over the cleaning times[ Þ 0887 Published by Elsevier Science Ltd[ All rights reserved[ Nomenclature