Verification of the method of reconstructing convective velocity fields on the basis of temperature fields in vertical, differential and equally heated, open and closed channels

•A method of reconstructing velocity fields solely on the basis of a known temperature in free convection heat transfer is proposed.•Theoretical considerations and numerical simulation tests are presented.•Two published cases were taken into consideration to experimentally validate the correctness of the method.•The method provides new opportunities for thermal imaging cameras such as the visualisation of air velocity fields.