Thermal drive can appear in miscellaneous force fields, for example, centrifugal, surface tension and electromagnetic fields as well as in gravitational fields. The origin of the flow and the consequent effects including the heat transfer enhancement, environmental pollution and increase in isotope separation efficiency are emphasized. The physical mechanisms of different thermal instability problems are presented. The critical criterions of instability obtained in terms of various dynamic or thermodynamic approaches are very important for material processing, nuclear safety, drag reduction and thermal pollution of water sources.