The flows generated by lifting force can be met as in environment as in a number of technical devices. These flows emerge due to volume force which depends on the difference in densities caused by transfer of thermal energy as a result of temperature non-uniformity. Convection flows, which cause heat transfer between surfaces and air, emerge near heated or cooled surfaces. The densities of both liquid and gas depend on temperature. Therefore with the temperature gradient in liquid or gas mass forces are different at different points. This causes motion of gas or liquid which can be defined by direction of the field of mass forces, distribution of temperature in liquid and geometric shape of volume.
