  The thermal expansion of a fluid combined with a temperature-dependent
viscosity introduces nonlinearities in the Navier-Stokes equations unrelated to
the convective momentum current. The couplings generate the possibility for net
fluid flow at the microscale controlled by external heating. This novel
thermo-mechanical effect is investigated for a thin fluid chamber by a
numerical solution of the Navier-Stokes equations and analytically by a
perturbation expansion. A demonstration experiment confirms the basic mechanism
and quantitatively validates our theoretical analysis.
