Charge injection enhanced natural convection heat transfer in horizontal concentric annuli filled with a dielectric liquid

•Natural convection heat transfer is enhanced by imposing a DC electric field.•Existence of a threshold of the electric driving parameter.•The independence of heat transfer rate on Ra for high electric driving parameter.•Numerical validation for the independence of heat transfer on Ra.

The natural convection heat transfer in a highly insulating liquid contained between two horizontal concentric cylinders is shown by two-dimensional numerical simulations to be noticeably enhanced by imposing a direct current electric field. This augmentation of heat transfer is due to the radial flow motion induced by unipolar injection of ions. It is found that there exists a threshold of the electric driving parameter T, above which the heat transfer enhancement due to the electric effect becomes significant. For relatively small T values, the mean Nusselt numbers are closely related to the flow pattern and the Rayleigh number Ra. In addition, for sufficiently high T values, the flow is fully dominated by the Coulomb force, and thus the heat transfer rate no long depends on Ra.