Enhancement of Natural Convection in Circular and Triangular Ducts Using Corona Discharge in Air and Nitrogen

A computational eort is undertaken to investigate the eect of corona discharge in air and
nitrogen gas on the enhancement of heat transfer. A corona is a visible luminous emission that
occurs in the vicinity of sharp edges where the electric eld is intense. This phenomenon is
associated with gas ionization and acceleration of ions in strong electric elds, dragging the
gas particles and generating a secondary
ow, known as corona wind. Corona wind may be
employed as an active enhancement technique for heat transfer. Here, corona wind is used to
enhance natural convection inside circular tubes and triangular ducts. The paper describes, not
only the enhancement of heat transfer, but also, the shortcoming and challenges encountered
in the computational modeling of corona discharge. It is shown that the solution of the electric
charge density suers from some degree of irregularity and asymmetry, while an azimuthally
symmetric solution is expected. If this deciency is not rectied, the resulting electric body force
and the predicted
ow eld are not accurate. Two remedies are recommended to improve the
solution, namely, articial viscosity and structured grids. Moreover, the present computations
indicate that, for the Rayleigh number of 3737 and the applied voltage of 8.25-9.5 kV, the corona
discharge enhances heat transfer by 17.9-106.9.