  Spark plasma discharges induce vortex rings and a hot gas kernel. We develop
a model to describe the late stage of the spark induced flow and the role of
the vortex rings in the entrainment of cold ambient gas and the cooling of the
hot gas kernel. The model is tested in a plasma-induced flow, using density and
velocity measurements obtained from simultaneous stereoscopic particle image
velocimetry (S-PIV) and background oriented schlieren (BOS). We show that the
spatial distribution of the hot kernel follows the motion of the vortex rings,
whose radial expansion increases with the electrical energy deposited during
the spark discharge. The vortex ring cooling model establishes that entrainment
in the convective cooling regime is induced by the vortex rings and governs the
cooling of the hot gas kernel, and the rate of cooling increases with the
electrical energy deposited during the spark discharge.
