We experimentally examined thermohydraulic characteristics of liquid phase when an atmospheric-pressure argon arc-discharge is injected into water. We find that the water flow velocity induced by the arc-jet injection becomes faster as the discharge current increases. It is considered that this is partly because the arc-flow velocity of the plume became increased due to larger enthalpy. It is also found that the maximum of Nusselt number has its maximum at about 8000 K. It is considered that the surface recombination rate coefficient becomes maximum at about this temperature, and the recombination energy is efficiently used for heating the liquid phase.