Are you looking for what happens on a micro scale, or on a macro scale?
The "release" of heated liquid under pressure involves passing through some sort of orifice or valve or other pressure-and-flow-control device, in the process of going from the high-pressure place to the low-pressure place. That valve isn't going to open instantaneously and the fluid transfer from one vessel into the other isn't going to happen instantaneously.
You're going to get liquid flashing to vapour (in the form of bubbles) as the liquid passes through the orifice.
The liquid will be propelled out of the high-pressure vessel by pressurised vapour above the surface of the liquid inside the high-pressure vessel.
As the pressure in the high-pressure vessel drops owing to the mass-flow-rate exiting that vessel, you're going to get liquid flashing to vapour at that surface interface. If it happens quickly enough, you're going to get vapour bubbles inside the liquid at nucleation sites.
As the liquid (or two-phase mixture) travels into the orifice, its velocity increases which means its pressure drops (Bernoulli) so the vapour phase will increase and the bubbles themselves will expand as both the pressure drops and more liquid flashes to vapour at the liquid-vapour interface within each bubble.
All of the above heat-transfer and fluid-transfer considerations apply when you look at all of these phenomena at a micro scale.
You've got transient conditions, two-phase flow, viscous flow, phase-change, heat transfer, and fluid mixing all happening at the same time.
Good luck!
