>>10874716If you want room temperature water to flash steam then I am not sure you even need a pipe with the pressure differential required. Anyway what you want is a series of coupled differential equations.
One to describe the changing heat of vaporization due to pressure drop. Another one to describe the changing boiling point due to pressure drop. And a third one describing heat transfer. The heat transfer equation is composed of the energy leaving the "liquid" part of the system cooling what remains, and the heat coming in from some external source. You need to find the initial enthalpy of the water you are working at (steam tables, their basis 0K, I think) and then calculate how much of that enthalpy gets converted into steam due to the pressure effects.
