A converging nozzle increases the flow velocity and decreases the static pressure as per Bernoulli equation. Can a liquid flow through a converging nozzle result in static pressure below the vapour pressure of liquid and evaporation of liquid?
Hello Amit,
If you'd like to model a nozzle and perform simulations, you absolutely can do it by using ANSYS Fluent or CFX software. You need a cavitation model. Most common one is the Rayleigh-Plesset. I suggest reviewing the Rayleigh Plesset equation and do some research on this topic. Note that Bernoulli is no longer applicable once a phase change occurs. Also bubble dynamics and vaporization is different for each fluid. Hope this helps.
Dear Dr Karakas,
I am not interested in simulation of two phase flow through the nozzle. I am only interested in knowing whether the liquid can be vaporised by decreasing the area of the nozzle sufficiently or in other words whether the change of phase depends on static pressure or total pressure.
Hello Amit,
The answer is yes, if the static pressure drops below the saturation pressure of the fluid, the vaporization will occur.
This means that you can not flow a liquid above a particular flow rate through a pipe of a given area without vaporising it.
Is it correct, Dr Karakas?
Amit,
Not necessarily. If your inlet pressure is high with low temperature (fluid is overly subcooled) or the pressure drop across of the nozzle is not too high, cavitation (vaporization) won't occur. Fluid properties, geometry of the nozzle (area reduction from inlet to outlet), fluid velocity (mass flow rate), inlet conditions (Pressure and Temperature) all impact whether or not cavitation will occur.
But we will always have a high value of flow rate through a pipe (not nozzle) for any inlet condition beyond which vaporisation will occur.
For a pump, there would be a minimum pipe area for a fixed flow rate below which vaporisation will occur.
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