# What is the time constant to evaporate a liquid

1. Apr 5, 2013

### 246ohms

I have a liquid that is stored at pressure. This liquid is then released to a lower pressure where it should become a gas. The problem is how long does it take for the liquid to turn to gas.

There must be some delay - even a very small one - but how to calculate it.

Example - a jet of liquid butane is sprayed into the atmosphere, according to a simple Joule Thompson expansion it should all turn to gas instantly. But it takes time, does anyone know how to determine the time? If there is some momentum in the process what are the controlling factors and are there any constants one can use in an equation.

Another way to look at this is how far downstream of the jet of butane will it be gas, 1mm, 100mm - depends on the exit velocity I suppose.

Any ideas welcomed.

246

2. Apr 6, 2013

### akdude1

I'm not completely sure but I think it depends of the liquid and the exit velocity, pressure difference so on...

3. Apr 6, 2013

### 246ohms

Some basic numbers, liquid at 140C and 32 bara is sqirted from nozzle into the atmosphere so around 1 bara. The exit temperature after the process stabalises is around 18C. This conditins should be all gas and superheated by about 14C but in the expansion process some liquid becomes supercooled and it takes a small amount of time to evaporate or flash. The process of just expanding the liquid should turn it all to gas instantly.

But liquid is still present

If the process were differant say with the liquid at 30C then part of the liquid would remain in state until sufficient heat is absorbed to evaporate it, this not the scenario we are looking at.