# Evaporating Water with a Boiler Type Vessel

#### tommyb1982

I am attempting to evaporate water to the atmosphere with a boiler type vessel. Normal operating pressure of the vessel would be 5 psig. How much water could potentially be evaporated? Also, what issues come to mind with this concept?

#### Woody

If you are evaporating to Atmosphere, there is no limit to the amount of water that could be evaporated.
However if you are limited to 5 psi over atmospheric, there will be a limit to how fast you can evaporate the water.

The actual limit will depend on lots of details you have not supplied;

The energy rate available from your source of heat
The amount of Water,
The size of the Vent from your Boiler to Atmosphere,
etc...

#### benit13

You can estimate the rate of evaporation using the equation for latent heat transfer:

$$\displaystyle \dot{m} = \frac{\dot{Q}}{h_{liq-vap}}$$

where m is the evaporation rate (in kg/s), Q is the rated power output of your boiler (in W) and $$\displaystyle h_{liq-vap}$$ is the specific enthalpy of liquid-to-vapour phase change of water.

At room temperature and pressure, $$\displaystyle h_{liq-vap} = 2265$$ kJ/kg, but it's actually a function of temperature and pressure, so it's probably a little bit lower than this. You should recalculate this constant at the boiling point of water at that pressure (which I think is about 108 deg. C at 134 kPa).