Work done by expansion of liquidfied natural gas to atmosphere

[casts_by_fly]

Hi All,

Been try at this for a week now and I know I'm missing something. I'm too far out of university to remember how to do it, but just close enough to know that I should remember.

Anyway, I have a steel can containing a mixture of liquidfied hydrocarbon gasses (butane/i-butane/propane) at 40 psi internal pressure. Most of the hydrocarbons are liquified, though there is some headspace. Additionally there is another fluid in the container that is being expelled by the propellant (they are mixed, but not miscible if it matters). They are released through a valve to the atmosphere in short bursts with time between the bursts for the can to return to room temperature (nominally 300K). How much work does the compressed hydrocarbon do on the other liquid when released to the atmostphere? If I were to replace the propellant with a battery, how much energy would the battery need to hold to be able to get the same work into the other liquid?

I feel like it is an expansion problem, but can't decide between isothermal (because both the internal gas and the released gas return to room temp) or adiabatic (because the expansion is rapid and there is immediate cooling from both the expansion of the gas and the evaporation of liquid to gas in the container). Neither seems to fit though.

I tried to work it out from a kinetics standpoint by figuring out the velocity of the ejecta and the mass ejected, but the number was very low for what I was expecting.

Any help in setting this up?

Thanks,
Rick

 

[RonL]

Hi All,

Been try at this for a week now and I know I'm missing something. I'm too far out of university to remember how to do it, but just close enough to know that I should remember.

Anyway, I have a steel can containing a mixture of liquidfied hydrocarbon gasses (butane/i-butane/propane) at 40 psi internal pressure. Most of the hydrocarbons are liquified, though there is some headspace. Additionally there is another fluid in the container that is being expelled by the propellant (they are mixed, but not miscible if it matters). They are released through a valve to the atmosphere in short bursts with time between the bursts for the can to return to room temperature (nominally 300K). How much work does the compressed hydrocarbon do on the other liquid when released to the atmostphere? If I were to replace the propellant with a battery, how much energy would the battery need to hold to be able to get the same work into the other liquid?

I feel like it is an expansion problem, but can't decide between isothermal (because both the internal gas and the released gas return to room temp) or adiabatic (because the expansion is rapid and there is immediate cooling from both the expansion of the gas and the evaporation of liquid to gas in the container). Neither seems to fit though.

I tried to work it out from a kinetics standpoint by figuring out the velocity of the ejecta and the mass ejected, but the number was very low for what I was expecting.

Any help in setting this up?

Thanks,
Rick

I'm a little surprised someone has not responded to this, It sounds a lot like some things I have brought up, my math sucks so I won't be of much help, but there are some very sharp people here, just hope I have not worn them down too much.

Bump!

RonL