"expand a liquid gas without changing phases" What this means?

The pressure/volume of a liquid just before it is a gas on an isotherm.

Please, describe the process of expending a liquid gas without changing phases. 

• Decrease the pressure while increasing the volume until just before it becomes a gas.  I can send you an isotherm graph if you would like.

Smith, Jason. "Information Transfer Economics." Insights from Non-ideal Information Transfer in Physical Processes. N.p., 01 Jan. 1970. 

Dear Laura, 

Ok, I'am agree with you. we can do this process of expansion by reducing pressure. With this process the liquid will be more cold and a small fraction of liquid can be evaporated. This phenomenon is observed in thermal machines and especially in the air condtioners and refrigerators. 

Best  regards!

I see.  But but fridges and air conditioners have a heat sink.  Joule Thompson effect.  Not here though.

Between you and me Joule Thompson is dead.😉

One issue I can point out is some potential energy may be lost to friction for irreversible isothermal expansion. The work done, however, outweighs work lost. Mathematicallay irreversible isothermal expansion is not viewed as an integral. I guess we are talking an adiabatic process which is how brakes work??? Umm 😐 🤔 Let’s see Pascals Principal. Negative Work is also done for reversible isothermal expansion with no friction loss. Reversible isothermal expansion can be viewed as area under an integral. I can see if I can find a graph and figure in a ppt I put together that illustrates this. Thanks for asking.

This is for compression but expansion is just the reverse essentially. I also point out how the brakes on your car work.  It's called hydraulics and is so clever its my favorite principal that I have learned.  Mind boggling I think. The red rectangle equates to work done on an irreversible compression I guess. The work loss is the remaining work under the integral or the area above the rectangle and below the dashed lines for a irreversible process. for an reversible process,  it is the area under the integral; the rectangle and area in between dashed lines.