Can someone tell me where to start with this question?

Question

Consider two tanks, A and B, connected by a valve. Each has a volume of 200L, and tank A has R-12 at 25 degrees C, 10% liquid and 90% vapor by volume, while tank B is evacuated. The valve is now opened and saturated vapor flows from A to B until the pressure in B has reached that in A, at which point the valve is closed. This process occurs slowly such that all temperatures stay at 25 degrees C throughout the process. How much has the quality changed in tank A during the process?

How do I set this up?

Answer 1

Mesab,

How do you determine "m", the initial mass of the gas in tank "A"...

You say it's given- but it's not.

'Seems to me you'd need vapor-pressure vs. temperature data for R-12-- and/or the densities of the liquid and gas phases as a function of temperature and pressure...

Added later:

Thanks for the help from "Left Field" :)

I talk about density- you talk about its reciprocal, specific volume.

Either way, we need the equivalent of a steam table or Mollier chart for R-12.

The question was "where to start"...

What's that R-12 Mollier-style chart called?

Answer 2

If you know the temperature of the R-12 and that it is saturated, you should be able to look on a chart to find the specific volume of the liquid and the specific volume of the gas. Knowing the volume of one tank to be 200L, I believe you could come up with the total mass in the system.

In the final state, the volume has doubled, and I would assume that all vapor has transferred to tank B before the valve is closed again. Knowing the specific volume of the saturated vapor, you should be able to calculate how much mass has been "removed". Knowing the new amount of mass in tank A, 200L = (mass liquid)x(specific volume liquid)+(total mass - mass liquid)x(specific volume gas). Solve for mass liquid.

Answer 3

PV=mRT (general gas law), R is the freon R-12 gas Constance.
m is the mass, P, V,T are pressure volume and temperature respectively.

The pressure in tankB is P=mRT/V , the value of rhs of the eq. is given so P will be determined. This P is given to equal the pressure in tankA. use the general gas law eq. again and find V of the gas in tankA. That will give how much liquid has been evaporated during the constant temperature flow. This in turn tells about the quality. Good luck. m=PV/RT. And originally for isothermal expansion (PV) in tankA=(PV)in tankB+tankA this how you get P Then you get m.
I like to mention here at the end of the process and knowing your final pressure and volume you go to the psychometric chart and obtain your quality o f R-12. (If you know the density of R-12 and the volume m=density*volume)