Applying the Energy BalanceA rigid, well-insulated tank

Step 1 of 3

We have to determine  the energy transfer by work in stirring the two-phase mixture of ammonia until only saturated vapor at higher pressure remains in the tank.

The energy transfer by work can be determined using the expression,

where,  and account, for the transfer of energy by heat and work
           between the system and its surroundings during the process  

            respectively.

          accounts for change in internal energy between

           the end states.

 Since it is insulated there is no exchange of heat.

Thus,

where,

         is the internal energy of the mixture  before the stirring and it is given by

where, and are the masses of saturated

            liquid and vapour ammonia respectively in kg

            and are the internal energies of saturated

             liquid and vapour ammonia in kJ

and is  internal energy of the mixture after the stirring and it is given by

Now, both the phases of saturated ammonia are at a constant pressure of 40 lbf/in2 or 2.75 bar.

By referring to the table A-14 in the book Fundamentals of Engineering Thermodynamics, 7th Edition. We have the values for and at a constant pressure of 2.75 bar as

m3/kg , 0.4408 m3/kg , 127.26 kJ/kg and 1307.67 kJ/kg