Use the attached PH diagram for propane to answer the follow

Use the attached P-H diagram for propane to answer the following problems. Propane at 10 MPa and 110 degree C is throttled to 1 MPa. Determine the final temperature. The throttling process is isenthalpic (delta H = 0). Some of the propane condenses. Estimate the phase fraction.

Solution

The attached ph diagram resolution is less. So the values cannot be read clearly. But i am explaining the procedure to find the answer.

It is given that initially Propane is at 10 Mpa and 110^o C. Since yaxis indicates pressure, locate 10Mpa in yaxis, then move horizontally till u meet the Temperature =110^oC line. This is our initial point. (Point A) Now it is throttled to 1 MPa.

Throttling is an isenthalpic process, That means the enthalpy remains same durijng the process. Since x axis is enthalpy , the enthalpy remains constant when we move vertically. So move vertically from A to point B which is at a pressure of 1 MPa. ( 1 MPa can be seen from the Yaxis)

This is our final position (Point B) . See from the graph what is the temperature at this point. Let this temperature be T_b

The point B will come inside the dome. The enthalpy at B can be obtained from graph by lookin at the xcoordinate of B. To find the phase fraction of propane use the equation,

h= h_f + x(h_g-h_f)

where h is the enthalpy at point B, h_f is the enthalpy of saturated liquid at temperature T_b, h_g is the temperature of saturated vapour at T_{b .} x is the phasefraction.

Since h , h_f and  h_g are known from the graph , the phase fraction x can be calculated ffrom the equation

  h= h_f + x(h_g-h_f)