A vapor is compressed in a frictionless piston-cylinder such that the volume changes from 100 to 10 in3 . The initial pressure is 50 psia and temperature is held constant at 100°F. Calculate the work in ft lbf. The vapor can be assumed to be an ideal gas.

Respuesta :

Explanation:

The given data is as follows.

         Initial volume ([tex]V_{1}[/tex]) = 100 [tex]in^{3}[/tex]

         Final volume ([tex]V_{2}[/tex]) = 10 [tex]in^{3}[/tex]

         Initial pressure ([tex]P_{1}[/tex]) = 50 psia = 50 [tex]\frac{pounds}{in^{2}}[/tex]

          Temperature = [tex]100^{o}F[/tex]

So, we assume that vapors are also ideal gas.

Hence, the work done for ideal gas will be calculated as follows.

                 W = [tex]P \int dV[/tex]

Since, it is given that the temperature is constant so, it is an isothermal process.

Therefore, work done for isothermal process is as follows.

                  W = [tex]P_{1}V_{1} ln (\frac{V_{2}}{V_{1}})[/tex]

Putting the values into the above formula as follows.

                W = [tex]P_{1}V_{1} ln (\frac{V_{2}}{V_{1}})[/tex]    

                     = [tex]50 pounds/in^{2} \times 100 in^{3} \times ln (\frac{10}{100})[/tex]

                     = -11512.925 lbf-in

As there are 12 inch present in 1 ft. So, converting lbf-in into lbf-ft as follows.

                W = [tex]\frac{-11512.925}{12} lbf-ft[/tex]

                     = -959.41 lbf-ft

The negative sign means work is supplied.

Thus, we can conclude that the work done is -959.41 lbf-ft.