Page 49 - Advanced Thermodynamics for Engineers, Second Edition
P. 49

2.15 PROBLEMS        33




                     Using the following data, show the pressure at which graphite and diamond are in


                     equilibrium at a temperature of 25 C. The data for these two phases of carbon at 25 C and
                     1 bar are given in the following table:
                                                       Graphite             Diamond
                         Specific Gibbs energy, g/(kJ/kg)  0                 269
                                        3
                         Specific volume, v/(m /kg)     0.446   10  3        0.285   10  3
                                                 1
                         Isothermal compressibility, k/(bar )  2.96   10  6  0.158   10  6

                     It may be assumed that the variation of kv with pressure is negligible, and the lower value of the
                     solution may be used.
                     [17,990 bar]
               P2.15 Van der Waals equation for water is given by

                                                0:004619T    0:017034
                                           p ¼
                                               v   0:0016891    v 2
                                                              3
                     where p ¼ pressure (bar), v ¼ specific volume (m /kmol), T ¼ temperature (K).




                     Draw a p–v diagram for the following isotherms: 250 C, 270 C, 300 C, 330 C, 374 C,


                     390 C.
                     Compare the computed specific volumes with Steam Table values and explain the differences
                     in terms of the value of p c v c =<T c :
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