Page 248 - Standard Handbook Of Petroleum & Natural Gas Engineering

Thermodynamics 221

Figure 2-34. Thermodynamic properties of carbon dioxide [21]).

Referring to Figure 2-35 (process diagram), the first law for this steady-state flow
system becomes

M(h,-h,)+Q = (2)(285-315)+60=OBtu/s

Because energy is not created, the device does not violate the first law. Application of
the second law (Equation 2-1 14) yields

60
P, = M(S,-S,)+& = (2)(1.215-1.318)+
Tc (-140 + 460)

= -0.206+0.1875= -0.0185Bt~/s*"R
Because the rate of entropy production is negative, the device violates the second
law and is therefore impossible. Note that the device would be theoretically possible
if the final pressure were specified as 400 psia or less by the inventor. That is, at
P, = 400 psia, T, = 40°F, h, = 290 Btu/lb,, and S, = 1.25 Btu/lbm"R, the entropy
production rate would be

Ps = 2(1.25-1.318)+0.1875 = +0.0515Btu/s*OR

Because entropy is produced in this case, the device is theoretically possible.