The critical temperature of methane is 191 k or 82c

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Unformatted text preview: mmonly used in various cryogenic applications. The critical temperature of methane is 191 K (or 82°C), and thus methane must be maintained below 191 K to keep it in liquid phase. The properties of liquid methane at various temperatures and pressures are given in Table 7–1. Determine the entropy change of liquid methane as it undergoes a process from 110 K and 1 MPa to 120 K and 5 MPa (a) using actual data for methane and (b) approximating liquid methane as an incompressible substance. What is the error involved in the latter case? P2 = 5 MPa T2 = 120 K Heat SOLUTION The entropy change of methane during a process is to be determined using actual data and assuming it to be incompressible. Analysis (a) We consider a unit mass of liquid methane (Fig. 7–29). The entropies of the methane at the initial and final states are State 1: P1 T1 1 MPa 110 K s1 Cp1 4.875 kJ/kg · K 3.471 kJ/kg · K State 2: Methane pump P2 T2 5 MPa 120 K s2 Cp2 5.145 kJ/kg · K 3.486 kJ/kg · K P1 = 1 MPa T1 = 110 K FIGURE 7–29 S...
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