Thermodynamics

cen84959_ch03.qxd 4/11/05 12:23 PM Page 132132 | ThermodynamicsP, kPa160v f = 0.0007437R-134aP = 160 kPam = 4 kgv g = 0.12348T = 15.60Ch f = 31.21 h g = 241.11 h, kJ/kgFIGURE 3–39Schematic and P-v diagram forExample 3–5.v, m 3 /kgbe determined by comparing a suitable property to the saturated liquid andsaturated vapor values. From the information given, we can determine thespecific volume:At 160 kPa, we readv V m0.080 m34 kg(Table A–12)Obviously, v f v v g , and, the refrigerant is in the saturated mixtureregion. Thus, the temperature must be the saturation temperature at thespecified pressure:(b) Quality can be determined fromv f 0.0007437 m 3 >kgv g 0.12348 m 3 >kg 0.02 m 3 >kgT T sat @ 160 kPa 15.60°Cx v v f 0.02 0.0007437v fg 0.12348 0.0007437 0.157(c) At 160 kPa, we also read from Table A–12 that h f 31.21 kJ/kg and h fg 209.90 kJ/kg. Then,h h f xh fgv u hT,°C m 3 /kg kJ/kg kJ/kgSat.100150…1300Sat.200250P = 0.1 MPa (99.61°C)1.69411.69591.9367…7.2605P = 0.5 MPa (151.83°C)0.374830.425030.474432505.62506.22582.9…4687.22560.72643.32723.8FIGURE 3–40A partial listing of Table A–6.2675.02675.82776.6…5413.32748.12855.82961.0 64.2 kJ>kg(d) The mass of the vapor is 31.21 kJ>kg 10.1572 1209.90 kJ>kg2m g xm t 10.1572 14 kg2 0.628 kgand the volume occupied by the vapor phase isV g m g v g 10.628 kg210.12348 m 3 >kg2 0.0775 m 3 1or 77.5 L2The rest of the volume (2.5 L) is occupied by the liquid.Property tables are also available for saturated solid–vapor mixtures.Properties of saturated ice–water vapor mixtures, for example, are listed inTable A–8. Saturated solid–vapor mixtures can be handled just as saturatedliquid–vapor mixtures.2 Superheated VaporIn the region to the right of the saturated vapor line and at temperaturesabove the critical point temperature, a substance exists as superheated vapor.Since the superheated region is a single-phase region (vapor phase only),temperature and pressure are no longer dependent properties and they canconveniently be used as the two independent properties in the tables. Theformat of the superheated vapor tables is illustrated in Fig. 3–40.In these tables, the properties are listed against temperature for selectedpressures starting with the saturated vapor data. The saturation temperatureis given in parentheses following the pressure value.