2. Thermodynamic Properties of a Pure Substance
2.6 Key Equations
Pressure, temperature, and specific volume
| Pressure | P=F/A |
| Absolute and gauge pressures | Pgauge = Pabs –Patm |
| Absolute and vacuum pressures | Pvac = Patm –Pabs |
| Density | ρ=m/V |
| Specific volume | v=V/m=1/ρ |
| Conversion of temperatures in Kelvin and Celsius degrees | T(K)=T(∘C)+273.15 |
Energy, enthalpy, and entropy
| Total stored energy in a system | E=U+KE+PE=mu+12 mV2+mgz(V:velocity) |
| Total stored specific energy in a system | e=Em=u+12 V2+gz(V:velocity) |
| Enthalpy | H=U+PV |
| Specific internal energy | u=U/m |
| Specific enthalpy | h=H/m and h=u+Pv |
| Specific entropy | s=S/m |
Saturated liquid-vapour two-phase mixtures
| Quality | x=mgmmix |
| Specific volume | v=vf+x(vg−vf)=(1− x)vf+xvg |
| Specific internal energy | u=uf+x(ug−uf)=(1− x)uf+xug |
| Specific enthalpy | h=hf+x(hg−hf)=(1− x)hf+xhg |
| Specific entropy | s=sf+x(sg−sf)=(1− x)sf+xsg |
Compressed liquid (when the compressed liquid tables are not available)
| Specific volume | v\approx\ v_{f@T} |
| Specific internal energy | u\approx\ u_{f@T} |
| Specific enthalpy | h\approx\ h_{f@T} |
| Specific entropy | s\approx\ s_{f@T} |
