On P-T diagram, by comparing the slope of saturated Steam in adiabatic process with the slope of gas-liquid equilibrium curve, the corresponding single-phase state of the saturated steam after expantion is determined. 在p-T图上,通过饱和蒸汽作绝热膨胀时的斜率与气液平衡曲线的斜率的大小比较,来判断饱和蒸汽经绝热膨胀后对应的单相态。