At Point A:
x = vapor fraction
1-x = liquid fraction
Point A represents a mixture of saturated liquid and vapor at pressure, PA. The enthapy at A, HA, is a weighted average of the enthalpies of the saturated phases:
This is the same formula used to balance a seesaw.
Hence the name "lever rule." The lever rule can also be used for other properties besides H, like volume.
VA = xVV + (1-x)VL
VA = (0.3)(43400) + (1-0.3)(1.003)
Notice that the saturated liquid's contribution to the volume is almost negligible compared to the contribution of the vapor.
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