SURFACE FORCES AND CAPILLARY PRESSURE
Surface forces and capilliary pressure Surface Tension and Interfacial Tensions I n dealing with multiphase systems, it is necessary to consider the effect of the forces acting at the interface when two immiscible fluids are in contact. When these two fluids are liquid and gas, the term "surface tension" is used to describe the forces acting on the interface. When the interface is between two liquids, the acting forces are called interfacial tensions. Consider the two immiscible fluids, air (or gas), and water (or oil), as shown schematically in Figure.7-1 A liquid molecule, which is remote from the interface, is surrounded by other liquid molecules, thus having a resulting net attractive force on the molecule of zero. A molecule at the interface, however, has a force acting on it from the air (gas) molecules lying immediately above the interface and from liquid molecules lying below the interface. Resulting forces are unbalanced and give rise to surface tension. The u...