(423c) Coalescence Factor: A Dimensionless Group to Predict the Coalescence of Dynamic Foams

Much research has investigated the stability of foams, however, predicting dynamic foam stability remain elusive. Building on the law of conservation of momentum and using dimension analysis (Buckingham PI Theory), a dimensionless group, coalescence factor C_f, was defined to indicate the onset of coalescence. Coalescence factor describes the balance between dynamic surface tension and the applied deformation force.

Experiments show that changes of air flow-rates, orifice diameter, surfactant concentration, and type of surfactant (SDS and Teepol) affect the coalescence factor. Figure 1 shows an example of the coalescence factor for different orifice diameters (5.0cm, 1.5cm, and 0.3cm) at the CMC (critical micelle concentration) of Teepol with varying air flowrate. Close agreement was found between the onset of coalescence, determined by image analysis and ERT and a coalescence factor greater than unity. The relationship between coalescence factor and N_c, the number of coalescence events, also showed a critical point at coalescence factor >1.0. Through various experiments, it has been shown that coalescence factor can predict the coalescence of dynamic foams.