Flow pattern and pressure loss of foam flow in horizontal pipes: Role of surfactant type and dynamic surface tension

In this work, the flow patterns and pressure losses of 12 kinds of gas–liquid systems (two different surfactants were selected, and their concentrations were changed in an aqueous solution, which served as the test liquid) in horizontal pipes were studied. To explore the potential mechanisms influencing flow patterns, the equilibrium and dynamic surface tensions of surfactant solutions were surveyed, and the aggregate morphologies of surfactants were observed by using cryo-TEM. Based on the experimental findings, a generalized flow pattern map was proposed. Furthermore, the relationship between the pressure loss and the flow pattern of the foam flow was investigated. The results revealed two types of foam flow: full-foaming flow (FFO) and foam flow containing liquid (FCL). Each type of flow had three subflow patterns. The formation of different flow patterns is closely related to the ability of surfactant molecules to adsorb on bubbles and reduce surface tension in a short period, which is affected by aggregates and their structures. The product of the Weber and Bond numbers was determined to be the appropriate combination of non-dimensional numbers for the proposed generalised flow pattern map. Moreover, above a critical Bond number of the gas–liquid system, FFO cannot be formed. Finally, the flow pattern can be effectively separated according to pressure drop data.