► Approaches that relate the foam drainage rate and bubble terminal velocity are found to be problematic. ► The above problem is mainly due to the inter-bubble normal force in the foam. ► Reported successful applications in the literature are due to faulty algorithms or visual illusions.
The drift-flux analysis of one-dimensional two-phase flow of Wallis (Wallis, G.B., 1969. One-dimensional two-phase flow. McGraw-Hill Book Company, New York.) is utilised for the first time to model the behaviour of pneumatic foam flowing vertically through an expansion or an contraction. It is demonstrated that, although a sudden contraction of flow area decreases the liquid fraction, it does not...
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