Experimental techniques continued flow rate measurement

In a third paper by the Bernard and Holm group, visual studies (in a sand-packed capillary tube, 0.25 mm in diameter) and gas tracer measurements were also used to elucidate flow mechanisms ( ). Bubbles were observed to break into smaller bubbles at the exits of constrictions between sand grains (see Capillary Snap-Off, below), and bubbles tended to coalesce in pore spaces as they entered constrictions (see Coalescence, below). It was concluded that liquid moved through the film network between bubbles, that gas moved by a dynamic process of the breakage and formation of films (lamellae) between bubbles, that there were no continuous gas path, and that flow rates were a function of the number and strength of the aqueous films between the bubbles. As in the previous studies (it is important to note), flow measurements were made at low pressures with a steady-state method. Thus, the dispersions studied were true foams (dispersions of a gaseous phase in a liquid phase), and the experimental technique avoided long-lived transient effects, which are produced by nonsteady-state flow and are extremely difficult to interpret. 

Finally, a mention to the reverse-flow (RF) GC technique, which is a variation of IGC where the probe molecule is injected at a middle point of the column containing the adsorbent as stationary phase, and the direction of carrier gas flow is reversed from time to time. This creates extra chromatographic peaks on the continuous signal. This technique allows to measured different physicochemical quantities, including rate constant of surface and gaseous reactions, and experimental isotherms [54, 55]. 

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