FIG. 8 The results obtained for the water/tetradecane system in a quartz capillary, r=4.45 µm, at t=20°C. (a) B(τ) dependencies obtained at ∆P=0 (curve 1), −233 (curve 2), and −189 mmHg (curve 3). (b) Dependence of flow rate v on pressure drop ∆P.

Fig. 8b shows the experimentally obtained dependencies v(∆P) when the meniscus was shifted within a small portion of the capillary back and forth at various values of the pressure drop ∆P. In contrast to the B(τ) graphs shown in Fig. 8a, when meniscus motion was not limited to a small portion of the capillary, the l1e and l1 values were practically constant. Positive values of v correspond to advancing motion of water, when l1e=23.5 cm and l1=3.5 cm. Negative values of v correspond to receding motion of water, when l1e= 10.13 cm and l1=8.61 cm. From the slope of the graphs (the same in the cases v<0 and v>0), the viscosity of water and of tetradecane in thin capillary was calculated using Eq. (11). Calculated viscosities, 0.994 and 2.35 cPs, are close to bulk values. This shows evidence for the applicability of the Washburn equation in the form of Eq. (11) for viscous flow of immiscible liquids in thin capillaries.