You are asked to measure the viscosity of an emulsion, so you use a tube flow viscometer similar to that illustrated in Figure 3.4, with the container open to the atmosphere. The length of the tube is $10 \mathrm{~cm}$, its diameter is $2 \mathrm{~mm}$, and the diameter of the container is $3 \mathrm{in}$. When the level of the sample is $10 \mathrm{~cm}$ above the bottom of the container, the emulsion drains through the tube at a rate of $12 \mathrm{~cm}^{3} / \mathrm{min}$, and when the level is $20 \mathrm{~cm}$, the flow rate is $30 \mathrm{~cm}^{3} / \mathrm{min}$. The emulsion density is $1.3 \mathrm{~g} / \mathrm{cm}^{3}$.

(a) What can you tell from the data about the viscous properties of the emulsion?

(b) Determine the viscosity of the emulsion.

(c) What would the sample viscosity be at a shear rate of $500 \mathrm{~s}^{-1}$ ?

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Shear stress Pseudoplastic Bingham plastic Structural Shear rate Newtonian Dilatant FIGURE 3.4 Shear stress versus shear rate for various types of fluid behavior.