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Q.
The liquid flow is most stream lined when
Mechanical Properties of Fluids
Solution:
$$
\text { Critical Velocity }=\frac{\text { coefficient of viscocity } \times \text { Reynold's number }}{\text { Density } \times \text { Diameter }}
$$
For a liquid having large value of coefficient of viscocity, low density and flowing through a narrow tube, the value of critical velocity may be too large to be possessed by the liquid hence, the liquid be always be in streamline flow. Therefore, the liquid flow is most stream lined when liquid of high viscosity and low density flowing through a tube of small radius.