The less accurate equation covers the wider range −8 ☌? t?150 ☌ with the more limited accuracy of ☐.2%. The more accurate equation covers the range 0 ☌? t ?40 ☌ with an uncertainty of ☐.05%. The viscosity ratios have been correlated with the aid of two empirical equations. The ratios are used to generate absolute values with the aid of the standard NBS datum μ=1002.0 μPa s at 20 ☌. Fluids that don’t produce a constant are called Non-Newtonian fluids. Fluids that produce a viscosity constant are known as Newtonian fluids. Index Tables Reference Viscopedia Data from. The viscosity of water decreases smoothly from the freezing point while the density remains essentially constant except for the small maximum in density near 4C. In cgs units the unit is called the centistoke. Standard values of the ratio of viscosity at a temperature T to its value at 20 ☌ have been derived from the re‐analyzed data because the uncertainty of this ratio is an order of magnitude smaller than that of the absolute values. The units of dynamic viscosity are Ns/m 2 (Ns m -2 ), or mPa.s, or the SI unit Poiseuille (where 1 centi-Poiseuille 1 mPa.s for water at 20 o C). The kinematic viscosity is the dynamic viscosity divided by the density of the fluid. The latter are smaller than those embodied in the most recent International Formulation. The new analysis eliminates possible systematic errors and permits the establishment of realistic error bounds for water in its role as a standard reference substance for viscosity. This is done in terms of a new, theoretically‐based equation for the operation of a capillary viscometer rather than in terms of semi‐empirical equations used by the original authors.
The paper re‐analyzes the results of earlier, very precise measurements of the viscosity of water at essentially atmospheric pressure.
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