Standard viscometers and kinematic viscosity correlation: Kinematic viscosity of liquids, when obtained via an empirical conversion equation from measured efflux time, is characteristically determined using which viscometer?

Introduction / Context:
Several standardized cup viscometers measure efflux time of a fixed liquid volume through an orifice. Empirical equations then convert this “seconds” reading into kinematic viscosity (commonly in centistokes), enabling process and quality control for oils and fuels.

Given Data / Assumptions:

• Efflux-time measurement at controlled temperature.
• Empirical calibration linking time and kinematic viscosity.
• Newtonian fluids in the applicable range.

Concept / Approach:

The Saybolt universal viscometer (SUV) reports Saybolt seconds (SSU). ASTM correlations relate SSU to kinematic viscosity ν (cSt) using a formula of the form ν = a t − b / t over a defined range. Redwood and Engler also use time scales, but the widely taught textbook “equation” mapping time to ν in cSt is associated with the Saybolt universal method.

Step-by-Step Solution:

Verification / Alternative check:

Standards (e.g., ASTM D445/D446 and older Saybolt methods) present tables/curves consistent with the above conversion.

Why Other Options Are Wrong:

Redwood and Engler scales exist but are not the classical source of the cited ν–t equation in many syllabi; “None” contradicts common lab practice; Ford cups are used mainly for paints with different correlations.

Common Pitfalls:

Interchanging absolute and kinematic viscosity; ignoring temperature control that strongly affects ν.

Final Answer:

Saybolt universal viscometer