Relative viscosity and absolute viscosity are two concepts that describe the viscosity of a fluid. There are some differences between them.

Relative viscosity and absolute viscosity difference

Relative viscosity:

Relative viscosity is the viscosity of a fluid compared to a reference fluid (usually a solvent) at a given temperature. It is determined by measuring the flow properties of the fluid and the reference fluid. Relative viscosity is a dimensionless value that indicates how viscous the fluid increases relative to the reference fluid. Relative viscosity can be calculated by measuring the movement time or velocity of the fluid.

Relative viscosity and absolute viscosity difference

Absolute viscosity:

Absolute viscosity refers to the actual viscosity of a fluid, also known as dynamic viscosity or dynamic viscosity. It is determined by measuring the volume (flow rate) that a fluid passes through per unit area per unit time. Absolute viscosity is a physical quantity with units, usually used in units of PASCAL seconds (Pa·s) or millipa · second (mPa·s).

Absolute viscosity is an inherent property of fluid and can be directly used in the calculation and analysis of fluid dynamics. Relative viscosity is a comparative value with respect to a reference fluid and is often used to measure liquid mixtures and compare liquid properties.

The North and South tides remind you that the relationship between relative and absolute viscosity can be expressed by a constant called the constant of proportionality or the conversion factor between relative and absolute viscosity. This conversion factor depends on the reference fluid and temperature conditions used. To sum up, the relative viscosity is the comparison of the viscosity of the fluid with respect to the reference fluid, while the absolute viscosity is the physical quantity of the actual viscosity of the fluid.