How does water temperature affect viscosity?

Answer 1

Viscosity is a measure of the resistance of a fluid to being deformed either shear stress or extensional stress. It is commonly perceived as "thickness", or resistance to flow. Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. Thus, water is "thin", having a lower viscosity, while vegetable oil is "thick" having a higher viscosity. All real fluids (except superfluids) have some resistance to stress, but a fluid which has no resistance to shear stress is known as an ideal fluid or inviscid fluid. The study of viscosity is known as rheology.

Effect of temperature on the viscosity of a gas:
Sutherland's formula can be used to derive the dynamic viscosity of an ideal gas as a function of the temperature:

η=η0 ((T0+C)/(T+C))(T/T0)^3/2

η = viscosity in (Pa·s) at input temperature T
η0 = reference viscosity in (Pa·s) at reference temperature T0
T = input temperature in kelvin
T0 = reference temperature in kelvin
C = Sutherland's constant for the gasous material in question
Valid for temperatures between 0 < T < 555 K with an error due to pressure less than 10% below 3.45 MPa

Sutherland's constant and reference temperature for some gases
Gas C[K] T0[K] η0[10-6 Pa s]

air 120 291.15 18.27
nitrogen 111 300.55 17.81
oxygen 127 292.25 20.18
co2 240 293.15 14.8
CO 118 288.15 17.2
hydrogen72 293.85 8.76
ammonia370 293.15 9.82
SO2 416 293.65 12.54

Answer 2

As water temperature increases, the viscosity of water decreases. This is because higher temperatures cause water molecules to move more freely and quickly, reducing their resistance to flow. Conversely, lower temperatures lead to increased viscosity as water molecules slow down and become more densely packed.