Question

What is the effect of pressure on viscosity of liquid?

Answer 1

Let us get some idea about the viscosity. The quantity that defines a fluid's resistance to flow is known as viscosity. Fluids resist both the relative motion of submerged particles and the motion of layers of different velocities within them.

Complete answer:
The ratio of the shearing stress $\left( {\dfrac{F}{A}} \right)$ to the velocity gradient ( {\raise0.7ex\hbox{ {\vartriangle {v_x}} } \\!\mathord{\left/ {\vphantom {{\vartriangle {v_x}} {\vartriangle z}}}\right.} \\!\lower0.7ex\hbox{ {\vartriangle z} }}\,\,\,or\,\,{\raise0.7ex\hbox{ {d{v_x}} } \\!\mathord{\left/ {\vphantom {{d{v_x}} {dz}}}\right.} \\!\lower0.7ex\hbox{ {dz} }} ) in a fluid is known as viscosity (represented by the symbol $\eta$ "eta").
\eta = \dfrac{{{\raise0.7ex\hbox{ F } \\!\mathord{\left/ {\vphantom {F A}}\right.} \\!\lower0.7ex\hbox{ A }}}}{{{\raise0.7ex\hbox{ {d{v_x}} } \\!\mathord{\left/ {\vphantom {{d{v_x}} {dz}}}\right.} \\!\lower0.7ex\hbox{ {dz} }}}}
The pascal second [Pa s] is the SI unit for viscosity and has no other name. Despite its claim to be an international system, the International System of Units has had little effect on viscosity on a global scale. In today's science and technological literature, the pascal second is seldom used. The dyne second per square centimetre [ $dyne{\text{ }}s/c{m^2}$ ] is the most common unit of viscosity, and it is called poise [P] after the French physiologist Jean Poiseuille ( $1799-1869$ ).
While viscosity is usually unaffected by pressure, liquids subjected to high pressure often experience an increase in viscosity. Since liquids are usually incompressible, increasing the pressure does not bring the molecules closer together significantly. Simple molecular interaction models will not work to describe this behaviour, and there is no widely accepted more complex model that will. Of all the phases of matter, the liquid phase is perhaps the least known.

Note:
Let’s see how viscosity is important. It determines the ease with which machines can be started or operated under varying temperature conditions, especially in cold climates, as well as the sealing effect of oils and the rate of oil consumption. The viscosity of an oil is a measurement of its resistance to flow.