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Viscosity

Viscosity

When water is poured into a glass, it falls freely and quickly, whereas if honey or maple syrup is poured over a pancake, it flows slowly and sticks to the surface of the container. This difference in the flow of different kinds of liquids arises due to the fluid friction between the liquid layers and the liquid and the surrounding material. This property of fluids is called fluid viscosity. In this example, water has a lower viscosity than honey and maple syrup.
The SI unit of viscosity is...

Viscosity

Viscosity

Viscosity is a property of fluids that measures their resistance to flow. It is influenced by factors such as the surface area of contact, the gradient of flow speed, and the fluid's viscosity constant, called the coefficient of viscosity. The coefficient of viscosity, also known as dynamic viscosity, is denoted by the symbol η. It determines the proportionality between the viscous force and the gradient of flow speed.Newton's law of viscosity states that the viscous force on a faster-moving...

Viscosity of Fluid

Viscosity of Fluid

Viscosity measures the resistance a fluid offers to flow and deformation. It results from internal friction between layers of fluid moving relative to one another. Dynamic viscosity, denoted by the Greek letter mu (μ), quantifies the force needed to move one fluid layer over another. For Newtonian fluids like water and air, the relationship between the shearing stress and the rate of shearing strain is linear, meaning their viscosity remains constant regardless of the applied stress.

Steady, Laminar Flow Between Parallel Plates

Steady, Laminar Flow Between Parallel Plates

Understanding steady, laminar flow between parallel plates is essential for analyzing and designing flow in narrow rectangular channels, commonly found in various water conveyance and drainage systems. The Navier-Stokes equations govern fluid motion and are generally challenging to solve due to their nonlinearity. However, simplifications are possible in certain cases, like the steady laminar flow between parallel plates. For this scenario, we assume steady, incompressible, laminar flow.

Couette Flow

Couette Flow

Couette flow represents the flow of fluid between two parallel plates, with one plate fixed and the other moving with a constant velocity. This configuration allows for a simplified analysis using the Navier-Stokes equations, which govern fluid motion under conditions of viscosity and incompressibility. For Couette flow, the assumptions include a steady, laminar, incompressible flow with a zero-pressure gradient in the flow direction. This flow type is beneficial for understanding shear-driven...

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Hagen-Poiseuille flow describes a viscous fluid's steady, incompressible flow through a cylindrical tube with a constant radius R. This flow profile is often applied to understand fluid transport in narrow channels, such as capillaries. It serves as a foundational example of laminar flow. In this model, cylindrical coordinates (r,θ,z) are used to describe the radial (r), angular (θ), and axial (z) dimensions within the tube. For Hagen-Poiseuille flow, the velocity profile is purely axial,...

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Related Experiment Video

Updated: Jul 9, 2026

Fabrication, Operation and Flow Visualization in Surface-acoustic-wave-driven Acoustic-counterflow Microfluidics

Fabrication, Operation and Flow Visualization in Surface-acoustic-wave-driven Acoustic-counterflow Microfluidics

Published on: August 27, 2013

Electro-Viscous Effects on Liquid Flow in Microchannels.

¹Department of Mechanical & Industrial Engineering, University of Toronto, Toronto, Ontario, M5S 3G8, Canada

Journal of Colloid and Interface Science

|December 9, 2000

Summary

This summary is machine-generated.

The electro-viscous effect increases flow resistance in microchannels, particularly with higher ionic valence and lower concentrations. This study quanties the additional resistance in silicon microchannels, finding good agreement with a theoretical model for most tested liquids.

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Area of Science:

Fluid Dynamics
Electrokinetics
Surface Science

Background:

The electrical double layer at solid-liquid interfaces causes the electro-viscous effect.
This effect influences pressure-driven liquid flow in microchannels, leading to increased resistance.

Purpose of the Study:

To quantify the additional flow resistance due to the electrokinetic effect in microchannels.
To investigate the dependence of this resistance on channel height, ionic valence, and liquid concentration.

Main Methods:

Flow measurements in silicon microchannels of varying heights (14.1, 28.2, 40.5 µm).
Testing with deionized water and various KCl, AlCl(3), and LiCl solutions.
Calculation of zeta potentials from streaming potential data.

Main Results:

Significantly higher measured flow resistance (dP/dx) than predicted by conventional theory for pure water and KCl/LiCl solutions.
Flow resistance strongly depends on channel height, ionic valence, and concentration.
Good agreement between experimental data and a theoretical electro-viscous flow model for water, KCl, and AlCl(3) solutions.

Conclusions:

The electro-viscous effect demonstrably increases flow resistance in microchannels.
A theoretical model effectively predicts electrokinetic flow for many liquid systems.
The model's inability to interpret LiCl solution behavior suggests further investigation is needed.