Toothpaste as a typical example of a non-Newtonian fluid (Bingham Fluid)

Viscosity of liquids and gases

The viscosity of a fluid is a measure of the internal resistance to flow! It is caused by intermolecular forces and transport of momentum within the fluid. Learn more...
Velocity gradients in a laminar and turbulent boundary layer

Hydrodynamic boundary layer

The hydrodynamic boundary layer of a flow has a decisive influence on heat and mass transport. Learn more about it in this article.
Pressure difference as drive for flows

Hagen-Poiseuille equation for pipe flows with friction

The Hagen-Poiseuille equation describes the parabolic velocity profile of frictional, laminar pipe flows of incompressible, Newtonian fluids. Learn more about it in this article.
Demonstration of the siphon-spillway-principle

Siphon

This article provides answers to the following questions, among others: How does a siphon work?What is the maximum height to the apex of the flexible tube...
Division of the pressure drop to different causes

Energetic analysis of the Hagen-Poiseuille law

The Hagen-Poiseuille equation for describing the parabolic velocity profile of fluids in pipes applies only to long pipes for energy reasons! Learn more about it in this article.
Stratification of the earth's atmosphere

Barometric formula for an isothermal atmosphere

The barometric formula describes the decrease of air pressure with increasing altitude. Without the influence of the temperature changes, the air pressure decreases by about 1.2% per 100 meters...
Convective heat transfer between a heated pipe and a fluid flowing through it

Prandtl number

The Prandtl number is a dimensionless similarity parameter to describe the transport of heat and momentum. Learn more about it in this article.
Water tower

Applications and examples of hydrostatic pressure

This article provides answers to the following questions, among others: Which properties of the hydrostatic pressure could Pascal demonstrate with his barrel experiment?How does the pressure...
Hot air balloon

How does a hot air balloon work: Buoyancy in gases

Buoyant forces act not only in liquids but also in gases. This will be illustrated in the following by the example of a hot air balloon.
Hydrodynamische Grenzschicht, thermische Grenzschicht und Konzentrationsgrenzschicht

Dimensionless numbers of the boundary layers (Prandtl, Schmidt and Lewis number)

To describe the heat and mass transport, dimensionless numbers are introduced to describe the processes within the boundary layers. Learn more about this in this article.
Definition of the thermal boundary layer (temperature boundary layer)

Thermal and concentration boundary layer

In addition to the hydrodynamic boundary layer, the thermal boundary layer and the concentration boundary layer also have a decisive influence on the entire heat and mass transport in...
Pressure on a flat surface

Pressure in gases

This article provides answers to the following questions, among others: What causes the pressure in gases?How is the unit bar converted into the unit Pascal?What is...
Pressing a drawing pin together between two fingers

Pressure

This article provides answers to the following questions, among others: What is pressure?In what way does the contact pressure differ from a gas pressure or liquid...
Hydraulic bottle jack

How does a hydraulic jack work: Pascals law

A hydraulic jack is based on Pascal's law, which states that the pressure in liquids acts equally in all directions. This article...
Lewis number as a measure for the ratio of the thickness of the thermal boundary layer and the concentration boundary layer

Lewis number

The Lewis number is a dimensionless similarity parameter to describe heat and mass transport. Learn more about it in this article. This...
Convective heat transfer at a flat plate with laminar-turbulent flow

Calculation of the Nusselt numbers for forced flows over plates and in pipes

In this article you will find formulas for calculating the local and average Nusselt numbers for forced flows over plates and in pipes with circular cross sections.
Dry adiabatic and wet adiabatic lapse rate (temperature gradient)

Barometric formula for an adiabatic atmosphere

The barometric formula for an adiabatic atmosphere takes into account the decrease in temperature with increasing altitude and the associated effects on air pressure. More information about this and...
Influence of the hydrodynamic and thermal boundary layer on convective heat transfer

Nusselt number to describe convective heat transfer

The Nusselt number is a dimensionless similarity parameter to describe convective heat transfer, independent of the size of the system. Learn more about it in this article.
Aircraft model in a wind tunnel to study the flow around the aircraft

Reynolds number (laminar and turbulent flow)

The Reynolds number is a dimensionless similarity parameter for describing a forced flow, e.g. whether it is an alminar or turbulent flow. Learn more about it in this article.
Fluid element on a curved streamline

Equation of motion of a fluid on a streamline

In this article we want to derive the equation of motion of a fluid element on a streamline. For this purpose we describe the equation of motion in the...

Drag coefficient (friction and pressure drag)

Drag coefficients are dimensionless similarity parameters for describing the drag of flowed around bodies. Learn more about them in this article. This...
Container ship

How do boats float: Buoyancy in liquids

Buoyancy is the force directed against gravity that an object experiences when submerged in a fluid (liquid or gas). More information on how buoyancy is formed can be found...
Influence of vessel shape on hydrostatic pressure

Pressure in liquids (hydrostatic pressure)

This article provides answers to the following questions, among others: What causes the hydrostatic pressure in liquids?On which variables does the hydrostatic pressure depend?What is the...
Pathline (trajectory) of a paper ship in a steady stream

Streamlines, pathlines, streaklines and timelines

In order to make the flow of fluids "visible", one often uses the model of streamlines, pathlines (trajectories), streaklines or timelines. Learn more about the difference between these lines...
Schmidt number as a measure for the ratio of the thickness of the hydrodynamic boundary layer and the concentration boundary layer

Schmidt number

The Schmidt-number is a dimensionless similarity parameter to describe transport of mass and momentum. Learn more about this topic in this article.