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...
Illustration des Photonengases in einem Schwarzen Hohlkörper

Thermodynamic derivation of the Stefan-Boltzmann Law

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In this article the Stefan-Boltzmann-Law is to be derived using the laws of thermodynamics. This article provides answers to the following questions,...
Randomly distributed velocities of the particles of a gas

Pressure and temperature

This article provides answers to the following questions, among others: What is the kinetic theory of gases?What are the assumptions on which the kinetic theory of...
Thermographic image of a car

How does a thermal imaging camera work?

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This article provides answers to the following questions, among others: How do thermal imaging cameras work?Why is the thermal image displayed in false colors?
Cut through a gas filled thermometer (gas-in-metal thermometer)

How does a gas filled thermometer (gas-in-metal) work?

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This article provides answers to the following questions, among others: How do gas filled thermometers work?What are the advantages of gas-in-metal thermometers compared to liquid-in-metal...
Temperature curve along a heated thin rod

Heat equation (diffusion equation)

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The heat equation describes the temporal and spatial behavior of temperature for heat transport by thermal conduction. Read more about it in this article.
Thermal response with cooled and uncooled hand

Temperature scales

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This article provides answers to the following questions, among others: What is temperature in the physical sense a measure for?Which reference points are used as the...
Experiment to demonstrate heat transport by thermal conduction

Heat transfer by thermal conduction

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Heat transfer by thermal conduction means that heat is conducted through a material. Heat energy is transferred from molecule to molecule at the atomic level. More information on this...
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.
Thermal conduction through a house wall

Thermal conductivity (Fourier’s law)

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Thermal conductivity is a measure of how well or poorly a material conducts heat energy (measure of the strength of heat conduction)! You can read more about this in...
Visible radiation of a light bulb

Stefan–Boltzmann law & Kirchhoff’s law of thermal radiation

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The Stefan-Boltzmann law states that the radiant power of an object in thermal equilibrium is proportional to the fourth power of temperature and directly proportional to its surface! Learn...
Cut through a liquid filled thermometer (liquid-in-metal thermometer)

How does a liquid filled thermometer (liquid-in-metal) work?

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This article provides answers to the following questions, among others: How do a liquid-in-metal thermometers work?Why should the inner diameter of the coiled tube be kept...
Determination of thermal conductivity with the Transient Hot Wire method (HTW)

Transient-Hot-Wire method method for determining thermal conductivity (THW)

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With the Transient-Hot-Wire method (THW), the thermal conductivity is determined by the change in temperature over time at a certain distance from a heating wire. Learn more about the...
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.
Design of a Laser-Flash-Analyzer (LFA) for the determination of thermal diffusivity conductivity

Laser-Flash method for determining thermal conductivity (LFA)

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With the Laser-Flash method (Laser Flash Analyser, LFA), the thermal conductivity is determined by the temperature rise in a test sample that is heated by a short laser pulse...
Particle model of matter (oxygen, hydrogen, water)

Particle model of matter

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This article provides answers to the following questions, among others: What is the particle model of matter?How can the solid, liquid and gaseous states of...
Degrees of freedom of a molecule

Internal energy & heat capacity

This article provides answers to the following questions, among others: What is the internal energy of a gas?What are the characteristics of the thermal...
Speed distribution of an ideal gas for different temperatures

Maxwell–Boltzmann distribution

The Maxwell-Boltzmann distribution describes the molecular speed distribution of ideal gas molecules. Find out more in this article. This article provides answers...
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.
Spectral distribution of the intensity of the radiation of a blackbody (Planck spectrum)

Planck’s law and Wien’s displacement law

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Planck's law describes the radiation emitted by black bodies and Wien's displacement law the maximum of the spectral intensity of this radiation. Learn more about it in this article.
Mixing temperature when pouring cold milk into a cup of hot coffee

Heat and thermodynamic equilibrium

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In thermodynamics, heat is the transport of energy due to a temperature difference. Heat in this respect is never "contained" in an object! Learn more about the thermodynamic concept...
Principle of temperature measurement with a liquid-in-glass-thermometer

How does a liquid-in-glass thermometer work?

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This article provides answers to the following questions, among others: How do liquid thermometers work?What properties must thermometric liquids have?Why is mercury hardly used as a...
Temperature profile through the wall of a cylindrical pipe

Temperature profiles and heat flows through different geometries

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In this article we discuss temperature curves and heat flows through a plane wall, through a cylindrical pipe and through a hollow sphere.
Definition of the heat transfer coefficient for convective heat transport

Heat transfer coefficient for thermal convection

The heat transfer coefficient describes the convective heat transfer from a solid to a flowing fluid and vice versa! Learn more about it in this article.
Radiation of a black body into half-space

Different forms of Planck’s law

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Planck's law of radiation can be expressed in different forms. The most important ones are discussed in this article. This article provides...
Resistance thermometer (Pt100)

How does a resistance temperature detector (resistance thermometer) work?

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This article provides answers to the following questions, among others: How do resistance thermometers work?Why should the measurement current for an RTD be as low as...
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.
Balls on a vibrating plate

Derivation of the Maxwell-Boltzmann distribution function

The Maxwell-Boltzmann distribution function of the molecular speed of ideal gases can be derived from the barometric formula. This article shows the derivation.
Pressure distribution during compression of a gas

Equipartition theorem

This article provides answers to the following questions, among others: What statement does the equipartition theorem provide?What is a degree of freedom in the thermodynamic sense?Why...
Infrared thermometer (Pyrometer)

How does a infrared thermometer (pyrometer) work?

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This article provides answers to the following questions, among others: How do IR thermometers (pyrometers) work?What are the advantages of pyrometers?
Thermocouple

How does a thermocouple work?

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This article provides answers to the following questions, among others: How does a thermocouple work?What is the Seebeck effect?What are the differences between the types of...
Mean free path in a thin gas with low pressure and a dense gas with high pressure

Thermal conductivity of gases

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The thermal conductivity of ideal gases is not dependent on pressure for gases that are not too strongly thinned. This is no longer the case for gases with low...
Bimetal thermometer (spiral type)

How does a bimetallic strip thermometer work?

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This article provides answers to the following questions, among others: How do bimetal thermometers work?Why is the bimetal wrapped into a spiral or a helix?Why are...
Thermal image of a cup with hot tea and a building

Heat transfer (heat transport)

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Heat transfer is the transport of thermal energy from a warmer object to a cooler object. A distinction is made between thermal convection, thermal conduction and thermal radiation. You...
Mean free path

Mean free path & collision frequency

The mean free path is the average distance a particle travels without colliding with other particles! Learn more about the mean free path in this article!
Design of a velocity selector to determine the speed distribution in gases

Determination of the speed distribution in a gas

This article provides answers to the following questions, among others: How can the speeds of the particles in a gas be determined experimentally?What is a histogram?What...
Design of a Heat-Flow-Meter for determining thermal conductivity (HFM method)

Heat-Flow-Meter method for determining thermal conductivity (HFM)

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With the Heat-Flow-Meter method (HFM) the thermal conductivity is determined by comparative measurement of the heat flow using a reference sample. Learn more about this absolute measurement method in...
Heat flow from a hot object to a cooler one

Rate of heat flow: Definition and direction

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The rate of heat flow refers to the heat energy transferred per unit of time ("heat output"). The drive for the heat flow is a temperature difference. Learn more...
Illustration of Brownian particle motion with balls

Temperature and particle motion

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This article provides answers to the following questions, among others: What is the general relationship between the temperature and the particle movement of a substance?Why does...
Design of a measuring device for the determination of thermal conductivity according to the Guarded-Hot-Plate Method (GHP)

Guarded-Hot-Plate method for determining thermal conductivity (GHP)

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With the Guarded-Hot-Plate method (GHP) the thermal conductivity is determined by the electrical power output of a hot plate with guided heat conduction. Learn more about this measurement method...
Sun as a blackbody with a surface temperature of 5778 K

Heat transfer by thermal radiation

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With thermal radiation, heat is transferred by electromagnetic waves without the presence of a substance! You can read more about this mechanism in this article.
White glow of a blackbody at 6000 K

Blackbody radiation

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Blackbody radiation (cavity radiation) is the thermal radiation of a blackbody, i.e. a body that absorbs all incident radiation. Find out more about blackbody radiation in this article.
Experimental setup for the measurement of thermal conductivity

Experimental setup for determining thermal conductivity

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In this article you can learn more about the experimental determination of the thermal conductivity of materials using steam and ice. 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.
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...