# Heat

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### Why are radiators usually located under a window?

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Central heating systems use the principle of thermal convection. The water is heated by a central heater and then transferred to the radiators by means of pumps. It is thus a...

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### Thermal and concentration boundary layer

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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 a flow....

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

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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. This article provides answers to...

### 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 from one...

### How does a thermos work? Design of a vacuum flask!

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The reason why hot tea or coffee stays warm for so long in a thermos is the special design of the flask. This design limits the different mechanisms of heat transfer...

### Difference between thermal conductivity, diffusivity, transmittance, resistance and heat transfer coefficient

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Learn more in this article about the differences and importance of thermal conductivity, thermal diffusivity, heat transfer coefficient, thermal transmittance and thermal resistance, etc. Thermal conductivity Thermal conductivity (lambda) describes the heat transfer...

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### 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 diluted. This is no longer the case for gases with low pressure. Learn...

### Why does metal feel colder than wood (human thermal response)

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Find out in this article why metal feels colder than wood of the same temperature, while at higher temperatures the metal suddenly feels warmer than wood. The property of an object to...

### 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 topic can...

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### 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 of heat...

### Gulf Stream & global ocean conveyor belt

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The Gulf Stream is an ocean current in the Atlantic Ocean which, as part of the earth's global conveyor belt, has a decisive influence on the climate in Northern and Western...

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### 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 about the...

### Thermal transmittance (U-value)

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The thermal transmittance (U-value or U-factor) describes the heat transfer through a solid object, which is located between two fluids (gas or liquid) with different temperatures. Learn more about it in...

### 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 experimental determination...

### 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. This article provides answers to the following questions, among...