Flashcards
6) Heat Conduction
Cards in this deck (20)
- 1What is conduction?Conduction is the transfer of energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interactions between the particles.
- Collision, vibration or flow of free electrons - 2What is convection?Convection is the mode of energy transfer between a solid surface and the adjacent liquid or gas that is in motion.
- 3What is Newton's law of cooling?
- 4What is radiation?Radiation is the energy emitted by matter in the form of electromagnetic waves (or photons) as a result of the changes in the electronic configurations of the atoms or molecules. Unlike conduction and convection, the transfer of energy by radiation does not require the presence of an intervening medium.
- 5Where does heat conduction occur? How do molecules act?Heat conduction can take place in solids, liquids, or gases.
In gases and liquids, conduction is due to the collisions of the molecules during their random motion.
• In solids, it is due to the combination of vibrations of molecules in a lattice and the energy transport by free electrons. - 6What is the rate of heat conduction proportional to?It is observed that the rate of heat conduction through a layer of constant thickness is proportional to the temperature difference across the layer and the area A normal to the direction of heat transfer, and is inversely proportional to the thickness of the layer.
- 7Therefore what equation can we use f?where the constant of proportionality k is the thermal conductivity of the material, which is a measure of the ability of a material to conduct heat.
Where delta is the thickness of the wall.
- 8What is thermal conductivity? Thermal conductivity of a solid?A measure of the ability of a material to conduct heat.
The thermal conductivity of a solid is obtained by adding the lattice and the electronic components/ - 9Thermal conductivity of pure metals?The thermal conductivity of pure metals is primarily due to the electronic component, whereas the thermal conductivity of nonmetals is primarily due to the lattice component.
- 10What does the lattice component of thermal conductivity depend on?The lattice component of thermal conductivity strongly depends on the way the molecules are arranged. For example, the thermal conductivity of diamond, which is a highly ordered crystalline solid, is much higher than the thermal conductivities of pure metals.
- 11What is Fourier's law of heat conduction? What is it based on?Fourier’s law states that the rate of flow of heat (namely heat flux) through a single homogeneous solid is directly proportional to the area A of the section perpendicular to the direction of the heat flow, and to the change of temperature with respect to the length of the path of the heat flow, dT/dx (namely temperature gradient).
One of the most important law of heat transfer. This is an empirical law based on observation. - 12Diagram of Fourier's law?
- 13See notes for 2 examples...
- 14The concept of thermal resistance?
- 15Continued concept of thermal resistance?
- 16See notes for heat conduction through multi-layer walls example...
- 17Equation for thermal resistance of convection:
- 18Equation for thermal resistance of conduction:
- 19What is a U value?A U-value is referred to as an overall heat transfer coefficient of a building element of composite structure such as a wall, floor or roof. This means that the lower the U value the better the insulation performance of the building envelope.
- 20Diagram of thermal resistance network? Total thermal resistance? So...
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- Thermodynamics 2 Flashcards on 6) Heat Conduction, created by Alice K on 03/11/2019.
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- Alice K
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