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Learn what thermal conductivity is, how to calculate it and what are its units. Find out the thermal conductivity of metals at different temperatures and test your knowledge with a quiz.
- 9 min
- Heat energy is caused by the movement of particles like atoms, ions, or molecules in gases, liquids and solids. Heat energy can be transmitted from...
- In thermodynamics, conductivity is a body’s ability to conduct heat through its physical structure.
- The SI unit of thermal conductivity is watts per meter-kelvin (Wm -1 K -1 ).
- The thermal conductivity of pure aluminium at 20° is 204 Wm -1 K -1 .
People also ask
What is the inverse of thermal conductivity?
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How do you calculate thermal conductivity?
In the International System of Units (SI), thermal conductivity is measured in watts per meter-kelvin (W/(m⋅K)). Some papers report in watts per centimeter-kelvin [W/(cm⋅K)]. However, physicists use other convenient units as well, e.g., in cgs units, where esu/(cm-sec-K) is used.
The thermal conductivity constant k is larger for materials that transfer heat well (like metal and stone), and k is small for materials that transfer heat poorly (like air and wood). How can k change if it is a constant?
- Overview
- The process of thermal conductivity
- Examples of thermal conductivity
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thermal conductivity, the ability of a substance to conduct heat or move heat from one location to another without the movement of the material conducting the heat. Thermal conductivity is measured in watts per meter kelvin (W/mK). For example, solid aluminum has a thermal conductivity of 237 W/mK at –73 °C (–99 °F), 236 W/mK at 0 °C (32 °F), and 232 W/mK at 327 °C (621 °F). Thermal conductivity of a material changes with temperature and can be related to changes in pressure, depending on the state of the material.
In physics, thermal conductivity is given the symbol k or λ. It represents one of three methods by which heat can be transferred from one location to another, the other two being convection and radiation. Fourier’s law of heat conduction gives the rate at which heat is transferred through thermal conductivity: q = –k∇T, where q is local heat flux density, and ∇T is the temperature gradient.
When heat is conducted through a solid, heat moves through molecular or atomic agitation and contact between particles. Heat transfer is not the result of atoms or molecules moving through the solid. In a solid, heat moves along a difference in temperature (called a temperature gradient) from an area of high temperature and thus high particle agitation to an area of low temperature and thus low particle agitation. This transfer of heat energy continues until all the material comprising the solid is at thermal equilibrium, meaning the temperature throughout the material is the same. The time needed for this to occur depends on several factors, including the magnitude of the temperature difference within the material and the thermal characteristics of the material itself. These characteristics include the material’s atomic or molecular composition and the distance, known as the path length, through which the heat must move.
When the conducting material is a liquid or a gas, heat moves through particle agitation as well as through movement of the atoms or molecules themselves. Thermal conduction occurs fastest in a solid and slowest in a gas. When matter is in the gas phase, particles have larger distances between them and so collide less often. These collisions transfer thermal energy, so fewer collisions lead to a lower rate of heat conduction.
When cooks prepare food, they often use metal frying pans. As a pan heats on a stovetop, thermal energy from the stovetop is transferred to the metal on the bottom of the pan. This energy is then conducted throughout the pan, ultimately cooking the food. However, over time, the heat will also conduct to the handle of the pan. Therefore, frying pan manufacturers will often carefully select a material for the handle of a pan that is a poor conductor of heat so that cooks will not be in danger of burning their hands.
Thermal touch, or how the body senses temperature when touching a hot or cold object, also follows the principles of thermal conductivity. When a person touches an object, the temperatures of the object and skin change depending on both their properties and their initial temperatures.
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Thermal conductivity is the ability of a substance to conduct heat without moving the material. It is measured in watts per meter kelvin (W/mK) and depends on temperature and pressure. Learn more about the process, examples, and applications of thermal conductivity.
Thermal conductivity units are [W/ (m K)] in the SI system and [Btu/ (hr ft °F)] in the Imperial system. See also thermal conductivity variations with temperature and pressure , for: Air , Ammonia , Carbon Dioxide and Water.
Online calculator, figures and table showing thermal conductivity of ethylene, also called ethene or acetene, C 2 H 4, at varying temperature and pressure - Imperial and SI Units.
May 22, 2019 · In SI units, thermal conductivity is measured in watts per meter-kelvin – W/(m·K). In Imperial units, thermal conductivity is measured in BTU/(hr·ft⋅°F).
