The effect of pressure is significant primarily in gases. Results for typical gases, liquids, and solids in appropriate temperature ranges are shown in Fig. See also: Electron Intermolecular forces Kinetic theory of matter Sound Thermal conduction in solidsīecause of the complexity of the mechanisms responsible for heat conduction, values of κ are usually determined experimentally. This is the basis of the Widemann-Franz law, which states that κ/σ T = constant (σ is the electrical conductivity and T the absolute temperature). In dielectric solids, energy is transmitted primarily by means of waves traveling through the atomic lattice in metals, the electrons behave like an electron gas and provide for energy transfer as well as electrical conduction. The process of heat conduction in liquids is believed to be similar to that of sound transmission. The thermal properties of matter are well-understood, particularly for gases, where theory involving intermolecular forces has yielded very accurate results. In engineering, the units most frequently used are Btu/(h)(ft)(☏). In the cgs system, it can be expressed in cal/(s) Where κ is seen to have the dimensions of a heat rate per unit area and per unit of temperature gradient. The mechanism for energy flow in liquids and solids is similar to that in gases in principle, but different in detail. These processes take place almost instantaneously in infinitesimal distances, the result being a quasi-equilibrium state with energy transfer. The reverse occurs in the high-temperature region. In colliding with molecules in the low-temperature region, the high-temperature molecules give up some of their energy. The flow of energy results from the random travel of high-temperature molecules into low-temperature regions and vice versa. This stored energy will be partly kinetic because of the random translational and rotational velocities of the molecules, partly potential because of internal vibrations, and partly ionic if the temperature (energy) level is high enough to cause dissociation. The temperature at any location can be interpreted as a quantitative specification of the mean kinetic and potential energy stored in the molecules or atoms at this location. See also: Air conditioning Earth Metal Temperatureįor an example of the conduction process, consider a gas such as nitrogen which normally consists of diatomic molecules. Also, the daily and yearly temperature variations near the surface of the Earth can be predicted reasonably well by assuming a simple sinusoidal temperature variation at the surface and treating the Earth as a semi-infinite solid. 1), air conditioning, food processing, and the pouring and curing of large concrete structures. Examples of essentially pure transient or periodic heat conduction and simple or complex combinations of the two are encountered in the heat-treating of metals ( Fig. Steady-state conduction is said to exist when the temperature at all locations in a substance is constant with time, as in the case of heat flow through a uniform wall. See also: Heat convection Heat radiation Heat transfer ![]() Conduction is one of the three basic methods of heat transfer, the other two being convection and radiation. Heat conduction occurs by atomic or molecular interactions. The flow of thermal energy through a substance from a higher- to a lower-temperature region. The two kinds of non-steady-state heat flow are periodic conduction and transient conduction. It accounts for the heat conducting ability of a substance and depends both on the particular substance involved and on the state of that substance. Thermal conductivity is an important property of matter. ![]() Steady-state conduction occurs when the temperature at all locations in a substance is constant with time. Heat conduction is the flow of thermal energy through a substance from a region of higher temperature to a region of lower temperature, which occurs by atomic or molecular interactions.Īlong with convection and radiation, conduction is one of three basic methods of heat transfer.
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