What is the thermal conductivity?

2011/10/1 15:51:21

Thermal conductivity (also known as "thermal conductivity" or "thermal conductivity") is an important physical quantity that reflects the thermal performance of materials. Heat conduction is one of the three basic forms of heat exchange (heat conduction, convection and radiation), and is a subject in various research fields such as engineering thermophysics, materials science, solid state physics, energy, environmental protection, etc. The thermal conductivity mechanism of materials depends to a large extent on its microstructure. Heat transfer depends on atoms, molecules' vibration around equilibrium positions, and free electron migration. Electron flow plays a dominant role in conductive metals, while lattice vibration plays a dominant role in insulators and most semiconductors. In 1882, French scientist J.Fourier established the theory of heat conduction. At present, various methods for measuring the thermal conductivity are based on Fourier's law of heat conduction. When there is a temperature gradient inside an object, heat is transferred from the high temperature to the low temperature. This phenomenon is called heat conduction. Fourier points out that the heat dQ passing through ds area in dt time is proportional to the temperature gradient inside the object, and the thermal conductivity when its proportional coefficient is: dQ/dt=-l .dt/dx .ds Where dQ/dt is the heat transfer rate, dt/dx is the temperature gradient in the direction perpendicular to the area ds, "-"indicates that heat is transferred from the high-temperature area to the low-temperature area, and l is the thermal conductivity coefficient, indicating the size of the object's thermal conductivity. in the formula, the unit of l is w m minus 1 power. k minus 1 power. For anisotropic materials, the thermal conductivity is different in all directions (usually represented by tensors). If you don't understand or not understand the above formula (the above belongs to the college higher physics course), I will use common language to express the thermal conductivity coefficient. Thermal conductivity is also called thermal conductivity or thermal conductivity. A physical quantity that characterizes the thermal conductivity of a substance. Two parallel planes with a distance of 1 meter and an area of 1 square meter are set in the interior of the substance perpendicular to the thermal conductivity direction. If the temperatures of the two planes differ by 1 degree, the heat transferred from one plane to the other within 1 second is defined as the thermal conductivity of the substance. Its unit is: watts/(meters. degrees Celsius). In the original engineering unit system, it was: kilocalories/(meters. hours. degrees Celsius). The reciprocal of thermal conductivity is called thermal conductivity. Other conditions being constant, the greater the thermal conductivity, the smaller the thermal conductivity, the thermal conductivity On the other hand, the less heat is conducted. Through the above formulas and definitions, it can be seen that the chip heat dissipation method relies on the temperature difference between the area of the substrate (copper or aluminum) in contact with the chip and the temperature in the chassis to dissipate heat through the air flow in the chassis. This heat dissipation amount is proportional to the area of the substrate. When the temperature in the chassis reaches a certain level, the heat dissipation capacity will be lost. In order to remove the heat emitted by the chip, strong wind is normally used. Therefore, the heat dissipation method without fan mute heat pipe is not desirable. In addition, according to the principle of aerodynamics (the formula is not included), the installation of the fan in the cabinet must have the same wind direction, i.e. front in and back out to form an air duct, so as to take away the heat in the cabinet and achieve the purpose of heat dissipation.