The law of heat conduction, also known as Fourier's law, shows that the heat passing through a given section per unit time is directly proportional to the rate of temperature change and the cross-sectional area perpendicular to the section, while the direction of heat transfer is opposite to the direction of temperature increase. We can express this law in two equivalent forms: the whole form and the difference form.
Newton's cooling law is a discrete extension of Fourier's law, and Ohm's law is an electrical extension of Fourier's law.
Expression:
English translation: Fourier law
English: Fourier Law
Fourier law is a basic law in heat transfer, which was put forward by the famous French scientist Fourier in 1822. ?
Literal expression of Fourier's law: In heat conduction, the heat passing through a given section per unit time is directly proportional to the rate of temperature change and the cross-sectional area perpendicular to the section, while the direction of heat transfer is opposite to the direction of temperature rise.
Heat flux JT of Fourier law? The manifestations are as follows:
It can be used to calculate heat conduction. Where is the heat flux of JT? (W m-2) is the heat transfer rate in the X direction per unit area perpendicular to the transmission direction. It is proportional to the temperature gradient dT/dx in this direction. The proportionality constant κ is a transport characteristic, called thermal conductivity (also called thermal conductivity), and the unit is (w m-1k-1). It can also be expressed as follows:
Where is dQ/dt? (above q) is the thermal conductivity (or it), and the unit is W. 。
Answer? Is the heat transfer area in m2.
t？ Is the temperature, and the unit is K.
x？ Is the coordinate on the heat conducting surface, and the unit is m.
Mathematical expression in general form:
Where: JT? Is the heat flux in the r direction perpendicular to the isothermal surface. Heat flow is a vector and can also be decomposed into several components.
The negative sign in the above formula indicates that the heat transfer direction is opposite to the temperature gradient direction.