What Is Heat Flux?

Heat flux, also known as heat flow, refers to the thermal energy that passes through an area per unit time. It is a directional vector. Its unit in the International System of Units is Joules per second (J / s, which is Watts). This can further define the heat flux density or heat flux density, that is, the heat flux through a unit area, the unit of which is in the international unit system is watts per square meter.

Heat flux or heat flux is sometimes called heat flux density [1] or heat flux intensity is the energy flux per unit time per unit area. In SI, the unit is Watts per square meter (Wm ^-2 ). It has both direction and magnitude, so it is a vector. In order to determine the heat flux at a certain point in space, the limit case of infinitely small surface dimensions needs to be considered.

Fourier's law is an important application of these concepts. ^[1]

For most solids under normal conditions, heat is mainly transmitted through conduction, and heat flux is adequately described by Fourier's law.

According to different heat conduction methods, heat flux is divided into conductive heat flux (conducted

The measurement of heat flux can be performed in several different ways. A commonly known but often impractical method is performed by measuring the temperature difference over a piece of material with a known thermal conductivity. This method is similar to the standard method of measuring current, where the voltage drop across a known resistance is measured. This method is often difficult to perform because the thermal resistance of the material under test is usually unknown. To determine thermal resistance, accurate material thickness and thermal conductivity values are required. Using thermal resistance and temperature measurements on both sides of the material, the heat flux can be calculated indirectly.

The second method of measuring heat flux is to directly measure the amount of heat transferred to the surface to which the heat flux sensor is mounted by using a heat flux sensor or a heat flux sensor. The most common type of heat flux sensor is a differential temperature thermopile, which is basically the same as the first measurement method mentioned, except that it has the advantage that the thermal resistance / conductivity need not be a known parameter. Since the heat flux sensor enables field measurement of existing heat fluxes by using the Seebeck effect, it is not necessary to know these parameters. However, differential thermopile heat flux sensors are already being calibrated to involve their output signal [V] to the heat flux value [W / (m ² K)]. Once the heat flux sensor is calibrated, it can be used to directly measure heat flux without the need for rare thermal resistance or thermal conductivity values. ^[3]

The sensor used to measure heat flux is called a heat flux sensor, also called a heat flow sensor.

The instrument used to measure heat flux is called a heat flux meter, also known as a heat flow meter. ^[3]