What Is the Connection Between Radiation, Convection and Conduction?

At the same time that objects emit radiant energy, they will continuously absorb the radiant energy emitted by other objects around them and convert it back into thermal energy. The heat transfer process in which objects emit radiant energy and absorb radiant energy is called radiation. Heat transfer. If radiant heat transfer is performed between two objects with different temperatures, the result of heat transfer is that the high-temperature object transfers heat to the low-temperature object. If the two objects have the same temperature, the radiant heat transfer between the objects is equal to zero, but the object The radiation and absorption process is still ongoing.

Relying on electromagnetic wave radiation to achieve hot and cold objects

Studying the law of heat radiation is very important for the reasonable design of heat transfer in the furnace, and also has positive significance for the labor protection of high-temperature furnace operators. When a system needs heat preservation, even if the temperature of the system is not high, the influence of radiant heat transfer cannot be ignored. Such as the thermos flask galvanized, is to reduce the heat loss caused by radiant heat transfer.

Theoretical research proves that the formula for calculating the black body's radiant power is called the Stefan-Boltzmann law. The constant is the radiation constant of the black body (also known as the Stefan-Boltzmann constant), and its value is 5.669 × 10 W / (mK). This formula shows that temperature versus

The rate of radiant heat transfer between two objects can be expressed as the surface temperature of the two objects; the surface area of an object; the angular coefficient based on it represents the fraction of the energy radiated by an object projected onto the surface, which depends on the Shape, size, and relative position; is the total emissivity, and its value is related to the blackness, size, shape, and relative position of the two objects. ^[4]

The process by which an object transfers energy in the form of electromagnetic waves is called radiation, and the transferred energy is called radiant energy. Objects can generate electromagnetic waves for different reasons. Among them, electromagnetic radiation caused by heat is thermal radiation. In the process of thermal radiation, the thermal energy of an object is converted into radiant energy. As long as the temperature of the object does not change, the emitted radiant energy also does not change. While the object is radiating energy outward, it may also continuously absorb the radiant energy emitted by other objects around it. The so-called radiant heat transfer is a comprehensive process of radiating and absorbing energy between different objects. Obviously, the net result of radiative heat transfer is that high-temperature objects transfer energy to low-temperature objects.

Thermal radiation and optical radiation are essentially the same, the only difference being the range of wavelengths. Theoretically, the wavelength of electromagnetic waves of thermal radiation is from zero to infinity, but the wavelength range of practical significance is 0.4 to 20 m, and the wavelength range of visible light is about 0.4 to 0.8 m, and the wavelength range of infrared light is 0.8 to 20 / m. Visible and infrared rays are collectively referred to as heat rays. However, the thermal rays of infrared rays play a decisive role in thermal radiation. Only at very high temperatures can the thermal effects of visible rays be perceived.

Heat rays, like visible light, obey the laws of reflection and refraction, and can travel straight in a homogeneous medium. In vacuum and most gases (inert gases and symmetrical diatomic gases), heat rays are completely transparent, but for most solids and liquids, heat rays are not transparent. Therefore, only radiant heat transfer can be performed between objects that can see each other. ^[5]