There are three basic ways of transmission: conduction, convection and radiation.Conduction is when two objects with a temperature difference are in contact with each other, heat is transferred from a high-temperature object to a low-temperature object,A typical example is hot plate heating.Convection refers to the mutual diffusion of fluids of different temperatures, fusion to achieve thermal energy transfer, the most typical example is the mixing and heating of hot water to cold water.Our most common hot blast stove is actually a mixture of convection and conduction.The hot air is brought into the furnace body by the fan to make the temperature of the furnace body reach the set temperature. This process is convection; then the hot air transfers heat by contacting the surface of the heated object, and this process is conduction.The common point of conduction and convection is that the contact of the object is required, or the heat source is in direct contact with the object to be heated, or the energy of the heat source is transferred to the object to be heated through a medium such as air.

The heat transfer method of radiation is completely different. It transfers energy through infrared light.The heat energy transferred from the sun to the earth is realized by infrared rays.It has the following two basic.

characteristics:

1. Infrared radiant heat transfer does not require a medium, non-contact heat transfer.The infrared light 

emitted by the heat source irradiates the surface of the object to be heated, and is absorbed by the molecules on the surface, causing the vibration energy level of the molecules to rise and the temperature.

2. The energy density of infrared heating is very large.The energy carried by infrared light is related to its 

wavelength and the power per unit area of the infrared light source, which can reach up to 1000kw/㎡.In the practical sense, the infrared power density can reach 200kw/㎡, and it is easy to design a general infrared heating furnace at 10-40kw/㎡.The hot air at 600°C does not have an energy of 40kw/㎡ at a speed of 10m/s.