1, conduction
Conduction refers to the transfer of heat through molecular vibration and collision inside an object. When a part of an object is heated, the heat will be gradually transmitted to the whole object through the collision between particles. Conduction is the main way of heat transfer between solid and liquid with solid structure. The speed of conduction depends on the thermal conductivity of the object.
2. Convection
Convection refers to the transfer of heat through the convective movement of a fluid (liquid or gas). When an object comes into contact with the surrounding fluid and is heated or cooled, the molecules of the fluid are heated and form a thermal convection cycle. Through convection, heat can be quickly transferred to far away places. Natural convection is caused by density difference, while forced convection needs external force to drive fluid.
Step 3 radiate
Radiation means that heat is transferred by electromagnetic radiation without medium. When the temperature is higher than absolute zero, all objects will emit electromagnetic radiation, including thermal radiation. The energy of thermal radiation propagates in the form of light, and light can propagate through vacuum without the influence of medium. Radiation is the fastest way of heat transfer, and it is also the only way of heat transfer without medium.
Application scope of heat transfer:
1. Building and HVAC system: heat transfer is used to control indoor temperature, including conduction, convection and radiation. For example, the exchange of indoor and outdoor temperatures is prevented by the conduction of walls and windows, the air is heated or cooled by convection through air conditioning systems, and heat is transferred indoors by radiation.
2. Cooling system and radiator: Heat transfer plays an important role in the cooling and heat dissipation of automobiles, electronic equipment, power systems and industrial processes. Through conduction, convection and radiation, heat is transferred from the heat source to the cooling medium, so that the temperature of the equipment is kept within a safe range.
3. Utilization of heat energy: Heat transfer is used for the collection, conversion and utilization of heat energy. For example, solar water heaters use radiant heat transfer to convert solar energy into heat energy and supply hot water. Heat exchangers and steam generators use conduction, convection and radiation to transfer heat for heating, industrial production and power generation.