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| Understanding of System -> Reflective Insulation System -> Fundamental of Heat Transfer |
| Understanding and Using of Radiant Barrier and Refelctive Insulation System Fundamentals of Heat Transfer
thremalThere is three ways of heat transfer :
- Conduction-direct contact of heat source through solid or fluid materials
- Convection-heat transfer through physical movement of air
- Radiation-heat transfer by radiant energy through an air space
thremalConduction
- Conduction is the direct flow of heat through a material resulting from physical contact.
- A typical example of conduction would be the heat transferred from hot coffee, through the cup, to the hand holding the cup.
- Another example, as shown below, the contents of the kettle boils from heat transferred from the burner to the kettle.
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保温Convection
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| therConvection in buildings is the transfer of heat caused by the movement of heated air. In a building space, warm air rises and cold air settles to create a convection loop and is termed free convection. Convection can also be caused mechanically, (termed forced convection), by a fan or by wind.
therOne of the example will be usage of heater in winter and air-conditioning in summer.
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Radiation
therRadiation is the transfer of heat (infra-red radiant energy) from a hot surface to a cold surface through air or vacuum. All surfaces including a radiator, stove, a ceiling or roof and ordinary insulation radiate to different degrees. The radiant heat is invisible and has no temperature, just energy. When this energy strikes another surface, it is absorbed and increases the temperature of that surface. This concept can be understood with the following example: On a bright sunny day, radiation from the sun strikes the outer surfaces of walls and roofs and is absorbed causing the surface to heat up, temperature rise, the outer surface of the wall and roof now become radiation source which is then radiated again, through the air spaces in the building, to other surfaces within the building. |
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Which is the major contributor for heat gain and lose? Conduction? Convection or radiation?
therAnalysis have been done to study which mode of the heat transfer is the major contributor for summer heat gain and winter heat lose. therStudy had found that radiation heat contributes more then 85% of the total heat transfer in any close system, example, residential houses.
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