CONDUCTION, CONVECTION, RADIATION HEAT TRANSFER.

MODES OF HEAT TRANSFER 

• CONDUCTION HEAT TRANSFER
• CONVECTION HEAT TRANSFER
• RADIATION HEAT TRANSFER

CONDUCTION HEAT TRANSFER 

• Conduction heat transfer is single phase phenomenon , its tack place due to molecular impact & electrons flow 
• we know that every substance having molecular structure and molecules are vibrating continuously
• when molecular impact take place heat transferred form one molecule to another molecule
• In metals the atomic structure consist of electrons, due to high temperature energy level of electron increases & it leaves its atom carrying excess energy this phenomenon is similar to flow of current
• for the conduction heat transfer always apply fourier's law of heat conduction
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CONVECTION HEAT TRANSFER

• convection heat transfer is a two phase phenomenon, in which at least one substance is fluid 
• the fluid molecules are free to move so they take heat from surface of the other substance accordingly heat is transferred
• For convection heat transfer always applying newtons cooling law
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RADIATION HEAT TRANSFER

• Radiation heat transfer does not required any medium for the heat transfer 
• in the radiation heat transfer heat is transfer through electromagnetic waves 
• heat flow from higher body temperature to lower body temperature
• For radiation heat transfer always apply stefan boltzman's law of heat transfeR
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THERMAL CONDUCTIVITY

• Thermal conductivity is the ability of materials to conduct the heat through it,
•  it can be also defined as the the rate of heat transfer through a unit thickness of material per unit area per unit temperature difference 

1. thermal conductivity of material is a measure of how heat will flow in that material 
2. the large value of thermal conductivity indicates that the material is good good heat conductor and the low value indicates that material is poor heat conductor or insulator
3. the thermal conductivity is measure in watt per metre per degree celsius or watt per metre kelvin
4. thermal conductivity of substances is high in solid phase and lowest in gaseous phase

FACTORS ON WHICH THERMAL CONDUCTIVITY DEPENDS

1. The value of thermal conductivity depends upon the manner in which energy transferred, 
2. The pure metals allow faster transmission of heat energy through the vibration or crystal latics,therefore metal in pure state has maximum thermal conductivity and is a good conductor
3. the thermal conductivity decreases by increases impurities in metal 
1. more non-metals are poor heat conductor hence its called as thermal insulator