1 What are the two mechanisms of conduction heat transfer in

1) What are the two mechanisms of conduction heat transfer in metals ?

2) Explain how conduction of heat through gases occurs ??? and what system properties and conditions lead to higher or lower conductivities ???

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please answer the questions not just putting whatever. Thanks

Solution

1) Two mechanisms of conduction heat transfer in metals are :

(a) By means of Free Electrons( especially in metals) -: This mode of heat conduction is through free electrons, which are free to move through the lattice structure of the metal, present in the metal. Free electrons provide an energy flux in the direction of decreasing temperature.

(b) By means of Lattice Vibration (especially in non metals) -: This mode of heat conduction is through the vibrational energy in the lattice structure.

In solids as temperature increases molecules will begin to vibrate. Molecules having higher temperature at the hot part of the body will vibrate with more agitation than molecules at the lower temperature part of the body. In conduction heat transfer kinetic energy is translated between the molecules which are very adjacent to each other while vibrating and this energy is kept on transferring from hot region to the cold region.

2) In case of gases conduction is due to momentum transfer by molecular movement is called diffusion. During collision,the less active particlesalso gets excited, i.e., thermal energy is imparted to them. The process is repeated layer after layer of molecules.

System properties and conditions for Thermal conductivity (k) :

(a) Temperature : Increasing the temperature,

k ( of solids) => decreases because the electron flow decreases.

k( of liquids) => decreases beacuse the intermolecular distance is increased.

k (of Gases) => increases because k for gases is the function of Temperature and degree of randomness increases.,i.e, faster collision of molecules takes place.

order of themal conductivity of different materials decreases in the following order:

1. Pure metals

2. Alloys

3. Non Metals

4. Liquids

5. Gases