Natural Convection-Radiation reaction in a cube filled with Gas

In convection, heat is transferred from one body to another with a medium present between and the heat travels from the heated body to the medium and then to the cold body and because of which heat is transferred to the surroundings. 

Density plays an important role in the heat transfer process as it does not follow the law of reflection and refraction.

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Radiation is the transfer of heat due to the emission of electromagnetic waves. 

Radiation and convection always need a medium to transfer heat from one body to another. Heat transfer is seen in all bodies whose temperature is greater than 0 K. It does not follow the law of reflection and refraction. 

Considering a cube which is filled with any gas, there can be two instances 

• Heating the cube externally and 
• Transfer of heat from the hot air present inside the cube 

Heating the cube externally: 

• In this process, first, the cube has to be heated and then the heat has to be transferred to the gas in the cube for uniform heating inside the cube. 
• The energy given to the cube can be in the form of heat, electricity, friction, or any other form. In this process, the main mode of heat transfer process involved is convection as the heat is transferred from a wall to the fluid i.e. air. 
• The heat supplied is first used to heat the walls of the cube. Based on the thickness of the wall of the cube time to heat the cube varies. 
• When the walls get heated up, these walls transfer the heat to the air present inside the cube, which in turn gets heated up. This process continues till the air inside the cube gets heated up and the temperature of the walls of the cube and the air present reaches the same temperature. 

Heat getting transferred from cube to the surroundings: 

• In this, the heat from the cube gets transferred to the surroundings. 
• In this case, the main mode of heat transfer is radiation. 
• The time taken is very less and the process is very rapid and can be easily checked or felt by placing the cube inside the water and we can see steam coming out which shows the transfer of heat. 
• The air present inside the cube is heated to a higher temperature than the surrounding. 

The air collides with the walls of the cube which transfers the heat to the walls and the temperature inside the cube gets lowered down and the walls of the cube gain heat and then transfers the heat to the surrounding medium. This process takes lesser time than convection as the change in temperature is more and the object size is smaller. 

The heat getting transferred is referred to as loss which cannot be reused, but the loss of the heat can be reduced by adding insulators or other materials that have less thermal coefficient (rate of heat transfer is less).

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Natural Convection-Radiation reaction in a cube filled with Gas