Before we go the methods of Heat Transfer lets first understand Temperature, Thermal Energy and Thermal Equilibrium :
Temperature :
Any Solid / Liquid / Gasious model of matter consist of particles which Vibrate, Translate – move from one location to another and Rotate about an imaginary axis. These motions give the particles kinetic energy. Temperature is a measure of the average amount of kinetic energy possessed by the particles in a sample of matter. The more the particles vibrate, translate and rotate, the greater the temperature of the object.
Thermal Energy :
Thermal energy is produced when a rise in temperature causes atoms and molecules to move faster and collide with each other. The energy that comes from the temperature of the heated substance is called thermal energy.
Differance between Themerature and Thermal Energy :
- Temperature is a measure of the average kinetic energy.
- Thermal energy is the total energy an object has due to the internal motions of its particles.
Thermal equilibrium :
Two physical systems are in thermal equilibrium if there is no net flow of thermal energy between them when they are connected by a path permeable to heat.
Heat Transfer :
- Heat is a flow of energy from a higher temperature object to a lower temperature object.
- It is the temperature difference between the two neighboring objects that causes this heat transfer.
- The heat transfer continues until the two objects have reached thermal equilibrium and both are at the same temperature.
Methods of Heat Transfer :
- There are 3 methods of Heat Transfer :
- Conduction is the transfer of heat energy by direct contact,
- Convection is the movement of heat by actual motion of matter;
- Radiation is the transfer of energy with the help of electromagnetic waves.
Conduction :
- Conduction is process which enables direct transfer of heat through the matter, due to the difference in temperature, between adjacent parts of the object.
- When two objects are in direct contact with one another, there will be transfer of heat from the hotter object to the colder, it is due to conduction.
- The objects which permit heat to travel easily through them are called conductors.
Convection :
- Convection is form of heat transfer, by movement of matter, that occurs in fluids (Liquid and Gas).
- Fluid’s molecules move freely from one place to another, It happens naturally or forcefully.
- Gravity plays great role in natural convection such that when the substance is heated from below, leads to the expansion of the hotter part.
- Due to buoyancy, the hotter substance rises as it is less dense and the colder substance replaces it by sinking at the bottom, due to high density, which when gets hot moves upward, and the process continues.
- In convection, on heating up the substance, it’s molecules disperse and moves apart.
- When the convection is performed forcefully, the substance is compelled to move upwards by any physical means such as fan.
Radiation :
- In this process, the energy is transmitted through electromagnetic waves called as radiant energy.
- Hot objects generally emit thermal energy to cooler surroundings. Radiant energy is capable of travelling in the vacuum from its source to the cooler surroundings.
- This heat transfer does not require medium.
- It refers to the movement of heat in waves, as it does not need molecules to travel through.
- The object need not be in direct contact with one another to transmit heat.
- Colour, Surface orientation, etc. are some of the surface properties on which radiation depends.