Processes of thermal heat energy:

(i) Conduction

Heat gets transferred from one atom to the other.

Heat conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their heat energy to these neighboring particles. Heat is transferred by conduction when adjacent atoms vibrate against one another, or as electrons move from one atom to another. 

Conduction is the most significant means of heat transfer within a solid or between solid objects in thermal contact. Gases and liquids are less conductive, hence convection is more dominant in gases and liquids. 

Thermal contact conductance is the study of heat conduction between solid bodies in contact. Hence, due to heat conduction, materials that can easily conduct heat tend to spread heat faster, thus materials that are poor conductors of heat should be used.

(ii) Convection

Convection is the transfer of heat from one place to another by the movement of fluids. It is a process that is essentially the transfer of heat via mass transfer. Bulk motion of fluid enhances heat transfer in many physical situations, such as, between a solid surface and the fluid. Convection is usually the dominant form of heat transfer in liquids and gases.

Convection occurs when bulk fluid motion, for example, steams and currents are caused by buoyancy forces that result from density variations due to variations of temperature in the fluid. Forced convection is a term used when the streams and currents in the fluid are induced by external means—such as fans, stirrers, and pumps—creating an artificially induced convection current. 

Thus, convection accounts for how heat travels within liquids and gases and thus, some substances, such as water, are poor conductors of heat and air, is a poor conductor of heat as well.

(iii) Radiation

Radiation is often concentrated to penetrate items.

Thermal radiation is energy emitted by matter as electromagnetic waves due to the pool of thermal energy that all matter possesses that has a temperature above absolute zero. Thermal radiation still occurs without the presence of matter through vacuum.

Thermal radiation is a direct result of the random movements of atoms and molecules in matter. Since these atoms and molecules are composed of charged particles (protons and electrons), their movement results in the emission of electromagnetic radiation, which carries energy away from the surface.

Unlike conductive and convective forms of heat transfer, thermal radiation can be concentrated in a small spot by using reflecting mirrors, which is exploited in concentrating solar power generation.

Hence, radiation allows heat to be transferred no matter what the circumstances are. It is often used in thermal flasks to ensure the substance in it will not lose or gain heat easily.

(iv) Advection

Advection is a way of transportation. It often refers to horizontal transportation of heat and humidity.

The way the silt is advected (transported) downstream in the rivers, in the same way everything can be advected in any fluid. Advection is also important part of hydrological cycle; in formation of oragraphic clouds and the precipitaton of water from clouds.

For heat, by transferring matter, energy, including thermal energy, is moved by the physical transfer of a hot or cold object from one place to another. Placing hot water in a bottle and heating a bed are examples of advection. Another practical example is thermal hydraulics.