Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes
In general, heat transfer describes the flow of heat (thermal energy) due to temperature differences and the subsequent temperature distribution and changes.
According to thermodynamic systems, heat transfer is defined as
The motion of heat across the border of the system due to a difference in temperature among the device and its surroundings. Interestingly, the difference in temperature is said to be a ‘potential’ that causes the transfer of heat from one point to another. Besides, heat is also known as flux.
Heat can travel shift from one place to another in several ways. The different modes of heat transfer include:
Meanwhile, if the temperature difference exists between the two systems, heat will find a way to transfer from the higher to the lower system.
The process in which heat flows from objects with higher temperature to objects with lower temperature.
An area of higher kinetic energy transfers thermal energy towards the decrease kinetic energy area. High-speed particles clash with particles transferring at a slow speed, as a result, slow speed particles increase their kinetic energy. This is a typical form of heat transfer and takes location through physical contact. Conduction is also known as thermal conduction or heat conduction.
Conduction Equation
The coefficient of thermal conductivity shows that a metal body conducts heat better when it comes to conduction. The rate of conduction can be calculated by the following equation:
Q = [K.A.(Thot−Tcold)]d
Where,
Conduction Examples
Following are the examples of conduction:
The movement of fluid molecules from higher temperature regions to lower temperature regions.
Convection Equation
As the temperature of the liquid increases, the liquid’s volume also has to increase by the same factor and this effect is known as displacement. The equation to calculate the rate of convection is as follows:
Q = hc ∙ A ∙ (Ts – Tf)
Where,
Convection Examples
Examples of convection include:
Thermal radiation is generated by the emission of electromagnetic waves. These waves carry away the energy from the emitting body. Radiation takes place via a vacuum or transparent medium which can be either solid or liquid. Thermal radiation is the result of the random movement of molecules in the matter. The motion of charged electrons and protons is responsible for the emission of electromagnetic radiation.
Radiation Equation
As temperature rises, the wavelengths in the spectra of the radiation emitted decreases and shorter wavelengths radiations are emitted. Thermal radiation can be calculated by Stefan-Boltzmann law:
P = e ∙ σ ∙ A· (Tr – Tc)4
Where,
Radiation Example
Following are the examples of radiation:
SI system | Joule |
MKS system | cal |
Rate of transfer of heat | KW |