The complete guide about Heat Transfer System. Here you can get Some Important Terms Used in Heat Transfer – Methods of Heat Transfer ect.
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
Some important definitions
Terms that we must know to understand the science of heat transfer are given below:
1.Steady:– Steady is generally used for properties. Steady property means there is no change in that property with time at a specified location.
For Example:– Steady temperature at a point p means no change in the temperature at point p with time.
2.Unsteady or transient:– Unsteady or transient is opposite of steady. It means the property may changes at a specified point with time.
For Example:– Transient temperature means temperature at point p change with time at point p.
3.Uniform:– It is also used for properties. Uniform property means there in no change in that property with position at a specified time or the property remain unchanged in the entire system.
For Example:– Uniform pressure means pressure at all points in the system is same.
4.Non-uniform:– It is opposite of uniform, it means that the property may change with position at a specified time.
For Example:– Non-uniform temperature means the temperature is not same at different points in the entire body at a specified time.
5. One dimensional flow:– It method warmness might also additionally transfer only in one direction. It is taken into consideration while the surface area is very large then the thickness.
Example:- Heat transfer thru lengthy aircraft wall, in a pipe, metallic pan utilized in kitchen etc.
6. Three dimensional flow:– It method warmness might also additionally transfer in all of the 3 directions of the coordinate axis. It is take into account while the floor vicinity is not sufficient massive then thickness.
7. Heat generation:– It is the phenomenon of generation of heat in that medium thru which heat transfer takes place. It occurs by the conversion of electrical, mechanical, chemical energy into heat. It is a volumetric phenomenon.
For Example:– Conversion of electrical energy into heat in a wire through which electricity flows or in iron.
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 Transfer Methods
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.
Conduction of Heat Transfer
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.
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
- Q is the transfer of heat per unit time
- K is the thermal conductivity of the body
- A is the area of heat transfer
- Thot is the temperature of the hot region
- Tcold is the temperature of the cold region
- d is the thickness of the body
Following are the examples of conduction:
- Ironing of clothes is an example of conduction wherein the heat is conducted from the iron to the clothes.
- Heat is transferred from hands to ice cube resulting in the melting of an ice dice while held in hands.
- Heat conduction through the sand on the beaches. This can be experienced during summers. Sand is a good conductor of heat.
Convection of Heat Transfer
The movement of fluid molecules from higher temperature regions to lower temperature regions.
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)
- Q is the heat transferred per unit time
- Hc is the coefficient of convective heat transfer
- A is the area of heat transfer
- Ts is the surface temperature
- Tf is the fluid temperature
Examples of convection include:
- Boiling of water, that is molecules that are denser move at the bottom while the molecules which are less dense move upwards resulting in the circular motion of the molecules so that water gets heated.
- Warm water around the equator moves towards the poles while cooler water at the poles moves towards the equator.
- Blood circulation in warm-blooded animals takes place with the help of convection, thereby regulating the body temperature.
Radiation of Heat Transfer
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.
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
- P is the net power of radiation
- A is the area of radiation
- Tr is the radiator temperature
- Tc is the surrounding temperature
- e is emissivity and σ is Stefan’s constant
Following are the examples of radiation:
- Microwave radiation emitted in the oven is an example of radiation.
- UV rays coming from the sun is an example of radiation.
- The release of alpha particles during the decaying of Uranium-238 into Thorium-234 is an example of radiation.
Unit of Heat Transfer
|Rate of transfer of heat||KW|