Introduction:
The study of temperature distribution and heat transfer is of great importance to engineers because of it’s almost occurrence in many branches of science and engineering। The first step in the optimal design of heat exchangers such as boilers, heaters, refrigerators, radiators and other devices is based on the analysis of heat transfer. This is essential to determine the feasibility and cost of undertaking, as well as the size of equipment required to transfer specified amount of heat in given time.
This project is mainly dealing with heat transfer through rectangular fins composed of two different materials that are Brass and Aluminum respectively. Whenever generation of excess heat takes place in a confined area, then we need to dissipate this heat into atmosphere, for this purpose extended surfaces are (fins) are used. These surfaces can be triangular, annular, square, rectangular or circular in cross- section. The rate of heat transfer from these fins depends on various parameters such as shape, size, thermal conductivity etc. This project model can be used to find effectiveness, temperature profile, and actual heat transfer and tip temperature of the fins. A comparison between two different materials at different temperatures can also be made with the help of this model. The detailed analysis is discussed further in the report.
Mechanisms of heat transfer:
The energy transfer of heat takes place by three distinct modes: Conduction, Convection and Radiation.
Heat conduction is the mode of heat transfer accomplished via two mechanisms:
By the molecular interaction whereby the energy exchange takes place by the kinetic motion or direct impact of molecules. Molecules at a relative high energy level (temperature) impart energy to adjacent molecules at lower energy levels. This type of energy transfer always exist so long as there is temperature gradient in a system comprising molecules of solid, liquid or gas.
By the drift of ‘free’ electrons as in case of metallic solids. The metallic alloys have a different concentration of free electrons and there ability to conduct heat is directly proportional to the concentration of free electrons in them.
Convection is possible only in the presence of a fluid medium. When a fluid flows inside a duct or over a solid body and the temperature of the body and fluid are different, heat transfer between fluid and solid surface will take place. This is due to the motion of fluid relative to the surface. This type of heat transfer is called convection. The transport of heat here is inseparably linked with the movement of the fluid itself. If the fluid motion is set up by buoyancy effects resulting from density variation caused by the temperature difference in the fluid, the heat transfer is said to be free or natural convection. On the other hand if the fluid motion is artificially created by means of an external agency like a blower or fan, the heat transfer is termed as force convection.
As the energy transfer between solid surface and the fluid at the surface can take place only by the conduction, the heat transfer by convection is always accompanied by conduction.
If two bodies at different temperatures are placed in evacuated adiabatic enclosure so that they are not in contact through a solid or liquid medium, the temperature of two bodies will tend to become equal. The mode of heat transfer by which equilibrium is achieved is called thermal radiation. Radiation is an electromagnetic wave phenomenon, and no medium is required for its propagation. In fact the energy transfer by radiation is maximum when the two bodies exchanging energy are separated by perfect vacuum. Thermal radiation depends only on the temperature and on the optical properties of the emitter.
Apart from the identification of different modes of heat transfer it is also important to determine whether a process is steady or unsteady. A steady process is one which is not dependent on time that is the rate of heat transfer does not vary with time. In steady state system there is no change in the internal energy of the system because the rate of energy influx is equal to rate of energy efflux.
When the temperature at various points varies with change in time then the process is called transient or unsteady process.
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