Heat Transfer Assignment Help
Heat transfer comes under the purview of thermodynamics. To put it simply, Heat transfer
deals with the amount of heat transfer that takes place in a system from one state of
equilibrium to another. This might not take into account the time taken for the heat transfer
or the amount of heat transferred over a period of time.
Why does heat transfer take place?
Heat is a form of energy that moves along temperature difference. Heat transfer is energy
transfer from one region to another because of the difference in temperature that exists
between them. If in a closed system, if there is a temperature difference, then heat transfer
must take place.
Engineers, especially chemical engineers are concerned with the amount of heat transferred
over a period of time as well as the distribution of temperature in a system over a period of
time. This is evident in most of the appliances at work. For example, in a room heater or in a
refrigerator the amount of heat transferred over a period of time is of much importance. In
both these cases, the higher the heat transferred in shorter period of time means efficiency.
Types of heat transfer
The heat that transfers can be differentiated into two types. One is Steady-state heat
transfer and other is unsteady-state heat transfer.
In steady-state heat transfer, the amount of heat transferred will be the same over a period
of time and the temperature in any location will not change with time. The formula is T = f
(x, y, z).
In unsteady-state heat transfer, the amount of heat transferred will not be the same with
the passage of time. The formula is T = f (x, y, z; t).
Modes of Heat Transfer
Conduction: Heat gets transferred when a difference of temperature exists in the medium.
The medium can either be a solid, liquid or a gas. This type of heat transfer is called
conduction. In heat transfer through conduction, the molecules in high energy state or
higher temperature transfer their energy to the molecules of low energy state or lower
temperature. Thermal energy in solids gets transferred both through electrons as well as by
vibrations. The heat transfer through electrons is very powerful compared to heat transfer
through vibrations. In most cases, metals are good conductors of electricity as well as heat,
due to the presence of large number of electrons. These electrons carry heat from one state
of temperature to another state of temperature in a similar fashion to carrying electrical
charge. The heat transfer rate gets deteriorated from solids to liquids to gases. In gases,
unless and until, high pressure is applied, there is negligible amount of heat transfer taking
Convection: When heat is transferred from the surface to a moving medium with difference
in temperature, then it is called convection. For heat transfer to occur in convection mode,
there must a presence of fluid particles. The movement of fluids between high temperature
region to low temperature region is what the basic governing law in convection heat
transfer. The faster the motion of fluids through the medium the greater will be the heat
transfer. In convection model, there are further two types of heat transfer. One is diffusion
method and the other is advection method.
Thermal Radiation: The third mode is called thermal radiation. According to thermal
radiation, any object with finite temperature will emit energy in the form of electromagnetic
waves. Thermal radiation does not require any medium for transfer. According to Maxwell,
the radiation emitted by a body is transferred in space in the form of electromagnetic
waves. According to Max Planck, the radiation emitted by a body is transferred in the form
of photon particles. Thermal radiation occurs due to a change in the electronic configuration
in the molecules.