Basic concept of Heat Transfer

Heat Energy and Heat Transfer

Heat is a form of energy in transition and it flows from one system to another, without transfer of mass, whenever there is a temperature difference between the systems. The process of heat transfer means the exchange in internal energy between the systems and in almost every phase of scientific and engineering work processes, we encounter the flow of heat energy. 

Modes of Heat Transfer

The heat transfer processes have been categorized into three basic modes: Conduction, Convection and Radiation.

Conduction – 

It is the energy transfer from the more energetic to the less energetic particles of a substance due to interaction between them, a microscopic activity.

 Heat Transfer by conduction = Qx =-k dt/dx  w/m2

Convection - 

  It is the energy transfer due to random molecular motion a long with the macroscopic motion of the fluid particles. 

Heat transfer by convection = Q = hc x A x (Tfluid-Tobject)

Radiation - 

It is the energy emitted by matter which is at finite temperature. All forms of matter emit radiation attributed to changes m the electron configuration of the constituent atoms or molecules The transfer of energy by conduction and convection requires the presence of a material medium whereas radiation does not. In fact radiation transfer is most efficient in vacuum.

Heat Transfer by Radiation

q = ε σ (Th4 - Tc4) Ac

T_h = hot body absolute temperature (K)

T_c = cold surroundings absolute temperature (K)

A_c = area of the object  (m²)

σ = 5.6703 10^-8 (W/m²K⁴)

The Stefan-Boltzmann Constant

Thermodynamics and Heat Transfer-Basic Difference

Thermodynamics is mainly concerned with the conversion of heat energy into other useful forms of energy on

(i)          the concept of thermal equilibrium (Zeroth Law),

(ii)        the First Law (the principle of conservation of energy) and

(iii)      The Second Law (the direction in which a particular process can take place).

Thermodynamics is silent about the heat energy exchange mechanism. The transfer of heat energy between systems can only take place whenever there is a temperature gradient and thus. Heat transfer is basically a non-equilibrium phenomenon

However, the subjects of heat transfer and thermodynamics are highly complementary. Many heat transfer problems can be solved by applying the principles of conservation of energy (the First Law).