Engineering Magazine

Heat transfer is the process by which thermal energy is exchanged between different objects or regions due to temperature differences

Law of Heat Transfer

1. Law of Conduction

2.Newtons Law of Cooling

3.Law of Radiation

                

    There are three main mechanisms of heat transfer: conduction, convection, and radiation.

Conduction: This process occurs when heat is transferred through direct contact between particles or molecules within a substance.         It’s prevalent in solids and is governed by Fourier’s Law of Heat Conduction.

Fourier’s Law of Heat Conduction:-   This law states that the rate of heat transfer through a material is directly proportional to the temperature difference across the material, the cross-sectional area of the material, and inversely proportional to the distance the heat has to travel.

In mathematical terms:

Q = -k * A * (ΔT / d)

where:

Q = Heat transferred per unit time

k = Thermal conductivity of the material

A = Cross-sectional area through which heat is transferred

ΔT = Temperature difference across the material

d = Distance over which heat is transferred

Convection: Convection involves the transfer of heat through the movement of fluids (liquids or gases). It can occur through natural convection (due to density differences causing fluid movement) or forced convection (assisted by external forces like fans or pumps).

Newton’s Law of Cooling describes convection in terms of the rate of heat transfer from a solid surface to a fluid:

Q = h * A * ΔT

where:

Q = Heat transferred per unit time

h = Heat transfer coefficient

A = Surface area through which heat is transferred

ΔT = Temperature difference between the solid surface and the fluid

Radiation: Radiation is the transfer of heat through electromagnetic waves, such as infrared radiation. All objects with a temperature above absolute zero emit radiation.

The Stefan-Boltzmann Law quantifies the total energy radiated by an object:

Q = ε * σ * A * T^4

where:

Q = Heat radiated per unit time

ε = Emissivity of the object (0 ≤ ε ≤ 1)

σ = Stefan-Boltzmann constant A = Surface area of the object

T = Absolute temperature of the object

These laws collectively explain how heat is transferred from hotter regions to cooler regions. Conduction is dominant in solids, convection in fluids, and radiation occurs in all objects regardless of the surrounding medium. The combination of these mechanisms determines the overall heat transfer in various situations