The document discusses the three main modes of heat transfer: conduction, which is the transfer of heat between objects in direct contact; convection, which is the transfer of heat by the movement of fluids like gases and liquids; and radiation, which is the transfer of heat through electromagnetic waves such as infrared and visible light. Specific examples are provided for each type of heat transfer, and the key equations governing conduction, convection, and radiation are defined.

1. HEAT TRANSFER
DR. ANERI PATWARI
MPT-CARDIORESPIRATORY
ASSISTANT PROFESSOR

4. CONDUCTION
•process by which heat is transferred from the hotter end to the colder end
of an object.

5. CONDUCTION
•The law of heat conduction, also known as Fourier's law, states that the
rate of heat transfer through a material is proportional to the
negative gradient in the temperature and to the area, at right angles to
that gradient, through which the heat flows
•q= -K ∇T
•where (including the SI units)
•Q is the local heat flux density, W/m2,
•K is the material's conductivity, W/(m·K),
•∇T is the temperature gradient, K/m.

6. CONDUCTION
EXAMPLES
•Ironing of clothes is an example of conduction where 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 cube when held in hands.
•Heat conduction through the sand at the beaches. This can be
experienced during summers. Sand is a good conductor of heat.

7. CONVECTION
•Transfer of heat from one place to another due to the
movement of fluid. Although often discussed as a distinct
method of heat transfer, convective heat transfer involves
the combined processes of conduction (heat diffusion)
and advection (heat transfer by bulk fluid flow).
Convection is usually the dominant form of heat transfer
in liquids and gases

8. CONVECTION
•The basic relationship for heat transfer by convection is:
•Q˙=ℎA(T− Tf)
•Where Q˙ is the heat transferred per unit time,
• A is the area of the object,
• h is the heat transfer coefficient,
• T is the object's surface temperature, and
• Tf is the fluid temperature

10. CONVECTION
EXAMPLES
•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.

11. RADIATION
Radiant heat is present in some or other form in our daily lives. Thermal
radiations are referred to as radiant heat. Thermal radiation is
generated by the emission of electromagnetic waves
These waves carry away the energy from the emitting body. Radiation
takes place through a vacuum or transparent medium which can be
either solid or liquid.
Thermal radiation is the result of the random motion of molecules in
matter.
Radiation heat transfer is measured by a device known as
thermocouple. A thermocouple is used for measuring the temperature.

12. RADIATION
•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 (σ = 5.67 × 10-8Wm-2K-4

13. RADIATION
•EXAMPLES
•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.

14. RADIATION