1. University of Halabja
college of science
Department physics
Heat transfer
Prepared by :
Shene Aziz

2. Outline
• What is heat transfer
• Types heat transfer
• Conduction
• Convection
• Radiation
• Same application of heat transfer

3. What is heat transfer
In general, heat transfer describes the flow of heat (thermal energy) due
to temperature differences and the subsequent temperature distribution
and changes. The study of transport phenomena concerns the exchange of
momentum, energy, and mass in the form of conduction, convection, and
radiation.

4. Types heat transfer

5. Conduction:
Conduction heat transfer is the transfer of heat by means of molecular
excitement within a material without bulk motion of the matter. Conduction
heat transfer in gases and liquids is due to the collisions and diffusion of the
molecules during their random motion. On the other hand, heat transfer in
solids is due to the combination of lattice vibrations of the molecules and the
energy transport by free electrons.

7. Convection :
Convective heat transfer is the transfer of heat between two bodies by currents of
moving gas or fluid. In free convection, air or water moves away from the heated
body as the warm air or water rises and is replaced by a cooler parcel of air or water.
In forced convection, air or water is forcibly moved across the body surface (such as
in wind or wind-generated water currents) and efficiently removes heat from the
body. Convection is a very efficient way of heat transfer because it maintains a
steep temperature gradient between the body and surrounding air or water.

9. Radiation :
Heat transfer from a body with a high temperature to a body with a lower
temperature, when bodies are not in direct physical contact with each other or when
they are separated in space, is called heat radiation [1], as schematically shown in.
All physical substances in solid, liquid, or gaseous states can emit energy via a
process of electromagnetic radiation because of vibrational and rotational
movement of their molecules and atoms [2]. The intensity of such energy flux
depends upon the temperature of the body and the nature of its surface [3]. The
radiation occurs at all temperatures, with the rate of emission increasing with the
temperature.

11. Same application of heat transfer
Heat transfer in the space environment and its applications in aerospace
engineering are of great significance in various fields, such as electronic
cooling, aircraft engine cooling, space shuttle thermal protection, space borne
thermal radiometers, aircraft environmental control systems, and cryogenic
systems for .