Lecture Notes (10); Handouts (30); Others (12) Basics of Heat Transfer, Student Slides-Basics of Heat Transfer, PDF, kb. One Dimensional Steady State Heat Conduction, Student Slides-One Dimensional Steady State Heat. Heat Transfer NOTES. Thermal Energy. TOTAL energy of motion in molecules of a substance. (therm=heat). Temperature. Average amount of energy in motion. A heat transfer textbook / John H. Lienhard IV and. John H. Lienhard V — 3rd ed. — Cambridge, MA: J.H. Lienhard V, c Includes bibliographic references.


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Any energy exchange between bodies occurs through one of these modes or a combination of them.

NPTEL :: Mechanical Engineering - Heat and Mass Transfer

Conduction is the transfer of heat through solids or stationery fluids. Convection uses the movement of fluids to heat transfer notes heat. Radiation does not require a medium for transferring heat; this mode uses the electromagnetic radiation emitted by an object for exchanging heat.

When you touch a hot object, the heat you feel is transferred through your skin by conduction. Two mechanisms explain how heat is transferred by conduction: Conduction through solids occurs by a combination of the two mechanisms; heat is conducted through heat transfer notes fluids primarily by molecular collisions.

In solids, atoms are bound to each other by a series of bonds, analogous to springs as shown in Figure 1.


When there is a temperature difference in the solid, the hot side of the solid experiences more vigorous atomic movements. The vibrations are transmitted through the springs to the cooler side of the solid. Eventually, they reach an equilibrium, where all the atoms are vibrating with the same energy.

Solids, especially metals, have heat transfer notes electrons, which are not bound to heat transfer notes particular atom and can freely move about the solid.

The electrons in the hot side of the solid move faster than heat transfer notes on the cooler side. This scenario is shown in Figure 1. As the electrons undergo a series of collisions, the faster electrons give off some of their energy to the slower electrons. Eventually, through a series of random collisions, an equilibrium is reached, where heat transfer notes electrons are moving at the same average velocity.

Conduction through electron collision is more effective than through lattice vibration; this is why metals generally are better heat conductors than ceramic materials, which do not have many free electrons.

The mechanism is identical to the electron collisions in metals. The effectiveness by which heat is transferred through a material is measured by the thermal conductivity, k.


A good conductor, such as copper, has a high conductivity; a poor conductor, or an insulator, has a low conductivity.

The rate of heat transfer by heat transfer notes is given by: In heat transfer, a positive q means that heat is flowing heat transfer notes the body, and a negative q represents heat leaving the body. The negative sign in Eqn.

EN43ME Lecture Notes

In a typical convective heat transfer, a hot surface heats the surrounding fluid, which is then carried away by fluid movement such as wind. The warm fluid is replaced by cooler heat transfer notes, which can draw more heat away from the surface.


Since the heated fluid is constantly replaced by cooler fluid, the rate of heat transfer is enhanced. Natural convection or free convection refers to a case heat transfer notes the fluid movement is created by the warm fluid itself.

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The density of fluid decrease as it is heated; thus, hot fluids are lighter than cool fluids. Warm heat transfer notes surrounding a hot object rises, and is replaced by cooler fluid.

The result is a circulation of air above the warm surface, as shown in Figure 1. Forced convection is what makes a windy, winter day feel much colder than a calm day with same temperature.

Heat transfer notes heat loss from your body is increased due to the constant replenishment of cold air by the wind.

Heat Transfer

Natural wind and fans are the two most common sources of forced convection. Convection coefficient, h, heat transfer notes the measure of how effectively a fluid transfers heat by convection.

Wind blowing at 5 mph has a lower h than wind at the same temperature blowing at 30 mph.

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