An Introduction to Heat Transfer

In this lecture, five engineering applications of heat transfer will be explored. Heat Transfer has numerous applications from electronics cooling to heating spacecrafts in outer space. 

In this lecture further details on conduction will be covered, mainly the thermal conductivity of materials.

In this lecture the factors that resist conduction heat transfer will be covered.

In this lecture, the equation to solve conduction also known as the Fourier Equation will be introduced

This video lecture covers how heat transfer through conduction is calculated

Student will be able to partially understand convection after watching this video

In this lecture, the details on convection will be revealed, in particular convective heat transfer coefficient

In this lecture, some of the factors that stifle convection have been covered.

Natural Convection is better when the fluid movement is unforced. Or in other words a fluid is not being pushed over a surface by means of a blower or a pump. 

For example if a hot surface gets in contact with air, the air particle right next to the surface will be passed on the heat energy which will increase their kinetic energy. These particles will leave the surface, creating a gap which is filled up by other molecules of lower kinetic energy or lower temperature. And thus the cycle continues. If the volume of the fluid is enclosed, its possible that the locus of particles forms a closed loop.  This is called a convection current where the hot fluid is constant replaced by colder fluid. 

The phenomenon is represented in the diagram.

Natural convection has many real life examples. For instance heat passed on the water in a sauce pan boiling over a hob.

Similarly the cooling down of the finned engine of a motorbike when it stops in another example.

To enhance natural convection, the area of heat transfer is sometimes increased. Heat sinks are used for this purpose. 

In this lecture a very basic formula for convection has been covered

In this video tutorial, a basic convection problem is solved using a simple equation

Unlike Conduction and Convection which require matter (solid or liquid) to transfer heat, Radiation does not.

Radiation is the transfer of heat through electromagnetic rays. Examples of radiative heating are numerous. The most obvious is the sun heating our planet.

One has to remember in the 90 million miles between earth and sun there is a vacuum. The is what we call space. There is a no matter, no solid molecules to vibrate or fluid molecules to convect. Yet the heat from the sun is received in the form of electromagnetic (light rays) and our planet is able to sustain life.

 Similarly one can feels the scorching sun on the beach even with a cool breeze. The camp fire provides heat despite several feet away. The BBQ gets cooked by halogen light heater etc.

It should be understood that every material object inside the universe emits electromagnets rays based on their temperature. Even desk and chair are emitting radiation and so does the sun. The difference is that desk and chair are emitting radiation in the infrared range whereas the sun is emitting portion of its radiation in visible range. The wavelength of radiation depends upon the heat of the object. Similarly every object is also receiving electromagnetic radiation emitted from other objects. Part of this received radiation is absorbed while part of it is reflected. As long as there the amount of radiation emitted is equal to the amount of radiation absorbed, the body remains in equilibrium.

If the object under consideration loses more radiation than it receives, than it would cool and its temperature would drop. In fact, before refrigerator were a household product, ice was made in the mid evil ages through radiative cooling.

On a cloudless night, if one looks upwards toward the sky, the within 15 seconds, the face feels cooler. This is because it the face is losing radiation to outer space while its receiving little radiation from it. 

For making ice a few centuries earlier, a shallow basin  facing the sky would be carved out in  stone. Water would be filled in the basin and would be left overnight. The water would freeze and ice would be scrapped from the basin. This procedure was used to make ice even in regions near the equator.  In the northern hemisphere a block would be placed on the east or south-east side of the basin to protect it from the sun rays in the morning.

This lecture explores how radiative heat gain / loss can be avoided.

In this lecture the calculation and equations of radiation are covered

This video tutorial looks at solving a basic radiation problem using Stefan Boltzman Law

Examples of Heat Transfer from nature and engineering are explored in this lecture

The video summarizes all the important points learned in this course