Heat Transfer · 6 min read
Conduction
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Introduction to Heat Transfer
Heat is like a visitor that always wants to move from a very hot place to a cooler place. If you put a metal spoon inside a hot bowl of pepper soup, you will notice the handle becomes hot after some time. This movement of heat through a solid material is what we call Conduction.
Understanding Conduction
In every solid object, there are tiny particles called atoms. When one end of the object gets hot, the particles there start vibrating very fast. They hit their neighbors and pass the heat energy along, just like how people standing in a queue might push each other until the push reaches the front.
Simply put, conduction is heat traveling through a solid without the solid itself moving from one place to another.
Conductors and Insulators
Materials do not carry heat at the same speed. Some are fast, while others are very slow. We group them into two types:
Conductors: These are materials that allow heat to pass through them easily. Metals like copper, aluminum, and silver are great conductors. This is why our cooking pots are made of metal.
Insulators: These are materials that do not allow heat to pass through easily. Examples include wood, plastic, cork, and air. This is why the handle of a frying pan is often made of plastic or wood.
Factors affecting the rate of conduction
The speed at which heat moves through a material depends on four things:
1. The temperature difference between the two ends: The hotter one side is compared to the other, the faster heat flows.
2. The cross-sectional area: A thick rod will conduct more heat than a thin wire.
3. The length of the material: Heat travels faster through a short stick than a very long one.
4. The nature of the material: Copper will always conduct heat faster than iron because of its internal structure.
Thermal Conductivity Calculation
We use a formula to calculate the amount of heat (Q) conducted through a material over a period of time (t). The formula is: Q/t = (k * A * (T2 - T1)) / L.
In this formula, 'k' is the Thermal Conductivity of the material, 'A' is the area, 'T2 - T1' is the temperature difference, and 'L' is the thickness or length.
Worked Example
A glass window has an area of 0.5 m2 and a thickness of 0.02 m. If the inside temperature is 30 degrees C and the outside is 20 degrees C, calculate the rate of heat flow. (Take k for glass = 0.8 W m-1 K-1).
Solution: Rate of heat flow is Q/t. Formula: Q/t = (k * A * change in T) / L. Calculation: (0.8 * 0.5 * (30 - 20)) / 0.02 = (0.8 * 0.5 * 10) / 0.02 = 4 / 0.02 = 200 Watts (J s-1).
Key points
- •Conduction happens mainly in solids.
- •Heat moves from hot regions to cold regions.
- •Metals are good conductors; wood and plastic are insulators.
- •There is no bulk movement of the material during conduction.
- •Thermal conductivity measures how well a material conducts heat.