Heat Transfer: Physics and Case Study

I realized that I never wrote any article on this blog about heat transfer and thermal analysis… such a shame not to write about such a fascinating topic!

If you never really did heat transfer analysis or if you never really thought about it, you are missing something huge!

Here the trip that I propose to you in this article:

I will first tell you what the temperature actually means and where it comes from, then I’ll describe to you the 3 different types of heat transfer that exist in nature and finally, I’ll tell you how to do thermal analysis with FEA.

How does that sound? ;-)

If that sounds good to you, let’s start the ride!

What does the temperature represent?

The concept of temperature seems so obvious that we generally don’t even ask ourselves where it comes from.

Now I feel that you start to become curious… ;-)

From where is this concept of temperature even coming from?

To answer this question, we have to dive into the realm of the ? Angstromscopic ? (what? This word doesn’t exist? Yep, I just invented it)

Let’s take a close look at some water.

As (nearly) everyone knows, water is composed of molecules H2O

If the molecules of water are well structured under a certain crystal form, they form a solid… in the case of water, those molecules form ice.

Well, it happens that those molecules can be closer to one another… and loose from one another…and they can also vibrate.

Temperature describes the vibration of the molecules.

When the vibration of the molecules is very weak, they become immobilized and stay close to one another.

Temperature is then very low.

When the vibration increases, a certain movement becomes to be allowed and the water becomes liquid.

When the vibration increases even more, the molecules detach from one another and water becomes a gas.

What makes the temperature increase?

Energy, of course! When you give some energy to the molecules, they vibrate more and the temperature increases.

You can think about it like that, when you feed your body with food, you get your cells some energy, that’s why your body starts to generate heat and becomes hotter. When you don’t eat, you become cold.

Now you understand what is temperature!

Temperature is just a name to describe the state of vibration of the molecules.

So… in some way, it makes sense…. if the Newtonian mechanics can describe the movement of mechanical parts, then we have other equations to describe the movement of the infinitely smaller (Quantum mechanics ;-) )

How does Heat propagate?

When we think about it at a conceptual level, heat transfer is just a name to describe the way molecules are transmitting their state of vibration to other molecules around them.

When ? Cold ? molecules which are immobile enter in contact with vibrating ? Hot ? molecules, there is a transfer of energy between them.

In simple words, immobile molecule will start to vibrate a little, while vibrating molecules will start to slow down.

So, if every heat transfer can be described like that, why do we have different ways to transfer heat??

Good question ;-)

Because there is a difference due to the medium those molecules belongs to!

Some molecules are in a liquid form (like water), while others may be inside a solid or a gas.

Due to this difference of medium and physical form, scientists who have observed the transfer of heat between solids, liquids, and gas have determined certain laws based on their observations.

How do we quantify the transfer of heat?

Now, that we have the definition of temperature, we know how to quantify the vibration of molecules at a certain point.

By the way, the temperature at which there is absolutely no vibration is called the absolute temperature in the Kelvin Scale.

T = 0 K

To go from Kelvin to Celsius (or Fahrenheit), we just have to do a simple translation of the temperature scale T(Kelvin) = T (°C) + 273,15K

There’s just a problem…

Temperature is an absolute value.

How do we quantify the speed at which the temperature flows??

Well, for that, we just have to look at 2 theoretical points 1 and 2 at which we take the temperature.

A temperature flow is as the name indicates it, a difference of temperature between 2 points divided by the distance between these 2 points.

If this distance becomes infinitely small, this quotient becomes… a derivative.

Ok, now that we know that, how do we apply it to engineering to predict the heat flow in various materials and media?

Let’s talk together now about the 3 fundamental ways to transfer heat

Heat transfer inside a solid medium: Conduction

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Read the full article on my blog here.

https://feaforall.com/heat-transfer/