I grew up in the south of France, and I absolutely NEVER understood why they
were selling coats with fur on the hood. I found it excessively
ugly and to be honest really unnecessary. In the south of France, come on!
And then I moved to Quebec. And there again was this damn fur lining trend everywhere around
hoods. So when I had to buy my first winter coat, this very one by the way,
I got one with removable fur because I didn't want to have to wear this thing.
Parenthesis, all the furs that I bought in my life (despite myself you will understand) are
synthetic furs, I do not at any given point promote the purchase of animal fur.
But anyway, it was this coat that I had bought 11 winters ago now and I am
still wearing today, with fur which I immediately removed. Well,
I found myself very devoid of it when the winter did come. *hm?* Believe me, I quickly, very quickly,
put that piece of fur back on. All of a sudden, in Quebec, fur was much more useful
than it had been in the south of France. That is pretty obvious, I agree. But how?
Or... What? How do little hairs placed around the face protect us from the cold?
Some peoples completely understood how to make use of fur,
these are the peoples of the north, for example, the Inuit, an indigenous people of northern Canada.
Look at these furs. What a presence! So, I did not find the French word to designate
this type of fur then as I find that it doesn't really look like a hood anymore,
I'll call it a mane (and if you know the French word,
tell me and I'll add it in the description). You will see that between our stunted furs
and their prestigious manes, there has to be a noticeable difference in efficiency.
At first I thought that the only use of the fur was to catch snowflakes,
that it was a kind of snow visor, or even a frost catcher,
since exhaling of humid air eventually freezes on the hairs of the fur.
But this is clearly not its most important function. First of all,
the fur helps make sure that my body heat doesn't go away,
in other words, to reduce heat transfers.
You know, we are walking radiators,
continuously producing heat. This means that the layer of air that is
closest to our skin is particularly hot, and the farther we get from our skin,
the more the temperature decreases. When a gust of wind removes this layer of hot air,
it cools us down because we have to heat up another layer of air. So the goal of the game
is to try and keep air movements to a minimum near the face to avoid
this phenomenon of convection, since that is what it's called (as I'm
sure you know). And for that, the majestic hood manes are very effective.
Let's say we have some headwind, as the fur is placed around the face,
you'd think that it wouldn't protect our face, and yet!
Let’s say we have a ball that moves through the air. The air goes around the ball,
like this. But here, in the middle, right there, since the air separates on each side,
that is an area where the air doesn't go. This spot here,
is called the stagnation point. The air is still. And if the air is still,
right now, we're keeping our warmth! There is no convection!
With my tiny fur it won't do not much difference but with a
big mane, it increases the size of the object to be bypassed and therefore the area
of stagnation. Increasing the diameter of the head with the fur allows us
to have more stable air zones in the middle and less heat loss!
Ok, what if we're not facing the wind then?
This is different! We will take as an example the extreme case where the wind would come right on the
side and where you could that that it'd sweep off our entire layer of precious warm air. Yes but no,
not if you have a beautiful mane! And here the important thing is no longer
the diameter but the hairs themselves, especially the fact that they are all of
different sizes. It allows them to kind of hang on to the air.
“Hang on to the air” is a bit difficult to demonstrate so let's make a small model.
I made a small channel with a bit of plasticine in which I poured
a viscous liquid (it's just water, flour and food coloring). And,
you see the fluid is flowing in my channel. On the other hand, what you also see,
is that the fluid moves faster in the middle than on the sides. You can
follow water bubbles and see that he there really is a difference in speed.
There are a combination of factors that explain this speed difference but one of them
is the contact with the walls. When the fluid is free to flow, in the center,
it flows at maximum speed. But on the sides, much closer to the surface,
the fluid hardly moves anymore due to the friction of the fluid with
the wall. And the further away we get from the wall, the more free the fluid becomes
to flow, until we get to its maximum speed of movement.
All the space occupied by the transition from zero speed to
maximum fluid movement speed, is called a boundary layer. And it
depends on the roughness of the wall. If we had a much rougher wall,
the liquid would “stick” more and the transition zone would be wider.
The walls of our channel represent our mane. With all these hairs of
different lengths, we have a strong roughness and the air is extremely slowed down close to the face,
and when the transition zone is over and the wind picks up its speed,
our face... is no longer there!
What fur ultimately does is that it creates a microclimate around the
face. A micro climate which changes depending on the wind's direction.
We can clearly see here that the performance of the fur is not the same depending on the wind's angle of approach.
Heat transfers for large manes are at a minimum when the wind comes from the side.
But maybe the most important thing is to compare heat transfers with a mane
with heat transfers without a hood at all. Or even to compare them between
having a hood without fur, and having a hood with fur like mine.
This data comes from this article which is,
according to my research, the only one to have quantified the heat transfers of
furry hoods. Inuit furs, due to their geometry,
allow them to reduce heat transfers. The heat loss is 2-6 times lower
and the biggest difference is when the wind comes from the side.
In summary, the fur creates a calm environment in front of the face which
reduces heat transfers and therefore the risk of frostbite. Whether beautiful or ugly,
in any case, that reconciles me with their use because at least they're effective!
All we just talked about is fuild mechanics and I would like to thank Professor Bruno
Blais from Polytechnique Montreal who helped me understand the reference article.
If you find that this video has brought you something, I invite you to subscribe
because this is very Scilabus. We dive into lots of different topics. It never sounds
that exciting but it's always cooler than we thought. Which is the worst marketing
slogan ever... But anyway, subscribe and see you next time. Until then...
This video is sponsored by NordVPN. I'm sure that you are starting to understand
what a VPN is. Personally, I checked, and I've been using VPNs since 2004,
which gives you an idea of ​​my age. Private services like NordVPN weren't
as prevalent at the time and it was my university that provided us with a VPN to
give us access to university resources from home. We fooled the web into thinking
that we were at university while we were simply at home. A private VPN like
NordVPN does the same thing but at a country's scale. By connecting from the
server of one country or another, we get to access content that would only be visible from that
country. This is often the main use of a VPN. If this kind of service interests you,
then you can subscribe by going to nordvpn.com/scilabus. This will give you
access to a 70% discount if you take a 3 year subscription, which amounts to around
of 3 euros per month. And if you enter the code SCILABUS, you will receive an additional free month.
In short, nordvpn.com/scilabus with the code SCILABUS and a big thank you to NordVPN for the support.