Article | The whole point of popular science
In the hot summer, holding a watermelon and eating it in an air-conditioned room is the life that many people dream of. However, not everyone is accustomed to using air conditioners, and they may even feel that using them for a long time will cause dizziness, nasal congestion, etc.
Therefore, fans have become the refrigeration equipment with the lowest cost and harm, but the cooling effect they can bring is often not as good as that of air conditioners. When the outside temperature is too high, the hot air blows out instead , making people hotter and hotter. The more uncomfortable it becomes.
So, how should you use an electric fan to achieve the cooling effect as quickly as possible? Let’s first understand the cooling principle of the fan. How does the
fan cool down?
When there is a certain gradient between the temperature of the object and the temperature of the environment, the temperature transition phenomenon will occur. Different from the cooling principle of air conditioners, fans use the physical principle of air convection .
When the temperature around the human body is higher than the ambient temperature and the body is sweating, the electric fan can speed up the air flow, increase the evaporation rate of sweat on the body surface, take away the excess heat around the body , and make the body temperature gradually transition to the ambient temperature.
If the indoor temperature is relatively high, you can cool it down by promoting air circulation. People can feel cool when they are inside.
However, in many cases, the cooling effect of the electric fan is not ideal, and it may even become hotter as it blows.
So, where should the electric fan be placed and how should it blow to be the coolest?
Which position is the coolest to place an electric fan? A foreign physics teacher did an experiment
Most people use fans to blow directly face to face, but this method is actually wrong. In order to verify the coolest position of the fan, a foreign science teacher did an experiment. Teacher
used a long yellow plastic bag and asked a question: Can you believe that I can blow up this plastic bag with just one breath?
In order to verify the answer, he first took a deep breath and blew air directly against the plastic bag with his mouth. The result was obvious. He couldn't blow it at all. Even after blowing ten more times, the plastic bag still showed only a slight sign of bulging.
Then, he let out all the air in the bag and blew it again, but this time the method was different from the previous one.
He pulled the plastic bag some distance away and then blew . He blew a breath easily, and the whole plastic bag actually bulged up! Teacher
said that he uses Bernoulli's principle . leaves a certain distance when blowing, so that the surrounding air can easily flow into the low-pressure area . When more air enters the plastic bag, it will naturally expand. Woke up.
Finally, the teacher said that this principle can also be used in daily life, such as the use of electric fans.
Blow the electric fan towards the open window while keeping it some distance away. Just like the air flows into the plastic bag, the hot air in the room will also be blown outside, making the whole room cooler.
And what is the optimal distance between the electric fan and the window?
A blogger conducted an experiment with an electric fan and wind meter . He placed the fan at the window with the best ventilation effect, and then opened a window in another room to place the wind meter.
When the fan blew against the room, the anemometer in the other room barely changed, indicating that the air circulation effect was almost non-existent; he placed the fan on the windowsill and blew it toward the window, and found that the anemometer changed very slowly.
Then, he gradually moved the fan back. When the fan was 0.55 meters away from the window, the speed of the anemometer reached 0.6m/s. After continuous experiments,
concluded that when the fan is 0.5m-2.1m away from the window, the wind meter data is the best, which means that the air convection effect is optimal.
Therefore, in order to achieve the coolest effect, the fan is best placed 0.5 meters to 2.1 meters away from the window, and it should blow toward the window rather than directly.
Many netizens said that they learned a lot after reading this. It turns out that they have been using the wrong fan since they were young. I tried this method and it really worked. It is indeed important to learn mathematics, physics and chemistry well!
So, what is Bernoulli’s Law and ? Where else can it be used?
Bernoulli's Law
Bernoulli's Law was proposed by Daniel Bernoulli in 1726. was a century earlier than the discovery of The Law of Conservation of Energy . It is mainly applicable to the ideal that there is no frictional resistance. fluid.
The main content of Bernoulli's law is:
In water flow or air flow, pressure and speed change in inverse proportion. If the speed is small, the pressure will be large. If the speed is large, the pressure will be small, but their sum will not change.
Among them, p represents the pressure of the fluid, ρ represents the density of the fluid, g is the acceleration of gravity, h is the height, and V is the velocity of the fluid. Expressed in words: pressure potential energy + gravitational potential energy + kinetic energy = constant.
For air, its gravity is negligible, so kinetic energy and pressure potential energy are inversely proportional.
Therefore, Bernoulli's law can be applied to fans because the air gravity is almost zero and the frictional resistance is negligible. Many misuses of Bernoulli's law are to ignore the role of friction.
When firefighters rescue fires, also use Bernoulli's principle to let outside air flow into the room and discharge the billowing smoke for timely rescue.
However, bladeless fans cannot use Bernoulli's law to achieve the purpose of cooling. Do you know the principle?
