What is the reason for the fog on the windshield before heating the air conditioner in winter, and how to solve it?

Because the temperature of the windshield is low, it is sure to fog when hot air blows alternately. At this time, open the external circulation, then blow the wind on the windshield and turn on the air conditioner switch, and the fog will disappear immediately without changing the air conditioner temperature. Turn off the air conditioner after a while, because the air conditioner is a compressor and refrigeration.

The principle of window fogging is caused by "large temperature difference between internal heat and external cold", which is only macroscopic water vapor liquefaction and microscopic related to saturated air pressure. When the external temperature is high, the saturation pressure of water vapor is high, while when the glass temperature is low, the saturation pressure of water vapor decreases near the glass. When the temperature difference is large enough and the saturation pressure is low enough, water will liquefy. The closer to the glass water, the lower the saturated air pressure, and the easier the water will liquefy.

Water molecules in the air are constantly moving irregularly. When there is no temperature difference, water molecules keep hitting the glass and flying out of it. Because the lower the temperature, the slower the movement speed, so the water molecules from the hot air touch the cold glass, the movement speed slows down and can't fly out in time, while the water molecules outside keep touching the glass, so there is more and more water on the glass, and finally they converge into small drops.

Saturation pressure can be understood as the maximum amount of a certain gas (such as water vapor and alcohol vapor) that can exist in the air at a certain temperature. When the actual amount of a gas in the air is greater than this amount, it will liquefy. Glass and water are permeable, so water will fog on the glass, but mercury will not fog. Therefore, the principle of some glass defogging agents is to cover the glass surface with a waterproof film.

Methods and skills of defogging

In the case of little fog, you can properly open the windows on both sides to let the air convection, thus eliminating the temperature difference on both sides of the windshield, and naturally it is difficult to form fog.

In case of fog in winter, you can try to turn on the outside circulation mode and reduce the fog. Start the car first in winter, and when the water temperature rises to normal temperature, you can turn on the hot air system, so that there will be no fog again during driving, because the car is dry.

Applying glass water on the inside of the front windshield can prevent the glass from fogging. In fact, applying glass water requires the alcohol content in it. Dip the mixture with a dry towel and smear it on the inside of the glass. After drying, wipe off the water stains with a dry towel. Under normal circumstances, it can be wiped once a month.

China News Network-Car Tips