Humidification and drying of sub-cotton The principle of humidification and drying of sub-cotton
In order to make the moisture of the cotton reach suitable finishing conditions, when the moisture of the cotton is too low, it should be humidified appropriately, and when the moisture of the cotton is too high, it needs to be dried. According to the situation in my country, except for some areas where the cotton content is too low and requires proper humidification, the cotton content in most areas often needs to be dried because the moisture content is too high.
1. The principle of humidification and drying of cotton wool
The degree of dryness and humidity of the air is called humidity, and humidity can be divided into absolute humidity and relative humidity. The mass of water vapor contained in the air is called the absolute humidity of the air, which is an indicator of the amount of water vapor contained in the air. The ratio of the partial pressure of water vapor in the air to the partial pressure of saturated water vapor at the same temperature is called the relative humidity of the air, which is an indicator of whether the air is dry or humid. When the absolute humidity of the air remains unchanged, increasing the temperature of the air can increase the saturated water vapor volume and reduce the relative humidity, resulting in accelerated evaporation of cotton fiber moisture.
From the perspective of relative humidity, at a certain temperature, the lower the relative humidity of the air, the faster the water in the cotton fiber evaporates, and vice versa. When the relative humidity of the air increases to a certain level, instead of evaporating moisture from the fibers, the cotton fibers will absorb moisture from the air. When other conditions remain unchanged, the higher the air temperature and the lower the relative humidity, the faster the water in the cotton fiber evaporates; conversely, it is difficult for the water in the cotton fiber to evaporate. Therefore, the relative humidity and temperature of the air are closely related to the moisture absorption and release of cotton fibers. After the air is heated, its ability to hold water vapor increases rapidly. When the temperature rises from 25°C to 100°C, although the temperature only increases 4 times, the saturated humidity of the air will increase 25 times.
From the perspective of absolute humidity, the difference in vapor pressure between cotton and air is the driving force that causes cotton to remove moisture or add moisture. Moisture generally moves from areas of high vapor pressure to areas of low vapor pressure. If the water vapor pressure of the air around the cotton is smaller than the vapor pressure of the moisture in the wet cotton, the moisture in the cotton can be dried. Increasing the air temperature will further increase the vapor pressure difference between the cotton and the surrounding air, which can speed up the drying of cotton. When the vapor pressure of cotton moisture is equal to the vapor pressure of the surrounding air, the cotton moisture is in equilibrium and moisture will not enter or exit the cotton.
2. The law of cotton’s response to drying
The Southwest Ginning Research Laboratory in the United States completed a series of experiments to determine when stationary cotton petals are exposed to hot air with different hot air speeds, different winds and different times. Patterns of cotton fiber response to drying. Tests have shown that when the hot air temperature at the mixing point of cotton and hot air is 93.3°C and the wind speed is 6.1m/s, the original moisture content of cotton fiber is 10% to 20%, or even 23%, and it can be dried within 10 seconds. When the moisture content is below 8%, it takes about 15 seconds to bake until the moisture content is below 6%.
The factors that control the drying speed and drying volume are: the temperature and relative humidity of the dry air (hot air), the hot air volume and speed, the time the cotton is exposed to the hot air, and the moisture content of the cotton when entering the dryer.
The drying of cotton moisture (not counting the accumulated water on the cotton surface) is carried out at a decreasing speed. The speed is fast at the beginning, and as the cotton gradually dries, the drying speed also gradually slows down. From a ginning perspective, cotton fiber moisture is more important than cotton seed moisture.
AAAVSGREHTRY45
