Dry ice is the solid of CO2 ~! A small amount of inhalation is harmless to human body, and excessive inhalation will make people dizzy. If it exceeds the amount, they will go directly to God. People still live on o2, which is deeply processed by liquid co2. It is colorless, odorless and nontoxic (you will suffocate if you breathe too much). Carbon dioxide gas is usually mixed with various impurities. Impure impurities need to be removed by other refining devices such as washing tower, desulfurization tower, drying tower and deodorization tower, so that the purity of carbon dioxide can reach above 99.9%. This refined gas is compressed and cooled into liquid carbon dioxide, which is sprayed into the snow-making tank of dry ice from the nozzle, and part of it solidifies into snow. Compressing this snow can make dry ice. Fourth, the nature of dry ice 1) The cooling capacity of dry ice Dry ice sublimates by absorbing the surrounding heat. The so-called sublimation means that a solid becomes a gas directly without going through a liquid state. When the temperature is constant, the heat required to change from solid to gas is called latent heat, and the heat required for sublimation is called sublimation heat. Obtaining heat from the surrounding environment will reduce the temperature of the surrounding environment, so the greater the latent heat, the greater its cooling capacity and the better its effect as a coolant. The sublimation temperature of dry ice in the atmosphere is -78.9℃, and the latent heat is-0/37 calories per kilogram/kloc. When the temperature rises from -78.9℃ to 0℃, the required heat is {0-(-78.9)} * 0.2 = 16 kcal/kg (specific heat capacity is 0.2 kcal/kg). Heating to 0℃ requires more heat than 16 kcal. The cooling force to 0℃ is equivalent to153kcal {0-(-78.9)} * 0.2+137 =16+137 =153kcal/kg 2) dry ice. The heat absorbed by dry ice is 1.9 times that of ice. Compared with the specific gravity in solid state, the specific gravity of dry ice is 1.56, that of ice is 0.9, and that of dry ice is 1.73 times that of ice. Therefore, if we compare the cooling power under the same volume, 1.9* 1.73=3.287. Theoretically, dry ice is about 3.3 times that of ice. (in fact, it is about 3 times), so it can be used as a refrigerant for railway freight cars, ships, freight cars, etc., saving space, saving refrigeration effect that ice can't reach, eliminating the trouble of replacement, and being suitable for long-distance transportation. 3) Properties of carbon dioxide gas Carbon dioxide gas is inert and nonflammable, so it is very stable. According to temperature and pressure, it can be divided into three States: liquid, solid and gas. In the absence of atmospheric pressure, the pressure of liquid carbon dioxide is at least above 5.28 kg/cm2. Under this pressure, liquid carbon dioxide can become solid and gaseous. The temperature of liquefied carbon dioxide gas with a pressure of 5.28Kg/cm2 is -56.6℃. The temperature and pressure at this time are called "three key points". Carbon dioxide in this state can coexist in liquids, gases and solids. However, when the temperature is above 3 1. 1℃, it can't become liquid under any pressure and compression. This temperature is called critical temperature, and the pressure at this time (75.28 Kg/cm2) is called critical pressure.