Liquid nitrogen
2019-03-07 Views（）
Liquid nitrogen: liquid nitrogen. It is inert, colorless, odorless, non-corrosive, non-flammable, and extremely low in temperature. Nitrogen constitutes the majority of the atmosphere [volume ratio 78.03%]. Nitrogen is inactive and does not support combustion. A large amount of endothermic contact during vaporization causes frostbite. At normal pressure, the liquid nitrogen temperature is -196 ° C; 1 cubic meter of liquid nitrogen can be expanded to 696 cubic meters of 21 ° C pure gaseous nitrogen. Liquid nitrogen is a colorless, odorless, low temperature gaseous state under high pressure.
Liquid nitrogen (often written as LN2) is a liquid form formed by nitrogen at low temperatures. Nitrogen has a boiling point of -196 ° C. At normal atmospheric pressure, if it is below this, liquid nitrogen is formed; if pressurized, liquid nitrogen can be obtained at a higher temperature. The direct contact of human skin with liquid nitrogen is no problem at all, and it will be frostbitten and irreversible in more than 2 seconds.
In the industry, liquid nitrogen is obtained by fractional distillation of air. After purifying the air, it is liquefied in a pressurized, cooled environment, and separated by the boiling points of the components in the air. Nitrogen (78.09% of the air volume) was first released (and not liquefied), followed by 0.93% argon in the air and finally 20.95% oxygen.
Another feature of liquid nitrogen as a raw material for refrigeration is its fast cooling rate and short quick freezing time. It can quickly cross the ice crystal node of the product, and form uniform fine ice crystals inside the product while seamlessly spraying and cooling. The moisture and nutritive value of the product can improve the production efficiency, product quality preservation and nutritional value of the product, which is unmatched by the quick freezing equipment of Freon and liquid ammonia as refrigeration raw materials.
The liquid nitrogen refrigeration rate is about twice as fast as the traditional Freon and liquid ammonia refrigeration, and the total investment in equipment is 30% lower than the traditional investment. This is an incontrovertible fact. Moreover, liquid nitrogen is recognized as the safest and most environmentally friendly refrigerant in the world. Therefore, it is believed that in the future development trend of the fast-freezing refrigeration industry, liquid nitrogen as the refrigeration raw material will definitely replace Freon and liquid ammonia, which will definitely become the first choice for refrigeration in the industry!