How does Subzero temperatures obtained?

Modern discoveries have enabled sub-zero temperatures to be obtained by cooling air to about -300° Centigrade (-508° Fahrenheit) by compressing it and passing it into low pressure chambers through nozzles. The result is a sudden and violent expansion, causing the air to be drastically cooled. In home refrigerators Freon-12 gas is used instead of air, and the temperatures are much less drastic. The temperature in the freezing compartment of a domestic refrigerator is about -4°C or 25°F, and that of a deep freezer about -15°C or 5°F.

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