Cryogenics studies materials at extremely low temperatures. NIST defines cryogenics as below −180°C (93.15 K). Special sensors like RTDs and silicon diodes measure cryogenic temperatures
Absolute zero is the lowest limit of thermodynamic temperature scale. International standard is 0 kelvin, −273.15°C or −459.67°F. Kelvin and Rankine scales set their zero points at absolute zero
Joule-Thomson effect describes temperature change of real gases during expansion. Process occurs when gas expands through valve while keeping it insulated. Effect is purely due to deviation from ideal gas behavior
Evaporative cooling cools air through water evaporation using latent heat. Water absorbs significant heat during evaporation, unlike refrigeration systems. Process works best in dry climates with low relative humidity
Ice harvesting began around 1000 BC in ancient civilizations. Persians may have been first to use ice for food preservation. Ice trade developed in 19th century, leading to cold chains
Liquid nitrogen has a boiling point of −196 °C and is colorless. Produced industrially by fractional distillation of liquid air. Has viscosity one-tenth that of acetone. Can be stored in vacuum flasks at 77 K