# Temperature

## Understanding Temperature

• Temperature is a measure of the average kinetic energy of particles within a substance.
• It’s a fundamental component of understanding how cryogenics and vacuum technology works because it influences the behaviours of gases and vapours to a great extent.
• Changes in temperature can cause a change of state in substances, from solid to liquid (melting), liquid to gas (boiling) or solid to gas (sublimation).
• We usually measure temperature using the units degrees Celsius (°C), kelvin (K), or degrees Fahrenheit (°F).

## Properties Affected by Temperature

• Raise in temperature generally increases the volume of a substance. This is due to the increase in kinetic energy causing particles to move more and take up extra space.
• The temperature of a substance is directly related to its pressure — as temperature increases, so does pressure.
• Pressure and volume also have a relationship with temperature, often expressed by Gay-Lussac’s Law: the pressure of a gas at constant volume is directly proportional to the temperature, usually written as P1/T1 = P2/T2.

## Temperature in Cryogenics

• Cryogenics is the study of how materials behave at very low temperatures, generally below -150 degrees Celsius.
• Understanding temperature is crucial in cryogenics as reductions in temperature can change material properties, such as resistance to electricity and thermal capacity.
• One of the main uses of cryogenics is in the production of liquified gases, such as helium and nitrogen.
• A cryocooler is a device used to achieve low temperatures. It works by extracting heat from a system and expelling it to an area of higher temperature.

## Temperature in Vacuum Technology

• In vacuum technology, having control over temperature is crucial as it affects the rate of outgassing — the process where trapped gases are released from materials within the vacuum chamber.
• A vacuum is a space where the pressure is significantly below atmospheric pressure, and this causes substances to boil at much lower temperatures than they usually would at standard pressure.
• Temperature control is essential for maintaining the integrity of a vacuum system. For instance, high temperatures could cause components to fail, whilst low temperatures could cause unwanted condensation.