What is a non-condensable gas in a refrigeration system?

A non-condensable gas in a refrigeration system is defined as a gas that cannot be condensed at the system's operating pressures and temperatures. These gases are typically inert gases such as air or nitrogen that may enter the refrigeration system unintentionally. Unlike refrigerants, which are specifically designed to change phases (from gas to liquid and vice versa) during the refrigeration cycle, non-condensable gases remain in gaseous form and do not participate in the refrigeration process.

When non-condensable gases are present in a refrigeration system, they can negatively impact system performance by raising the condenser pressure, which can lead to increased energy consumption and potential system failure. Therefore, it's crucial to identify and remove these gases to maintain optimal efficiency in the refrigeration system.

The other options do not align with this definition: some gases can indeed be condensed at higher temperatures or pressures (contrasting with the characteristics of non-condensable gases), specific refrigerants serve distinct functions and may not be categorized as non-condensable, and while decomposition may produce byproducts, that is not the primary definition of a non-condensable gas.