For which condition is the pressure/temperature relationship for ammonia valid?

The pressure/temperature relationship for ammonia is specifically valid in a saturated condition. In this context, "saturated" refers to the state where ammonia exists in equilibrium between its liquid and vapor phases at a specific temperature and pressure. When ammonia is in a saturated condition, it can either be fully liquid, fully vapor, or in a state where both phases coexist, allowing for clear and reliable calculations of its properties.

This relationship is crucial for understanding how ammonia behaves as a refrigerant in various applications, as it helps in determining efficient operating conditions for refrigeration cycles. In such systems, knowing the saturation points allows engineers to design systems that optimize performance and reliability based on the pressures and temperatures involved.

In contrast, when ammonia is in a vapor, mixed, or superheated state, the pressure/temperature relationship may not strictly hold. For example, in a superheated state, the vapor can exist at temperature and pressure combinations that do not correspond to saturation conditions, altering the expected relationships. Thus, the pressure/temperature relationship is strictly valid when ammonia is in a saturated condition.