What condition must ammonia be in for pressure/temperature relationship validity?

For the pressure/temperature relationship of ammonia to be valid, it must be in a saturated condition. In this state, ammonia exists in equilibrium between its liquid and vapor phases, meaning that any change in pressure will directly correspond to a change in temperature, as defined by the ammonia phase diagram.

In a saturated condition, the properties of the ammonia can be accurately predicted and calculated based on standardized tables that are available for refrigerants, including ammonia. These tables provide critical data on pressure and temperature relationships that are essential for system design and troubleshooting in refrigeration applications.

If ammonia were in a sub-cooled or superheated state, the relationship between pressure and temperature would not be valid as it would no longer adhere to the equilibrium conditions necessary for accurate prediction through the phase diagram. In these states, additional complexities arise, requiring separate calculations or adjustments to understand the properties of ammonia, thus affirming that the saturated condition is the only appropriate state for the reliable application of the pressure/temperature relationship.