What is the difference in enthalpy of ammonia at saturation conditions between 1165.8 kPa abs and 236.2 kPa abs?

The correct choice identifies the difference in enthalpy at saturation conditions specifically related to the hf (enthalpy of the saturated liquid) values for ammonia at the given pressures. This is a critical aspect in thermodynamics, where understanding changes in enthalpy between different states—such as saturated liquid and saturated vapor—is essential for calculations involving heat transfer, refrigeration cycles, and energy efficiency.

For ammonia, the hf value represents the enthalpy of the liquid phase at both pressures. The difference in enthalpy at saturation conditions between two pressures can be derived from the steam tables or refrigerant property tables for ammonia, allowing engineers to find specific values for hf at the specified pressures of 1165.8 kPa abs and 236.2 kPa abs.

In this case, the enthalpy change indicates that at the higher pressure, the liquid ammonia's enthalpy is higher than at the lower pressure, which is typical due to the increase in temperature and energy associated with higher pressure states. The correct answer provides the calculated enthalpy difference representing these conditions, thus making it the accurate choice in this scenario. This understanding is crucial for applications in power engineering where ammonia is commonly used as a refrigerant.