In which state does refrigerant enter the evaporator?

The refrigerant enters the evaporator as a saturated refrigerant because this state allows for the efficient heat absorption necessary for the refrigeration cycle to function effectively. A saturated refrigerant is a mixture of liquid and vapor, which means that it can absorb heat from the environment as it evaporates completely into vapor.

When the refrigerant enters the evaporator in a saturated state, it is at a specific pressure and temperature where the liquid can transition to gas. This is crucial because, as the refrigerant absorbs heat, it changes state from liquid to vapor, extracting heat from the surroundings and providing the cooling effect required in refrigeration systems. The saturated state ensures that the maximum amount of heat is absorbed before the refrigerant exits the evaporator, enhancing the overall efficiency of the refrigeration system.

Other states, such as a superheated gas or liquid refrigerant, would not provide the same efficiency in heat absorption within the evaporator, while an unsaturated gas may lack the necessary latent heat capacity to effectively cool the system. Thus, the saturated state is optimal for the function of the evaporator in a refrigeration cycle.