What must the temperature of the medium being cooled be in relation to the evaporator temperature?

The temperature of the medium being cooled must be above the evaporator temperature for proper operation of the refrigeration cycle. This is because the evaporator is designed to absorb heat from the medium, which, in turn, causes the refrigerant within the evaporator to evaporate and absorb that heat. If the medium's temperature were below the evaporator temperature, heat transfer wouldn’t effectively occur, as heat naturally flows from warmer to cooler areas.

For efficient cooling, it is necessary for the refrigerant to take on heat from the environment or medium that is at a higher temperature. Therefore, this relationship ensures that the refrigerant can effectively absorb heat and maintain the cooling process. In practice, engineers design systems with this principle in mind to ensure optimal performance of the refrigeration system.