ANS:C - create more suction head.

Circulation pump is located below the evaporator to avoid cavitation. Explanation:

1. Cavitation: Cavitation is the formation and subsequent collapse of vapor bubbles in a liquid when the local pressure falls below the vapor pressure of the liquid. It typically occurs in regions of high flow velocity or low pressure, such as near the impeller of a pump.
2. Location of the Pump: Placing the circulation pump below the evaporator helps to ensure that the pump is always submerged in liquid. This positioning prevents the formation of vapor bubbles and subsequent cavitation because the pressure at the inlet of the pump remains above the vapor pressure of the liquid.
3. Avoiding Cavitation: Cavitation can damage pump components, decrease pump efficiency, and cause noise and vibration. By locating the pump below the evaporator, where the liquid level is maintained, the risk of cavitation is minimized, ensuring smooth and efficient pump operation.
4. Other Considerations: While locating the pump below the evaporator also helps to maintain prime and can potentially create more suction head due to the higher liquid level, the primary reason for this arrangement is to prevent cavitation.