25. Why minimum recirculation is necessary for a pump and how much the value will be and what are methods to predict the loss of minimum flow?

Without re-circulation, the fluid in the pump will be churned repeatedly resulting in heating/vaporization up of the fuild.This will result in sealing glands/pump internals being damaged. Typically, inferred from low flow by Flow switches In suction pipes or high differential temperature between suction and discharge by temperature swicTCH.