4. The process, which causes the air to enter the impeller blades of a centrifugal compressor at __________ velocity (without effecting the mass of air to flow and velocity of flow) is known as prewhirl.
7. The intercooler pressure, for minimum work required, for a two stage reciprocating air compressor, is given by (where p1 = Intake pressure of air, p2 = Intercooler pressure, and p3 = Delivery pressure of air)