Impeller : it's blades are designed in a way to carry liquid and provide centrifugal force to carrying liquid and increases velocity and volute is provided to convert high velocity into pressure.
Agitato: it is used to homogenise mixture in tanks, in simple words it mades provision of currents in liquid.
Variable area meter:
Variable area ,variable flowrate ,pressure constant. Area is adjusted to keep the pressure constant and this change is proportional to the flowrate.
Eg.rotameter,cylinder and piston type flowmeters.
Variable head meter:
Variable pressure, variable flowrate,area constant.flow is proportional to sqrt(∆p).
Eg.orifice meter, venturimeter
Simple distillation condenses the liquid only once whereas fractional distillation condenses it many times.
Also boiling point difference should be high for simple distillation.boiling point difference should be low ( less than 40°C ) for fractional distillation.