Steam jet ejjector can be use to creat a vacuume and it can be also use as thermocompressor...e.g inmultiple effect evaporator it can be use as a vacuume creator and also also it can be use as thermocompressor
Centrifugal Pump use Impeller to flow the liquid, while P.D pumps use screw, gear or piston etc to flow the liquid.
Centrifugal pumps usually use for high flow rate and low pressure while P.D pumps use for the opposite operation of centrifugal pump.
Centrifugal gives continuous flow of liquid while PD pumps give Pulsive flow with high pressure.
Centrifugal pumps and positive displacement pumps are the teo major classes of pumps.
Positive displacement pumps directly apply pressure on liquids by reciprocating of piston or by rotating members which form chambers alternatively filled and emptied.
Centrifugal pumps on the other hand generates high rotational velocities and then convert resulting kinetic energy of the liquid to pressure energy.
Steam ejector is helpful to create a vacuum in process equipment let's take an example in a process plant there is only stripper of distillation here their was a steam jet ejector it sucks the 8 bar steam out if distillation and sent this steam to process and on the other hand it is creating a vacuum inside the stripper so there are 2 advantage
Centrifugal pump is use for pumping low viscous fluids where as PD pump is use for high viscous fluid
centrifugal pump is use when we required continuous high flow rate where as PD PUMP for low flow rate
Centrifugal works on centrifugal force and PD works as, first it will suck and then discharge with the help of piston
Priming has to be done in centrifugal pump to avoid cavitation, no need such activity in PD pump
Note : PD means positive displacement