Centrifugal Pump Working Principle:
Centrifugal pump uses centrifugal force to transfer fluid (Liquid & gas) from one pressure to higher pressure or one place to another place with the help of pressure difference. Fluid enters the pump at the center of the impeller. The rotating action exactly flings (throws) the water to the outside of impeller, thereby imparting velocity or kinetic energy to it. This kinetic energy converts to pressure energy in the volute. There are many types of centrifugal pump available in the market.
The simplest type of centrifugal pump consists of an impeller fitted on to the shaft, rotating in a volute casing. Liquid enters in the pump through impeller eye. Entered liquid picked up by the vanes of the impeller and accelerated to a high velocity by the rotation of the impeller and discharge by centrifugal force into the casing and then out the discharge pipe.
Centrifugal Pump Energy Conversion:
Centrifugal Pump not pressurizing the liquid like positive displacement pump. Liquid entering the impeller is flung/ throw into the volute with increased velocity. In simple words, impeller imparts the kinetic energy to the liquid. First liquid enters the volute. The cross-section area of volute increases toward the discharge. As a result of increasing volute cross-section, liquid velocity, and kinetic energy decrease.
According to the law of conservation of energy, a decrease in kinetic energy results in the increase of some other types of energy. The total energy of flowing liquid depends on several components. There is a gravitational energy due to an elevation of liquid above the ground, kinetic energy due to motion, pressure energy, and heat energy. The elevation difference between pump suction and discharge is very small.
Therefore, a consequence of a change in potential energy is insignificant. Also change in temperature of suction and discharge liquid is very small. Maximum 1 oC increase in heat energy suggests due to internal friction. Therefore, a consequence of a change in heat energy is also insignificant. So the conclusion is that the change in kinetic energy results mainly in the change of pressure energy. Kinetic energy decrease, pressure energy increases.
The efficiency of the centrifugal pump indicates how much of the supplied energy is converted into pressure energy and how much was wasted in frictional losses. Conversion of kinetic energy into pressure energy is accomplished through volute and diffuser. Volute is the scroll in a casing surrounding the impeller. The diffuser is a stationary piece adjacent to impeller exit. The diffuser has multiple passages of increasing cross section for converting velocity to pressure.