Professional paper
Forms of energy liquid pumping plant dynamic turbopump with radial impellers
Igor Župančić
; Javna vatrogasna postrojba grada Zagreba, Zagreb, Hrvatska
Abstract
This tekst covers fluid energy shape which uses in pump system. A pump is machine that imparts energy to a liquid to increase its pressure and move it from one point to another. There are many pump classification. One classification is acording to the method energy is imparted to the liquid: kinetic energy, or positive displacement. A centrifugal pump is of kinetic energy type because it imparts energy to a liquid by means of centrifugal force produced by a rotating impeller. Displacement pumps are of lower flow range and have pulsating flow rate. Centrifugal pump is rotodinamic pump that uses a rotating impeller to increase the pressure of liquid. They are commonly used to move liquids through a piping system. The liquid enters to the pump impeller along or near to the rotating axis and is accelerated bay the impeler, flowing radially outward into diffuser or volute chamber (casing), from where it exist into the downstream piping system. Like most pumps, a centrifugal pumps converts mechanical energy from a motor to energy of a moving fluid (liquid). Some of energy goes into kinetic energy of liquid motion and some into potential energy, represented by a liquid pressure or by lifting the liquid against gravity to higher level. The two major components of a centrifugal pumps are impeller and the casing in which it rotates. The transfer of energy from mechanical rotation of the impeller to the motion and pressure of the liquid is usually described by means of centrifugal force. Power from the driver, which is an electric motor, a diesel engine or a steam turbine (not for firefigting use) is transmitted to the pump through the shaft, rotating the impeller at high speed. In the modern centrifugal pump, most of the energy conversation is due to the outward force that curved impeller blades impart on the liquid. Invariability, some of the energy also pushes the liquid into a circular motion, and this circular motion can also convey some energy and increase the pressure at the outlet. The pumps are identified by the direction of the flow through impeller, with refernce to the axis of rotation. The total head of the pump is the energy imparted to the liquid as it passes through the pump. It may be expressed in various units of pressure, but for fire protection it’s generally given in units for pressure-bar or in units for long-m. The total head is calculated by subtracting the energy in the incoming fluid from the energy in the discharging liquid. Neto positive suction head (NPSH) is the pressure head that causes liquid to flow through the suction pipe and fitting into the eye of a pump impeller. The pump itself has no ability to ‘lift’ and the suction pressure depends on the nature of the supply. There are a two kinds of NPSH to consider. Pump NPSH is a function of the pump design and varies with the capacity and speed of any pump and with the design of different pumps. Available NPSH is a function of the system in which the pump operates and can be calculated readily. When the water source is above the pump, available NPSH is equal atmospheric pressure plus static head on suction minus friction and fitting losses in suction pipping minus vapor pressure of liquid. For any pump installation, the available system NPSH must be equal or greater than the pump NPSH at the desired operating condition. Pumps suppliers set the NPSH required (NPSHR) for a given pump. The (NPSHR) takes into account any potential head losses that might occur between the pump’ suction nozzle and impeller, thus ensuring that the liquid doesn’t drop below it’s vapour pressure.
Keywords
Hrčak ID:
125618
URI
Publication date:
23.7.2014.
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