Let´s see the possibility of friction loss enhancement in EDP by way of example of a centrifugal electric driven pump. Let´s analyze balance of loss in power in EPD power end not taking into consideration loss in its pump part (fig. 1, pos. I).
Total power losses Nå in EDP electric drive come from several components:
where Nst - losses of steel anchor from hysteresis and whirling currents; Ndr - friction loss; Nс - loss in copper coil; Na - added loss while load.
Stator and rotor of EPD SV power end are separated with a case that makes rotor immersion into heat-transfer fluid possible. Because of this rotor´s friction loss upon heat-transfer Ndr.r , being part of friction loss becomes higher:
where Ndr.b - friction loss in bearings.
EPD SV refer to microsized supercharger in which diameter sizes of pump and power end parts of a rotor are comparable. Friction losses Ndr.r on rotor depend on type of rotary surface and consist of 2 components: friction losses upon frontal surfaces of a rotor and friction losses upon cylindrical surfaces of a rotor. In EDP the first type of losses is dominating for a pump part, and the second type -for power end part of a rotor. For EP rotor construction rationalization it is necessary to estimate losses in power from friction upon pump separately from power end rotor .
As an example, illustrating the opportunities of rotor construction optimization, let´s analyze friction losses in EDP with electro engine DB-9 и characteristics: pressure Н= 60J/kg; consumption of a heat-transfer agent =140×10-6 m3/s and rotating speed n=6000 r/min; clearance gap D=0.3×10-3 m; working medium viscosity n=0.7×10-6 m2/sec; working medium density r=691 kg/m3 ; speed of fluid in a clearance gap between rotor and body v=15×10-6 m3/sec. Calculated value of loss relative density in a pump part of a rotor, including element with the largest diameter - rotor wheel (RW), in the EDP will be =0.844. Thus, the most part of friction losses comes to the pump part of the rotor.
Dependance ~ , points at advisability of decreasing diameter rotor sizes, particularly diameter RW drw.. One of the constructive methods of decreasing diameter drw is transition to multistage EDP. Parameter consequence of this becomes coefficient of each stage specific speed ns growth.
Let´s look at the opportunities of decrease by increasing stages of EDP TCS to 2-3, considering that pressure coefficient of each stage will be unchanged , H=0.587.
While transition in EDP from 1 to 2 staged variant drw should decrease from 32×10-3 m to 23×10-3 m, and in 3 staged EDP to 19×10-3 m. Coefficient of special speed of a stage grows, respectively from ns=67 to ns =112 and ns =152. Relative value of friction loss in a pump part of the rotor with growth of number of stages decreases to 0.677 in 2 staged variant of EDP and to 0.549 in 3-staged EDP, respectively 20% and 35% in comparison to initial level =0.844. Such changes of EDP are acceptable from technical point of view and positive from energetic point of view.
The viewed method of friction loss decrease upon rotor EDP is acceptable for different vaned light-duty machine, for instance compresses and ventilators of aero cosmic significance, radial sizes of rotor driving and force parts of which are comparable. Its realization allows decreasing friction loss upon rotor and decreasing power consumption.
The work was submitted to international scientific conference «Prospects for the development of university science», Dagomys (Sochi), September 21-24, 2009. Came to the editorial office on 03.08.2009.