Method for determining concentration of liquid cavitation cores

FIELD: physics.

SUBSTANCE: in through portion of pipe with choking of through portion cavitation flow lock mode is set, and in zone of low density value of critical pressure of cavitation and liquid flow are determined, which flow is used to determined liquid speed in pipe neck. Received critical pressure value of cavitation is aligned with pressure of saturated steam of pumped liquid, after that to specially built calculation graph dependencies of relative value of critical pressure of critical speed of flow in channel neck are applied in the moment of setting of lock mode with different concentration of cores target concentration of cores of cavitation of pumped liquid is determined.

EFFECT: higher efficiency.

4 dwg

 

The invention relates to techniques for studies of thermophysical properties of liquids and can be used in the evaluation of strength properties of liquids, research anti-cavitation resistance, such as a pumping device for pumping oil.

There are various ways to determine the concentration of cavitation nuclei holographying, ultrasonic, optical, hydrodynamic (see Gavrilov LR Experimental study of the spectral distribution of cavitation nuclei in the water. M, Power plant engineering, 1966, No. 2, p.41-42; Barabanova GY and other research on the relationship between strength and size of the cavitation nuclei “Acoustic magazine” so XXVII, issue 1, 1981, s.43-49).

A disadvantage of the known methods require sophisticated equipment.

The closest in technical essence is the hydrodynamic method of determining the concentration of cavitation nuclei, based on the registration number of the formed cavities in the area of depression at specified tensile stresses (see Barabanova GY, etc. determining the concentration of cavitation nuclei in the water. “Acoustic magazine”, THH, 1977, C-860).

The disadvantage of this registration is done using sophisticated optical equipment, besides having limited resolution, which in turn is due to a limitation stage of Cavit the tion, i.e. the repetition frequency of the cavities. In addition, the disadvantages of this method include the need for baseline information, the distribution density of the nuclei, their sizes.

The purpose of the invention is improving the efficiency of the method by simplifying the method of determining the concentration of cavitation nuclei, corresponding to the developed cavitation regime, leading to a sharp deterioration of parameters of hydraulic system (for example, reduced pressure drop efficiency of a centrifugal pump).

This objective is achieved in that in the flow area of the tube with compression of the flowing part of installing cavity mode locking of consumption and in the area of depression measure the value of the critical cavitation pressure and flow rate, which determines its speed in the neck of the tube, the obtained value of the critical cavitation pressure refers to the saturated vapor pressure of the pumped liquid, then put on a pre-built calculation schedule based relative values of the critical pressure critical flow velocity in the throat of the channel in the time setting mode locking at different concentration of cavitation nuclei and by interpolation, determine the desired concentration of cavitation nuclei of the fluid.

To determine the desired concentration of the nuclei cavitate the pumped liquid used according to pre-constructed based on the relationships describing the specified cavitation mode:

where Kt- coefficient of thermal lag;

Nvthe concentration of cavitation nuclei (the number of critical nuclei per unit volume);

A - factor

g is the density of the fluid;

n is the coefficient characterizing the degree of growth of the bubble over time;

L is the distance from the section corresponding to the condition of the start of growth of the germinal vesicle to the output section Peregudova section of the channel;

Ra - dimensionless complex, Ra=p-R1l;

wherep- coefficient of thermal cavitation (Rakhmatullin SHE Cavitation in the hydraulic system of trunk pipelines. M.: Nedra, 1986, s);

P1ltrue vapour pressure (TPID) of the pumped liquid;

- the relative value of the critical cavitation pressure;

W - velocity in the form of cross-clamping section for maximum performance;

Θkr- the dimensionless complex, Θkr=Bp·g· WOCD,

where g is the density of the fluid.

Figure 1 shows a diagram of a device for implementing the method by changing the critical pressure and the further definition of the desired parameter - the concentration of cavitation nuclei in the liquid.

Figure 2 shows a plot of the relative values of the critical cavitation pressurefrom the velocity of the fluid in the form of cross-clamping section of WOCDdifferent concentrations of cavitation nuclei Nvthe fluid. According topre-built for the specific conditions of pumping on the basis of the equations (1).

As an example, the joint solution of equations (1) in the graph shown in figure 3.

The circuit device includes a pipe 1, the discharging of the fluid from the pipeline 2, which are sequentially meter 3, the node temperature measuring 4, tube parijatam section 5. Inlet and outlet tubes are valves 6. The pressure in the tube is measured by the pressure gauges 7.

The method is as follows.

Using valves 6 in the flow area of the tube 5 set cavitation mode corresponding to the mode locking of the flow that is shown in figure 4, when the last remains unchanged when increasing the pressure difference at the inlet and the outlet of the tube (the horizontal part of Q=f(P1-P5) by reducing back pressure P5and in this mode, pressure gauges 7 measure the value of the critical cavitation pressure (Pkr=P2- the pressure p is Regata section of the tube (shown in figure 4 phantom lines - shows how to defineand at the same time with the help of the counter 3 are measuring the fluid flow, which determine its speed - WOCD. The obtained value of the critical pressure, is related to the saturated vapor pressure of the pumped liquid is applied on the pre-constructed graph (Fig.2)and by interpolation to determine the concentration of cavitation of the fluid.

The proposed method is simple compared with the prototype and can be used, for example, in operating conditions of the pipeline without the use of complicated equipment.

Calculation example for plotting

The calculation for building each dependency is for a given value of the concentration of cavitation nuclei based on the properties of the fluid. The calculation is reduced to the solution of the closed system of equations with two unknowns:

using the graphic-analytical method.

The coefficient characterizing the degree of growth of the bubble over time, n=1.0 for the inertial model of the growth of the bubble.

The criterion of thermal cavitation Inp=52· 10-5m2/h, P1l=1,13· 105n/m2

The dimensionless complexes: Ra=58,76 and

The length of the zone with the pressure line the existing condition of loss of stability of the bubble, equals the length of the narrow cylindrical part of the cavitation tube L=20· 10-3m; factor

Tot- coefficient of thermal lag.

For the accepted value of the concentration of Nv=103.

Asking different values offor a given speed WOCDat the joint solution of the equations system, we find the coefficient KT1and KT2corresponding to the condition of the pressure drop in narrow cylindrical part of the suction tube to the extreme.

For example, for speed in the narrowest part of the suction tube on the mode locking at WOCD=10 m/s we obtain the following estimates:

Intersection curveswill give the value ofat a speed of WOCD=10 m/s for Nv=const=103(figure 3). Other points are similar (see figure 2).

In the practical determination of the concentration of cavitation nuclei on the graph are plotted the experimental points obtained for mode locking of costs in the narrow cross-section at different speeds WOCDand built the experimental dependenceand then by interpolating the determined desired led is in N v.

To illustrate this in figure 2 shows the experimental points obtained at speeds WOCD=18,0 m/s; 19,0 m/s and 33.0 m/s; 35,0 m/s and the desired curve is located between the calculated curves for Nv=104and Nv=105. By interpolation, we establish that the desired curve corresponds to the concentration of nuclei is equal to Nv=5· 104m3.

The method of determining the concentration of nuclei of cavitation of the liquid, including the registration of critical cavitation pressure in the tube with compression of the pumping fluid in the cavitation regime, characterized in that in the flow area of the tube with compression of the flowing part of installing cavity mode locking of consumption and in the area of depression measure the value of the critical cavitation pressure and flow rate, which determines its speed in the neck of the tube, the obtained value of the critical cavitation pressure refers to the saturated vapor pressure of the pumped liquid, then bring on the pre-built calculation schedule based relative values of the critical pressure critical flow velocity in the throat of the channel in the time setting mode locking when different concentration of cavitation nuclei and by interpolation, determine the desired concentration of cavitation nuclei of the pumped liquid is barb.



 

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