CN112833030A - Pump station field flow monitoring method based on front-located shaft type water inlet flow channel - Google Patents
Pump station field flow monitoring method based on front-located shaft type water inlet flow channel Download PDFInfo
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
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Abstract
The invention discloses a pump station field flow monitoring method based on a front-located shaft type water inlet flow channel, and belongs to the technical field of hydraulic engineering pump stations. The method is characterized in that: measuring flow by using the relationship between the static pressure difference between the front end of the front shaft type water inlet channel shaft and the inlet of the water pump impeller chamber and the flow passing through the water inlet channel; the high-pressure piezometer tube is arranged at the front end of the vertical shaft type water inlet flow passage to obtain the highest static pressure in the water inlet flow passage; the low-pressure measuring pipe is arranged in front of the inlet of the impeller chamber with the largest flow velocity to obtain the lowest static pressure in the water inlet flow channel; the maximum static pressure difference can be obtained by subtracting the lowest static pressure from the highest static pressure, and the flow can be calculated according to the maximum static pressure difference, so that the flow measurement precision can be improved; calculating the head loss coefficient of the water inlet flow channel by a numerical calculation method of a water inlet flow field; the static pressure difference is converted into an electric signal by using a differential pressure transmitter and is sent to a computer for relevant calculation. The pump station field flow monitoring method provided by the invention is simple, reliable and low in cost, and can be operated for a long time without failure.
Description
Technical Field
The invention belongs to the technical field of hydraulic engineering pump stations, and particularly relates to a pump station field flow monitoring method based on a front-located shaft type water inlet flow channel, which can be applied to field flow monitoring of large and medium-sized pump stations adopting a front-located shaft type tubular pump device.
Background
The low-lift pump station is widely applied to important fields of water resource allocation, cross-basin water transfer, irrigation, urban water supply and the like. The preposed shaft type tubular pump device is the most applied pump device type in the low-lift large-flow pump station in China at present. With the continuous development of national economy, water resources become increasingly scarce resources, and a plurality of low-lift pump stations related to the water resources monitor and measure the conveyed flow and water quantity. Meanwhile, the real-time monitoring of the flow of the pump station plays an important role in the stable operation and the economic operation of the pump station. In recent years, as more and more low-lift pump station projects are put into operation, more and more attention is paid to pump station field flow monitoring and water quantity metering.
The instrument mainly used for monitoring the large flow on the site of the low-lift pump station is an ultrasonic flowmeter at present. The flowmeter has high manufacturing cost and complex application and maintenance, and the service life of expensive instruments can be greatly reduced due to sundries such as silt, aquatic weeds and the like contained in water, so that the flowmeter cannot be used as a reliable means for monitoring the flow and the water quantity on site of a low-lift pump station for a long time.
Disclosure of Invention
The invention aims to solve the problems, and provides a simple, reliable and cheap pump station field flow monitoring method based on a front-located shaft type water inlet flow channel so as to solve the problem of long-term monitoring of the field flow of a low-lift pump station. The invention is characterized in that: measuring flow by using the relationship between the static pressure difference between the front end of a vertical shaft in a water inlet flow passage of the front-located vertical shaft type tubular pump device and an inlet of a water pump impeller chamber and the flow passing through the water inlet flow passage; arranging a high-pressure piezometer tube at the front end of a vertical shaft of the vertical shaft type water inlet flow channel, and obtaining the highest static pressure in the water inlet flow channel by utilizing the characteristic that the flow velocity of the front end of the vertical shaft in the direction opposite to the water flow is zero; arranging a low-pressure measuring pipe in front of the inlet of the impeller chamber with the largest flow velocity to obtain the lowest static pressure in the water inlet flow channel; the maximum static pressure difference of the determined flow can be obtained by subtracting the lowest static pressure from the highest static pressure, and the field flow measurement precision of the pump station can be improved to the maximum extent according to the maximum static pressure difference; calculating a water inlet runner head loss coefficient in a flow calculation formula by a CFD numerical calculation method; the static pressure difference is converted into an electric signal by using a differential pressure transmitter, and the electric signal is sent to a computer for relevant calculation through analog-to-digital conversion.
The pump station field flow monitoring method based on the front-located shaft type water inlet flow channel can ensure that the derivation and calculation of the pump station field flow can be realized by using a simple pressure measuring pipe principle under the condition of less investment, the accuracy of data is ensured by calibrating a model test and field measurement, and the problems of complex use and maintenance and short service life can be avoided.
In order to realize the purpose of the invention, the pump station adopting the front-located shaft type tubular pump device adopts the following technical scheme:
1. arranging a high-pressure measuring pipe along the water flow direction at the front end of a vertical shaft of the vertical shaft type water inlet flow passage, wherein the pipe orifice of the high-pressure measuring pipe is flush with the front end of the vertical shaft and is opposite to the incoming flow direction of the water inlet flow passage, and the center line of the high-pressure measuring pipe and the center of the water pump impeller are positioned at the same elevation;
2. the distance between the outlet of the shaft type water inlet runner and the inlet of the impeller chamber of the water pump is 0.1D0A low-pressure piezometer tube arranged perpendicular to the direction of water flow, D0The diameter of the water pump impeller is adopted, the pipe orifice of the low-pressure measuring pipe is flush with the inner wall of the water inlet flow channel, and the position of the center line of the low-pressure measuring pipe and the center of the water pump impeller are positioned at the same elevation; the area of the cross section of the flow passage at the position of the low-pressure piezometer tube is A2；
3. A differential pressure transmitter is arranged in the vertical shaft, the lower part of the differential pressure transmitter is provided with a high-pressure interface and a low-pressure interface, and the upper part of the differential pressure transmitter is provided with a high-pressure exhaust port and a low-pressure exhaust port;
4. a high-pressure three-way pipe is arranged in the vertical shaft, one end of the high-pressure three-way pipe is communicated with the high-pressure measuring pipe, the other end of the high-pressure three-way pipe is communicated with a high-pressure interface of the differential pressure transmitter, and a middle hole of the high-pressure three-way pipe is communicated with a high-pressure inflation valve; the high-pressure inflation valve is connected with a compressed air source through a pipeline so as to be convenient for introducing compressed air to dredge when the high-pressure piezometer pipe is blocked; when the high-pressure measuring pipe is blocked, closing a high-pressure three-way pipe control valve arranged between the high-pressure three-way pipe and the differential pressure transmitter, opening a high-pressure inflation valve to introduce compressed air, and dredging the high-pressure measuring pipe; after dredging is finished, closing the high-pressure inflation valve and opening the high-pressure three-way pipe control valve;
5. a low-pressure three-way pipe is arranged in the vertical shaft of the water inlet flow passage, one end of the low-pressure three-way pipe is communicated with the low-pressure measuring pipe, the other end of the low-pressure three-way pipe is communicated with a low-pressure interface of the differential pressure transmitter, and a middle hole of the low-pressure three-way pipe is communicated with a low-pressure inflation valve; the low-pressure inflation valve is connected with a compressed air source through a pipeline so as to be convenient for introducing compressed air to dredge when the low-pressure piezometer tube is blocked; when the low-pressure measuring pipe is blocked, closing a low-pressure three-way pipe control valve arranged between the low-pressure three-way pipe and the differential pressure transmitter, opening a low-pressure inflation valve to introduce compressed air, and dredging the low-pressure measuring pipe; after dredging is finished, closing the low-pressure inflation valve and opening the low-pressure three-way pipe control valve;
6. the high-pressure exhaust port and the low-pressure exhaust port are respectively connected with a high-pressure exhaust valve and a low-pressure exhaust valve, and the high-pressure exhaust valve and the low-pressure exhaust valve are both lower than the central line of the impeller of the water pump by at least 0.5m so as to ensure that air in the high-pressure measuring pipe, the low-pressure measuring pipe and the pipeline is smoothly exhausted;
7. an electric signal output cable of the differential pressure transmitter is led out from a pipeline pre-embedded in the wall of the vertical shaft well and is connected with an analog-to-digital converter and a computer in a pump station unit control room;
8. before the water pump unit is started, the high-pressure exhaust valve is opened, so that water in the water inlet flow channel is continuously discharged from the high-pressure exhaust valve through the high-pressure piezometer tube and a pipeline connected with the high-pressure piezometer tube, the water is continuously discharged for a period of time until no bubbles are discharged from the high-pressure exhaust valve, and then the high-pressure exhaust valve is closed;
9. before the water pump unit is started, the low-pressure exhaust valve is opened, so that water in the water inlet channel is continuously discharged from the low-pressure exhaust valve through the low-pressure piezometer tube and a pipeline connected with the low-pressure piezometer tube, the water is continuously discharged for a period of time until no bubbles are discharged from the low-pressure exhaust valve, and then the low-pressure drain valve is closed;
10. switching on a power supply of the differential pressure transmitter; after the water pump unit is started for a period of time and enters a stable operation state, the differential pressure transmitter transmits current analog quantity expressing the static pressure difference to the analog-to-digital converter; the analog-to-digital converter converts the current analog quantity into a digital quantity and then sends the digital quantity to a related input port of a computer; the computer calculates and displays the flow passing through the water inlet channel and the water quantity in a certain period on a screen according to the received digital quantity;
11. the flow passing through the water inlet flow channel is calculated according to the following formula:
Q＝k(△p)0.5 (1)
where Q is the flow rate in m3/s；
k-flow coefficient of inlet channel, unit m4·(s·N1/2)-1；
Δ p-the static pressure difference between the high and low pressure pipes, in Pa;
12. calculation of flow coefficient k of water inlet channel
According to the research result, the three-dimensional water flow in the preposed shaft type water inlet channel flows uniformly and smoothly, and accords with the gradual change flow condition in hydraulics, so the flow coefficient k of the water inlet channel in the formula (1) is calculated according to the following process:
and (3) listing an energy equation for a section J-J where the high-pressure measuring pipe is located and a section C-C where the low-pressure measuring pipe is located by taking the central line of the water pump impeller as a reference:
(2) the variables in the formula are illustrated below:
Z1and Z2The vertical distances m of the high-pressure measuring pipe and the low-pressure measuring pipe relative to the center line of the water pump impeller are respectively; because the high-pressure measuring pipe and the low-pressure measuring pipe are arranged inThe centers of the two parts are all level with the central line of the impeller of the water pump, so Z2＝Z1；
P1-static pressure, in Pa, of the orifice of said high-pressure piezometer tube;
P2-static pressure, in Pa, of the orifice of said low-pressure manometer;
rho-density of water in kg/m3；
g-acceleration of gravity, unit m/s2；
Xi-head loss coefficient of the water inlet channel, and xi is a constant because the flow in the water inlet channel accords with the condition of the gradual change flow;
according to the cross-sectional area A of the pressure measuring section C-C2And flow rate
The following can be obtained:
in the formula, A2- -flow passage cross-sectional area at the low-pressure piezometer tube, m2；
From the above formulae, it is possible to obtain:
(4) flow coefficient of water inlet channel in formula
13. Calculating a head loss coefficient xi of the water inlet flow passage;
(4) in the formula, the water inlet channel head loss coefficient xi is obtained by calculating a three-dimensional numerical value of the water inlet channel flow field, and the specific process is as follows:
the calculation area of the water inlet flow channel flow field is composed of a pump station forebay, a front shaft type water inlet flow channel, a water pump impeller, an impeller chamber and a water outlet pipe; constructing a three-dimensional model of the water inlet runner according to the scheme of the front-located shaft type water inlet runner and the positions of the high-pressure measuring sections J-J and the low-pressure measuring sections C-C;
secondly, the inlet section of the flow field of the water inlet channel is arranged in a front pool of the pump station, and the distance between the inlet section and the inlet of the water inlet channel is 3D0(ii) a The front pool incoming flow is vertical to the inlet section, the incoming flow velocity is uniformly distributed, and the boundary condition of the inlet section of the water inlet flow field is a velocity inlet boundary condition;
thirdly, the outlet section of the flow field of the water inlet flow channel is arranged on the outlet section of the water outlet pipe, and the distance between the outlet section and the center of the water pump impeller is 5D0(ii) a After flowing into the water outlet pipe from the guide blade outlet, the water flow passes through the 5D0The water outlet pipe with the length is used for adjusting the water flow direction, the flow in the pipeline is fully developed, and the boundary condition of the outlet section of the water inlet flow field is a free outflow boundary condition;
setting the water pump impeller as a periodic boundary condition according to the rotating speed of the water pump impeller;
fifthly, calculating the value of the flow field of the water inlet flow channel, and obtaining the total pressure E of the pressure measuring section J-J according to the value calculation result1And total pressure E of pressure measuring section C-C2(ii) a Calculating the head loss coefficient xi of the water inlet flow passage according to the following formula:
in the formula, E1-measuring the total pressure of the section J-J in Pa;
E2-the total pressure of the pressure measuring section C-C, in Pa;
M＝Q×T (7)
where M is the amount of water in M3；
T-duration of the period of time during which the amount of water is metered, in units of s.
Compared with the prior art, the method has the following beneficial effects:
firstly, the invention provides a simple, practical, accurate, reliable, durable and low-cost method for monitoring the field flow of the pump station by adopting the front-located shaft type tubular pump.
Secondly, the invention skillfully solves the most difficult flow measurement problem in the field monitoring of the pump station and provides an effective tool for the real-time monitoring of the operation condition of the low-lift pump station unit.
Thirdly, the invention can conveniently solve the problem of measuring the water delivery quantity of the low-lift pump station for water resource allocation, cross-basin water transfer, irrigation and urban water supply.
Drawings
FIG. 1(a) is a schematic view of a front-located shaft type intake runner pump station flow monitoring elevation arrangement of the present invention;
FIG. 1(b) is a schematic view of a flow monitoring plan of a front-located shaft type water inlet channel pump station according to the present invention;
FIG. 2 is a diagram of a calculated area of the flow field of the leading riser approach of the present invention;
in the figure: the system comprises a vertical shaft 1, a high-pressure measuring pipe 2, an impeller 3, an impeller chamber 4, a low-pressure measuring pipe 5, a differential pressure transmitter 7, a high-pressure interface 8, a low-pressure interface 9, a high-pressure exhaust port 10, a low-pressure exhaust port 11, a high-pressure three-way pipe 12, a high-pressure three-way pipe 121, a high-pressure three-way pipe 122, a high-pressure three-way pipe 123, a middle hole of the high-pressure three-way pipe 13, a low-pressure inflation valve 14, a low-pressure three-way pipe 141, a low-pressure three-way pipe 142, a low-pressure three-way pipe 143, a middle hole of the low-pressure three-way pipe 15, a high-pressure exhaust valve 16, a low-pressure exhaust valve 17, an electric signal output cable 18, a pipeline 19, an analog-to-digital converter 20, a computer 21, a forebay 22.
Detailed Description
The invention is further illustrated with reference to the following figures and examples.
A pump station field flow monitoring method based on a front-located shaft type water inlet flow channel adopts the following technical scheme:
1. a high-pressure measuring pipe 2 along the water flow direction is arranged at the front end of a vertical shaft 1 of a vertical shaft type water inlet flow passage, the pipe orifice of the high-pressure measuring pipe 2 is flush with the front end of the vertical shaft 1 and is opposite to the incoming flow direction of the water inlet flow passage, and the center line of the high-pressure measuring pipe 2 and the center of a water pump impeller 3 are positioned at the same elevation, as shown in a figure 1 (a);
2. the distance between the outlet of the shaft type water inlet channel and the inlet of the water pump impeller chamber 4 is 0.1D0A low-pressure piezometer tube 5, D perpendicular to the water flow direction is arranged0The diameter of the water pump impeller is the same as that of the inlet water flow channel, and the orifice of the low-pressure piezometer tube 5 is flush with the inner wall of the inlet water flow channel, as shown in fig. 1 (a); the position of the central line of the low-pressure piezometer tube 5 and the center of the water pump impeller 3 are positioned at the same elevation, as shown in fig. 1 (b); the cross-sectional area of the flow passage at the position of the low-pressure piezometer tube 5 is A2；
3. A differential pressure transmitter 7 is arranged in the shaft 1, the lower part of the differential pressure transmitter 7 is provided with a high-pressure interface 8 and a low-pressure interface 9, and the upper part of the differential pressure transmitter 7 is provided with a high-pressure exhaust port 10 and a low-pressure exhaust port 11, as shown in fig. 1 (a);
4. a high-pressure three-way pipe 12 is arranged in the shaft 1, one end 121 of the high-pressure three-way pipe 12 is communicated with the high-pressure measuring pipe 2, the other end 122 of the high-pressure three-way pipe is communicated with the high-pressure interface 8 of the differential pressure transmitter 7, and a middle hole 123 of the high-pressure three-way pipe 12 is communicated with the high-pressure inflation valve 13, as shown in fig. 1 (a); the high-pressure inflation valve 13 is connected with a compressed air source 28 through a pipeline so as to be convenient for introducing compressed air for dredging when the high-pressure piezometer tube 2 is blocked; when the high-pressure measuring pipe 2 is blocked, closing a high-pressure three-way pipe control valve 29 arranged between the high-pressure three-way pipe 12 and the differential pressure transmitter 7, opening a high-pressure inflation valve 13 to introduce compressed air, and dredging the high-pressure measuring pipe 2; after dredging is finished, closing the high-pressure inflation valve 13 and opening the high-pressure three-way pipe control valve 29;
5. a low-pressure three-way pipe 14 is arranged in the shaft 1, one end 141 of the low-pressure three-way pipe 14 is communicated with a low-pressure measuring pipe 5, the other end 142 of the low-pressure three-way pipe is communicated with a low-pressure interface 9 of a differential pressure transmitter 7, and a middle hole 143 of the low-pressure three-way pipe 14 is communicated with a low-pressure inflation valve 15, as shown in fig. 1 (b); the low-pressure inflation valve 15 is connected with a compressed air source 28 through a pipeline so as to be convenient for introducing compressed air for dredging when the low-pressure piezometer tube 5 is blocked; when the low-pressure measuring pipe 5 is blocked, closing a low-pressure three-way pipe control valve 30 arranged between the low-pressure three-way pipe 14 and the differential pressure transmitter 7, opening a low-pressure inflation valve 15 to introduce compressed air, and dredging the low-pressure measuring pipe 5; after dredging is finished, closing the low-pressure inflation valve 15 and opening the low-pressure three-way pipe control valve 30;
6. the high-pressure exhaust port 10 and the low-pressure exhaust port 11 are respectively connected with a high-pressure exhaust valve 16 and a low-pressure exhaust valve 17, and the high-pressure exhaust valve 16 and the low-pressure exhaust valve 17 are both lower than the central line of the water pump impeller 3 by at least 0.5m so as to ensure that air in the high-pressure measuring pipe 2, the low-pressure measuring pipe 5 and a pipeline is smoothly exhausted, as shown in fig. 1 (a);
7. an electric signal output cable 18 of the differential pressure transmitter 7 is led out from a pipeline 19 pre-buried in the wall of the vertical shaft 1 and is connected with an analog-to-digital converter 20 and a computer 21 in a pump station unit control room;
8. calculating the head loss coefficient xi of the water inlet flow passage
And (3) carrying out three-dimensional numerical calculation on the flow field of the water inlet flow channel:
the water inlet flow channel flow field calculation area comprises a pump station forebay 22, a front vertical shaft type water inlet flow channel 23, a water pump impeller 3, an impeller chamber 4, a guide vane body 24 and a water outlet pipe 25; constructing a three-dimensional model of the water inlet runner according to the scheme of the front shaft type water inlet runner 23 and the positions of the high-pressure measuring sections J-J and the low-pressure measuring sections C-C;
② the inlet section 26 of the water inlet flow channel flow field is arranged in the pump station forebay 22 3D away from the inlet section of the water inlet flow channel0Here, the boundary condition of the inlet section 26 is a velocity inlet boundary condition;
thirdly, an outlet section 27 of the water inlet flow channel flow field is arranged on the outlet section 27 of the water outlet pipe 25, and the outlet section 27 of the water outlet pipe 25 is 5D away from the center of the water pump impeller 30(ii) a The boundary condition of the outlet cross section 27 is a free outflow boundary condition;
setting the water pump impeller 3 as a periodic boundary condition according to the rotating speed of the water pump impeller;
calculating the numerical value of the flow field of the water inlet flow channel, and calculating the head loss coefficient xi of the water inlet flow channel 23 according to the formula (6) according to the numerical value calculation result;
9. the flow coefficient of the intake runner 23 is calculated according to the following formula
10. Before the water pump unit is started, the high-pressure exhaust valve 16 is opened, so that water in the water inlet channel 23 is continuously discharged from the high-pressure exhaust valve 16 through the high-pressure piezometer tube 2 and a pipeline connected with the high-pressure piezometer tube, the water is continuously discharged for a period of time until no bubbles are completely discharged from the high-pressure exhaust valve 16, and then the high-pressure exhaust valve 16 is closed;
11. before the water pump unit is started, the low-pressure exhaust valve 17 is opened, so that water in the water inlet channel 23 is continuously discharged from the low-pressure exhaust valve 17 through the low-pressure piezometer tube 5 and a pipeline connected with the low-pressure piezometer tube, the water is continuously discharged for a period of time until no bubbles are discharged from the low-pressure exhaust valve 17, and then the low-pressure exhaust valve 17 is closed;
12. the power supply of the differential pressure transmitter 7 is connected; after the water pump unit is started for a period of time and enters a stable operation state, the differential pressure transmitter 7 transmits current analog quantity expressing the static pressure difference to the analog-to-digital converter 20; the analog-to-digital converter 20 converts the current analog quantity output by the differential pressure transmitter 7 into a digital quantity and then sends the digital quantity to a relevant input port of a computer 21;
13. the computer 21 calculates the flow rate of the water inlet channel 23 according to the received digital quantity by the following formula:
Q＝k(△p)0.5
where Q is the flow rate in m3/s；
Δ p-the static pressure difference between the high pressure pipe 2 and the low pressure pipe 5, in Pa;
14. the amount of water passing through the water inlet channel 23 is calculated by the following formula
M＝Q×T
Where M is the amount of water in M3；
T-duration of the period of time during which the amount of water is metered, in units of s.
Examples
A certain low-lift pump station adopts a front-mounted shaft type tubular pump device, the diameter of a water pump impeller is 4.0m, and the designed flow of a single water pump is 50m3(s) area A of pressure measuring section C-C of leading shaft type water inlet flow passage2＝10.79m3. The technical scheme of the invention is adopted to detect the flow passing through the water inlet channel, and the steps are as follows:
carrying out three-dimensional flow field numerical calculation on the flow field of the preposed shaft type water inlet flow channel 23, and calculating to obtain total pressures of pressure measuring sections J-J and C-C which are 58163Pa and 57487Pa respectively according to the numerical calculation result;
calculating a head loss coefficient ξ of the water inlet channel 23 according to the formula (5):
secondly, calculating the flow coefficient k of the water inlet channel 23 according to the formula (6):
before the water pump unit is started, opening the high-pressure exhaust valve 16 to enable water in the water inlet flow channel 23 to be continuously discharged from the high-pressure exhaust valve 16 through the high-pressure measuring pipe 2 and a pipeline connected with the high-pressure measuring pipe, continuously discharging for a period of time until no bubbles are confirmed to be discharged from the high-pressure exhaust valve 16, and then closing the high-pressure exhaust valve 16;
before the water pump unit is started, the low-pressure exhaust valve 17 is opened, so that water in the water inlet channel 23 is continuously discharged from the low-pressure exhaust valve 17 through the low-pressure piezometer tube 5 and a pipeline connected with the low-pressure piezometer tube, the water is continuously discharged for a period of time until no bubbles are discharged from the low-pressure exhaust valve 17, and then the low-pressure exhaust valve 17 is closed;
connecting the power supply of the differential pressure transmitter 7; after the water pump unit is started for a period of time and enters a stable operation state, the differential pressure transmitter 7 transmits current analog quantity expressing the static pressure difference to the analog-to-digital converter 20; analog-to-digital converter 20 converts the current analog quantity output from differential pressure transmitter 7 into a digital quantity, whose value is 13976 (Pa);
sixthly, the digital quantity is input into the computer 21 through a relevant port of the computer 21; the computer 21 calculates the flow rate through the water inlet channel 23:
Q＝k(△p)0.5＝0.42456×139760.5＝50.2m3/s
the screen of the computer 21 shows that the flow rate of the inflow channel 23 is 50.2m3/s；
(7) Calculating the water quantity passing through the water pump unit after 30 minutes of operation:
M＝Q×T＝50.2×30×60＝90360m3
the screen of the computer 21 displays that the water quantity passing through the water inlet channel 23 is 90360m3。
Claims (1)
1. A pump station on-site flow monitoring method based on a front-located shaft type water inlet channel is characterized in that flow measurement is carried out by utilizing the relation between the static pressure difference between the front end of a shaft in the water inlet channel of a front-located shaft type tubular pump device and the inlet of a water pump impeller chamber and the flow passing through the water inlet channel; the method comprises the following steps:
(1) arranging a high-pressure measuring pipe along the water flow direction at the front end of a vertical shaft of the vertical shaft type water inlet flow channel, wherein the pipe orifice of the high-pressure measuring pipe is flush with the front end of the inlet of the water inlet flow channel and is opposite to the incoming flow direction of the water inlet flow channel, and the center line of the high-pressure measuring pipe and the center of the water pump impeller are positioned at the same elevation;
(2) the distance between the outlet of the shaft type water inlet runner and the inlet of the impeller chamber of the water pump is 0.1D0A low-pressure piezometer tube arranged perpendicular to the direction of water flow, D0The diameter of the water pump impeller; the pipe orifice of the low-pressure measuring pipe is flush with the inner wall of the water inlet flow passage, and the position of the central line of the low-pressure measuring pipe and the center of the water pump impeller are positioned at the same elevation; the area of the cross section of the flow passage at the position of the low-pressure piezometer tube is A2；
(3) A differential pressure transmitter is arranged in the vertical shaft, the lower part of the differential pressure transmitter is provided with a high-pressure interface and a low-pressure interface, and the upper part of the differential pressure transmitter is provided with a high-pressure exhaust port and a low-pressure exhaust port;
(4) a high-pressure three-way pipe is arranged in the vertical shaft, one end of the high-pressure three-way pipe is communicated with the high-pressure measuring pipe, the other end of the high-pressure three-way pipe is communicated with a high-pressure interface of the differential pressure transmitter, and a middle hole of the high-pressure three-way pipe is communicated with a high-pressure inflation valve; the high-pressure inflation valve is connected with a compressed air source through a pipeline; when the high-pressure measuring pipe is blocked, closing a high-pressure three-way pipe control valve arranged between the high-pressure three-way pipe and the differential pressure transmitter, opening a high-pressure inflation valve to introduce compressed air, and dredging the high-pressure measuring pipe; after dredging is finished, closing the high-pressure inflation valve and opening the high-pressure three-way pipe control valve;
(5) a low-pressure three-way pipe is arranged near the pipe orifice of the low-pressure measuring pipe, one end of the low-pressure three-way pipe is communicated with the low-pressure measuring pipe, the other end of the low-pressure three-way pipe is communicated with a low-pressure interface of the differential pressure transmitter, and a middle hole of the low-pressure three-way pipe is communicated with a low-pressure inflation valve; the low-pressure inflation valve is connected with a compressed air source through a pipeline; when the low-pressure measuring pipe is blocked, closing a low-pressure three-way pipe control valve arranged between the low-pressure three-way pipe and the differential pressure transmitter, opening a low-pressure inflation valve to introduce compressed air, and dredging the low-pressure measuring pipe; after dredging is finished, closing the low-pressure inflation valve and opening the low-pressure three-way pipe control valve;
(6) the high-pressure exhaust port and the low-pressure exhaust port are respectively connected with a high-pressure exhaust valve and a low-pressure exhaust valve, and the high-pressure exhaust valve and the low-pressure exhaust valve are both lower than the central line of the impeller of the water pump by at least 0.5m so as to ensure that air in the high-pressure measuring pipe, the low-pressure measuring pipe and the pipeline is smoothly exhausted;
(7) an electric signal output cable of the differential pressure transmitter is led out from a pipeline pre-embedded in a shaft wall of the vertical shaft and is connected with an analog-to-digital converter and a computer in a pump station unit control room;
(8) before the water pump unit is started, the high-pressure exhaust valve is opened, so that water in the water inlet runner is continuously discharged from the high-pressure exhaust valve through the high-pressure piezometer pipe and a pipeline connected with the high-pressure piezometer pipe, the water is continuously discharged for a period of time until no bubbles are discharged from the high-pressure exhaust valve, and then the high-pressure exhaust valve is closed;
(9) before the water pump unit is started, the low-pressure exhaust valve is opened, so that water in the water inlet channel is continuously discharged from the low-pressure exhaust valve through the low-pressure piezometer tube and a pipeline connected with the low-pressure piezometer tube, the water is continuously discharged for a period of time until no bubbles are discharged from the low-pressure exhaust valve, and then the low-pressure exhaust valve is closed;
(10) switching on a power supply of the differential pressure transmitter; after the water pump unit is started for a period of time and enters a stable operation state, the differential pressure transmitter transmits current analog quantity expressing the static pressure difference to the analog-to-digital converter; the analog-to-digital converter converts the current analog quantity into a digital quantity and then sends the digital quantity to a related input port of a computer; the computer calculates and displays the flow passing through the water inlet channel and the water quantity in a certain period on a screen according to the received digital quantity;
(11) the flow rate of the water inlet flow channel is calculated according to the following formula:
Q＝k(△p)0.5 (1)
where Q is the flow rate in m3/s；
k-flow coefficient of inlet channel, unit m4/(s·N1/2)；
Δ p-the static pressure difference between the high and low pressure pipes, in Pa;
(12) the flow coefficient k of the water inlet channel is calculated according to the following formula:
where ρ -density of water, unit kg/m3；
ξ -head loss coefficient of the intake runner;
A2- -flow passage cross-sectional area at the low pressure piezometer tube, in m2；
(13) And carrying out three-dimensional numerical calculation on the flow field of the water inlet flow channel, and obtaining a head loss coefficient xi of the water inlet flow channel according to a numerical calculation result, wherein the specific process is as follows:
the water inlet flow channel flow field calculation area comprises a pump station forebay, a front vertical shaft type water inlet flow channel, a water pump impeller, an impeller chamber, a guide vane body and a water outlet pipe; constructing a three-dimensional model of the water inlet runner according to the scheme of the front-located shaft type water inlet runner and the positions of the high-pressure measuring sections J-J and the low-pressure measuring sections C-C;
secondly, the inlet section of the flow field of the water inlet flow channel is arranged in the front pool of the pump station at a distance of 3D from the inlet section of the water inlet flow channel0The boundary condition of the inlet section is a speed inlet boundary condition;
thirdly, the outlet section of the water inlet flow channel flow field is arranged on the outlet section of the water outlet pipe, and the distance between the outlet section of the water outlet pipe and the center of the water pump impeller is 5D0(ii) a The boundary condition of the outlet section is a free outflow boundary condition;
setting the water pump impeller as a periodic boundary condition according to the rotating speed of the water pump impeller;
fifthly, calculating the value of the flow field of the water inlet flow channel, and obtaining the total pressure E of the pressure measuring section J-J according to the value calculation result1And total pressure E of pressure measuring section C-C2(ii) a Calculating the head loss coefficient xi of the water inlet flow passage according to the following formula:
in the formula, E1-measuring the total pressure of the section J-J in Pa;
E2-the total pressure of the pressure measuring section C-C, in Pa;
(14) the water passing through the water inlet channel is calculated according to the flow measured in a certain time period and the time length of the time period according to the following formula:
M＝Q×T (7)
where M is the amount of water in M3；
T-duration of the period of time during which the amount of water is metered, in units of s.
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| CN114251277A (en) * | 2021-12-22 | 2022-03-29 | 南水北调东线江苏水源有限责任公司 | Method for monitoring operation condition of water pump by comparing water flow pulsation conditions before and after pump section |
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