Cavitation monitoring method for fire pump
阅读说明：本技术 一种消防泵汽蚀监控方法 (Cavitation monitoring method for fire pump ) 是由 蒋敦军 康秀峰 刘冬桂 于 2019-12-03 设计创作，主要内容包括：本发明公开了一种消防泵汽蚀监控方法,包括以下步骤：获取水的饱和蒸汽压及消防泵的运行和结构相关参数并予以存储；按照固定的时间间隔实时采集消防泵的吸入口压力、流量和通过水温并予以存储；查表获得当前水温对应的饱和蒸汽压,并计算一系列汽蚀余量值；对消防泵进行汽蚀情况判定,根据判定结果采取针对性措施并给出相应的原因提示。本发明从消防泵有效汽蚀余量与必需汽蚀余量这两方面客观现象的比较出发,同时考虑到了吸入口压力、流量和水温对有效汽蚀余量的影响,考察因素全面、直接,具有分析结果可靠性高的优点。(The invention discloses a cavitation monitoring method for a fire pump, which comprises the following steps: acquiring and storing saturated vapor pressure of water and relevant parameters of operation and structure of a fire pump; acquiring the pressure and flow of a suction inlet of a fire pump and the passing water temperature in real time according to a fixed time interval and storing the pressure, flow and passing water temperature; looking up a table to obtain saturated vapor pressure corresponding to the current water temperature, and calculating a series of vapor etching residue values; and judging the cavitation condition of the fire fighting pump, taking targeted measures according to the judgment result and giving corresponding reason prompts. The invention starts from the comparison of two objective phenomena of the effective cavitation allowance and the necessary cavitation allowance of the fire pump, simultaneously considers the influence of the pressure, the flow and the water temperature of the suction inlet on the effective cavitation allowance, has comprehensive and direct investigation factors, and has the advantage of high reliability of analysis results.)
1. A fire pump cavitation monitoring method comprises the following steps:
1) temperature T-vaporization pressure P of the obtained watervAccording to the curve and depending on the temperature T of the water-the evaporation pressure PvObtaining the temperature T and the vaporization pressure P of a plurality of groups of water by a curvevThe corresponding data of (2) are stored in a table form; obtaining the fire pump flow Q-necessary cavitation allowance (NPSH)rCurve and according to the fire pump flow Q-required cavitation margin (NPSH)rCurve acquisition of multiple sets of fire pump flow Q and necessary cavitation allowance (NPSH)rThe corresponding data of (2) are stored in a table form; obtaining the nominal diameter D of the flange of the suction inlet of the fire pumpiAnd storing;
2) real-time acquisition of suction port pressure value P of fire pump according to fixed time intervaliThe flow Q and the passing water temperature value T are stored;
3) obtaining the vaporization pressure P corresponding to the temperature T of the current water by looking up a tablevCalculating a series of cavitation residual values of the fire pump;
4) and judging the cavitation condition of the fire fighting pump, taking targeted measures according to the judgment result and giving corresponding reason prompts.
2. The fire pump cavitation monitoring method according to claim 1, the specific operation of step 3) is as follows:
calculating the current value of the effective cavitation margin (NPSH) of the fire pumpaIShort term predictive value (NPSH)aIIAnd long term prediction (NPSH)aIIIAnd the current required cavitation margin value (NPSH) of the fire pumprI：
3.1) calculating the current value of the effective cavitation allowance (NPSH) of the fire pumpaIThe formula is as follows:
in the formula (1), PiI、viIAnd PVIRespectively the current value of the pressure of a suction inlet, the current value of the speed of the suction inlet and the current value of the vaporization pressure of water of the fire pump; rho and g are the density and the gravity acceleration of water respectively; wherein, the current value P of the suction inlet pressure of the fire pumpiIThe pressure sensor of the suction inlet collects the data; current value P of the pressure of vaporization of waterVIAccording to the current value T of the water temperature acquired by a temperature sensor in the inlet pipeline of the fire pumpITemperature T and vaporization pressure P of water examinationvCorresponding to the table, and obtaining the current value T of the water temperatureIThe vaporization pressure P corresponding to the temperature T of the two closest watervAnd carrying out interpolation calculation to obtain; current value v of suction inlet speediIFlow current value Q acquired by fire pump outlet pipeline flowmeterIDivided by the area S of the fire pump suction inletiObtaining;
3.2) calculating the effective cavitation allowance short-term prediction value (NPSH) of the fire pumpaIIThe formula is as follows:
in the formula (3), PiII、viIIAnd PVIIRespectively a short-term predicted value of suction inlet pressure, a short-term predicted value of suction inlet speed and a short-term predicted value of vaporization pressure of water of the fire pump;
3.3) calculating the effective steam of the fire pumpLong-term predicted value of erosion allowance (NPSH)aIIIThe formula is as follows:
in the formula (4), PiIII、viIIIAnd PVIIIRespectively a long-term predicted value of suction inlet pressure, a long-term predicted value of suction inlet speed and a long-term predicted value of vaporization pressure of water of the fire pump;
3.4) calculating the current required cavitation residual value (NPSH) of the fire pumprIAccording to the current flow value Q collected by the outlet pipeline flowmeter of the fire pumpIChecking the flow Q and the required cavitation allowance (NPSH) of the fire pump obtained in the step 1)rCorresponding data table, obtaining the necessary cavitation allowance (NPSH) corresponding to two fire pump flow rates Q close to the data tablerAnd then the calculation of interpolation is carried out.
3. The fire pump cavitation monitoring method according to claim 2, the specific operation of step 4) is as follows:
respectively comparing the current values of the effective cavitation residual amounts (NPSH)aIShort-term prediction value (NPSH) of effective cavitation allowance of fire pumpaIILong-term predicted value (NPSH) of effective cavitation allowance of fire pumpaIIIThe three parts and the current required cavitation residual value (NPSH) of the fire pumprIComparing, outputting corresponding states according to comparison results, prompting and synchronously taking targeted measures:
4.1) judgment (NPSH)aI≤(NPSH)rIIf the cavitation erosion is not met, outputting a prompt of 'cavitation erosion has occurred at present', and reducing the opening degree of a fire pump outlet pipeline valve until reaching (NPSH)aI>(NPSH)rIThen, the step 4.2) is carried out; otherwise, turning to step 4.2);
4.2) judgment (NPSH)aII≤(NPSH)rIIf yes, outputting a prompt of 'possibly being cavitation will' and corresponding suggestion, inquiring whether the user agrees to make automatic intervention, and if yes, reducing the opening degree of a fire pump outlet pipeline valve until (NPSH)aII>(NPSH)rIThen, the step 4.3) is carried out, and if the user does not agree, the step 4.3) is directly carried out; otherwise, turning to step 4.3);
4.3) judgment (NPSH)aIII≤(NPSH)rIIf yes, outputting a prompt of 'possible cavitation in the future', and returning to the step 4.1); otherwise, return to step 4.1).
4. The method for monitoring cavitation of fire pump in claim 3, wherein the short-term predicted value P of the suction pressure of the fire pump in step 3.2)iIIShort-term predicted value v of speed of suction inletiIIAnd a short-term predicted value P of the vaporization pressure of waterVIIThe acquisition method comprises the following steps:
3.2.1) according to the pressure value P of the suction inlet of the fire pump at different moments collected in the step 2iFlow Q time series and water temperature T, extracting m collected values each containing a current value, and composing respective short-term history series X ═ X in chronological order1,x2,…,xm]Wherein m is a positive integer between 5 and 20, and X is the acquired suction pressure value P of the fire pumpiA short term history sequence of flow Q or temperature T of the water;
3.2.2) determining the weighted arithmetic mean X of the respective short-term historical sequence valuesIII.e. short-term predicted values P for the pressure at the suction inlet of the fire pumpiIIShort-term flow prediction value QIIAnd a short-term predicted value T of water temperatureII：
In formula (5) fjAs weighting factors:
3.2.3) short-term flow prediction QIIDivided by the suction inlet area SiObtaining a short-term predicted value v of the speed of the suction inletiIIAccording to the short-term predicted value T of the water temperatureIITemperature T and steam of water examinationChange pressure PvCorresponding to the table to obtain the short-term predicted value T of water temperatureIIThe vaporization pressures corresponding to the temperatures of the two close water are interpolated to obtain a short-term prediction value P of the vaporization pressures of the waterVII。
5. The method for monitoring cavitation of fire pump according to claim 4, wherein the long-term predicted value P of the suction pressure of the fire pump in step 3.3)iIIIThe long-term predicted value v of the speed of the suction inletiIIIAnd long-term predicted value P of vaporization pressure of waterVIIIThe acquisition method comprises the following steps:
3.3.1) pressure value P of suction inlet of fire pump acquired in step 2iTime series, flow Q time series and water temperature T time series, extracting the latest n collection values respectively containing the current values, and forming the respective long-term history series Y (Y) according to the chronological order1,y2,…,xn]Wherein n is an even number between 20 and 100, and Y is a collected suction pressure value P of the fire pumpiA long history sequence of flow Q or temperature T of the water;
3.3.2) calculating the arithmetic mean of the first half of the long-term history sequence YAnd the second half arithmetic mean
3.3.3) obtaining Long-term predicted values Y for the respective Long-term historical sequence valuesIIII.e. long-term predicted value P of suction inlet pressure of fire pumpiIIILong-term flow prediction value QIIIAnd long-term predicted value of water temperatureTIII：
3.3.4) Long-term prediction of Q from flowIIIDivided by the suction inlet area SiObtaining a long-term predicted value v of the speed of the suction inletiIIIAccording to the long-term predicted value T of the water temperatureIIITemperature T and vaporization pressure P of water examinationvCorresponding to the table to obtain the long-term predicted value T of the water temperatureIIIThe vaporization pressure P corresponding to the temperature T of the two closest watervAnd interpolation calculation is carried out to obtain a long-term predicted value P of the vaporization pressure of the waterVIII。
6. The fire pump cavitation monitoring method of claim 3, wherein the corresponding suggestion of the "cavitation is about to be expected" prompt in step 4.2) is made by obtaining a short-term key influence parameter, wherein the short-term key influence parameter adopts a characteristic value A, and the calculation formula of the characteristic value A is as follows:
in the formula (10), max represents the maximum value of the three values in parentheses;
if the short-term key impact parameter is
if the short-term key impact parameter is
if the short-term key impact parameter is
7. The fire pump cavitation monitoring method of claim 3, wherein the corresponding suggestion of the "possible cavitation in the future" prompt in step 4.3) is made by obtaining a long-term key influence parameter, wherein the long-term key influence parameter is a characteristic value B, and the calculation formula of the characteristic value B is as follows:
in the formula (11), max represents the maximum value among three values in parentheses,
if the long-term key impact parameter is
if the long-term key impact parameter is
if long term key shadowThe response parameter is
Technical Field
The invention belongs to the technical field of fire pump monitoring, and particularly relates to a fire pump cavitation monitoring method.
Background
With the development of economic society, people pay more and more attention to safety problems. Among them, fire is a safety accident that is widely regarded by people. When a fire occurs, the most common method is to use a fire pump to deliver water to extinguish the fire. However, the environment of the fire extinguishing site is often very complex, various factors are full of uncertainty, once the fire pump fails due to some subjective or objective reasons, the normal work and water delivery of the fire pump are affected, and further, the fire extinguishing work is easily caused with adverse consequences. Cavitation is a very common type of operational failure in the operation of fire pumps. When the conditions of over-high delivery flow, over-high water temperature, insufficient water supply pressure and the like occur in the operation process of the fire pump, the effective cavitation allowance of the fire pump is possibly lower than the necessary cavitation allowance of the fire pump, cavitation is caused, water flow in the area near the inlet of the impeller is vaporized, adverse effects of obvious reduction of flow and lift, aggravation of vibration and impact, damage to the impeller and the like are brought, and the smooth operation of fire fighting is interfered.
In order to ensure smooth water flow conveying in the fire extinguishing process of the fire pump and avoid serious consequences caused by cavitation, monitoring and alarming of cavitation are required in the operation process of the fire pump. Many cavitation monitoring technologies of hydraulic machinery such as pumps and the like are developed, and the currently known cavitation monitoring technology is mainly designed to grasp the vibration phenomenon of the hydraulic machinery structure induced in the cavitation generation and development process and focuses on the analysis and processing of vibration signals. However, these techniques have three disadvantages: firstly, vibration signal monitoring of hydraulic machinery such as pumps and the like depends on a high-precision and easily-damaged vibration sensor and an auxiliary signal analysis device thereof, so that the manufacturing cost is high, and a professional installation and maintenance technology is required; secondly, the environment of a place where the fire pump operates is severe, conditions in all aspects are complex, and various environmental factors can interfere with vibration of equipment, so that the reliability of cavitation diagnosis is influenced; thirdly, whether cavitation occurs can only be simply judged by means of vibration monitoring, but possible reasons for the cavitation cannot be given, and therefore the fault removing operation of field personnel cannot be guided.
Therefore, it is necessary to develop a monitoring method for fire pump cavitation, which is economically applicable, stable and reliable, and controls and prevents the fire pump cavitation in parallel, and design a corresponding monitoring device to effectively monitor, control and prevent the pump cavitation in a complex environment and under various uncertain conditions, by fully paying attention to various possible factors in the actual operating environment of the fire pump, aiming at the defects of the prior known technical scheme.
Disclosure of Invention
In order to solve the technical problems, the invention provides a fire pump cavitation monitoring method which is stable, reliable, economical, applicable, strong in pertinence, comprehensive in investigation factor and integrated in prevention and control.
The technical scheme adopted by the invention is as follows: a fire pump cavitation monitoring method comprises the following steps:
1) temperature T-vaporization pressure P of the obtained watervAccording to the curve and depending on the temperature T of the water-the evaporation pressure PvObtaining the temperature T and the vaporization pressure P of a plurality of groups of water by a curvevThe corresponding data of (2) are stored in a table form; obtaining the fire pump flow Q-necessary cavitation allowance (NPSH)rCurve and according to the fire pump flow Q-required cavitation margin (NPSH)rCurve acquisition of multiple sets of fire pump flow Q and necessary cavitation allowance (NPSH)rThe corresponding data of (2) are stored in a table form; obtaining the nominal diameter D of the flange of the suction inlet of the fire pumpiAnd storing;
2) real-time acquisition of suction port pressure value P of fire pump according to fixed time intervaliFlow Q, temperature T through the water, and store:
3) obtaining the vaporization pressure P corresponding to the temperature T of the current water by looking up a tablevCalculating a series of cavitation residual values of the fire pump;
4) and judging the cavitation condition of the fire fighting pump, taking targeted measures according to the judgment result and giving corresponding reason prompts.
In the method for monitoring cavitation of the fire pump, the specific operation of the step 3) is as follows:
3.1) calculating the current value (NPSH) of the effective cavitation allowance of the fire pumpaIShort term predictive value (NPSH)aIIAnd long term prediction (NPSH)aIIIAnd the current required cavitation margin value (NPSH) of the fire pumprI：
Calculating the current value of the effective cavitation margin (NPSH) of the fire pumpaIThe formula is as follows:
in the formula (1), PiI、viIAnd PVIRespectively the current value of the pressure of the suction inlet of the fire pump and the suction inletA current value of the velocity and a current value of the vaporization pressure of the water; rho and g are the density and the gravity acceleration of water respectively; wherein, the current value P of the suction inlet pressure of the fire pumpiIThe pressure sensor of the suction inlet collects the data; current value P of the pressure of vaporization of waterVIAccording to the current value T of the water temperature acquired by a temperature sensor in the inlet pipeline of the fire pumpITemperature T and vaporization pressure P of water examinationvCorresponding to the table, and performing interpolation calculation to obtain the result; current value v of suction inlet speediIFlow current value Q acquired by fire pump outlet pipeline flowmeterIDivided by the area S of the fire pump suction inletiObtaining;
3.2) calculating the effective cavitation allowance short-term prediction value (NPSH) of the fire pumpaIIThe formula is as follows:
in the formula (3), PiII、viIIAnd PVIIRespectively a short-term predicted value of suction inlet pressure, a short-term predicted value of suction inlet speed and a short-term predicted value of vaporization pressure of water of the fire pump;
3.3) calculating the effective cavitation allowance long-term prediction value (NPSH) of the fire pumpaIIIThe formula is as follows:
in the formula (4), PiIII、viIIIAnd PVIIIRespectively a long-term predicted value of suction inlet pressure, a long-term predicted value of suction inlet speed and a long-term predicted value of vaporization pressure of water of the fire pump;
3.4) calculating the current required cavitation residual value (NPSH) of the fire pumprIAccording to the current flow value Q collected by the outlet pipeline flowmeter of the fire pumpIChecking the flow Q of the fire pump obtained in the step 1) and the required cavitation allowance (NPSH)rCorresponding data table, obtaining the current value Q of the flowITwo close necessary cavitation margins (NPSH)rAnd then the calculation of interpolation is carried out.
In the method for monitoring cavitation of the fire pump, the specific operation of the step 4) is as follows:
respectively comparing the current values of the effective cavitation residual amounts (NPSH)aIShort-term prediction value (NPSH) of effective cavitation allowance of fire pumpaIILong-term predicted value (NPSH) of effective cavitation allowance of fire pumpaIIICurrent required cavitation margin value (NPSH) of fire pumprIComparing, outputting corresponding states according to comparison results, prompting and synchronously taking targeted measures:
4.1) judgment (NPSH)aI≤(NPSH)rIIf the cavitation erosion is not met, outputting a prompt of 'cavitation erosion has occurred at present', and reducing the opening degree of a fire pump outlet pipeline valve until reaching (NPSH)aI>(NPSH)rIThen, the step 4.2) is carried out; otherwise, turning to step 4.2);
4.2) judgment (NPSH)aII≤(NPSH)rIIf yes, outputting a prompt of 'possibly being cavitation will' and corresponding suggestion, inquiring whether the user agrees to make automatic intervention, and if yes, reducing the opening degree of a fire pump outlet pipeline valve until (NPSH)aII>(NPSH)rIThen, the step 4.3) is carried out, and if the user does not agree, the step 4.3) is directly carried out; otherwise, turning to step 4.3);
4.3) judgment (NPSH)aIII≤(NPSH)rIIf yes, outputting a prompt of 'possible cavitation in the future', and returning to the step 4.1); otherwise, return to step 4.1).
In the method for monitoring cavitation of fire pump, the short-term predicted value P of the pressure of the suction inlet of the fire pump in the step 3.2)iIIShort-term predicted value v of speed of suction inletiIIAnd a short-term predicted value P of the vaporization pressure of waterVIIThe acquisition method comprises the following steps:
3.2.1) according to the pressure value P of the suction inlet of the fire pump at different moments collected in the step 2iFlow Q time series and water temperature T, extracting m collected values each containing a current value, and composing respective short-term history series X ═ X in chronological order1,x2,…,xm]Where m is a positive integer between 5 and 20 and X is the acquisitionThe obtained pressure value P of the suction inlet of the fire pumpiA short term history sequence of flow Q or temperature T of the water;
3.2.2) determining the weighted arithmetic mean X of the respective short-term historical sequence valuesIII.e. short-term predicted values P for the pressure at the suction inlet of the fire pumpiIIShort-term flow prediction value QIIAnd a short-term predicted value T of water temperatureII：
In formula (5) fjAs weighting factors:
3.2.3) short-term flow prediction QIIDivided by the suction inlet area SiObtaining a short-term predicted value v of the speed of the suction inletiIIShort-term predicted value T of water temperatureIITemperature T and vaporization pressure P of water examinationvCorresponding to the table to obtain the short-term predicted value T of water temperatureIIThe vaporization pressures corresponding to the temperatures of the two close water are interpolated to obtain a short-term prediction value P of the vaporization pressures of the waterVII。
In the method for monitoring cavitation of fire pump, the long-term predicted value P of the pressure at the suction inlet of the fire pump in the step 3.3)iIIIThe long-term predicted value v of the speed of the suction inletiIIIAnd long-term predicted value P of vaporization pressure of waterVIIIThe acquisition method comprises the following steps:
3.3.1) pressure value P of suction inlet of fire pump acquired in step 2iTime series, flow Q time series and water temperature T time series, extracting the latest n collection values respectively containing the current values, and forming the respective long-term history series Y (Y) according to the chronological order1,y2,…,xn]Wherein n is an even number between 20 and 100, and Y is a collected suction pressure value P of the fire pumpiA long history sequence of flow Q or temperature T of the water;
3.3.2) finding the Long-term History sequence YFirst half arithmetic mean of
3.3.3) obtaining Long-term predicted values Y for the respective Long-term historical sequence valuesIIII.e. long-term predicted value P of suction inlet pressure of fire pumpiIIILong-term flow prediction value QIIIAnd long-term predicted value T of water temperatureIII：
3.3.4) Long-term prediction of Q from flowIIIDivided by the suction inlet area SiObtaining a long-term predicted value v of the speed of the suction inletiIIIAccording to the long-term predicted value T of the water temperatureIIITemperature T and vaporization pressure P of water examinationvCorresponding to the table to obtain the long-term predicted value T of the water temperatureIIIThe vaporization pressure P corresponding to the temperature T of the two closest watervAnd interpolation calculation is carried out to obtain a long-term predicted value P of the vaporization pressure of the waterVIII。
In the method for monitoring cavitation of fire pump, the corresponding suggestion of "possibly about cavitation" in step 4.2) is made by obtaining a short-term key influence parameter, wherein the short-term key influence parameter adopts a characteristic value a, and a calculation formula of the characteristic value a is as follows:
in the formula (10), max represents the maximum value of the three values in parentheses;
if the short-term key impact parameter isThe corresponding suggestion of the prompt is that 'the water level change condition at the water intake position is required to be checked and the water intake blockage is eliminated when the pressure of the suction inlet of the fire pump is predicted to be too low';
if the short-term key impact parameter is
if the short-term key impact parameter is
In the method for monitoring cavitation of fire pump, the suggestion of "possible cavitation in the future" in step 4.3) is made by obtaining a long-term key influence parameter, wherein the long-term key influence parameter adopts a characteristic value B, and the calculation formula of the characteristic value B is as follows:
in the formula (11), max represents the maximum value among three values in parentheses,
if the long-term key impact parameter is
if the long-term key impact parameter is
if the long-term key impact parameter is
Compared with the prior art, the invention has the beneficial effects that:
1. the invention starts from the comparison of two objective phenomena of the effective cavitation allowance and the necessary cavitation allowance of the fire pump, simultaneously considers the influence of the pressure, the flow and the water temperature of the suction inlet on the effective cavitation allowance, has comprehensive and direct investigation factors and high reliability of the analysis result.
2. The invention divides the effective cavitation residual value of the fire pump into a current value, a short-term predicted value and a long-term predicted value, compares the current value, the short-term predicted value and the long-term predicted value with the necessary cavitation residual value, and respectively makes regulation and control and alarm prompt and suggestions and other measures according to the comparison result, thereby not only meeting the regulation and control requirement when cavitation occurs, but also performing trend analysis and interpretation when cavitation does not occur, giving a prompt for possible cavitation occurrence risks and giving corresponding suggestions, therefore, the invention fully considers the requirements of two aspects of cavitation prevention and control, and can furthest ensure that the normal water delivery work of the fire pump is not influenced by cavitation faults in the operation process.
3. The fire pump cavitation monitoring method provided by the invention has the advantages of high reliability, strong stability, clear logic and easiness in programming realization.
Drawings
FIG. 1 is a flow chart of the present invention.
Fig. 2 is a flow chart of the fire pump cavitation judgment and the targeted measures thereof.
Fig. 3 is a block diagram of a fire pump cavitation monitoring device used in the present invention.
Detailed Description
The invention is further described below with reference to the figures and examples.
As shown in fig. 1, the present invention comprises the steps of:
1. temperature T-vaporization pressure P of the obtained watervAccording to the curve and depending on the temperature T of the water-the evaporation pressure PvObtaining the temperature T and the vaporization pressure P of a plurality of groups of water by a curvevThe corresponding data of (2) are stored in a table form; obtaining the fire pump flow Q-necessary cavitation allowance (NPSH)rCurve and according to the fire pump flow Q-required cavitation margin (NPSH)rCurve acquisition of multiple sets of fire pump flow Q and necessary cavitation allowance (NPSH)rThe corresponding data of (2) are stored in a table form; obtaining the nominal diameter D of the flange of the suction inlet of the fire pumpiAnd stored.
2. Real-time acquisition of suction port pressure value P of fire pump according to fixed time intervaliFlow value Q, temperature T of the passing water, and storing:
acquiring the suction inlet pressure value P of the fire pump in real time by using a pressure sensor at fixed time intervalsiThe flow Q that the outlet pipeline of the fire pump passes through is collected in real time by using a flow sensor, the temperature T of water in the inlet pipeline of the fire pump is collected in real time by using a temperature sensor, and the temperature T is stored in a time series mode, wherein the fixed time interval is between 10 seconds and 1 minute.
3. Looking up a table to obtain the vaporization pressure P of the water corresponding to the temperature T of the current watervAnd respectively calculating the current value (NPSH) of the effective cavitation allowance of the fire pumpaIShort term predictive value (NPSH)aIIAnd long term prediction (NPSH)aIIIAnd the current required cavitation margin value (NPSH) of the fire pumprI。
3.1 calculating the current value of the effective cavitation margin (NPSH) of the fire pumpaIThe formula is as follows:
in the formula (1), PiI、viIAnd PVIRespectively the current value of the pressure of a suction inlet, the current value of the speed of the suction inlet and the current value of the vaporization pressure of water of the fire pump, wherein rho and g are respectively the density and the gravity acceleration of the water, and the rho and g are respectively 1000kg/m3And 9.8m/s2. Wherein, the current value P of the suction inlet pressure of the fire pumpiIThe pressure sensor of the suction inlet collects the data; the current value of the vaporization pressure of the water is obtained according to the current value T of the water temperature acquired by a temperature sensor in the inlet pipeline of the fire pumpITemperature T and vaporization pressure P of water examinationvObtaining the current value T of water temperatureIThe vaporization pressures corresponding to the temperatures of the two adjacent water are obtained by interpolation calculation; current value v of suction inlet speediIFlow current value Q acquired by fire pump outlet pipeline flowmeterIDivided by the area S of the fire pump suction inletiIs obtained, wherein the suction inlet area SiThe calculation formula of (A) is as follows:
in the formula (2), DiIs the nominal diameter of the flange of the suction inlet of the fire pump.
3.2 calculating the effective cavitation margin short-term predicted value (NPSH) of the fire pumpaIIThe formula is as follows:
in the formula (3), PiII、viIIAnd PVIIThe short-term predicted value of the suction inlet pressure, the short-term predicted value of the suction inlet speed and the short-term predicted value of the vaporization pressure of the water of the fire pump are respectively. Short-term prediction value P of suction inlet pressureiIIShort-term predicted value v of speed of suction inletiIIAnd a short-term predicted value P of the vaporization pressure of waterVIIThe steps of (1) obtaining are as follows:
3.2.1 pressure value P of suction inlet of fire pump acquired in step 2iExtracting m collection values respectively containing current values from the time series, the flow Q time series and the temperature T time series of the water, and forming respective short-term historical sequences X [ X ] according to the chronological order1,x2,…,xm]Wherein m is a positive integer between 5 and 20, and X is the acquired suction pressure value P of the fire pumpiA short term history sequence of flow Q and temperature T of the water;
3.2.2 weighted arithmetic mean X is determined for each short-term historical sequence valueIII.e. short-term predicted values P for the pressure at the suction inlet of the fire pumpiIIShort-term flow prediction value QIIAnd a short-term predicted value T of water temperatureII：
In formula (5) fjAs weighting factors:
3.2.3 short-term flow prediction QIIDivided by the suction inlet area SiObtaining a short-term predicted value v of the speed of the suction inletiIIAccording to the short-term predicted value T of the water temperatureIITemperature T and vaporization pressure P of water examinationvCorresponding to the data table to obtain a short-term predicted value T of the water temperatureIIThe vaporization pressure P corresponding to the temperature T of the two closest watervObtaining a short-term predicted value P of the vaporization pressure of the water through interpolation calculationVII。
3.3 calculating the effective cavitation margin of the fire pump Long-term prediction value (NPSH)aIIIThe formula is as follows:
in the formula (4), PiIII、viIIIAnd PVIIISuction inlet pressure of fire pump for long periodsA predicted value, a suction inlet speed long-term predicted value and a water vaporization pressure long-term predicted value.
The long-term predicted value P of the suction inlet pressure of the fire pumpiIIIThe long-term predicted value v of the speed of the suction inletiIIIAnd long-term predicted value P of vaporization pressure of waterVIIIThe acquisition method comprises the following steps:
3.3.1) pressure value P of suction inlet of fire pump acquired in step 2iTime series, flow Q time series and water temperature T time series, extracting the latest n collection values respectively containing the current values, and forming the respective long-term history series Y (Y) according to the chronological order1,y2,…,xn]Wherein n is an even number between 20 and 100, and Y is a collected suction pressure value P of the fire pumpiA long history sequence of flow Q or temperature T of the water;
3.3.2) calculating the arithmetic mean of the first half of the long-term history sequence Y
3.3.3) obtaining Long-term predicted values Y for the respective Long-term historical sequence valuesIIII.e. long-term predicted value P of suction inlet pressure of fire pumpiIIILong-term flow prediction value QIIIAnd long-term predicted value T of water temperatureIII：
3.3.4) Long-term prediction of Q from flowIIIDivided by suctionMouth area SiObtaining a long-term predicted value v of the speed of the suction inletiIIIAccording to the long-term predicted value T of the water temperatureIIITemperature T and vaporization pressure P of water examinationvCorresponding to the table to obtain the long-term predicted value T of the water temperatureIIIThe vaporization pressure P corresponding to the temperature T of the two closest watervAnd interpolation calculation is carried out to obtain a long-term predicted value P of the vaporization pressure of the waterVIII。
3.4 calculating the current required cavitation residual value (NPSH) of the fire pumprIAccording to the current flow value Q acquired by the fire pump outlet pipeline flowmeterIChecking the fire pump flow Q-required cavitation allowance (NPSH) obtained in step 1rCorresponding data table, obtaining the current value Q of the flowITwo close necessary cavitation margins (NPSH)rAnd then the calculation of interpolation is carried out.
4. Judging the cavitation condition of the fire fighting pump, taking targeted measures according to the judgment result and giving corresponding reason prompts:
respectively comparing the current values (NPSH) of the effective cavitation marginsaIShort-term prediction value (NPSH) of effective cavitation allowance of fire pumpaIILong-term predicted value (NPSH) of effective cavitation allowance of fire pumpaIIICurrent required cavitation margin value (NPSH) of fire pumprIComparing the sizes, outputting corresponding status prompts according to the comparison result, and synchronously taking targeted measures, as shown in fig. 2, the flow is as follows:
4.1 judgment (NPSH)aI≤(NPSH)rIIf the cavitation erosion is not met, outputting a current cavitation erosion prompt, and reducing the opening degree of a fire pump outlet pipeline valve until (NPSH)aI>(NPSH)rIThen, the step 4.2 is carried out; otherwise, turning to step 4.2;
4.2 judgment (NPSH)aII≤(NPSH)rIIf yes, outputting a prompt and corresponding suggestion that cavitation is about to occur, inquiring whether the user agrees to make automatic intervention, and if yes, reducing the opening degree of a fire pump outlet pipeline valve until (NPSH)aII>(NPSH)rIThen, turning to a substep 4.3, and directly turning to the substep 4.3 if the user does not agree; otherwise, go to4.3;
the corresponding suggestion of the prompt of the possibility of cavitation is made by acquiring a short-term key influence parameter, wherein the short-term key influence parameter adopts a characteristic value A, and the calculation formula of the characteristic value A is as follows:
in the formula (10), max represents the maximum value of the three values in parentheses;
if the short-term key impact parameter is
if the short-term key impact parameter isThe corresponding suggestion is prompted as "predict fire pump flow will be too large, please note control flow";
if the short-term key impact parameter is
4.3 judgment (NPSH)aIII≤(NPSH)rIIf yes, outputting a future cavitation possibility prompt and a corresponding suggestion, and returning to the step 4.1; otherwise, return to step 4.1.
The corresponding suggestion of the prompt of the future possible cavitation is made by acquiring a long-term key influence parameter, wherein the long-term key influence parameter adopts a characteristic value B, and the calculation formula of the characteristic value B is as follows:
in the formula (11), max represents the maximum value among three values in parentheses,
If the long-term key impact parameter is
if the long-term key impact parameter is
if the long-term key impact parameter is
As shown in fig. 3, a fire pump cavitation monitoring device includes an input module, an acquisition module, a storage module, an operation module, a control module and a human-computer interaction module:
the input module, the acquisition module, the operation module, the control module and the human-computer interaction module are electrically connected with the storage module.
The input module is used for inputting the temperature T-vaporization pressure P of watervCurve and fire pump flow Q-required cavitation margin (NPSH)rData table corresponding to curves and nominal diameter D of flange of suction port of fire pumpi。
The acquisition module comprises a pressure sensor arranged at the suction inlet of the fire pump, a flow sensor arranged at the outlet pipeline of the fire pump and a temperature sensor arranged in the inlet pipeline of the fire pump and submerged in water, wherein the pressure sensor, the flow sensor and the temperature sensor are respectively used for acquiring the pressure value P of the suction inlet of the fire pump in real time according to a fixed time intervaliThe flow rate Q through the outlet pipe uses the temperature T of the water in the inlet pipe.
The storage module stores data provided by the input module, the acquisition module, the operation module, the control module and the human-computer interaction module, and transmits related data to the operation module, the control module and the human-computer interaction module according to requirements.
The operation module is used for processing and calculating data, and synchronously acquiring the current value (NPSH) of the effective cavitation allowance of the fire pump in real time with the sensor signal of the acquisition moduleaIShort term predictive value (NPSH)aIILong term predictive value (NPSH)aIIIAnd the current value of the required cavitation margin (NPSH)rIAnd (4) calculating and comparing, judging key influence parameters according to conditions, and finally outputting an operation result to the control module and the human-computer interaction module.
The control module is used for receiving the instruction result output by the operation module, reducing the flow of the fire pump by reducing the opening of the outlet valve of the fire pump, and further increasing the current value (NPSH) of the effective cavitation allowance of the fire pumpaIOr short term predicted value of effective cavitation margin (NPSH)aII。
The man-machine interaction module is used for receiving the result output by the operation module, outputting a prompt and a corresponding suggestion, and inquiring whether the user agrees to make automatic intervention and returning an instruction whether the user agrees to the prompt under the condition of outputting a prompt of 'possibly being about to erode'.
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