CN110377949B - Model calculation method for vacuum breaker valve under large air inlet condition - Google Patents

Model calculation method for vacuum breaker valve under large air inlet condition Download PDF

Info

Publication number
CN110377949B
CN110377949B CN201910506787.1A CN201910506787A CN110377949B CN 110377949 B CN110377949 B CN 110377949B CN 201910506787 A CN201910506787 A CN 201910506787A CN 110377949 B CN110377949 B CN 110377949B
Authority
CN
China
Prior art keywords
valve
vacuum
gas
water
air
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
CN201910506787.1A
Other languages
Chinese (zh)
Other versions
CN110377949A (en
Inventor
张健
张小莹
范呈昱
俞晓东
陈�胜
陈旭云
倪尉翔
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hohai University HHU
Original Assignee
Hohai University HHU
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hohai University HHU filed Critical Hohai University HHU
Priority to CN201910506787.1A priority Critical patent/CN110377949B/en
Publication of CN110377949A publication Critical patent/CN110377949A/en
Application granted granted Critical
Publication of CN110377949B publication Critical patent/CN110377949B/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16K—VALVES; TAPS; COCKS; ACTUATING-FLOATS; DEVICES FOR VENTING OR AERATING
    • F16K17/00—Safety valves; Equalising valves, e.g. pressure relief valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
    • F16L55/00—Devices or appurtenances for use in, or in connection with, pipes or pipe systems
    • F16L55/04—Devices damping pulsations or vibrations in fluids
    • F16L55/045—Devices damping pulsations or vibrations in fluids specially adapted to prevent or minimise the effects of water hammer
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/10—Geometric CAD
    • G06F30/17—Mechanical parametric or variational design
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2111/00—Details relating to CAD techniques
    • G06F2111/10—Numerical modelling
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2113/00—Details relating to the application field
    • G06F2113/14—Pipes
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
    • G06F2119/06—Power analysis or power optimisation

Landscapes

  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Geometry (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Evolutionary Computation (AREA)
  • Mechanical Engineering (AREA)
  • Computational Mathematics (AREA)
  • Mathematical Analysis (AREA)
  • Mathematical Optimization (AREA)
  • Pure & Applied Mathematics (AREA)
  • Pipeline Systems (AREA)
  • Jet Pumps And Other Pumps (AREA)

Abstract

The invention belongs to the technical field of water hammer protection, and provides a model calculation method of a vacuum break valve under a larger air inlet condition for a siphon type water outlet flow passage. The vacuum breaker valve arranged on the siphon type outlet pipeline working under the negative pressure condition is taken as a research object, the air valve model is assumed to be modified appropriately, and the vacuum breaker valve model suitable for the larger air inlet condition is deduced. And simultaneously solving the deduced mathematical model of the vacuum breaking valve, a characteristic line equation, a continuous equation and other basic equations to obtain a calculation formula of the pressure at the vacuum breaking valve. The mathematical model and the calculation formula of the vacuum breaker valve can better simulate the actual air inlet and exhaust characteristics of the vacuum breaker valve on the siphon-type water outlet channel, and realize the accurate calculation of the hydraulic transition process of the water supply system containing the vacuum breaker valve. The invention provides a basis for model verification of the vacuum breaker valve water hammer protection theory, is used for perfecting the water hammer protection theory system, and has higher scientific research and practical application values.

Description

Model calculation method for vacuum breaker valve under large air inlet condition
Technical Field
The invention relates to the technical field of water hammer protection of long-distance water supply engineering, in particular to a model calculation method for a vacuum breaking valve under a larger air inlet condition.
Background
Due to the reasons of unbalanced water resource distribution, unbalanced regional production and economic development, environment and the like, water supply shortage exists in part of regions, and a plurality of long-distance water supply projects are built for relieving the situation. Except for the gravity flow for water supply under the condition of few landforms, most water supply projects need to adopt a pressurization mode for water supply. For a large low-lift water delivery pump station pressurized by an axial flow pump or a mixed flow pump, if a siphon-type water outlet flow channel is adopted behind the pump, a vacuum breaking valve is usually arranged at a hump of the pump station to perform safety protection of a water hammer. When the vacuum degree of the hump position exceeds the set limit due to the normal shutdown or accident shutdown of the water pump and other reasons, the vacuum breaking valve can be quickly opened to supplement air into the pipeline under the action of vacuum pressure, so that the method can prevent the pressure in the pipeline from further reducing and play the role of negative pressure protection, and the siphon can be broken along with the continuous increase of the air input, thereby playing the role of water diversion and flow cutoff and further preventing the formation of reverse siphon and the overhigh reverse rotation speed of the water pump. The vacuum breaker valve numerical model is the basis of numerical simulation calculation, and the reliability of the determined vacuum breaker valve protection scheme is directly influenced, so that the vacuum breaker valve numerical model is of great significance to the research of the vacuum breaker valve numerical model.
The vacuum breaking valve belongs to a safety valve, the working principle of the vacuum breaking valve is similar to that of an air valve, and when the vacuum breaking valve is used for negative pressure protection of a common pipeline or a common container, the air inlet and exhaust amount is small, so that numerical simulation can be performed by approximately using an air valve model. However, the operating characteristics of the vacuum breaker valve on the siphon-type water outlet channel are different from those of the air valve mainly by the following two points: one is the difference in intake pressure. The air inlet pressure of the air valve is 0m water column, namely when vacuum is generated at the beginning, the valve opens air inlet, and for the vacuum breaker valve on the siphon type water outlet flow channel, as the hump position has certain vacuum degree under the stable operation state, the air inlet pressure of the vacuum breaker valve is smaller than the minimum pressure of the hump under each stable operation working condition; according to the pump station design specification (GB50265-2010), if a vacuum breaker valve is arranged for protection, the vacuum degree is preferably more than 2m, but the maximum vacuum degree at the top of a hump is not more than 7.5m, the air inlet pressure of the vacuum breaker valve is between-2.0 and-7.5 m. The second is the difference of the valve body size and the air intake and exhaust amount. The valve diameter of the common air valve is smaller and is about 1/8-1/12 main pipe diameter, so that the air inflow is less in the transition process, and the water hammer protection requirement can be met by arranging a large number of air valves and through the synergistic effect; on the other hand, the air valve is difficult to exhaust after air enters, so that air is detained in the pipeline, pressure fluctuation is caused, and damages such as pipe explosion are easily caused. The vacuum breaker valve has relatively large size and needs less number, and usually only one vacuum breaker valve is arranged on one siphon water outlet channel, so that the air flow quantity after opening is far beyond the air inflow of a common air valve due to the function of water diversion and flow cutoff.
The invention provides a calculation method of a vacuum break valve numerical model suitable for more air inlet conditions by combining the two main differences, taking an air valve numerical model theory as a basis, changing the assumption of a gas thermodynamic change process in an air valve and replacing an ideal gas isothermal process with an ideal gas isentropic process.
Disclosure of Invention
The purpose of the invention is as follows: the vacuum breaking valve plays an important role in water hammer protection of water supply engineering, but in the previous research, the difference of air inlet pressure between the vacuum breaking valve and an air valve and the difference of the sizes of the valve bodies of the vacuum breaking valve and the air inlet and the air outlet are not considered, the air valve model is still used for replacing the vacuum breaking valve model to calculate the hydraulic transition process under the condition of large air inlet, so that the deviation exists in the mathematical model of the vacuum breaking valve, the inaccuracy of the vacuum breaking valve model enables the error of the numerical simulation calculation result to be large, and further the reliability of the protection scheme of the vacuum breaking valve is directly influenced, so that the derivation of the mathematical model of the vacuum breaking valve under the condition of large air inlet is necessary. According to the reset of the assumed conditions of the model, the deduced mathematical model of the vacuum breaking valve can better simulate the actual air inlet and exhaust characteristics of the vacuum breaking valve so as to provide a design scheme for the actual water supply engineering. The invention provides a model calculation method of a vacuum breaker valve under a large air inlet condition, which realizes accurate calculation of numerical simulation of a hydraulic transition process by a mathematical model.
The technical scheme is as follows: in order to solve the above technical problems, the present invention provides a model calculation method for a vacuum break valve satisfying a large air intake condition,
the vacuum breaker valve which is arranged at the hump of the siphon type water outlet pipeline and works under the negative pressure condition is used as the center, and the vacuum breaker valve meets the requirement of large air inlet condition and supplies air into the pipeline under the vacuum pressure; a mathematical model of the vacuum breaking valve is deduced on the basis of an air valve model, the gas temperature is changed from isothermal change to an isentropic adiabatic process, and the liquid level reduction is changed from a constant value to a variable value.
Specifically, in the mathematical model of the vacuum break valve, the relational expression of the gas in the valve and the temperature thereof at any time is as follows:
Figure BDA0002092086080000021
in the formula, Tn,2Is the temperature in the valve, P, of the nth periodn,2And represents the gas pressure in the nth period, Pa is the atmospheric pressure, K is the coefficient, and Ta is the atmospheric temperature.
Specifically, a mathematical model of the vacuum breaker valve is utilized, and a characteristic line compatibility equation, a continuity equation and a pressure balance equation are combined to perform simultaneous solution, so that a calculation formula of the pressure at the vacuum breaker valve is obtained:
Figure BDA0002092086080000031
wherein P is the gas pressure in the vacuum breaker valve, unit pa; v0Volume of initial air pocket in time period, unit m3△ t is the calculation time step length in unit s and Q10Is the inflow of the initial section i of the time interval in m3/s；Q20Is the discharge of the initial section i of the time interval in m3/s；PaIs atmospheric pressure, in Pa; gamma is the water gravity in kg/(m)2·s2)；Z10The height of the liquid surface at the side of the water inlet tank of the valve is broken by the initial vacuum in a time interval, and the unit is m; z20The initial vacuum breaks the liquid surface height of the valve outlet side in m. A. the1For measuring the gas-liquid interface area of the water inlet pool, unit m2；A2For measuring the gas-liquid interface area of the water outlet pool in m2；CM、BM、Cp、BpIs a characteristic compatibility coefficient; m is0The unit kg is the mass of gas in the valve at the beginning of the time interval;
Figure BDA0002092086080000032
is the air mass flow at the beginning of the time interval, unit kg/s,
Figure BDA0002092086080000033
the unit kg/s is the mass flow of air generated by a vacuum breaking valve; r is the gas constant in J/(kg. K).
The vacuum breaker valve arranged at the hump of the siphon water outlet pipeline working under the negative pressure condition is used as the center, and the vacuum breaker valve can supplement air into the pipeline under the action of vacuum pressure by meeting the larger air inlet condition, so that the pressure in the pipeline is prevented from being further reduced, and the siphon breaking has the functions of dividing water and cutting off the flow. Therefore, a valve is usually required to be arranged on the siphon-type water outlet flow passage for negative pressure control, which makes the system simple in arrangement and easy to operate and manage, but also puts high requirements on the reliability of vacuum break valve protection. The vacuum breaker valve numerical model is the basis of numerical simulation calculation, and the reliability of the determined vacuum breaker valve protection scheme is directly influenced, so that the method has important significance for the research of the vacuum breaker valve numerical model under the condition of larger air inlet.
Has the advantages that: the mathematical model and the calculation formula of the vacuum breaker valve can better simulate the actual air inlet and exhaust characteristics of the vacuum breaker valve on the siphon-type water outlet channel, and realize the accurate calculation of the hydraulic transition process of the water supply system containing the vacuum breaker valve. The invention provides a basis for model verification of the vacuum breaker valve water hammer protection theory, is used for perfecting the water hammer protection theory system, and has higher scientific research and practical application values.
By assuming the thermodynamic change process of gas in the valve in the air valve model, the isothermal process of the ideal gas is replaced by the isentropic process of the ideal gas, and the operating characteristic of larger air input of the siphon type water outlet channel vacuum breaker valve is combined, the numerical model of the vacuum breaker valve suitable for more air inlet conditions is deduced, and reference can be provided for the numerical simulation and theoretical setting of the vacuum breaker valve.
Drawings
FIG. 1 is a diagram of a vacuum break valve node;
FIG. 2 is a water supply system layout;
FIG. 3 is a schematic diagram of the relative pressure change of gases within a vacuum break valve;
FIG. 4 is a schematic graph illustrating the process of varying the inlet speed of the vacuum breaker valve;
FIG. 5 is a schematic diagram of the temperature profile of the gas within the vacuum break valve.
Detailed Description
In this embodiment, the vacuum breaker valve disposed on the siphon-type outlet pipe working under negative pressure is used as a research object, and the assumption of the air valve model is modified appropriately, so that the vacuum breaker valve model is suitable for more intake conditions, and a mathematical model of the vacuum breaker valve suitable for larger intake conditions is derived, and the calculation derivation process is as follows: 1. air inlet and exhaust process of vacuum breaker valve model
Based on the four assumed conditions of the air valve, the assumption of the vacuum break valve model can be obtained by modifying the air valve model assumed conditions a and d:
a. the air is approximate to ideal gas and flows into and out of the vacuum breaking valve in an isentropic manner;
b. the thermodynamic change of the gas in the valve complies with the ideal gas isentropic heat insulation process;
c. the air entering the vacuum breaker valve does not move along with the flow of the water body and is kept near the node of the vacuum breaker valve;
d. the gas-liquid interface is always kept horizontal.
Assuming 1 is consistent with the air valve model assumption and assuming 3 is the same as the air valve model assumption, the effect of air is also limited to the vacuum break valve node; the gas temperature in the vacuum breaking valve in the step 2 is assumed to be not isothermal, not atmospheric temperature Ta, but to follow an isentropic adiabatic process; assume 4 takes into account the drop in liquid level height and is therefore a variable rather than constant.
Assuming that 1, the air intake and exhaust characteristics of the vacuum break valve satisfy the expressions (1) to (4);
the air flows into 0.5283p at subsonic isentropica＜p＜pa：
Figure BDA0002092086080000051
In the formula:
Figure BDA0002092086080000052
is the mass flow of air through the vacuum break valve, kg/s; cinIs the flow coefficient into the vacuum break valve; a. theinIs the intake area, m2；paAtmospheric pressure, Pa; rhoaIn terms of atmospheric density, kg/m3(ii) a p is the gas pressure in the vacuum break valve, Pa.
The air flows into the cylinder with the critical flow velocity in the isentropic way, and p is less than or equal to 0.5283pa：
Figure BDA0002092086080000053
In the formula: r is a gas constant, J/(kg. K); t isaAtmospheric temperature, K.
The air flows out with subsonic isentropic
Figure BDA0002092086080000054
Figure BDA0002092086080000055
In the formula: coutIs the flow coefficient out of the vacuum breaker valve; a. theoutIs the exhaust area, m2(ii) a T is gas in the vacuum breaking valveTemperature, K.
The air flows out with critical flow velocity in isentropic
Figure BDA0002092086080000056
Figure BDA0002092086080000057
Assuming 1-4 by the vacuum break valve model, the air intake and exhaust processes in different periods can be as follows:
a first period:
initially the vacuum break valve is closed and no gas is present in the valve, and after a first time interval Δ t, air is admitted Δ m1After the gas part flows in the isentropic mode, the isentropic mode changes to the end of the first period, and the ideal gas state equation and the multi-party equation can obtain:
paV1,a k＝p1,inV1,in k＝p1,2V1,2 k(5)
Figure BDA0002092086080000058
for the above formula dual-subscript parameters, the first subscript represents the number of time segments, and the second subscript has the same meaning as before. It is clear from the above formula (5) that when p is1,in＝p1,2When, V1,in k＝V1,2 kSo that is represented by formula (6), T1,in＝T1,2。
A second period of time:
for the second period Δ t, assume the intake air Δ m for the first period1The volume occupied by the constant entropy change at the end of the second time interval is V2,yThen the part of gas has:
p1,2V1,2 k＝p2,2V2,y k(7)
Figure BDA0002092086080000061
in combination with formulas (5) to (8), the following results are obtained:
Figure BDA0002092086080000062
in addition, if air is admitted for the second period, the mass change Δ m2Comprises the following steps:
paV2,a k＝p2,inV2,in k(10)
Figure BDA0002092086080000063
from formulas (10) and (11), it is possible to obtain:
Figure BDA0002092086080000064
comparing formula (9) with formula (12), it is apparent that when p is2,in＝p2,2When, T2,in＝T2,2。
If the air is exhausted in the second time interval, the foot mark in representing the air intake in the formula can be replaced by the foot mark out representing the air exhaust, and the same principle is adopted when the air is exhausted2,out＝p2,2When, T2,out＝T2,2。
In one aspect, paV1,a k＝p2,2V2,y kAnd p isaV2,a k＝p2,inV2,in kWhen p is2,in＝p2,2：
Figure BDA0002092086080000065
On the other hand, when p is represented by formula (8) and formula (11)2,in＝p2,2Into T2,in＝T2,2Obtaining:
Figure BDA0002092086080000066
an n-th period:
is prepared from (13) and (14) It can be seen that the gas state in the second end of the period can be equivalent to isentropic intake Δ m1+Δm2Accordingly, assuming that the process is still established at the end of the nth period, the gas in the valve at the end of the nth period satisfies:
Figure BDA0002092086080000071
Figure BDA0002092086080000072
period n + 1:
at the end of the nth period, the gas in the valve is subjected to isentropic change to the end of the (n + 1) th period, so that the conditions are met:
Figure BDA0002092086080000073
in addition, the gas mass change Δ m for the n +1 th periodn+1Comprises the following steps:
Figure BDA0002092086080000074
from the formulae (17) and (18), it is clear that when p isn+1,in＝pn+1,2When, Tn+1,in＝Tn+1,2。
Because the gas state in the valve can be equivalent to isentropic air intake at any time
Figure BDA0002092086080000075
Therefore, the relational expression of the gas in the valve and the temperature thereof at any time is obtained:
Figure BDA0002092086080000076
2. vacuum break valve mathematical model derivation
As shown in the attached figure 1, the section i is the section where the vacuum breaker valve is located, and the characteristic line compatibility equation, the continuity equation, the pressure balance equation and the water level fluctuation equation are respectively as follows:
C+:H1＝CP-BPQ1
C-:H2＝CM+BMQ2(20)
Figure BDA0002092086080000081
Figure BDA0002092086080000082
Figure BDA0002092086080000083
Figure BDA0002092086080000084
in the formula: h1Breaking a water head m of a pressure measuring pipe at the side of a water inlet tank of the valve by vacuum; h2Breaking a water head m of a pressure measuring pipe at the side of the water outlet tank of the valve by vacuum; q1Is the inflow of section i, m3/s；Q2Is the flow rate of section i, m3S; v is the gas volume, m3(ii) a Gamma is the water gravity, kg/(m)2·s2)；Z1The height m of the liquid surface at the side of the water inlet tank of the vacuum breaking valve is adopted; z2The height m of the liquid surface at the side of the water outlet pool of the valve is broken by vacuum; a. the1For measuring gas-liquid interface area, m, of the water inlet tank2；A2For measuring the gas-liquid interface area, m, of the water outlet pool2。
According to equations (20) and (22):
Figure BDA0002092086080000085
the gas-liquid interface area is related to the channel design and is only a function of the liquid surface height, and if the gas-liquid interface area is considered to be constant, the following are provided:
Figure BDA0002092086080000086
Figure BDA0002092086080000087
substituting formula (25) for formula (24) to obtain:
Figure BDA0002092086080000088
Figure BDA0002092086080000089
the vacuum break valve model obtained by substituting equation (19), equation (23) and equation (26) into equation (27) is:
Figure BDA0002092086080000091
Figure BDA0002092086080000092
in the formula: v0Is the initial cavitation volume of the time period, m3；m0The mass of gas in the valve is kg at the beginning of the time interval;
Figure BDA0002092086080000093
the air mass flow at the beginning of the time period is kg/s.
In equation (28) only the pressure p and the air mass flow
Figure BDA0002092086080000094
Is an unknown quantity, and
Figure BDA0002092086080000095
as a function of the pressure p, it can be calculated from equations (1) to (4), so that the pressure p can be solved.
When the intake air amount is small, if the liquid level height change is ignored, Z10→Z、Z1→Z、Z20→Z、Z2→Z，A1→∞、A2→ infinity, the above formula (28) can be simplified toThe air valve model is in the same form, so the air valve model can be regarded as a special case of the vacuum breaking valve model under the condition of less air intake; the difference in the form to the right of the two equations is in the temperature term due to the different assumptions of the thermodynamic changes of the gas within the valve.
The model is applied to the simulation calculation of the vacuum breaker valve on the water conveying pipeline in the long-distance water conveying engineering. The system layout diagram is shown in fig. 2, and the water supply system mainly comprises the following components: a water suction pool, a water outlet pool, a water pump, a siphon and a vacuum breaker valve. Design flow rate of 10m3The water pump has the rated lift of 12m, the rotating speed of the water pump of 250r/min and the rated power of 1600kw, and as can be seen from figure 2, the water level of the water suction pool is 28 meters, and the water level of the water outlet pool is 38.5 meters; the water level of an inlet of the siphon pipeline is 25m, the water level of an outlet of the siphon pipeline is 30m, and the water level of the top of the siphon pipeline is 37 m; the siphon had a horizontal length of 105 m and a diameter of 2.4 m. The vacuum breaking valve is positioned at the top of the siphon pipeline, the air inlet pressure is-3 m, and the diameter is 0.3 m. The vacuum break valve arranged on the siphon pipe in fig. 1 and the whole siphon outlet pipe were numerically simulated using a conventional air valve model and a derived vacuum break valve model, respectively. On the basis of the one-dimensional characteristic line method, mathematical models of an air valve and a vacuum breaking valve are programmed by using a FORTRAN language, and when the air valve model and the vacuum breaking valve model are adopted to simulate the vacuum breaking valve at the top of the siphon pipe, the calculation results are shown in fig. 3, 4 and 5.
The variation of the relative pressure of the gas in the pipeline is shown in figure 3. After the pumping outage accident occurs, the vacuum degree at the top of the siphon tube reaches a set limit, the vacuum breaking valve is opened, and the gas pressure in the valve rapidly rises to the normal pressure. When the vacuum break valve is simulated by an air valve model, the negative pressure wave rapidly propagates to rapidly reduce the relative pressure of the gas to 1 meter, and when t is 3.6s, the gas pressure is reduced to-2.5 m, then the gas pressure slowly rises, and when t is 16s, the relative pressure finally approaches 0m and remains unchanged. Since the water level of the vacuum break valve is not changeable in the air valve model assumption, the water level is higher than the normal water level, resulting in a small relative pressure. Thus, the relative pressure of the gas first decreases and then gradually rises to zero. When the vacuum break valve model was used for the simulation calculations, the relative pressure suddenly dropped to-2.8 m and then rapidly increased to 0m, with the gas pressure remaining unchanged (0 m). Since the water level of the vacuum break valve is variable in the vacuum break valve model, the relative pressure of the gas inside the valve is maintained at approximately normal pressure after the vacuum break valve is opened.
The intake air speed changes at different times are shown in fig. 4. When the air valve model is used for simulating the inlet speed of the vacuum breaker valve, the air inlet speed is gradually increased from 0, reaches a maximum value of 136.9m/s when t is 3.6s, and then is gradually reduced. When t is 26.86s, the intake speed is less than 0, and the vacuum break valve starts to exhaust. Because the water level is not changed, the calculated water level of the water inlet is always higher than the actual water level, so that the gas pressure in the valve is too low, the gas inlet speed is continuously increased to a larger value, and then the gas inlet speed is slowly reduced until the gas is exhausted, so that the gas inlet and exhaust period of the vacuum breaking valve is long. When the vacuum breaker valve model is adopted to simulate the air inlet speed of the vacuum breaker valve, air enters and exits the vacuum breaker valve periodically along with the pressure of a water hammer, the maximum air inlet speed is low, the maximum air inlet amount is not more than 22.5m/s, the minimum air inlet amount is not less than-22.5 m/s, and the period is short.
The different course of the air pressure variation leads to a different course of the temperature variation as shown in fig. 5. When the air valve model is adopted to carry out numerical simulation on the temperature of the gas in the vacuum breaker valve, the thermodynamic change of the gas in the valve follows an ideal gas isothermal process, the environmental temperature is kept unchanged no matter how the temperature of the gas in the valve changes, and the temperature of the gas in the valve is kept unchanged at 273K. When a vacuum breaking valve model is adopted for simulation, the temperature of gas in the valve is periodically changed along with the change of gas pressure. The highest temperature was 273.63K, the lowest temperature was 272.61K, and the variation was small. For the project, the gas pressure fluctuation is not large, the change of the calculated temperature is small, and therefore the influence of the temperature can be ignored.
The analysis shows that the calculation result is reasonable and accords with common knowledge. According to the requirements of the air intake and exhaust performance of the vacuum breaker valve on the siphon pipeline, the air valve model and the vacuum breaker valve model are respectively used for carrying out numerical simulation on the vacuum breaker valve arranged on the siphon water outlet flow passage according to the embodiment, according to the comparison of simulation results, the calculation result of the vacuum breaker valve model is closer to the air intake and exhaust characteristics of the actual vacuum breaker valve, and the calculation result of the vacuum breaker valve model is more consistent with common knowledge. The derived mathematical model of the vacuum break valve is described as being applicable to the simulation calculations for the vacuum break valve under larger inlet conditions.
The present invention is not limited to the above embodiments, and may include other embodiments or modifications within the scope of the present invention.

Claims (3)

1. A model calculation method for a vacuum break valve under a large air inlet condition is characterized by comprising the following steps: the vacuum breaker valve which is arranged at the hump of the siphon type water outlet pipeline and works under the negative pressure condition is used as the center, and the vacuum breaker valve meets the requirement of large air inlet condition and supplies air into the pipeline under the vacuum pressure; deducing a mathematical model of the vacuum breaking valve on the basis of the air valve model, wherein the gas temperature is changed from isothermal change to the constant entropy insulation process, and the liquid level height reduction is changed from a constant value to a variable value; in the mathematical model of the vacuum break valve, the relational expression of the gas in the valve and the temperature at any moment is as follows:
Figure FDA0002356470450000011
in the formula, Tn,2Temperature in valve, p, of the n-th periodn,2Representing the gas pressure, p, during the n-th periodaIs atmospheric pressure, K is the coefficient, TaIs at atmospheric temperature;
performing simultaneous solution by using a mathematical model of the vacuum breaker valve and combining a characteristic line compatibility equation, a continuity equation and a pressure balance equation to obtain a calculation formula of the pressure at the vacuum breaker valve:
Figure FDA0002356470450000012
wherein p is the gas pressure in the vacuum breaker valve, unit pa; v0Volume of initial air pocket in time period, unit m3(ii) a Δ t is as a meterCalculating the time step length and the unit s; q10Is the inflow of the initial section i of the time interval in m3/s；Q20Is the discharge of the initial section i of the time interval in m3/s；PaIs atmospheric pressure, in Pa; gamma is the water gravity in kg/(m)2·s2)；Z10The height of the liquid surface at the side of the water inlet tank of the valve is broken by the initial vacuum in a time interval, and the unit is m; z20The height of the liquid surface at the side of the outlet tank of the valve is destroyed by initial vacuum in unit m; a. the1For measuring the gas-liquid interface area of the water inlet pool, unit m2；A2For measuring the gas-liquid interface area of the water outlet pool in m2；CM、BM、Cp、BpIs a characteristic compatibility coefficient; m is0The unit kg is the mass of gas in the valve at the beginning of the time interval;
Figure FDA0002356470450000013
is the air mass flow at the beginning of the time interval, unit kg/s,
Figure FDA0002356470450000014
the unit kg/s is the mass flow of air generated by a vacuum breaking valve; r is a gas constant with the unit J/(kg. K);
the characteristic line method compatibility equation is as follows:
C+:H1＝CP-BPQ1
C-:H2＝CM+BMQ2
the continuous equation is:
Figure FDA0002356470450000021
the pressure balance equation is:
Figure FDA0002356470450000022
the method also comprises a water level fluctuation equation:
Figure FDA0002356470450000023
Figure FDA0002356470450000024
in the formula: h1Breaking a water head m of a pressure measuring pipe at the side of a water inlet tank of the valve by vacuum; h2Breaking a water head m of a pressure measuring pipe at the side of the water outlet tank of the valve by vacuum; q1Is the inflow of section i, m3/s；Q2Is the flow rate of section i, m3S; v is the gas volume, m3(ii) a Gamma is the water gravity, kg/(m)2·s2)；Z1The height m of the liquid surface at the side of the water inlet tank of the vacuum breaking valve is adopted; z2The height m of the liquid surface at the side of the water outlet pool of the valve is broken by vacuum; a. the1For measuring gas-liquid interface area, m, of the water inlet tank2；A2For measuring the gas-liquid interface area, m, of the water outlet pool2。
2. The model calculation method of a vacuum break valve under large gas intake condition according to claim 1, characterized in that: the vacuum breaking valve protects a water hammer at a hump of pressurized water supply in a way of breaking siphonage and water diversion and flow cutoff.
3. The model calculation method of a vacuum break valve under large gas intake condition according to claim 1, characterized in that: the mathematical model of the vacuum break valve conforms to four assumed conditions:
a. the air is approximate to ideal gas and flows into and out of the vacuum breaking valve in an isentropic manner;
b. the thermodynamic change of the gas in the valve complies with the ideal gas isentropic heat insulation process;
c. the air entering the vacuum breaker valve does not move along with the flow of the water body and is kept near the node of the vacuum breaker valve;
d. the gas-liquid interface is always kept horizontal.
CN201910506787.1A 2019-06-12 2019-06-12 Model calculation method for vacuum breaker valve under large air inlet condition Active CN110377949B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN201910506787.1A CN110377949B (en) 2019-06-12 2019-06-12 Model calculation method for vacuum breaker valve under large air inlet condition

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN201910506787.1A CN110377949B (en) 2019-06-12 2019-06-12 Model calculation method for vacuum breaker valve under large air inlet condition

Publications (2)

Publication Number Publication Date
CN110377949A CN110377949A (en) 2019-10-25
CN110377949B true CN110377949B (en) 2020-04-03

Family

ID=68250118

Family Applications (1)

Application Number Title Priority Date Filing Date
CN201910506787.1A Active CN110377949B (en) 2019-06-12 2019-06-12 Model calculation method for vacuum breaker valve under large air inlet condition

Country Status (1)

Country Link
CN (1) CN110377949B (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111191357B (en) * 2019-12-24 2023-01-17 中国大唐集团科学技术研究院有限公司西北电力试验研究院 Pipeline air resistance phenomenon judgment method based on ideal gas model

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106842928A (en) * 2017-02-13 2017-06-13 中国水利水电科学研究院 The valve closing optimal control method of long range big flow water-carriage system transient process

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10100935B2 (en) * 2015-09-11 2018-10-16 Mueller International, Llc Air valve seat and land

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106842928A (en) * 2017-02-13 2017-06-13 中国水利水电科学研究院 The valve closing optimal control method of long range big flow water-carriage system transient process

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
具有特殊地形条件的长距离供水工程水锤防护;石林 等;《水力发电学报》;20190531;第38卷(第5期);第81-88页 *
虹吸式出水流道虹吸形成过程数值模拟;李海峰 等;《排灌机械工程学报》;20151118;第33卷(第11期);第932-939页 *
长距离输水工程弥合水锤防护措施研究;张志胜 等;《人民长江》;20190528;第50卷(第5期);第127-132、139页 *

Also Published As

Publication number Publication date
CN110377949A (en) 2019-10-25

Similar Documents

Publication Publication Date Title
CN109918787B (en) Finite volume method based simulation method for gas-liquid two-phase homogeneous mass flow in water delivery pipeline
Lomakin Investigation of two-phase flow in axial-centrifugal impeller by hydrodynamic modeling methods
CN105676640B (en) Fanjet acceleration control rule design method based on Bezier
CN110377949B (en) Model calculation method for vacuum breaker valve under large air inlet condition
CN101545570B (en) Device for air-valve surge chambers for controlling pipeline transient liquid-column separation
CN107167383A (en) Circulating HTHP gas-liquid two-phase erosive wear experimental provision and method
CN102629110A (en) Pressurized water reactor hardware-in-the-loop simulation system based on physical model
CN109359265B (en) Method and device for determining allowable value of water flow inertia time constant of pumped storage pressure regulating chamber
Shi et al. Numerical investigation of two-phase flow characteristics in multiphase pump with split vane impellers
CN109296343A (en) A kind of gas well mining technology assessment system integration and method
CN106919772A (en) High-velocity flow free flow drain cavern gas supplementary structure method of construction and gas supplementary structure
CN106528994B (en) A kind of pressure regulation chamber venting hole wind speed simulation method coupled based on gas-liquid interface
Rezvaya et al. The numerical research of the flow in the inlet of the high-head hydraulic turbine
CN102435414B (en) Method of decompression test of air entrainment and cavitation alleviation model
Wu et al. Research on air valve of water supply pipelines
CN105740501B (en) A kind of pump installation hydraulic stability analysis method based on permanent numerical computations
Hui et al. Experimental investigation of pressurized packing saturator for humid air turbine cycle
CN105507856A (en) Device and method for throttling wellheads of gas storages
CN110362869A (en) A kind of analogy method of the vane pump gas liquid two-phase flow based on CFD-PBM
CN106523839B (en) The method for reducing pressure piping large flow fluid pressure using pipeline depressurization device
CN105181337A (en) Test bed engine oil supply system and application method thereof
CN114154276A (en) Long-distance heat supply system pump-stopping water hammer numerical simulation algorithm considering steam cavity cutoff closing
CN208885652U (en) A kind of hydrodynamic force high pressure water extraction device
Liedman et al. Dynamic simulation of a centrifugal compressor system
Liu et al. Research and instance analysis on joint water hammer protection of long-distance water supply system

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination
GR01 Patent grant
GR01 Patent grant