Undisturbed experimental apparatus for pulse liquid flow coefficient measurement and method of use

Abstract

The present application relates to the technical field of volume, flow, mass flow or liquid level measurement, and discloses a non-disturbance experimental device for pulse liquid flow coefficient measurement and a use method, in the present application, a gravity liquid supply source not affected by downstream pulsation is adopted to avoid errors caused by changes in the working condition of the liquid source due to pulsation; all structures that may cause disturbance in the main pipeline are removed to the bypass or outside the pipeline to ensure that the only structure in the main pipeline that can affect the flow coefficient of the pulse flow is the experimental orifice plate, and the measurement itself does not affect the measurement result; with the aid of the continuous weighing-time domain discrete sampling-back difference-approximate derivative FFT low-pass filtering mode, the measurement can be normally carried out under the premise of not being able to contact the main flow channel; by controlling the structure of the main flow channel, the flow velocity distribution on the flow cross section is ensured not to change due to the change of the main flow channel, so that the main flow channel does not affect the measurement result; the above points are combined to eliminate the system error caused by the pulse liquid flow coefficient experimental device itself.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of volume, flow rate, mass flow rate or liquid level measurement, in particular to a non-disturbance experimental device for pulse liquid flow coefficient measurement and a use method. BACKGROUND

[0002] Flow coefficient is a key parameter in fluid mechanics and engineering for describing the flow characteristics of fluid passing through a specific device (such as valve, orifice plate, nozzle, etc.), reflecting the flow capacity or efficiency of the device. Its specific definition and application vary depending on the scene.

[0003] Generally, flow coefficient represents the ratio of actual flow rate to ideal flow rate, which is a correction coefficient for fluid flow measurement, and is represented by symbol C d . While in the field of valves, it represents the flow rate through the valve under unit pressure difference when the valve is fully open, and is represented by symbol C v or K v . To avoid confusion, the term "valve flow coefficient" with a prefix is used in engineering to specifically refer to "flow coefficient" in the context of valves, and "flow coefficient" without a prefix refers to the ratio of actual flow rate to theoretical flow rate. The "flow coefficient" in this paper is the correction coefficient for fluid flow measurement without a prefix.

[0004] Considering that flow rate is a difficult-to-measure physical quantity, flow measurement is usually indirect by measuring the secondary effects such as temperature difference, pressure difference, etc. that have a functional relationship with flow rate. The most simple and common measurement method is to indirectly measure flow rate by measuring the pressure difference before and after the orifice plate. Ideally, the square root of the pressure difference before and after the orifice plate is linearly related to the flow rate, and measuring the pressure difference before and after the orifice plate can measure the flow rate under ideal conditions. However, in actual situations, due to factors such as energy loss and friction, the relationship between the square root of the pressure difference and the flow rate is not linear. Therefore, a correction parameter, i.e. the so-called "flow coefficient", is needed. The theoretical flow rate calculated by the pressure difference before and after the orifice plate is multiplied by this correction parameter to obtain the relatively accurate flow rate. Therefore, flow coefficient is an extremely important parameter for flow measurement.

[0005] In steady flow, the flow coefficient is a fixed value between 0 and 1 (because energy loss and friction will only reduce the actual flow), which can be plotted by a series of experiments. But in unsteady flow, this assumption may not be true. In the process of actual production and life, there are many valuable unsteady flows, and the most typical one is pulse flow. For example, plunger pump, a very common high-pressure pump, due to its structure, the output is not the steady flow of centrifugal pump, but pulse flow. In addition, there are many practical application scenarios that require pulse flow, such as water hammer cleaning. In these scenarios, if you want to monitor the flow, you need to study the flow coefficient of pulse flow.

[0006] Current research shows that the flow coefficient in pulse flow will be affected by many factors, including pulse frequency, amplitude, average flow rate and system pressure. In some cases, such as high pressure and low flow rate conditions, the flow coefficient of pulse flow may be much lower than that of steady flow. In other scenarios, due to the influence of inertia, it is theoretically possible to obtain a peak transient flow coefficient that is significantly higher than the steady flow coefficient (even close to 1). These all need to study and accurately measure the flow coefficient of pulse flow, which requires a reliable experimental device.

[0007] The existing pulse flow coefficient experimental device is based on the conventional flow coefficient measurement device, and adds a pulse flow generation device. Including three ideas of replacing the liquid source with a pulse liquid source (such as replacing it with a plunger pump), adding a circulating on-off valve or similar device in the main flow path, and adding a circulating on-off valve or similar device in the bypass.

[0008] But the inventors found in actual research that the existing pulse flow coefficient experimental device is unreliable. Many structures that do not affect the flow measurement in the steady state will affect the pulse flow measurement device, causing disturbances that we do not want, weakening or amplifying the impact of the pulse, causing unpredictable systematic errors in the measurement results, and many phenomena that should occur cannot be observed (such as in some specific pressure difference pulse scenarios, the peak transient flow coefficient should be close to 1, but the actual measurement is not), or many phenomena that should not occur (such as the opening and closing speed of the valve causing different jets). But it is not reliable to say which structures will affect the pulse flow measurement device. In actual measurement, we found that almost all structures in the pipeline will cause systematic errors, and even the measurement itself will affect the flow coefficient measurement (the flow coefficient measurement requires measuring the fluid flow and the pressure difference before and after the orifice plate, and usually the pressure is measured by introducing a pitot tube into the pipeline, and the flow is measured by introducing a rotor, orifice plate or vortex street into the pipeline, which will change the shape of the flow passage). Even if there is nothing in the pipeline except the orifice plate, pipe joints, reducers, elbows and pipe bends will also affect the measurement. Even part of the liquid supply device will fluctuate due to pulse flow, introducing errors (such as centrifugal pumps, which have a so-called "operating curve").

[0009] But relying on existing technology, it is impossible to achieve a pipeline with nothing but an orifice plate. The most affected is the measurement of flow, and there are two existing non-contact flow measurement methods, one is electromagnetic flowmeter, which is only suitable for conductive liquids (additional electrolyte is required when measuring pure water flow, which will affect the measurement results, and it cannot measure oil flow at all). The purity of the medium is also required (uneven fluid conductivity will affect the measurement results). The other is the weighing method (GB / T17612-1998 Weighing Method for Measuring Fluid Flow in Closed Pipeline), which has high accuracy, but is limited by its principle. The weighing method obtains the average flow of the fluid in a period of time, so it is only suitable for the flow measurement of steady-state fluid or fluid with slowly increasing / decreasing flow. In actual use, it is found that if the existing weighing method is used to measure the flow of pulse flow, the obtained flow value will not fluctuate with time (see the accompanying drawings). From the weighing curve, only the fluctuation caused by measurement error can be seen, and the overall trend is a straight line). Figure 3

[0010] At present, it can be determined that pipe joints, elbows and pipe bends will not affect the pulse liquid flow coefficient as long as they do not cause boundary layer separation without changing the flow velocity distribution on the flow cross section. SUMMARY

[0011] ​The present application provides a non-disturbance experimental device and a use method for pulse liquid flow coefficient measurement.

[0012] The technical problem to be solved is that the existing pulse liquid flow coefficient measurement device can weaken or amplify the influence of the pulse due to the internal structure of the flow channel, measuring instruments, liquid supply device, pipeline connection and other factors, resulting in unpredictable system error in the measurement results.

[0013] To solve the above technical problems, the present application adopts the following technical solutions: a non-disturbance experimental device for pulse liquid flow coefficient measurement, which uses a high liquid tank with an overflow weir to supply liquid to the experimental device, and the liquid level of the high liquid tank is kept stable by continuously replenishing liquid and discharging excess liquid along the overflow weir during the experiment.

[0014] From the liquid level of the high liquid tank, an upstream non-reducing valve, a bypass pulse generating device, an upstream non-intervention pressure measuring device, an experimental orifice plate, a downstream non-intervention pressure measuring device, a bubble flushing device, a downstream non-reducing valve and an out-of-pipe flow measuring device are sequentially arranged along a non-reducing pipeline, which is referred to as the main flow channel; in the main flow channel, the part between the upstream non-reducing valve and the downstream non-reducing valve is a horizontally arranged straight pipe, and the downstream of the downstream non-reducing valve is a horizontal straight pipe for forming a free-falling liquid flow, the liquid flow is sprayed from the horizontal straight pipe and falls into the out-of-pipe flow measuring device;

[0015] In the fully open state of the upstream non-reducing valve and the downstream non-reducing valve, the flow passage in the valve and the flow passage cross-sectional area of the main flow channel are the same and aligned;

[0016] The bypass pulse generating device is arranged on a bypass pipeline which is communicated with the main flow channel at one end and has an outlet falling into a liquid receiving container at the other end, and introduces pulses in the main flow channel by cyclically opening and closing;

[0017] The experimental orifice plate is an orifice plate with a plate surface perpendicular to the main flow channel and detachably sealed in the main flow channel;

[0018] The upstream non-intervention pressure measuring device and the downstream non-intervention pressure measuring device both measure the pressure by drawing liquid from the main flow channel through a bypass pipeline communicated with the main flow channel at one end;

[0019] The bubble flushing device is communicated with the main flow channel downstream of the experimental orifice plate and adjacent to the experimental orifice plate at one end, and is communicated with the main flow channel at the position behind the upstream non-reducing valve at the other end, and is used to flush the bubbles downstream of the experimental orifice plate by drawing liquid from the upstream of the experimental orifice plate before the experiment;

[0020] The out-of-pipe flow measuring device is a non-contact flow measuring device for collecting the liquid flowing out of the end of the main flow channel;

[0021] The pipe joints, bends and pipe bending parts in the main flow channel shall not cause boundary layer separation.

[0022] Further, the upstream and downstream non-reducing valves are ball valves with the same inner diameter as the main pipeline.

[0023] Further, the high liquid tank is divided into three sections by the overflow weir and the disturbance-eliminating sieve plate arranged parallel to the overflow weir. Among the three sections, the middle section is the upper liquid section, the section downstream of the overflow weir is the overflow section, and the remaining section is the lower liquid section.

[0024] The bottom of the lower liquid section is in communication with the inlet end of the main flow channel, and the maximum liquid flow in the experiment is denoted as Q. The upper liquid section is in communication with the liquid supply pipe, and the liquid flow in the liquid supply pipe is not less than Q.

[0025] The disturbance-eliminating sieve plate is a sieve plate with throttling holes as sieve holes, which is used to prevent the pressure fluctuation caused by the liquid supply pipe from being transmitted to the lower liquid section.

[0026] Further, in the main flow channel, the portion between the upstream and downstream non-reducing valves is a hard pipe made of transparent material, and the remaining portion is a steel wire hose. The angle of the bending portion of the steel wire hose is not less than 90 degrees, and the bending head is a round corner.

[0027] In the steel wire hose, the portion within one meter range below the high liquid tank and the ground forms a minimum angle, which is not less than 60 degrees.

[0028] Further, the bypass pulse generating device is a normally closed direct-acting electromagnetic valve. The direct-acting electromagnetic valve is electrically connected with the PLC controller and is cyclically opened and closed under the control of the PLC controller. The outlet position of the direct-acting electromagnetic valve is arranged at the same height as the main flow channel between the upstream and downstream non-reducing valves.

[0029] The bubble flushing device includes a pagoda head arranged on the side of the main flow channel downstream of the experimental hole plate. A drain pipe is detachably mounted behind the direct-acting electromagnetic valve. The other end of the drain pipe is in communication with the pagoda head. When the drain pipe is in communication with the pagoda head and the direct-acting electromagnetic valve, a complete bubble flushing device is formed. After the bubble flushing is completed, the drain pipe is separated from the direct-acting electromagnetic valve, and the jet flow behind the direct-acting electromagnetic valve directly passes through the air.

[0030] Further, the out-of-pipe flow measuring device is a weighing platform provided with a liquid receiving container at the top. The weighing platform is electrically connected with the computer through a data acquisition instrument.

[0031] A soft film is suspended above the liquid receiving container to receive the water flow and eliminate the interference of water flow impact on the weighing result. A sponge is arranged in the liquid receiving container to eliminate the interference of water waves on the weighing result. The soft film extends obliquely downward and is lapped onto the sponge.

[0032] The method for using the undisturbed experimental device for pulse liquid flow coefficient measurement adopts the above-mentioned undisturbed experimental device for pulse liquid flow coefficient measurement to perform high-frequency pulse flow coefficient measurement, and comprises the following steps:

[0033] Step one: open the upstream non-reducing valve and the downstream non-reducing valve, so that the liquid fills and flows through the main flow channel and falls into the out-of-pipe flow measurement device, and check whether there is a boundary layer separation in the main flow channel except the experimental orifice plate, and if there is a boundary layer separation, adjust the main flow channel until there is no boundary layer separation;

[0034] Step two: start the bubble flushing device to flush away the bubbles in the downstream pipeline of the experimental orifice plate, and then close the downstream non-reducing valve;

[0035] Step three: open the downstream non-reducing valve and open the bypass pulse generating device, introduce pulse flow in the main flow channel by intermittently discharging liquid in the bypass, record the pressure fluctuation of the pulse flow, and record the total mass fluctuation of the pulse flow falling into the weighing platform, calculate the mass flow fluctuation of the pulse flow according to the total mass fluctuation, and record the completion, then close the downstream non-reducing valve;

[0036] Step four: calculate the flow coefficient curve of the pulse flow in a complete cycle according to the pressure fluctuation and the mass flow fluctuation of the pulse flow.

[0037] Further, in step three, the mass flow fluctuation is calculated in the following way:

[0038] Step a1: time-domain discrete sampling of the total mass fluctuation of the pulse flow, and the sampling frequency is not less than 5 times the fluctuation frequency of the pulse liquid flow;

[0039] Step a2: backward difference of each sampling point to obtain the approximate derivative of the mass flow with respect to time of each sampling point except the first sampling point;

[0040] Step a3: draw a broken line graph with time as the independent variable and the approximate derivative of the mass flow with respect to time of each sampling point as the dependent variable;

[0041] Step a4: FFT low-pass filter the broken line graph with a cut-off frequency higher than the fluctuation frequency of the pulse liquid flow, and take a complete cycle from the filtered curve, which is recorded as the flow standard cycle line;

[0042] The upstream non-interventional pressure measuring device and the downstream non-interventional pressure measuring device are the high-pressure port and the low-pressure port of the same differential pressure meter, and in step three, the pressure fluctuation is obtained in the following way:

[0043] Step b1: time-domain discrete sampling of the differential pressure of the pulse flow before and after the orifice plate, and the sampling frequency is not less than 5 times the fluctuation frequency of the pulse liquid flow;

[0044] Step b2: draw a line graph with time as the independent variable and the differential pressure value of each sampling point as the dependent variable;

[0045] Step b3: take a complete cycle from the line, denoted as the differential pressure standard cycle line;

[0046] In step four, the flow coefficient curve is obtained in the following way:

[0047] Step c1: respectively from the differential pressure standard cycle line and the flow standard cycle line, take points by close interpolation with the same sampling frequency, sort the points in time order, and establish a corresponding relationship between the nth point on the differential pressure standard cycle line and the nth point on the flow standard cycle line,

[0048] Step c2: calculate a flow coefficient based on each pair of points;

[0049] Step c3: plot the results obtained as a line graph with dimensionless time as the independent variable and flow coefficient as the dependent variable;

[0050] In the dimensionless process, the first data point is taken as the 0 point of time, and the reciprocal of the fluctuation frequency of the pulse liquid flow is used to dimensionless time.

[0051] Further, the main flow channel is a transparent pipeline, and in step one, the boundary layer separation condition is checked by the following method:

[0052] Add a colored particle suspension to the high-level liquid tank, and observe the liquid color along the main flow channel. If there is a part of the main flow channel where the liquid color is darker due to the enrichment of particles in the suspension, it indicates that there is a boundary layer separation at that part.

[0053] Further, in step one, the following method is used to ensure that the liquid can fill the main flow channel before the downstream non-reducing valve:

[0054] Open the upstream non-reducing valve and the downstream non-reducing valve to continuously release liquid until no bubbles come out of the high-level liquid tank, then fully open the bypass pipeline of the pulse generating device to continuously release liquid, and flush the remaining bubbles in the main flow channel before the experimental hole plate from the bypass pipeline until the liquid fills the main flow channel and flows through the main flow channel to fall into the pipeline outside the flow measurement device, then close the bypass pipeline of the pulse generating device and the upstream non-reducing valve.

[0055] Compared with the prior art, the undisturbed experimental device and method for measuring the flow coefficient of pulse liquid flow of the present application have the following beneficial effects:

[0056] In the present application, by using a gravity liquid supply source that is not affected by the downstream pulsation, errors caused by changes in the working condition of the liquid source due to pulsation of the liquid flow during the experiment are avoided;

[0057] By removing all structures that can introduce disturbance in the main pipeline, including pulse generating device and measuring instrument, to bypass or outside the pipe, ensuring that the only structure that can affect the flow coefficient of the pulse flow in the entire main pipeline is the experimental orifice plate, thereby avoiding the influence of the measurement process on the measurement results;

[0058] By using continuous weighing-time domain discrete sampling-back difference-approximate derivative FFT low pass filtering, the weighing method that cannot measure the flow of pulse flow can be used for non-contact flow measurement, thereby ensuring that the measurement can be carried out normally under the premise that the main flow channel cannot be contacted;

[0059] By strictly controlling the structure of the main flow channel itself, the flow velocity distribution on the flow cross section of the main flow channel is ensured not to change due to factors such as variable diameter, elbow, bending, pipe joint, etc., so that the main flow channel itself also does not affect the measurement results;

[0060] The above points are combined to eliminate the system error caused by the experimental device itself in the measurement process of the flow coefficient of pulse liquid flow, so that the phenomenon that should not appear does not appear, and the phenomenon that should appear cannot be observed due to the interference of the experimental device. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 The structure diagram of the non-disturbance experimental device for measuring the flow coefficient of pulse liquid flow in the application is shown, and the bypass pulse generating device is not placed flat in the figure to avoid obstruction;

[0062] Figure 2 A group of liquid pulse flow coefficient diagrams obtained by using the application are shown, the horizontal coordinate is dimensionless time, the vertical coordinate is flow coefficient, and T is the fluctuation period length of liquid pulse;

[0063] Figure 3 The original data curve obtained by using the out-of-pipe flow measurement device is shown, the horizontal coordinate is time, the unit is second, and the vertical coordinate is the total mass of the pulse flow falling into the out-of-pipe flow measurement device, the unit is kilogram;

[0064] Figure 4 The graph of the change of the mass flow of the pulse flow with time obtained by processing is shown, the horizontal coordinate is time, the unit is second, and the vertical coordinate is the mass flow of the pulse flow falling into the out-of-pipe flow measurement device, the unit is kilogram per second;

[0065] In the figure, 11 is a high liquid tank, 12 is a disturbance removal sieve plate, 13 is an overflow weir, 21 is an upstream variable-diameter-free valve, 22 is a downstream variable-diameter-free valve, 3 is a bypass pulse generating device, 4 is an experimental orifice plate, 51 is an upstream non-intervention pressure measuring device, 52 is a downstream non-intervention pressure measuring device, 6 is a bubble flushing device, 7 is an out-of-pipe flow measurement device, and 8 is a PIV device. DETAILED DESCRIPTION

[0066] In the example of the experimental device in a transverse research project for studying the cooling effect of the pulse flow, in this embodiment, the orifice plate is 5 mm thick, the orifice diameter is 2 mm, the main flow channel inner diameter is 10 mm, the pressure head provided by the liquid source is 94 kiloPascal, and the steady-state flow rate is 0.03634 kg / s.

[0067] Differential pressure gauge: BXJC-3051, provided by Hengshui Beixiang Precision Measurement Electronics Technology Co., Ltd.

[0068] Data acquisition instrument: 34972A, provided by Agilent;

[0069] PLC controller: HY6A-6MR-7 on-off type controller, provided by Huoyun Electric Control;

[0070] Solenoid valve: JSX31-SE703R-5G-B, provided by SMC Corporation of Japan;

[0071] Weighing sensor: DY500, provided by Anhui Dayang Sensor.

[0072] As shown in Figure 1 , the undisturbed experimental device for measuring the flow coefficient of pulse liquid flow uses a high liquid tank 11 with an overflow weir 13 to supply liquid to the experimental device, and the liquid level in the high liquid tank 11 is kept stable by continuously replenishing liquid and discharging excess liquid along the overflow weir 13 during the experiment.

[0073] The experimental device is not called a "measuring device" because it is not only used for measurement, but also used for other experiments, such as installing a PIV device 8 (Particle Image Velocimetry) to study the velocity distribution of the liquid flow.

[0074] As shown in Figure 2 , the flow coefficient of pulse liquid flow fluctuates greatly, and in this case, if the upstream liquid source is a device such as a centrifugal pump that provides a pressure head that changes with flow, or a positive displacement pump that does not change the flow regardless of the pipe resistance, but only automatically provides a larger pressure head, it will inevitably bring a huge system error to the measurement result, and this error cannot be corrected by an automatic valve or similar device. Therefore, in this invention, a high liquid tank 11 is used to supply liquid, which provides a pressure head that is not affected by the downstream.

[0075] From the liquid level of the high tank 11, an upstream non-reducing valve 21, a bypass pulse generator 3, an upstream non-intrusive pressure measuring device 51, an experimental orifice plate 4, a downstream non-intrusive pressure measuring device 52, a bubble flushing device 6, a downstream non-reducing valve 22 and an out-of-pipe flow measuring device 7 are sequentially arranged along a non-reducing pipeline, which is referred to as a main flow passage; in the main flow passage, the part between the upstream non-reducing valve 21 and the downstream non-reducing valve 22 is a horizontal straight pipe, and the part downstream of the downstream non-reducing valve 22 is a horizontal straight pipe for forming a free-fall liquid flow, the liquid flow is sprayed from the horizontal straight pipe and falls into the out-of-pipe flow measuring device;

[0076] Non-reducing, that is, the inner diameter of the entire main flow passage is completely consistent from beginning to end. Pipeline reducing will cause boundary layer separation due to sudden contraction or sudden expansion, and boundary layer separation will cause the liquid flow rate distribution on the flow passage cross section to change. Note that the non-reducing here includes the pipe joint part, and the pipeline connection should be connected in a way that the pipe is sleeved outside the butt joint part to prevent leakage. If it is difficult to achieve non-reducing throughout the main flow passage, the following compromise can be used: the part between the upstream non-reducing valve 21 and the downstream non-reducing valve 22 is a non-reducing hard pipe, and the distance between the upstream non-intrusive pressure measuring device 51 and the upstream non-reducing valve 21 is not less than 20 times the inner diameter of the pipe, and the pipe diameter of the remaining part of the main flow passage is greater than that of the hard pipe part, and is connected with the hard pipe part through a reducing pipe joint with gradually changing inner diameter. In this way, boundary layer separation can also be avoided.

[0077] As for the part of the main flow passage downstream of the downstream non-reducing valve 22 being a horizontal straight pipe for forming a free-fall liquid flow, the liquid flow is sprayed from the horizontal straight pipe and falls into the out-of-pipe flow measuring device, because if an additional pipeline is provided here, not only will the pulse be weakened, but the liquid level difference in the entire main flow passage will be equivalent to the height difference between the liquid level of the high tank and the liquid level of the liquid receiving container of the out-of-pipe flow measuring device 7, but the liquid level of the liquid receiving container will change during the experiment, which will cause the pressure head provided by the liquid source to fluctuate, thereby introducing system error. If no pipeline is provided, the liquid flow falls directly, and the liquid level difference in the entire main flow passage is equivalent to the height difference between the liquid level of the high tank and the main flow passage between the upstream non-reducing valve 21 and the downstream non-reducing valve 22, which is stable.

[0078] When the upstream non-reducing valve 21 and the downstream non-reducing valve 22 are fully open, the flow passage in the valve and the flow passage cross-sectional area of the main flow passage are the same and aligned;

[0079] That is, the two valves in the fully open state are equivalent to part of the main flow passage, which is a section of pipeline that does not cause disturbance.

[0080] The bypass pulse generating device 3 is arranged on the bypass pipe which is communicated with the main flow channel at one end and has an outlet falling into the liquid receiving container at the other end, and the pulse is introduced into the main flow channel by the cycle opening and closing of the bypass pipe;

[0081] That is, the pulse is generated by intermittently opening and closing the bypass pipe to discharge liquid in this embodiment.

[0082] The experimental hole plate 4 is a hole plate which is perpendicular to the main flow channel and is detachably sealed in the main flow channel. In this embodiment, the experimental hole plate 4 is detachably arranged in the main flow channel by clamping the experimental hole plate 4 in the flange. The experimental hole plate is detachable so as to replace the hole plate with different hole diameters according to the requirement.

[0083] The upstream non-intervention pressure measuring device 51 and the downstream non-intervention pressure measuring device 52 measure the pressure by drawing liquid from the main flow channel through the bypass pipe which is communicated with the main flow channel at one end;

[0084] In the pressure measuring process, the bypass pipe for drawing liquid does not need to have fluid flow therein, and is only used to transmit pressure, so as not to affect the fluid flow in the main pipe.

[0085] The bubble flushing device 6 is communicated with the main flow channel downstream of the experimental hole plate 4 and adjacent to the experimental hole plate 4 at one end, and is communicated with the main flow channel at the position downstream of the upstream non-reducing valve 21 at the other end, and is used to flush the bubbles downstream of the experimental hole plate 4 by drawing liquid from the upstream of the experimental hole plate 4 before the experiment;

[0086] The bubbles in the main flow channel downstream of the experimental hole plate 4 are often ignored. Due to the throttling effect of the experimental hole plate 4, the pressure of the fluid downstream of the experimental hole plate 4 is sharply reduced, which causes the dissolved gas in the liquid flow to be precipitated and attached to the pipe wall to form bubbles of different sizes. Moreover, the experimental hole plate 4 itself causes a certain degree of boundary layer separation, and a region which is difficult to be flushed is introduced downstream, so that the bubbles cannot be carried away by the liquid flow in the experiment. If it is a steady flow, the bubbles do not cause any influence, but in the pulse flow, the bubbles expand and shrink with the fluctuation of the fluid pressure, weaken the influence of the pulse, and thus reduce the fluctuation amplitude of the finally measured flow coefficient.

[0087] The pipe outside flow measuring device 7 is a non-contact flow measuring device for collecting the liquid flowing out of the end of the main flow channel.

[0088] The pipe joints, bends and pipe bending parts in the main flow channel should not cause boundary layer separation.

[0089] In this embodiment, the upstream non-reducing valve 21 and the downstream non-reducing valve 22 are both ball valves with the same diameter as the inner diameter of the main pipe. The ball valve is a valve with a circular internal flow cross section and aligned with the front and rear pipes.

[0090] The high liquid tank 11 is divided into three sections by the overflow weir 13 and the disturbance-eliminating sieve plate 12 arranged in parallel to the overflow weir 13. Among the three sections, the one in the middle is called the upper liquid section, the one downstream of the liquid overflowing from the overflow weir 13 is called the overflow section, and the rest is called the lower liquid section.

[0091] The bottom of the lower liquid section is communicated with the inlet end of the main flow channel, the maximum liquid flow in the experiment is called Q, the upper liquid section is communicated with the liquid supply pipe, and the liquid flow in the liquid supply pipe is not less than Q.

[0092] The disturbance-eliminating sieve plate 12 is a sieve plate with throttle holes as sieve holes, which is used to prevent the pressure fluctuation caused by the liquid supply pipe from being transmitted to the lower liquid section.

[0093] The liquid source in the application is a liquid source provided with a stable pressure head by using a typical water tower pressure stabilization method; however, unlike general devices, a disturbance-eliminating sieve plate 12 is added here to avoid the disturbance caused by the water supply process from being transmitted to the lower water pipeline.

[0094] In the main flow channel, the part between the upstream non-reducing valve 21 and the downstream non-reducing valve 22 is a hard pipe made of transparent material (in this embodiment, an acrylic pipe), and the rest is a steel wire hose. The angle of the bending part of the steel wire hose should not be less than 90 degrees and should be a round corner elbow. The reason why the steel wire hose is used here is to ensure that no elbow is needed in the entire pipeline. It should be noted that a conventional hose cannot be used because the cross section of the conventional hose will change during bending.

[0095] In the steel wire hose, the part within one meter below the high liquid tank 11 should not have an angle with the ground less than 60 degrees.

[0096] If the angle of this section of the pipeline with the ground is too small, it will affect the natural flow of the liquid from the high liquid tank 11, and even the flow may be interrupted during the pulse liquid flow pulsation.

[0097] The bypass pulse generating device 3 is a normally closed direct-acting electromagnetic valve, which is electrically connected with the PLC controller and is cyclically opened and closed under the control of the PLC controller.

[0098] The PLC controller can realize programmed control of the opening and closing of the valve, and can be cyclically performed. The reason why the direct-acting electromagnetic valve is used is that this type of electromagnetic valve has a fast response.

[0099] The outlet position of the direct-acting electromagnetic valve is arranged at the same height as the main flow channel between the upstream non-reducing valve 21 and the downstream non-reducing valve 22.

[0100] The bubble flushing device 6 comprises a spire head opened in the side of the main flow channel downstream of the experimental hole plate 4, and a drain pipe detachably installed behind the direct-acting electromagnetic valve, the other end of the drain pipe being communicated with the spire head, and when the drain pipe is communicated with the spire head and the direct-acting electromagnetic valve, the complete bubble flushing device 6 is formed; after the bubble flushing is completed, the drain pipe is separated from the direct-acting electromagnetic valve, and the jet flow behind the direct-acting electromagnetic valve directly passes through the air.

[0101] Here, the water discharged by the upstream electromagnetic valve is used to flush the downstream bubbles, and when flushing is needed, the drain pipe is sleeved on the spire head, the valve is opened for flushing, and the drain pipe is pulled out after flushing.

[0102] In addition, during the formal experiment, the outlet position of the direct-acting electromagnetic valve and the main flow channel between the upstream and downstream non-reducing valves 21 and 22 must be level, and the drain pipe must be pulled out. Otherwise, a problem that is difficult to notice will be caused: the drain pipe brings negative pressure to the end of the main flow channel, which directly affects the experimental results.

[0103] The out-of-pipe flow measuring device 7 is a weighing platform provided with a liquid receiving container at the top, the out-of-pipe flow measuring device 7 is a weighing platform provided with a liquid receiving container at the top, the weighing platform is electrically connected with a computer through a data acquisition instrument; a soft film for receiving water flow to eliminate the interference of water flow impact on the weighing result is suspended above the liquid receiving container, a sponge for eliminating the interference of water waves on the weighing result is arranged in the liquid receiving container, and the soft film extends obliquely downward and is lapped on the sponge. The weighing platform in this embodiment is formed by connecting a flat plate above and below the cantilever beam weighing sensor, the cantilever beam weighing sensor is connected to the computer through an rs485 adapter, and the weighing data is continuously collected by using the matching software.

[0104] It should be noted that even if the soft film exists, the drop should be controlled, and the drop between the soft film and the outlet of the downstream non-reducing valve should not exceed 10 cm, otherwise the effect of eliminating the impact is not good.

[0105] The use method of the undisturbed experimental device for pulse liquid flow coefficient measurement adopts the above-mentioned undisturbed experimental device for pulse liquid flow coefficient measurement to measure the high-frequency pulse flow coefficient, and comprises the following steps:

[0106] Step one: open the upstream and downstream non-reducing valves 21 and 22, so that the liquid fills and flows through the main flow channel and falls into the out-of-pipe flow measuring device 7, check whether there is boundary layer separation in the part of the main flow channel except the experimental hole plate 4, if there is boundary layer separation, adjust the main flow channel (such as adjust the bending angle of the bending part of the hose), until there is no boundary layer separation;

[0107] Step two: start the bubble flushing device 6 to flush away the bubbles in the pipeline downstream of the experimental hole plate 4, and then close the downstream non-reducing valve 22;

[0108] This is to avoid the formation of bubbles again, while avoiding the downstream pipeline emptying during the experiment. If the valve is not closed, the liquid will continue to flow for a long time, and bubbles will form again. If only the upstream valve 21 is closed, the downstream of the experimental hole plate 4 will be empty. If both valves are closed, the subsequent experimental process operation will not be available.

[0109] Step three: open the downstream valve 22, and open the bypass pulse generating device 3, introduce a pulse flow in the main flow channel by intermittently discharging in the bypass, record the pressure fluctuation of the pulse flow, and record the total mass fluctuation of the pulse flow falling into the weighing table, calculate the mass flow fluctuation of the pulse flow according to the total mass fluctuation, and close the downstream valve 22 after recording is completed;

[0110] If it is necessary to repeat the measurement of multiple sets of experimental data, step three is repeated multiple times. During each repetition, the experimental hole plate 4 or other parameters that may affect the results can be changed according to the requirements, such as the fluctuation frequency.

[0111] Step four: according to the pressure fluctuation and mass flow fluctuation of the pulse flow, the flow coefficient curve of the pulse flow in a complete cycle is obtained.

[0112] In step three, the mass flow fluctuation is calculated as follows:

[0113] Step a1: time domain discrete sampling of the total mass fluctuation of the pulse flow as shown in Figure 3 The sampling frequency is not less than 5 times the fluctuation frequency of the pulse flow;

[0114] The sampling frequency of 5 times means that at least 5 points are collected in each fluctuation period, and more than 5 points can form a polyline that can at least show the shape. In actual sampling process, 10 times or even 20 times or more sampling frequency is required.

[0115] Step a2: backward difference of each sampling point, to obtain the approximate derivative of mass flow with respect to time of each sampling point except the first sampling point;

[0116] In the conventional weighing flow measurement method, the liquid flow is collected for a period of time, and then the increased mass in this period of time is divided by the time to obtain an average value. As shown in Figure 3 Using this method, the flow fluctuation cannot be measured.

[0117] In the present application, continuous weighing is used to obtain the mass-time curve, and the flow is obtained by deriving the curve. Since the function expression corresponding to the curve is unknown, the analytical solution of the derivative cannot be obtained, so the numerical solution of the derivative is obtained by backward difference.

[0118] Step a3: Plot a line graph with time as the independent variable and the approximate derivative of the mass flow rate at each sampling point with respect to time as the dependent variable;

[0119] Step a4: As Figure 4 As shown, the line graph is subjected to FFT low-pass filtering at a cutoff frequency higher than the ripple frequency of the pulsed liquid flow. A complete period is taken from the filtered curve and recorded as the standard flow period line.

[0120] like Figure 3 As shown, during the weighing process, the mass not only fluctuates with the flow rate but also undergoes random fluctuations. However, these random fluctuations, being random in nature, cannot last for long; their fluctuation periods are very short, and their frequencies are very high. Therefore, fluctuations with frequencies higher than the pulse flow rate are filtered out, resulting in a mass that is similar to... Figure 4 This is how you obtain reliable traffic data.

[0121] In this embodiment, the upstream non-invasive pressure measuring device 51 and the downstream non-invasive pressure measuring device 52 are the high-pressure port and low-pressure port of the same differential pressure gauge, respectively. The differential pressure gauge is connected to an Agilent data acquisition instrument and then to a computer, using the software of the data acquisition instrument to continuously collect pressure data. The pressure data required to calculate the flow coefficient is the differential pressure before and after the experimental orifice plate 4, which can be directly measured by the differential pressure gauge. Of course, two different pressure sensors can also be used as the upstream non-invasive pressure measuring device 51 and the downstream non-invasive pressure measuring device 52, but in actual operation, it was found that the pressure data measured downstream was unstable.

[0122] In step three, the pressure fluctuation is obtained using the following method:

[0123] Step b1: Discretize and sample the differential pressure of the pulse flow before and after the orifice plate in the time domain, with a sampling frequency not less than 5 times the fluctuation frequency of the pulse flow.

[0124] Step b2: Plot a line graph with time as the independent variable and the differential pressure value at each sampling point as the dependent variable;

[0125] Step b3: Take a complete cycle from the broken line and record it as the differential pressure standard cycle line;

[0126] In step four, the flow coefficient curve is obtained using the following method:

[0127] Step c1: Using the same sampling frequency, closely interpolate points from both the differential pressure standard period line and the flow rate standard period line. Sort the points in chronological order and establish a correspondence so that the nth point on the differential pressure standard period line corresponds to the nth point on the flow rate standard period line.

[0128] Here, the problem of aligning two different sets of data in time is solved. Their absolute times are difficult to align, but they can both be sampled at the same sampling frequency for a complete cycle, with the first point corresponding to the first point of the other set of data, and so on.

[0129] Step c2: A flow coefficient is calculated based on each pair of points, with the formula:

[0130]

[0131] Where Q and Q0 are the actual and theoretical flow rates through the orifice, β is the contraction ratio of the orifice to the pipe diameter, ε is the expansion coefficient of the fluid, A0 is the cross-sectional area of the orifice, ρ is the fluid density, and ΔP is the pressure difference across the orifice.

[0132] Step c3: The results are plotted as a step graph with the dimensionless time as the independent variable and the flow coefficient as the dependent variable.

[0133] In the dimensionless process, the first data point is taken as the 0 point of time, and the reciprocal of the pulse flow fluctuation frequency is used to dimensionless time.

[0134] The reciprocal of the fluctuation frequency, i.e. the length of a complete fluctuation period (not the wavelength), is dimensionless after dividing the time by the reciprocal of the fluctuation frequency, so that different fluctuation frequency measurement results can be compared on the same graph, like Figure 2 .

[0135] In this embodiment, the main flow channel is entirely transparent, and in step one, the following method is used to check the boundary layer separation condition:

[0136] Add a colored particle suspension to the high-level tank 11, and observe the liquid color along the main flow channel. If there is a part of the main flow channel where the liquid color is darker due to the enrichment of particles in the suspension, it indicates that there is boundary layer separation at that location.

[0137] In this embodiment, initially, a mixture of ferric chloride solution and sodium carbonate was used to generate a ferric hydroxide suspension (ferric hydroxide particles are red). However, since the upper water pipeline is made of iron, long-term non-use can cause rust to mix into the water. The water flowing out when the experimental device was first set up was this muddy water with fine rust, which was used to check the main flow channel.

[0138] In step one, the following method is used to ensure that the liquid can fill the main flow channel before the downstream non-variable diameter valve 22:

[0139] The upstream non-reducing valve 21 and the downstream non-reducing valve 22 are continuously opened to discharge liquid until no bubbles come out from the high liquid tank 11, then the bypass pipeline where the bypass pulse generator 3 is located is continuously opened to discharge liquid to flush the bubbles in the main flow channel in front of the experimental orifice plate 4 out of the bypass pipeline until the main flow channel is filled with liquid and the liquid flows through the main flow channel to fall into the pipeline outside flow measuring device 7, then the bypass pipeline where the bypass pulse generator 3 is located and the upstream non-reducing valve 21 are closed.

[0140] Here, due to the existence of the experimental orifice plate 4, the flow in the main flow channel is very small, and without intervention, the main flow channel will not be filled with liquid, and there is basically no pressure head.

[0141] The above-described embodiments are merely preferred embodiments of the present application and are not intended to limit the scope of the present application. Various modifications and improvements to the technical solutions of the present application made by those of ordinary skill in the art without departing from the design spirit of the present application shall fall within the protection scope of the present application as defined by the claims.

Claims

1. A undisturbed experimental apparatus for measuring the flow coefficient of pulsed liquid flow, characterized in that: The experimental apparatus is supplied with liquid from a high-level liquid tank (11) with an overflow weir (13). During the experiment, the liquid level of the high-level liquid tank (11) is kept stable by continuously replenishing the liquid and draining the excess liquid along the overflow weir (13). Starting from the liquid surface of the high-level liquid tank (11), along a pipe without diameter change, there are sequentially arranged an upstream non-diameter valve (21), a bypass pulse generating device (3), an upstream non-intervention pressure measuring device (51), an experimental orifice plate (4), a downstream non-intervention pressure measuring device (52), a bubble flushing device (6), a downstream non-diameter valve (22), and an external flow measuring device (7). The non-diameter pipe is referred to as the main channel. In the main channel, the part between the upstream non-diameter valve (21) and the downstream non-diameter valve (22) is a horizontally arranged straight pipe, and downstream of the downstream non-diameter valve (22) is a horizontal straight pipe for forming a free-fall liquid flow. The liquid flow is ejected from the horizontal straight pipe and falls into the external flow measuring device. When the upstream valve (21) and the downstream valve (22) are fully open, the flow channels inside the valves have the same cross-sectional area as the main flow channel and are aligned. The bypass pulse generating device (3) is installed on a bypass pipe with one end connected to the main channel and the other end outlet falling into the liquid receiving container, and introduces pulses into the main channel through cyclic opening and closing; The experimental perforated plate (4) is a perforated plate with its surface perpendicular to the main channel and which is detachably sealed in the main channel; Both the upstream non-invasive pressure measuring device (51) and the downstream non-invasive pressure measuring device (52) measure pressure by drawing liquid from the main channel through a bypass pipe connected to the main channel at one end. The bubble flushing device (6) is connected at one end to the main channel downstream of the experimental orifice plate (4) and adjacent to the experimental orifice plate (4), and at the other end to the main channel downstream of the upstream valve (21) without a reducing valve, and is used to flush the downstream bubbles from the upstream of the experimental orifice plate (4) with liquid before the experiment. The external flow measurement device (7) is a flow measurement device that collects the liquid flowing out from the end of the main channel without contact. The pipe joints, elbows, and bends in the main channel must not cause boundary layer separation.

2. The undisturbed experimental apparatus for measuring the flow coefficient of pulsed liquid flow according to claim 1, characterized in that: Both the upstream non-reducing valve (21) and the downstream non-reducing valve (22) are ball valves with the same inner diameter as the main pipeline.

3. The undisturbed experimental apparatus for measuring the flow coefficient of pulsed liquid flow according to claim 1, characterized in that: The high-level liquid tank (11) is divided into three compartments by an overflow weir (13) and a disturbance-eliminating screen plate (12) set parallel to the overflow weir (13). Among the three compartments, the one in the middle is called the upper liquid compartment, the one downstream of the overflow weir (13) is called the overflow compartment, and the remaining compartments are called the lower liquid compartments. The bottom of the lower liquid compartment is connected to the inlet end of the main channel. The maximum liquid flow rate of the main channel in the experiment is denoted as Q. The upper liquid compartment is connected to the liquid supply pipe, and the liquid flow rate in the liquid supply pipe is not less than Q. The disturbance-eliminating sieve plate (12) is a sieve plate with throttling holes as sieve holes, used to prevent pressure fluctuations caused by the liquid supply pipe from being transmitted to the lower liquid compartment.

4. The undisturbed experimental apparatus for measuring the flow coefficient of pulsed liquid flow according to claim 1, characterized in that: In the main channel, the part between the upstream valve (21) and the downstream valve (22) is a rigid pipe made of transparent material, and the rest is a steel wire hose. The angle of the bend of the steel wire hose shall not be less than 90 degrees and shall be a rounded bend. In the steel wire hose, the minimum angle between the portion located within one meter below the high-level liquid tank (11) and the ground shall not be less than 60 degrees.

5. The undisturbed experimental apparatus for measuring the flow coefficient of pulsed liquid flow according to claim 1, characterized in that: The bypass pulse generating device (3) is a normally closed direct-acting solenoid valve. The direct-acting solenoid valve is electrically connected to the PLC controller and is opened and closed cyclically under the control of the PLC controller. The outlet position of the direct-acting solenoid valve is set at the same height as the main channel between the upstream valve (21) and the downstream valve (22). The bubble flushing device (6) includes a pagoda head opened on the side of the main channel downstream of the experimental orifice plate (4). A drain pipe is detachably installed after the direct-acting solenoid valve. The other end of the drain pipe is connected to the pagoda head. When the drain pipe connects the pagoda head and the direct-acting solenoid valve, it constitutes a complete bubble flushing device (6). After the bubble flushing is completed, the drain pipe is separated from the direct-acting solenoid valve, and the jet after the direct-acting solenoid valve is directly connected to the air.

6. The undisturbed experimental apparatus for measuring the flow coefficient of pulsed liquid flow according to claim 1, characterized in that: The external flow measurement device (7) is a weighing platform with a liquid receiving container on top, and the weighing platform is electrically connected to a computer through a data acquisition instrument. A soft membrane is suspended above the liquid receiving container to catch the water flow and eliminate the interference caused by the water flow impact on the symmetry of the weighing result. A sponge is placed inside the liquid receiving container to eliminate the interference caused by the water wave on the symmetry of the weighing result. The soft membrane extends obliquely downward and rests on the sponge.

7. A method for using a undisturbed experimental apparatus for measuring the flow coefficient of pulsed liquid flow, characterized in that: The high-frequency pulse flow coefficient is measured using the undisturbed experimental apparatus for measuring pulsed liquid flow coefficient as described in claim 6, and includes the following steps: Step 1: Open the upstream valve (21) and the downstream valve (22) without reducing diameter, so that the liquid fills the main channel and flows through the main channel into the flow measurement device (7) outside the pipe. Check whether there is boundary layer separation in the main channel except for the experimental orifice plate (4). If there is boundary layer separation, adjust the main channel until there is no boundary layer separation. Step 2: Start the bubble flushing device (6) to flush away the bubbles in the downstream pipe of the experimental orifice plate (4), and then close the downstream valve without diameter change (22). Step 3: Open the downstream valve without diameter change (22) and turn on the bypass pulse generator (3). Introduce pulse flow in the main channel by intermittently releasing liquid through the bypass. Record the pressure fluctuation of the pulse flow and the total mass fluctuation of the pulse flow falling into the weighing platform. Calculate the mass flow rate fluctuation of the pulse flow based on the total mass fluctuation. After recording, close the downstream valve without diameter change (22). Step 4: Calculate the flow coefficient curve of the pulse flow over a complete cycle based on the pressure fluctuations and mass flow rate fluctuations of the pulse flow.

8. The method of using the undisturbed experimental apparatus for measuring the flow coefficient of pulsed liquid flow according to claim 7, characterized in that: In step three, the mass flow rate fluctuation is determined using the following method: Step a1: Discretize and sample the total mass fluctuation of the pulse flow in the time domain, with a sampling frequency not less than 5 times the fluctuation frequency of the pulse flow; Step a2: Perform backward difference on each sampling point to obtain the approximate derivative of the mass flow rate with respect to time for each sampling point except the first sampling point; Step a3: Plot a line graph with time as the independent variable and the approximate derivative of the mass flow rate at each sampling point with respect to time as the dependent variable; Step a4: Perform FFT low-pass filtering on the line graph with a cutoff frequency higher than the ripple frequency of the pulsed liquid flow, and take a complete period from the filtered curve as the standard flow period line. The upstream non-invasive pressure measuring device (51) and the downstream non-invasive pressure measuring device (52) are the high-pressure port and low-pressure port of the same differential pressure gauge, respectively. In step three, the pressure fluctuation is obtained in the following way: Step b1: Discretize and sample the differential pressure of the pulse flow before and after the orifice plate in the time domain, with a sampling frequency not less than 5 times the fluctuation frequency of the pulse flow. Step b2: Plot a line graph with time as the independent variable and the differential pressure value at each sampling point as the dependent variable; Step b3: Take a complete cycle from the broken line and record it as the differential pressure standard cycle line; In step four, the flow coefficient curve is obtained in the following way: Step c1: Using the same sampling frequency, closely interpolate points from both the differential pressure standard period line and the flow rate standard period line. Sort the points in chronological order and establish a correspondence so that the nth point on the differential pressure standard period line corresponds to the nth point on the flow rate standard period line. Step c2: Calculate a flow coefficient for each pair of points; Step c3: Plot the obtained results as a line graph with dimensionless time as the independent variable and the flow coefficient as the dependent variable; During the dimensionless process, the first data point is taken as the zero point of time, and the time is dimensionless by using the reciprocal of the fluctuation frequency of the pulsed liquid flow.

9. The method of using the undisturbed experimental apparatus for measuring the flow coefficient of pulsed liquid flow according to claim 7, characterized in that: The main channel is entirely transparent. In step one, the boundary layer separation status is checked using the following method: Add a suspension of colored particles to the high-level liquid tank (11) and observe the color of the liquid along the main channel. If there is a part in the main channel where the liquid color is darker due to the enrichment of particles in the suspension, it indicates that there is boundary layer separation at that point.

10. The method of using the undisturbed experimental apparatus for measuring the flow coefficient of pulsed liquid flow according to claim 7, characterized in that: In step one, the following method is used to ensure that the liquid can fill the main flow channel before the downstream valve (22) without reducing diameter: Open the upstream valve (21) and the downstream valve (22) to continuously release liquid until no more bubbles emerge from the high-level liquid tank (11). Then, fully open the bypass pipeline where the bypass pulse generator (3) is located to continuously release liquid, flushing out the residual bubbles in the main channel before the experimental orifice plate (4) from the bypass pipeline until the liquid fills the main channel and flows through the main channel into the external flow measurement device (7). Then, close the bypass pipeline where the bypass pulse generator (3) is located and the upstream valve (21).

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