CN112146718A - Mass flow measuring method based on vortex street sensor - Google Patents

Abstract

The invention relates to a mass flow measuring method based on a vortex street sensor, which comprises the following steps: by analyzing the amplitude information of the calibration result of the acceleration vortex street probe under the gas phase condition, the average value of the amplitudes is calculated, and the amplitude signal of the Z axis in the three-axis accelerometer, namely the lift amplitude A, is fitted_aObtaining a mass flow fitting formula under the gas phase condition with a curve graph of the gas phase flow velocity u; taking into account the presence of a non-linear region of the measured acceleration amplitude signal at low flow, i.e. amplitude signal A_aThere is a lower measurement limit with u, resulting in offsets b and u in the fit result₀A is_aFitting a formula between the rho and the flow velocity u; and obtaining a gas phase mass flow calculation formula.

Description

Mass flow measuring method based on vortex street sensor

Technical Field

The invention relates to the field of vortex street flow field measurement, in particular to a mass flow measurement method based on acceleration measurement.

Background

The vortex shedding flowmeter is a speed type flow meter based on the karman vortex shedding principle, is widely applied due to the characteristics of wide measurement range, high reliability, small pressure loss, insensitivity to fluid physical property change and the like, and is commonly used for measuring the volume flow of fluid in the industrial field. However, the mass flow rate to be directly obtained can only be measured by a mass flowmeter and cannot be directly obtained by a vortex shedding flowmeter. In the traditional method, if the mass flow is measured by a vortex shedding flowmeter, temperature and pressure compensation is needed, and the process is very complicated.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a mass flowmeter measuring method based on a vortex street sensor. The technical scheme of the invention is as follows:

a mass flow measuring method based on a vortex street sensor comprises the following steps:

(1) by analyzing the amplitude information of the calibration result of the acceleration vortex street probe under the gas phase condition, the average value of the amplitudes is calculated, and the amplitude signal of the Z axis in the three-axis accelerometer, namely the lift amplitude A, is fitted_aObtaining a mass flow fitting formula under the gas phase condition with a curve graph of the gas phase flow velocity u;

(2) taking into account the presence of a non-linear region of the measured acceleration amplitude signal at low flow, i.e. amplitude signal A_aThere is a lower measurement limit with u, resulting in offsets b and u in the fit result₀A is_aFitting formula of/[ rho ] and flow velocity u is as follows:

let K_vIs the volume meter coefficient; f is the frequency of the vortex street sensor and then is calculated according to the gas phase volume flow

And gas phase density expression

And S is the cross-sectional area of the pipeline, so that the gas phase mass flow is obtained:

in the formula, M_gIs the mass flow rate of the gas, Q_gIs the volumetric flow rate of the gas.

Drawings

FIG. 1 is a flow diagram of gas phase flow measurement for a positive pressure sonic nozzle.

FIG. 2 is a relationship diagram of an acceleration type vortex street probe u-Aa.

FIG. 3 is A_aAnd fitting the second time of the/rho and the u.

Figure 4 is a mass flow prediction.

In the drawings: 1: air supply (including air compressor machine, stabiliser, valve), 2: measurement pipe section, 3: a positive pressure method sonic nozzle gas flow standard device.

Detailed Description

Fig. 1 is a diagram of a positive pressure sonic nozzle flow calibration apparatus in this experiment. The device is composed of an air source 1 (comprising an air compressor, a pressure stabilizer and a valve), a measuring pipe section 2, a positive pressure method sonic nozzle air flow standard device 3 and a PLC control system for adjusting the systems. The gas circuit control system mainly provides stable gas sources under different pressure and temperature and humidity conditions for gas phase measurement and calibration experiments, and comprises an air compressor, an electric regulating valve, a vortex shedding flowmeter and the like. In this experiment, the sampling frequency of the vortex street signal was set to 60k, and the sampling time was set to 7 s. Amplitude and frequency information is obtained by researching the single-phase measurement characteristics of the probe. The probe is an acceleration type vortex street probe, and gas-phase vortex street measurement is mainly completed through a Z axis (a vortex street lifting force direction). In order to ensure that the acceleration type vortex street probe can accurately measure the mist flow, the performance of the acceleration type vortex street probe in single-phase measurement needs to be analyzed, so that a gas-phase calibration experiment needs to be carried out on a positive-pressure method sonic nozzle standard device, and the measurement accuracy and stability of the vortex street probe are identified through a calibration result.

Gas phase measurement calibration working condition: q_g＝7.67～35.03m³The pressure P is calibrated when U is 3.9-40.0 m/s, the nozzle temperature T is 28 DEG C₁＝300kPa， P₂A total of 30 measurement points were made at 400kPa and 3 replicates per measurement point were performed.

The gas phase flow calibration process is as follows: firstly, opening equipment such as an air compressor, an air pump, an industrial personal computer and the like according to the operating requirement specification, and entering a gas verification system; secondly, opening an air inlet valve according to different pressure and flow conditions, and preparing to carry out calibration work after the pressure, the frequency and the differential pressure are stable (about 30 min); in the calibration process, the calibration system is operated, signals measured by a probe are collected by the vortex street signal collecting system, a calibration result and measurement signals are stored after calibration is completed, so that one calibration is completed, and the same measurement point needs to be repeatedly calibrated for 3 times for verifying the reliability of the calibration system; slowly closing the gas path inlet valve, changing the measuring point through the nozzle, and repeating the experiment; and finally, after calibration is finished, operations such as shutdown, disconnection, pump shutdown and the like are carried out, and experimental data are processed.

Volume meter coefficient K for evaluating vortex shedding flowmeter_vThe calculation formula is shown as formula (1):

in the formula, K_vijThe ith point and the jth volume instrument coefficient; k_viThe coefficient of the ith point volume instrument is obtained; k_vIs the volume meter coefficient; f is the frequency of the table to be checked; q. q.s_vIs the actual volume flow of the meter under test.

The repeatability formula is as follows (2):

in the formula, σ_viIs the repeatability of the i point volumetric meter coefficients.

Through single-phase vortex street experimental calibration, the amplitude information of the calibration result of the acceleration type vortex street probe is analyzed, and the relation between the amplitude information and the gas phase flow rate is shown in a relation graph 2, namely a relation graph u-Aa of the acceleration type vortex street probe. It can be seen that the relationship of the quadratic curves is presented under different pressures, which lays a theoretical foundation for the single-phase and two-phase vortex street measurement.

Furthermore, fig. 2 is a relationship diagram of an acceleration type vortex street probe u-Aa. The difference of the laws is that the gas phase density under different pressures changes, so that the acceleration amplitude, the gas phase flow velocity and the density can be fitted, and the fitting formula is as follows:

wherein C is a constant; rho is gas phase density in kg/m³(ii) a u is gas phase flow rate, and the unit is m/s; a. the_aIs the acceleration amplitude, in g, calculated from equation (4):

in the formula, Aⁱ _maxAnd Aⁱ _minThe maximum value and the minimum value in the ith period of the acceleration signal in N periods are respectively.

In practical conditions, considering the problems of material and packaging of the probe, the measured acceleration amplitude signal has an obvious nonlinear region, namely the amplitude signal A, at low flow_aThere is a lower measurement limit with u, resulting in offsets b and u in the fit result₀And comprehensively considering, the fitting formula is optimized as follows:

a is to be_aThe fitting result of the fitting is shown in FIG. 3, and is A_aThe fitting curve of the second time of the/rho and u is as follows:

wherein the constant C is 0.0047 and the bias u₀And b 24.6200, 0.1924, respectively, determining the coefficients (R)²) It was found that the fitting effect was better at 0.9994, the sum variance (SSE) was 0.0018, and the Root Mean Square (RMSE) was 0.0102.

Due to the measuring characteristics of the acceleration type vortex street probe, the frequency f and the fluctuation amplitude A can be measured_aTwo sets of signals. According to the single-phase calibration result, the gas phase volume flow can be obtained by using the frequency information, and the gas phase density can be obtained by using the acceleration amplitude information, so that the acceleration type vortex street probe can not only measure the gas phase volume flow, but also directly measure the gas phase mass flow.

According to the gas phase calibration result, the instrument coefficient K_v337170, the volumetric flow rate is calculated as equation (7):

from the above fitting results, the gas phase density can be expressed as formula (8):

wherein u can be based on the gas phase flow rate Q_gAnd calculating to obtain a mass flow prediction model as shown in the formula (9):

wherein S is the cross-sectional area of the pipe. According to the prediction model, the experimental data are predicted, the prediction result is shown in figure 4, the mass flow prediction result is shown, and the prediction error is within +/-5%.

Claims (1)

1. A mass flow measuring method based on a vortex street sensor comprises the following steps:

(1) by analyzing the amplitude information of the calibration result of the acceleration vortex street probe under the gas phase condition, the average value of the amplitudes is calculated, and the amplitude signal of the Z axis in the three-axis accelerometer, namely the lift amplitude A, is fitted_aAnd obtaining a mass flow fitting formula under the gas phase condition with a curve graph of the gas phase flow velocity u.

(2) Taking into account the presence of a non-linear region of the measured acceleration amplitude signal at low flow, i.e. amplitude signal A_aThere is a lower measurement limit with u, resulting in offsets b and u in the fit result₀A is_aFitting formula of/[ rho ] and flow velocity u is as follows:

let K_vIs the volume meter coefficient; f is the frequency of the vortex street sensor and then is calculated according to the gas phase volume flow

And gas phase density expression

And S is the cross-sectional area of the pipeline, so that the gas phase mass flow is obtained:

in the formula, M_gIs the mass flow rate of the gas, Q_gIs the volumetric flow rate of the gas.

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