CN102538886A - Extra-pipe binding type thermal pulse gas flowmeter capable of resisting ambient temperature disturbances - Google Patents

Abstract

The invention belongs to the field of flow measurement of a compressed air system, and realizes an externally bundled thermal pulse gas flowmeter capable of resisting ambient temperature interference. The content of the invention mainly relates to a method and corresponding device for measuring the gas flow in the pipeline by using the periodically changing temperature field outside the pipeline, and according to the relationship between the variation of the temperature field affected by the heat transfer of the air and the gas flow. The invention generates a temperature field that changes periodically through an adaptive pulse heater installed on the outer wall of the gas pipeline. The thermal signal propagates along the axial direction of the pipeline and is mainly affected by the heat dissipation effect of the gas flow in the tube. According to the measurement of the outer wall of the pipeline upstream of the heater The temperature trend of the point is calculated to calculate the relative dynamic mean value. Since the relative dynamic mean value is proportional to the flow rate, the flow rate can be measured. The invention is a bundled installation method outside the tube, which is convenient for assembly and disassembly, and adopts a variable temperature field measurement method, which can effectively suppress the temperature interference of the external environment, and the measurement takes less time and is accurate and reliable.

Description

A bundled thermal pulse gas flowmeter outside the tube that can resist ambient temperature interference

technical field

The invention belongs to the field of flow measurement of compressed air systems, and relates to an externally bundled thermal pulse gas flowmeter capable of resisting ambient temperature interference.

Background technique

As a form of energy or an energy carrier, gas is more and more widely used in industry. In the field of compressor systems, gas flow is an important parameter in the system, and its measurement is the key technology. Gas flowmeters are used in It is widely used in many industrial production occasions.

Most of the flowmeters used for gas flow measurement on the market are interventional devices, such as thermal flowmeters, differential pressure flowmeters, target flowmeters, etc., which need to be connected to pipelines in series, which is not only complicated to operate, but also difficult to install during installation. It affects industrial production, and there are problems such as interference flow, pressure loss and fouling probe. The non-intervention measurement technology can avoid the above disadvantages without dismantling the original pipeline for flow measurement, and can also realize the advantages of multi-point measurement. However, the existing equipment, such as the ultrasonic type, is expensive and has extremely poor reliability, and its practicability is far from meeting the requirements of industrial sites. Therefore, the non-intrusive measurement technology of gas is quite difficult, and there is no mature technology and product at present. The research and development of this technology is of great significance to industrial development and economical energy saving.

The invention proposes a bundled heat pulse gas flowmeter outside the tube which can resist the interference of ambient temperature. When in use, it is directly bundled and installed outside the tube, which is convenient for assembly and disassembly without any interference to industrial production. In addition, the variable temperature field measurement method mentioned in the invention can effectively suppress the temperature interference of the external environment, and cooperate with the efficient self-adaptive pulse heater and heat shield, so that the measurement takes less time and the measurement results are accurate and reliable, which is in line with industrial On-site measurement requirements for pipeline gas flow. In addition, due to its low hardware cost, it can be widely used in industrial sites and realize multi-point detection, which is conducive to the monitoring of industrial production and achieves the goals of optimizing production, energy saving and emission reduction.

Contents of the invention

The purpose of the present invention is to provide a low-cost gas flow measuring device which is applied to the flow measurement of industrial gas pipelines and is easy to install, easy to operate, reliable in measurement.

Technical scheme of the present invention:

The method of measuring the gas flow by using the characteristics of the periodically changing temperature field of the pipeline, the measurement principle is as follows:

a) According to the pipeline that requires flow measurement, select a suitable measurement point and perform a simple cleaning treatment on the surface of the pipeline. Closely attach the heating surface of the instrument to the surface to be measured, and fix it with the matching strap. Power on the instrument, and set the cycle T of the heating pulse according to the diameter of the pipe to be tested. In order to fully heat the inner wall of the pipe, the cycle of the heating pulse cannot be too short. The value of the cycle is obtained by the following formula:

 （1）

(1)

Among them, k is the gain coefficient, C is the specific heat capacity of the pipe material, ρ is the density of the pipe material, l is the thermal conductivity of the pipe material, and d is the nominal diameter of the pipe.

According to the input pipe diameter data, the instrument automatically searches the industrial pipe standard data stored in the database to find the specific heat capacity, density and thermal conductivity of the corresponding pipe material. The reference value of the gain coefficient is automatically given by the controller, which determines the measurement time consumption and measurement accuracy. The smaller the value, the faster the measurement and the lower the accuracy, and vice versa. The user can set it by himself according to the reference value.

b) During measurement, the processor (6) sends a heating electric signal to the drive circuit (4), which drives the heat flow valve (14) to the heating station, the heater (11) works, the water-cooled refrigerator (13) unloads, and the heat Conducted from the heater (11) to the outer wall of the pipeline (1), the pipeline is heated; then, the processor (6) sends a cooling electric signal to the drive circuit (4), and the switching heat flow valve (14) is used as a cooling station, a heater ( 11) Unloading, the water-cooled refrigerator (13) works, heat is conducted from the outer wall of the pipeline (1) to the heater (11), and the pipeline is cooled. In this way, repeating the above operations realizes the generation of continuous heat pulses (that is, periodically changing temperature fields) propagating along the axial direction of the pipeline.

c) The temperature sensor (8) located upstream of the adaptive pulse heater (2) measures the temperature, and transmits the measured data to the processor (6) through the A/D converter (7).

Based on the above measured values, one of the temperature signal curves is selected as the effective segment, which includes three temperature change cycles, and the temperature trend (17) reflecting the characteristics of the temperature field can be obtained by linear fitting of the effective segment curve, and the relative dynamic mean value f is calculated.

，其中     

  （2）

,in

(2)

Among them: A is the dynamic mean value, A ₀ is the reference value when the gas flow rate is 0. A _b is the temperature trend base value (18), A _a is the temperature trend increase value (19), according to the relationship between flow and f ,

           （3）

(3)

Then, the flow Q of the measured object is calculated, where b is the flow correction coefficient, which corrects the deviation caused by selecting different temperature signal measurement sections.

Advantages of the present invention :

Aiming at the problem of gas flow measurement on the industrial site, the present invention proposes a bundled thermal pulse gas flowmeter outside the tube that can resist ambient temperature interference. As a measurement method outside the tube, the biggest difference from the traditional measurement method is: It does not need to be connected to the pipeline, avoiding all the problems caused by the direct contact with the fluid of today's serial instruments; making full use of the periodic changes in the temperature field, suppressing the interference of the ambient temperature, and according to the characteristics of the temperature field in a short period of time Solve the corresponding flow data; easy to operate, low hardware cost, easy to install and disassemble.

Description of drawings

Fig. 1 is a schematic diagram of the structure of the flow instrument of the present invention.

1—pipeline under test; 2—adaptive pulse heater; 3—heat shield;

4—drive circuit; 5—display panel; 6—processor;

7—A/D converter; 8—Temperature sensor;

Fig. 2 is a structural diagram of the self-adaptive pulse heater mentioned in the present invention

9—Outer wall of the pipe under test; 10—Inner heat conduction silicone grease; 11—Heater;

12—flexible mechanism; 13—water-cooled refrigerator; 14—heat flow valve;

15—External thermal grease;

Figure 3 is a simplified diagram of the parameters of the temperature signal (three cycles) mentioned in the present invention:

16—actually measured temperature-time signal; 17—temperature fitting trend;

18—Temperature trend base value; 19—Temperature trend increase value;

Detailed ways

The present invention will be further described below.

1. Adaptive pulse heater (2), characterized in that:

It mainly consists of a heat flow valve (14), a heater (11) and a water-cooled refrigerator (13). The heat flow valve (14) is mainly composed of Peltier semiconductor elements, the heater (11) is a ceramic heater assembly, and the cooling water pipe of the water-cooled refrigerator (4) is interspersed in the inner heat-conducting silicone grease (10). The adaptive pulse heater can generate a periodically changing heat signal as required. In order to strengthen the fit, the lower end of the heat flow valve (14) as the heating surface is coated with external heat-conducting silicone grease (15).

2. A temperature sensor (8), characterized by:

It consists of a platinum thermal resistance and is installed upstream of the adaptive pulse heater (2), where the relative dynamic mean is proportional to the flow.

3. A controller characterized by:

The controller is composed of a drive circuit (4), a processor (6), a display panel (5) and an A/D converter (7). After the instrument is powered on, input the diameter of the pipe to be measured, set the heating cycle (the instrument provides a preset value), and then start the measurement. The processor (6) sends an electrical signal to the drive circuit (4) to drive the heat flow valve (14), The heater (11) and the water-cooled refrigerator (13) work to generate a periodically changing thermal signal, and then the temperature sensor (8) measures the temperature field outside the tube wall affected by the air flow, and passes the measurement data through the A/D The converter (7) transmits it to the processor (6), finally calculates the flow, and displays the measurement process and calculation results on the display panel (5).

Claims (3)

1. A bundled thermal pulse gas flowmeter outside the pipe that can resist ambient temperature interference, is characterized in that: the self-adaptive pulse heater (2) attached to the outer wall of the pipeline

, the pipes on both sides of the heater produce a temperature field that changes periodically, where C is the specific heat capacity of the pipe material, ρ is the density, l is the thermal conductivity, and d is the nominal diameter; taking a point upstream of the heater as the measurement point, the The curve of the temperature at the measurement point changes with time is linearly fitted, and the obtained line segment is defined as the temperature trend, the temperature value at the starting point of the temperature trend is defined as the temperature trend reference value A _b , and the difference between the temperature value at the end point of the temperature trend and the starting point is defined as the temperature trend Increased value A _a , gas flow and relative dynamic mean

into an increasing relationship, where

, is the correction value considering the fitting error; the temperature sensor located in the upstream section of the heater measures the temperature at the outer wall of the pipe, calculates the relative dynamic mean value, and finally calculates the corresponding flow rate according to the incremental relationship. 2. According to claim 1, a bundled thermal pulse gas flowmeter outside the tube that can resist ambient temperature interference is characterized in that: the flexible mechanism (12) automatically adjusts the temperature of the heater according to the shape of the pipeline with different diameters. The radian of the bonding surface (heating surface) makes the heat flow valve (14) closely attached to the outer wall of the pipeline, ensuring sufficient heat transfer. 3. According to claim 1, a bundled thermal pulse gas flowmeter outside the tube that can resist ambient temperature interference is characterized in that: the processor (6) sends a heating electric signal to the drive circuit (4), and the drive circuit (4) The heat flow valve (14) goes to the heating station, the water-cooled refrigerator (13) is unloaded, and the line array heater (11) heats the pipeline with the axial direction of the pipeline as the heat transfer direction; then, the processor (6) sends refrigeration The electrical signal is sent to the drive circuit (4), the heat flow valve (14) is switched to the cooling station, the heater (11) is unloaded, and the water-cooled refrigerator (13) cools the pipeline. This is a cycle, and the above operations are repeated to achieve Generation of a periodically varying temperature field.

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