High temperature low flow rate flow meter and flow measurement method thereof

Abstract

The application discloses a high-temperature low-flow-rate flowmeter and a flow measurement method thereof. The high-temperature low-flow-rate flowmeter comprises a heating section pipeline and a stirring section pipeline connected to an outlet end of the heating section pipeline. A heating device is arranged outside the heating section pipeline and used for heating liquid metal flowing through the heating section pipeline. The stirring section pipeline adopts a Venturi tube, so that the temperature of the liquid metal at the outlet of the stirring section pipeline tends to be uniform. One temperature measuring point is arranged before the inlet of the heating section pipeline and after the outlet of the stirring section pipeline respectively, and is used for acquiring the temperature of the liquid metal before heating and the temperature of the liquid metal after heating respectively. The flow measurement method heats the liquid metal, measures the temperatures before and after heating, and then calculates the mass flow rate of the liquid metal based on energy balance. The application can realize high-precision, stable and long-term reliable flow measurement of the liquid metal under high-temperature super-low-flow-rate working conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flow measurement, in particular to a high-temperature low-flow-rate flowmeter and a flow measurement method thereof. BACKGROUND

[0002] In the accident condition of The Liquid Metal cooled Reactors (LMRs), the flow rate of liquid metal can be as low as 0.01-0.05 m / s. Precise measurement of the coolant flow rate in the reactor fuel assembly is of great significance to ensure the safe operation of LMRs, which can ensure the reactor to operate within the safe thermal limit, prevent local overheating of the fuel assembly and improve thermal efficiency.

[0003] Liquid metal has the characteristics of high temperature, strong corrosion and low Prandtl number. When the traditional industrial flow sensor directly measures the coolant flow rate under the ultra-low flow rate condition of LMRs, there are the following limitations:

[0004] (1) It is difficult to generate enough pressure difference under the ultra-low flow rate condition, resulting in insufficient measurement accuracy, such as Venturi flowmeter;

[0005] (2) The flow state under the ultra-low flow rate condition is difficult to be homogenized, resulting in insufficient measurement accuracy;

[0006] (3) The traditional industrial flow sensor has problems such as response degradation and response delay under extreme environmental conditions (such as ultra-low flow rate condition);

[0007] (4) Under high temperature and low flow rate, the temperature stratification phenomenon of liquid metal will seriously affect the accurate measurement of temperature, thereby reducing the measurement accuracy of thermal flowmeter;

[0008] (5) Some flowmeters are prone to failure under high temperature environment, and have insufficient stability and long-term operation performance, such as electromagnetic flowmeter, ultrasonic Doppler velocimeter, etc. SUMMARY

[0009] The purpose of the present application is to provide a high-temperature low-flow-rate flowmeter and a flow measurement method thereof, which solves the problem of precise measurement of liquid metal flow rate under high-temperature ultra-low flow rate condition in LMRs cooling system.

[0010] Technical solution: The high-temperature low-flow rate flowmeter comprises a heating section pipeline and a stirring section pipeline connected to the outlet end of the heating section pipeline, a heating device is arranged outside the heating section pipeline for heating liquid metal flowing through the heating section pipeline, the stirring section pipeline adopts a Venturi tube to make the temperature of liquid metal at the outlet of the stirring section pipeline tend to be uniform, and one temperature measuring point is arranged before the inlet of the heating section pipeline and after the outlet of the stirring section pipeline respectively for obtaining the temperature of liquid metal before heating and the temperature of liquid metal after heating.

[0011] Further, the heating device adopts an electric heating device.

[0012] Further, the electric heating device adopts an electric heating belt, and the electric heating belt is wound outside the heating section pipeline.

[0013] Further, the high-temperature low-flow rate flowmeter further comprises a first straight pipe section connected to the inlet end of the heating section pipeline and a second straight pipe section connected to the outlet end of the stirring section pipeline, and the two temperature measuring points are arranged on the first straight pipe section and the second straight pipe section respectively.

[0014] Further, the heating section pipeline and the stirring section pipeline are connected through flanges, the first straight pipe section and the heating section pipeline are connected through flanges, and the stirring section pipeline and the second straight pipe section are connected through flanges.

[0015] Further, the heating section pipeline and the stirring section pipeline are wrapped outside with heat insulation materials to form heat preservation layers.

[0016] Further, high-temperature heat insulation gaskets are arranged between the two flanges connected to each other to reduce heat transfer, and the flange connection positions are also wrapped with heat insulation materials.

[0017] Further, the heat insulation materials adopt rock wool, mineral wool, glass wool or polyurethane foam, and the high-temperature heat insulation gaskets adopt asbestos gaskets or aluminum silicate gaskets.

[0018] Further, the temperature measuring points adopt conventional industrial temperature sensors.

[0019] The flow measurement method of the high-temperature low-flow rate flowmeter comprises the following steps: heating liquid metal and measuring the temperature before and after heating, and calculating the mass flow rate of the liquid metal based on energy balance:

[0020]

[0021] Wherein, represents the mass flow rate of the liquid metal; P represents the heating power of the heating device; T in represents the temperature of the liquid metal before heating; T out represents the temperature of the liquid metal after heating; c p represents the specific heat capacity of the liquid metal.

[0022] Beneficial effects: Compared with the prior art, the present application has the following remarkable advantages:

[0023] The high-temperature low-flow-rate flowmeter of the present application is designed based on energy balance and Venturi effect, and has extremely low pressure loss and ultra-high limit working temperature; in addition, the flowmeter of the present application is designed based on the basic conservation law, and can provide accurate flow measurement under variable and extreme working conditions without complex calibration process. In particular, in the high-temperature, strongly corrosive liquid metal coolant environment, the flowmeter of the present application is basically not affected by the high-temperature corrosion and deposits of the liquid metal coolant, ensuring the continuous and accurate measurement of the flow.

[0024] In summary, the present application can realize high-precision, stable and long-term reliable flow measurement of liquid metal under high-temperature ultra-low flow-rate working conditions. At the same time, the flowmeter has simple structure, is easy to install and debug, and is suitable for popularization and application in various scenes. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a model schematic diagram of the high-temperature low-flow-rate flowmeter provided by the embodiment of the present application;

[0026] Figure 2 is a cross-sectional view of the high-temperature low-flow-rate flowmeter in the embodiment of the present application;

[0027] Figure 3 is a pressure distribution diagram of the fluid domain of the flowmeter model in numerical simulation in the embodiment of the present application;

[0028] Figure 4 is a pressure distribution diagram of the fluid domain of the flowmeter model in numerical simulation in the embodiment of the present application;

[0029] Figure 5 is a velocity field distribution diagram of the fluid domain of the flowmeter model in numerical simulation in the embodiment of the present application;

[0030] Figure 6 is a temperature variation diagram of different flow cross sections of the fluid domain of the flowmeter model in numerical simulation in the embodiment of the present application;

[0031] Figure 7 is a temperature variation diagram of different flow cross sections of the fluid domain of the flowmeter model without the mixing section pipeline in numerical simulation in the embodiment of the present application. DETAILED DESCRIPTION

[0032] The present application will be further described below in conjunction with the drawings.

[0033] As Figure 1 and Figure 2As shown, the embodiment of the present application provides a high-temperature low-flow rate flowmeter, which comprises a first straight pipe section 3, a heating section pipe 1, a mixing section pipe 2 and a second straight pipe section 4 connected in sequence through flanges. The heating section pipe 1 is externally provided with a heating device for heating liquid metal flowing through the heating section pipe 1. The mixing section pipe 2 adopts a Venturi tube so that the temperature of liquid metal at the outlet of the mixing section pipe 2 tends to be uniform. The first straight pipe section 3 and the second straight pipe section 4 are each provided with a temperature measuring point for respectively obtaining the temperature of liquid metal before heating and the temperature of liquid metal after heating.

[0034] In the embodiment, the heating device adopts an electric heating device, specifically, an electric heating tape. The electric heating tape is wound outside the heating section pipe 1. The electric heating tape belongs to the prior art. A common electric heating tape is wound by an electric heating wire (such as a nichrome wire), and the electric heating wire is wrapped by an insulating material (such as multi-layer alkali-free glass fiber). The electric heating has the advantages of fast heating speed, high thermal efficiency, long service life, accurate temperature control and high automation degree. When selecting the electric heating tape, the type, flow rate, initial temperature and target temperature of liquid metal in the pipe and other factors need to be considered comprehensively to select a suitable heating power.

[0035] In order to improve the heating efficiency, reduce heat loss and ensure the accuracy of subsequent temperature measurement, the flowmeter pipe needs to be insulated. In the embodiment, the heating section pipe 1 and the mixing section pipe 2 are wrapped with insulating materials to form an insulation layer, which ensures that heat is concentrated in the heating section pipe 1 and reduces heat loss outside the pipe. In addition, a high-temperature insulating gasket is arranged between the two flanges connected to each other, which can effectively reduce the heat transfer through the flange connection part. The flange connection position is also wrapped with insulating materials to avoid heat transfer to the outside of the pipe and reduce heat diffusion.

[0036] The insulating materials can be, for example, rock wool, mineral wool, glass wool, polyurethane foam, etc.

[0037] The high-temperature insulating gasket is made of a high-temperature resistant material, such as an asbestos gasket and an aluminum silicate gasket, which can effectively block heat flow.

[0038] The temperature measuring point can adopt a conventional industrial temperature sensor.

[0039] The embodiment of the present application also provides a flow measurement method of the high-temperature low-flow rate flowmeter described in the embodiment of the present application, which comprises heating liquid metal and measuring the temperature before and after heating, and calculating the mass flow rate of liquid metal based on energy balance:

[0040]

[0041] wherein, represents the mass flow rate of liquid metal, kgs -1 ; P represents the heating power of the heating device, W; Tin represents the temperature of liquid metal before heating, K; T out represents the temperature of liquid metal after heating, K; c p represents the specific heat capacity of liquid metal, Jkg -1 K -1 .

[0042] Because the heating power is small, and the specific heat capacity of liquid metal at high temperature changes little, the specific heat capacity can be regarded as a constant value.

[0043] The working principle of the high-temperature low-flow-rate flowmeter described in the embodiments of the present application is as follows.

[0044] The present application proposes a flowmeter based on the principle of energy balance, which calculates the mass flow rate by heating liquid metal and measuring the temperature before and after heating.

[0045] The key of the flowmeter is to obtain the representative temperature of liquid metal after heating. Only on the basis of accurately measuring the temperature difference, the accuracy of flow rate calculation can be ensured. The low Prandtl number characteristics of liquid metal and the weak turbulence intensity at ultra-low flow rate lead to the serious temperature stratification in the pipeline. In this case, the temperature near the wall of the pipeline is much higher than that in the mainstream area, which brings great difficulty to the measurement of the temperature of liquid metal after heating.

[0046] In order to improve the uniformity of temperature, the present application proposes a stirring strategy based on the Venturi effect. When liquid metal flows through the throat of the Venturi tube, the flow rate is significantly improved due to the extrusion of fluid, the turbulence intensity is increased, and the energy transfer process is accelerated. In the gradually expanding section, the temperature boundary layer is destroyed due to the formation of vortex flow, and the high temperature near the wall is quickly transferred to the mainstream area. After passing through the Venturi tube, the temperature of liquid metal tends to be uniform.

[0047] In order to verify the effectiveness of the present application, numerical simulation is used to analyze the flow field and temperature field of the flowmeter in depth.

[0048] Combining Figure 3 and Figure 4It can be found that the pressure at the inlet of the flowmeter is higher. When the liquid metal flows into the mixing section pipeline, the flow rate increases due to the gradual reduction of the flow cross section. According to the Bernoulli equation, the throttling effect of the throat causes a significant drop in the static pressure in the pipe, forming a negative pressure area. After the liquid metal flows out of the throat, the flow rate decreases and the static pressure gradually rises as the flow cross section gradually expands. At the same time, the pressure at the outlet section is slightly lower than that at the inlet section, because the diameters of the outlet section and the inlet section are the same, and the pressure loss before and after is mainly caused by the friction between the liquid metal and the pipe wall. Due to the significant change in the cross-sectional area of the flow channel in the mixing section pipeline, the pressure distribution of the flow field in the flowmeter changes significantly along the flow direction. It is calculated that the total pressure loss of the flowmeter model is about 188Pa, which is very small compared with the traditional flowmeter.

[0049] By Figure 5 It can be found that when the liquid metal passes through the converging section, the flow rate increases significantly as the cross-sectional area gradually decreases, reaching a maximum value at the throat. When the liquid metal flows through the diverging section, the flow rate gradually decreases as the cross-sectional area gradually increases. In the near-wall region of the diverging section, the vortex phenomenon enhances the turbulence intensity, which helps to achieve mixing, but also increases the corresponding pressure loss. In addition, Figure 5 The downward shift of the velocity distribution shown in FIG. 6 is mainly affected by the action of gravity.

[0050] By comparison Figure 6 And Figure 7 It can be found that the mixing strategy based on the Venturi effect proposed in the present application significantly improves the temperature uniformity of the liquid metal. In the comparative model without the mixing strategy, there is a clear temperature gradient in the heated liquid metal, and the temperature near the wall is higher than that in the center of the flow channel. In the basic model with the mixing strategy, the temperature distribution of the liquid metal tends to be uniform after passing through the mixing section. This shows that the mixing strategy based on the Venturi effect of the present application can effectively reduce the temperature stratification of the liquid metal, and help to improve the uniformity of the temperature distribution of the heated liquid metal.

[0051] In summary, the present application provides a practical and effective solution for measuring the flow rate of liquid metal in the cooling system of liquid metal cooled reactors (LMRs), especially in high temperature and ultra-low flow rate working conditions.

Claims

1. A flow measurement method for a high-temperature, low-velocity flow meter, characterized in that, The high-temperature, low-flow-rate flow meter includes a heating section pipeline and a mixing section pipeline connected to the outlet end of the heating section pipeline. A heating device is installed outside the heating section pipeline to heat the liquid metal flowing through it. The mixing section pipeline uses a Venturi tube to make the temperature of the liquid metal at the outlet of the mixing section pipeline more uniform. A temperature measuring point is set before the inlet of the heating section pipeline and after the outlet of the mixing section pipeline to obtain the temperature of the liquid metal before heating and the temperature of the liquid metal after heating, respectively. The flow measurement method includes: heating liquid metal and measuring the temperature before and after heating, and calculating the mass flow rate of the liquid metal based on energy balance. ； in, This indicates the mass flow rate of liquid metal. Indicates the heating power of the heating equipment; Indicates the temperature of the liquid metal before heating; This indicates the temperature of the liquid metal after heating; This indicates the specific heat capacity of a liquid metal.

2. The flow measurement method according to claim 1, characterized in that, The heating equipment is an electric heating device.

3. The flow measurement method according to claim 2, characterized in that, The electric heating equipment uses an electric heating belt, which is wrapped around the outside of the heating section pipeline.

4. The flow measurement method according to claim 1, characterized in that, It also includes a first straight pipe section connected to the inlet end of the heating section pipeline and a second straight pipe section connected to the outlet end of the mixing section pipeline, with two temperature measuring points set on the first and second straight pipe sections respectively.

5. The flow measurement method according to claim 4, characterized in that, The heating section pipeline is connected to the mixing section pipeline via flanges, the first straight pipe section is connected to the heating section pipeline via flanges, and the mixing section pipeline is connected to the second straight pipe section via flanges.

6. The flow measurement method according to claim 5, characterized in that, The heating section pipeline and the mixing section pipeline are wrapped with heat insulation material to form a heat insulation layer.

7. The flow measurement method according to claim 6, characterized in that, A high-temperature insulating gasket is placed between the two interconnected flanges to reduce heat transfer; the flange connection area is also wrapped with insulating material.

8. The flow measurement method according to claim 7, characterized in that, The insulation material is made of rock wool, mineral wool, glass wool or polyurethane foam, and the high-temperature insulation pad is made of asbestos pad or aluminum silicate pad.

9. The flow measurement method according to claim 1, characterized in that, The temperature measuring point uses a traditional industrial temperature sensor.

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