High-temperature low-flow-velocity flowmeter and flow measuring method thereof

Abstract

The invention discloses a high-temperature low-flow-velocity flowmeter and a flow measuring method thereof.The high-temperature low-flow-velocity flowmeter comprises a heating section pipeline and a stirring and mixing section pipeline connected to the outlet end of the heating section pipeline, and heating equipment is arranged outside the heating section pipeline and used for heating liquid metal flowing through the heating section pipeline; the mixing section pipeline adopts a Venturi tube, so that the temperature of liquid metal at an outlet of the mixing section pipeline tends to be uniform; temperature measuring points are arranged in front of an inlet of the heating section pipeline and behind an outlet of the stirring and mixing section pipeline respectively and used for obtaining the temperature of the liquid metal before heating and the temperature of the liquid metal after heating respectively; according to the flow measurement method, liquid metal is heated, the temperature before and after heating is measured, and then the mass flow of the liquid metal is calculated based on energy balance. According to the invention, high-precision, stable and long-term reliable flow measurement of the liquid metal under the working condition of high temperature and ultralow flow velocity can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of flow measurement, and in particular to a high-temperature and low-flow-rate flow meter and a flow measurement method thereof. Background Art

[0002] In the accident conditions of liquid metal cooled reactors (LMRs), the flow rate of liquid metal may be as low as 0.01-0.05 m / s. Accurate measurement of coolant flow in reactor fuel assemblies is of great significance to ensure the safe operation of LMRs, which can ensure that the reactor operates within safe thermal limits, prevent local overheating of fuel assemblies and improve thermal efficiency.

[0003] Liquid metal has the characteristics of high temperature, strong corrosion and low Prandtl number. When traditional industrial flow sensors directly measure the coolant flow under ultra-low flow conditions of LMRs, they have the following limitations:

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

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

[0006] (3) Traditional industrial flow sensors have problems such as response degradation and response delay under extreme environmental conditions (such as ultra-low flow rate conditions);

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

[0008] (5) Some flow meters are prone to failure in high temperature environments, and their stability and long-term operating performance are insufficient, such as electromagnetic flow meters and ultrasonic Doppler velocimeters. Summary of the invention

[0009] Purpose of the invention: The purpose of the present invention is to provide a high-temperature, low-flow rate flowmeter and a flow measurement method thereof, so as to solve the problem of accurate flow measurement of liquid metal under high-temperature and ultra-low flow rate conditions in the LMRs cooling system.

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

[0011] Furthermore, the heating device is an electric heating device.

[0012] Furthermore, the electric heating device adopts an electric heating belt, which is wound around the outside of the heating section pipeline.

[0013] Furthermore, the high-temperature, low-flow rate flowmeter 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, and two temperature measuring points are respectively set on the first straight pipe section and the second straight pipe section.

[0014] Furthermore, the heating section pipeline is connected to the mixing section pipeline via a flange, the first straight pipe section is connected to the heating section pipeline via a flange, and the mixing section pipeline is connected to the second straight pipe section via a flange.

[0015] Furthermore, the outside of the heating section pipeline and the mixing section pipeline is wrapped with insulation material to form a heat preservation layer.

[0016] Furthermore, a high-temperature insulation gasket is arranged between the two interconnected flanges to reduce heat transfer; the flange connection position is also wrapped with insulation material.

[0017] Furthermore, the thermal insulation material is made of rock wool, mineral wool, glass wool or polyurethane foam, and the high-temperature thermal insulation gasket is made of asbestos gasket or aluminum silicate gasket.

[0018] Furthermore, the temperature measurement point adopts a traditional industrial temperature sensor.

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

[0020]

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

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

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

[0024] In summary, the present invention can achieve high-precision, stable and long-term reliability flow measurement of liquid metal under high-temperature and ultra-low flow rate conditions. At the same time, the flow meter has a simple structure, is easy to install and debug, and is suitable for promotion and application in various scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0026] Figure 2 is a cross-sectional view of a high-temperature, low-flow-rate flowmeter according to an embodiment of the present invention;

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

[0028] Figure 4 is a pressure distribution diagram of the fluid domain of the flow meter model in the embodiment of the present invention at the central axis of the numerical simulation;

[0029] Figure 5 It is a velocity field distribution diagram of the fluid domain of the flow meter model in the mixing section pipeline in the numerical simulation in the embodiment of the present invention;

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

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

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

[0033] like Figure 1 and Figure 2As shown, an embodiment of the present invention provides a high-temperature, low-flow rate flowmeter, comprising a first straight pipe section 3, a heating section pipeline 1, a mixing section pipeline 2, and a second straight pipe section 4 which are sequentially connected through flanges, a heating device is arranged outside the heating section pipeline 1 for heating the liquid metal flowing through the heating section pipeline 1; the mixing section pipeline 2 adopts a Venturi tube so that the temperature of the liquid metal at the outlet of the mixing section pipeline 2 tends to be uniform; a temperature measuring point is arranged on each of the first straight pipe section 3 and the second straight pipe section 4, for respectively obtaining the temperature of the liquid metal before heating and the temperature of the liquid metal after heating.

[0034] In this embodiment, the heating device adopts an electric heating device, specifically, an electric heating belt is adopted, and the electric heating belt is wound around the outside of the heating section pipeline 1. The electric heating belt belongs to the prior art. The common electric heating belt is wound with an electric heating wire (such as a nickel-chromium alloy wire), and the electric heating wire is wrapped with an insulating material (such as multiple layers of alkali-free glass fiber). Electric heating has the advantages of fast heating speed, high thermal efficiency, long service life, precise temperature control, and high degree of automation. When selecting an electric heating belt, it is necessary to comprehensively consider factors such as the type of liquid metal in the pipe, flow rate, initial temperature, target temperature, etc., and 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 flow meter pipeline needs to be insulated. In this embodiment, the heating section pipeline 1 and the mixing section pipeline 2 are wrapped with insulation materials to form an insulation layer, ensuring that the heat is concentrated in the heating section pipeline 1 while reducing heat loss outside the pipeline. In addition, a high-temperature insulation gasket is arranged between the two interconnected flanges to effectively reduce the transfer of heat through the flange connection. The flange connection position is also wrapped with insulation material to prevent heat from being transferred to the outside of the pipeline and reduce heat diffusion.

[0036] Insulation materials can be used, such as rock wool, mineral wool, glass wool, polyurethane foam, etc.

[0037] High temperature insulation gaskets are made of high temperature resistant materials, such as asbestos gaskets, aluminum silicate gaskets, etc., which can effectively isolate heat flow.

[0038] The temperature measurement points can use traditional industrial temperature sensors.

[0039] The embodiment of the present invention further provides a flow measurement method of the high-temperature and low-flow-rate flow meter according to the embodiment of the present invention, comprising: heating liquid metal and measuring the temperature before and after heating, and calculating the mass flow of the liquid metal based on energy balance:

[0040]

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

[0042] Since the heating power is small and the constant-pressure 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 and low flow rate flow meter described in the embodiment of the present invention is as follows.

[0044] The present invention proposes a flow meter based on the energy balance principle, which heats liquid metal and measures the temperature before and after heating to calculate its mass flow rate.

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

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

[0047] In order to verify the effectiveness of the present invention, numerical simulation is used to conduct an in-depth analysis of the flow field and temperature field of the flow meter.

[0048] Combination Figure 3 and Figure 4It can be found that the pressure at the inlet of the flowmeter is relatively high. When the liquid metal flows into the mixing section pipeline, the flow velocity increases as the flow cross section gradually decreases. According to the Bernoulli equation, the throttling effect of the throat causes the static pressure in the tube to drop significantly, forming a negative pressure area. After the liquid metal flows out of the throat, as the flow cross section gradually expands, the flow velocity decreases and the static pressure gradually increases. At the same time, the pressure in the outlet section is slightly lower than that in the inlet section. This is because the diameters of the outlet section and the inlet section are the same, and the front and rear pressure loss 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 inside the flowmeter has changed significantly along the flow direction. According to calculations, the total pressure loss of the flowmeter model is about 188Pa, which is very small compared to traditional flowmeters.

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

[0050] contrast Figure 6 and Figure 7 It can be found that the mixing strategy based on the Venturi effect proposed in the present invention significantly improves the temperature uniformity of the liquid metal. In the comparison model without the mixing strategy, there is an obvious temperature gradient in the heated liquid metal, and the temperature of the near-wall area is higher than that of the center area of ​​the flow channel. In the basic model using 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 invention can effectively reduce the temperature stratification phenomenon of the liquid metal, and help to improve the uniformity of the temperature distribution of the liquid metal after heating.

[0051] In summary, the present invention provides a practical and effective solution for liquid metal flow measurement in the cooling system of liquid metal cooled reactors (LMRs), especially showing incomparable advantages in applications under high temperature and ultra-low flow rate conditions.

Claims

1. A high temperature and low flow rate flow meter, characterized in that: It comprises a heating section pipeline and a mixing section pipeline connected to the outlet end of the heating section pipeline. A heating device is arranged outside the heating section pipeline for heating the liquid metal flowing through the heating section pipeline. The mixing section pipeline adopts a venturi tube so that the temperature of the liquid metal at the outlet of the mixing section pipeline tends to be uniform. A temperature measuring point is arranged before the inlet of the heating section pipeline and after the outlet of the mixing section pipeline, respectively for obtaining the temperature of the liquid metal before heating and the temperature of the liquid metal after heating.

2. The high temperature and low flow rate flow meter according to claim 1, characterized in that: The heating device is an electric heating device.

3. The high temperature and low flow rate flow meter according to claim 2, characterized in that: The electric heating device adopts an electric heating belt, which is wound around the outside of the heating section pipeline.

4. The high temperature and low flow rate flow meter 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. Two temperature measuring points are respectively arranged on the first straight pipe section and the second straight pipe section.

5. The high temperature and low flow rate flow meter according to claim 4, characterized in that: The heating section pipeline is connected to the mixing section pipeline through a flange, the first straight pipe section is connected to the heating section pipeline through a flange, and the mixing section pipeline is connected to the second straight pipe section through a flange.

6. The high temperature and low flow rate flow meter according to claim 5, characterized in that: The outside of the heating section pipeline and the mixing section pipeline is wrapped with insulation material to form a heat preservation layer.

7. The high temperature and low flow rate flow meter according to claim 6, characterized in that: A high-temperature insulation gasket is arranged between the two interconnected flanges to reduce heat transfer; the flange connection position is also wrapped with insulation material.

8. The high temperature and low flow rate flow meter according to claim 7, characterized in that: The thermal insulation material is rock wool, mineral wool, glass wool or polyurethane foam, and the high-temperature thermal insulation gasket is asbestos gasket or aluminum silicate gasket.

9. The high temperature and low flow rate flow meter according to claim 1, characterized in that: The temperature measurement points adopt traditional industrial temperature sensors.

10. A flow measurement method of a high temperature and low flow rate flow meter according to claim 1, characterized in that: include: Heat the liquid metal and measure its temperature before and after heating, and calculate the mass flow rate of the liquid metal based on the energy balance: in, represents the mass flow rate of liquid metal; P represents the heating power of the heating equipment; T in Indicates the temperature of the liquid metal before heating; T out Indicates the temperature of the liquid metal after heating; c p Represents the specific heat capacity of liquid metal.

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