Two-phase flow control method for compressed air foam system in low-temperature environment

Abstract

The invention relates to a two-phase flow control method of a compressed air foam system in a low-temperature environment. The compressed air foam is a gas-liquid homogeneous mixture which is formed by injecting compressed air into a gas-liquid mixer, outputting the compressed air and a liquid-liquid mixer and fusing the compressed air with water and foam liquid; the method is characterized in that the specific two-phase flow control steps are as follows: under the condition that the flow of foam mixed liquid is maintained at a set value, the temperature and flow of gas output by a gas supply branch are regulated and controlled, and the set gas-liquid ratio is met; after the mixing ratio of foam liquid and water is regulated and controlled through the conductivity until the mixing ratio meets the deviation requirement, the foam mixed liquid and compressed gas are mixed in the gas-liquid mixer at the moment, and then whether the gas-liquid ratio continues to be adjusted or not is judged through 25% of drainage time, so that the two-phase flow is accurately controlled to meet the fire extinguishing performance requirement of compressed air foam. The problems that under the low-temperature environment, compressed air is lower than the dew point temperature and is prone to condensation, mixing ratio regulation and control are not accurate, and the actual drainage time of compressed air foam does not meet the requirement are solved.

Description

Technical Field

[0001] This invention specifically relates to a two-phase flow control method for a compressed air foam system under low-temperature conditions, belonging to the field of compressed air foam technology. Background Technology

[0002] Currently, compressed air foam systems (CAFS) are widely used in many key areas, especially as standard fire extinguishing systems in ultra-high voltage power transmission and transformation stations, extra-high voltage converter stations, and electrochemical energy storage power stations, playing a vital role in fire prevention and control scenarios. The specific working principle is as follows: compressed air is injected into a mixture of water and foam concentrate. Through the shearing action of high-speed airflow, the liquid is "torn" into tiny bubbles, forming a uniform and delicate foam structure, thus generating a stable and highly efficient fire extinguishing gas-liquid two-phase mixture—compressed air foam.

[0003] Patent document CN115569325A discloses a wide-adaptability containerized compressed air foam device and its control method. While the patent enables controllable flow rates for each channel, it does not consider the impact of low-temperature environments on the flow rates of compressed gas and foam mixtures, making it only applicable to ambient temperature conditions and offering a single control method. Patent document CN 115876506A discloses a test method for performance testing of high-flow-rate compressed air foam systems. This method also only considers ordinary ambient temperature and pressure conditions and focuses solely on foam expansion ratio and liquid separation time performance, without providing specific measures for adjustment. The expansion ratio refers to the ratio of foam volume to the volume of the foam mixture that forms the foam.

[0004] With the expansion of application scenarios and environments, especially in North and Northeast my country, compressed air foam devices operate in low-temperature environments. In these environments, water vapor in the gas easily condenses into liquid, affecting the gas-liquid ratio. Even worse, low temperatures can cause condensate in the compressed air to freeze, clogging control pipelines and potentially causing them to rupture. Although both the foam liquid tank and water tank have insulation measures, the mixing ratio of foam liquid and water is difficult to precisely control at low temperatures. The gas-liquid ratio and mixing ratio negatively impact the foaming ratio, liquid separation time, and other performance parameters of the compressed air foam. Furthermore, different fire stations have varying performance requirements for compressed air foam; optimizing performance requires a comprehensive consideration of parameters such as the mixing ratio and gas-liquid ratio, combined with specific scenario requirements to achieve a dynamic balance between stability and flowability. Therefore, it is clear that existing technologies, whether compressed air foam devices or control methods, are not entirely suitable for low-temperature environments. Summary of the Invention

[0005] The purpose of this invention is to provide a two-phase flow control method for a compressed air foam system in a low-temperature environment. This method can regulate both the gas and liquid streams. By adjusting the gas-liquid ratio and the mixing ratio, the flow rates of the gas, water, and foam liquid can be controlled. This method can effectively solve problems such as the easy condensation of compressed gas below the dew point temperature in low-temperature environments, inaccurate mixing ratio control, and the actual liquid separation time of compressed air foam not meeting requirements. This method achieves precise control of the two-phase flow rate of the compressed air foam system.

[0006] To achieve the above objectives, the technical solution of this invention is: a two-phase flow control method for a compressed air foam system under low-temperature conditions. Its innovation lies in: including a compressed air foam system comprising an air supply branch, a liquid supply branch, and a water supply branch. The liquid supply branch and the water supply branch are connected to the corresponding input terminals of a liquid-liquid mixer. The output terminals of the air supply branch and the liquid-liquid mixer are respectively connected to the corresponding input terminals of a gas-liquid mixer. The compressed air foam is a homogeneous gas-liquid mixture formed by injecting compressed air into the gas-liquid mixer via the air supply branch and mixing it with water and foam liquid output from the liquid-liquid mixer. Its innovation lies in: the specific two-phase flow control steps are as follows:

[0007] With the flow rate of the foam mixture output from the liquid-liquid mixer maintained at the set value, the gas temperature and flow rate output from the gas supply branch are regulated by adjusting the heating power and the opening of the electric regulating valve to meet the set gas-liquid ratio.

[0008] After adjusting the foam liquid and water mixing ratio to meet the deviation requirements by adjusting the conductivity, the foam liquid and compressed gas are then mixed in the gas-liquid mixer. The gas-liquid ratio is then adjusted again after 25% liquid separation time, thereby achieving precise control of the two-phase flow to meet the fire extinguishing performance requirements of compressed air foam.

[0009] In the above technical solution, the specific steps for controlling the gas-liquid ratio are as follows:

[0010] Step a: Measure the flow rate, pressure, and dew point temperature of the compressed gas output from the gas supply branch under low-temperature operating conditions.

[0011] Step b: Heat the compressed air to a temperature higher than the pressure dew point and keep it constant.

[0012] Step c: Adjust the compressed gas flow rate output from the gas supply branch at different heating temperatures.

[0013] Step d involves obtaining the relationship between compressed gas and gas flow rate at different temperatures, and then adjusting the gas-liquid ratio accordingly.

[0014] The low-temperature operating condition refers to the temperature of the compressed air and foam mixture being within the range of -30℃ to 5℃.

[0015] In the above technical solution, the specific steps for controlling the mixing ratio are as follows:

[0016] Step e: Measure the electrical conductivity of foam mixtures with different mixing ratios under normal temperature conditions.

[0017] Step f involves performing a low-temperature correction to the relationship between conductivity and mixing ratio.

[0018] Step g: Measure the conductivity and mixing ratio of the foam mixture under low-temperature conditions.

[0019] Step h: Adjust the mixing ratio of foam liquid and water according to the conductivity deviation.

[0020] The normal temperature condition refers to the temperature of the compressed air and foam mixture being 10℃ to 30℃, and the low temperature condition refers to the temperature of the compressed air and foam mixture being within the range of -30℃ to 5℃.

[0021] In the above technical solution, a gas flow meter and a temperature transmitter on the outlet side of the gas supply branch are used to measure the flow rate and temperature of the compressed gas output under low temperature conditions.

[0022] In the above technical solution, the dew point temperature value is directly obtained by the dew point temperature meter installed on the gas supply branch at a pressure of 0.8 to 1.0 MPa. Then, the pipeline is heated by electric heat tracing until the temperature of the compressed air detected by the temperature transmitter is higher than the pressure dew point value and constant. The heating power of electric heat tracing and the corresponding output gas flow rate and temperature value are recorded at this time.

[0023] In the above technical solution, the heating temperature of the electric heat tracing is kept constant, the flow rate is adjusted by the electric regulating valve on the gas supply branch, and the opening degree of the electric regulating valve and the corresponding output gas flow rate are recorded.

[0024] In the above technical solution, the heating power of the electric heat tracing is adjusted and kept constant, the flow rate is adjusted by the electric regulating valve on the gas supply branch, and the opening degree of the electric regulating valve and the corresponding output gas flow rate are recorded at different temperatures to obtain the correspondence between the actual output gas volume and gas temperature of the gas supply branch. By adjusting the heating temperature of the electric heat tracing and the opening degree of the electric regulating valve, the gas flow rate is controlled to meet the set gas-liquid ratio.

[0025] In the above technical solution, the dew point temperature meter is a mirror sensor or a capacitive sensor.

[0026] In the above technical solution, the gas-liquid ratio is the ratio of the volume of compressed air entering the gas-liquid mixer to the volume of foam mixture, and the gas-liquid ratio is in the range of 7:1 to 10:1.

[0027] In the above technical solution, in step e, a conductivity meter installed on the pipeline connecting the liquid-liquid mixer and the gas-liquid mixer calibrates the conductivity σ of the foam mixture under different mixing ratios at room temperature. 25℃ Using numerical analysis, the relationship between the conductivity of the foam mixture and the mixing ratio was obtained by fitting:

[0028] σ 25℃ =σ(R)

[0029] The mixing ratio is in the range of 0.1% ≤ R ≤ 6%.

[0030] In the above technical solution, in step f, the relationship between conductivity and mixing ratio is corrected at low temperature:

[0031] σ t =σ 25℃ ·(1+α·(t-25))

[0032] Calculate the conductivity σ of the mixture at the target mixing ratio R0. t (R0), where t is the temperature of the foam mixture under low temperature conditions, R is the mixing ratio, and α is the temperature coefficient.

[0033] In the above technical solution, in step g, the liquid supply branch is operated, and the conductivity σ of the mixture delivered from the outlet of the liquid-liquid mixer is measured in real time by a conductivity meter. The measured conductivity σ of the mixture and the target conductivity σ are then calculated. t (R0) Deviation:

[0034]

[0035] Where a0 is the allowable deviation of conductivity;

[0036] When a < 0, it is determined that the actual mixing ratio R is less than the target mixing ratio R0. The electric regulating valves on the liquid supply branch and the water supply branch are adjusted to increase the foam liquid flow rate and decrease the water flow rate until 0 ≤ a ≤ a0. At this time, the mixing ratio meets the system deviation requirements.

[0037] When a > a0, it is determined that the actual mixing ratio R is greater than the target mixing ratio R0. The electric regulating valves on the liquid supply branch and the water supply branch are adjusted to increase the water flow and decrease the foam liquid flow until 0 ≤ a ≤ a0. At this time, the mixing ratio meets the system deviation requirements.

[0038] When 0 ≤ a ≤ a0, the mixing ratio meets the system deviation requirement. At this time, the foam mixture and compressed gas are mixed at the set gas-liquid ratio.

[0039] If the 25% separation time is ≥3.5 min, then the compressed air foam liquid meets the fire extinguishing performance requirements, and the system can continue to operate at the current flow rate.

[0040] If the 25% separation time is less than 3.5 minutes, keep the flow rate and mixing ratio of the foam mixture unchanged, adjust the flow rate of compressed gas output from the gas supply branch, and change the gas-liquid ratio until the 25% separation time is greater than or equal to 3.5 minutes.

[0041] In the above technical solution, the allowable deviation of conductivity a0 is in the range of 0 to 0.3.

[0042] In the above technical solution, the gas supply branch includes an air compressor, which is connected to the corresponding input end pipeline of the gas-liquid mixer via a gas pipe. The gas pipe is sequentially equipped with a first gas flow meter, a first electric regulating valve, a check valve, a second gas flow meter, a dew point temperature meter, an electric heat tracing device, a temperature transmitter, and a third gas flow meter.

[0043] The liquid supply branch includes a foam liquid tank, which is connected to the corresponding input pipe of the liquid-liquid mixer via a foam liquid pipe. A second electric regulating valve and a first liquid flow meter are sequentially installed on the foam liquid pipe.

[0044] The water supply branch includes a water tank, which is connected to the input end of the liquid-liquid mixer via a water pipe. A third electric regulating valve and a second liquid flow meter are sequentially installed on the water pipe.

[0045] The liquid-liquid mixer is connected to the corresponding input end of the gas-liquid mixer through a water-liquid mixing pipe. The water-liquid mixing pipe is equipped with a conductivity meter, a fourth regulating valve, and a third liquid flow meter.

[0046] The positive effects of this invention are: after adopting the two-phase flow control method of the compressed air foam system under low temperature environment of this invention, the gas temperature and flow rate output by the gas supply branch are controlled and the set gas-liquid ratio is met by adjusting the heating power and the opening of the electric regulating valve, while maintaining the flow rate of the foam mixture at the set level.

[0047] After adjusting the foam liquid and water mixing ratio to meet the deviation requirements by adjusting the conductivity, the foam liquid and compressed gas are mixed in the gas-liquid mixer. Then, the gas-liquid ratio is adjusted again by using the 25% liquid separation time, so as to achieve precise control of the two-phase flow rate to meet the fire extinguishing performance requirements of compressed air foam.

[0048] Because low temperatures cause gaseous water in compressed air to condense into liquid at the dew point, and further freezing occurs below 0°C, as well as the difficulty in precisely controlling the mixing ratio, these problems are solved. The generated compressed air foam meets the 25% liquid separation time requirement. Therefore, this invention heats and adjusts the flow rate of compressed gas in a low-temperature environment, and adjusts the mixing ratio of foam liquid and water. That is, based on the fitted relationship, the flow rates of the two phases are adjusted from both the gas-liquid ratio and the mixing ratio by regulating the temperature and an electric regulating valve, thereby outputting compressed air foam that meets the fire extinguishing performance requirements.

[0049] This invention is not only rationally designed but also easy to operate. In low-temperature environments, compressed air is prone to high moisture content and even freezing of condensate, directly affecting the actual gas-liquid ratio of the compressed air foam. Furthermore, the liquid separation time of compressed air foam is highly correlated with the mixing ratio of foam liquid and water; in low-temperature environments, it is difficult to precisely control the mixing ratio to achieve the expected liquid separation time. This invention regulates the gas-liquid ratio by adjusting both the temperature and flow rate of the compressed air, and fits the relationship between gas temperature and flow rate. Simultaneously, it utilizes the correlation between conductivity and mixing ratio to adjust the liquid flow rate, enabling precise control of the two-phase flow of the compressed air foam system. This facilitates the production of compressed air foam with target fire extinguishing performance in low-temperature environments. Attached Figure Description

[0050] Figure 1 This is a flowchart of the control method of the present invention;

[0051] Figure 2 This is a schematic diagram of the structural principle of the two-phase flow control of a compressed air foam system under low-temperature conditions. Detailed Implementation

[0052] The present invention will be further described below with reference to the accompanying drawings and the given embodiments, but is not limited thereto.

[0053] Example 1

[0054] like Figure 1 , 2 As shown, a two-phase flow control method for a compressed air foam system in a low-temperature environment includes a compressed air foam system comprising an air supply branch, a liquid supply branch, and a water supply branch. The liquid supply branch and the water supply branch are connected to the corresponding input terminals of a liquid-liquid mixer 400. The output terminals of the air supply branch and the liquid-liquid mixer 400 are respectively connected to the corresponding input terminals of a gas-liquid mixer 500. The compressed air foam is a homogeneous gas-liquid mixture formed by injecting compressed air into the gas-liquid mixer via the air supply branch and mixing it with the foam liquid (composed of water and foam liquid) output by the liquid-liquid mixer. The specific two-phase flow control steps are as follows:

[0055] With the flow rate of the foam mixture output from the liquid-liquid mixer maintained at the set value, the gas temperature and flow rate output from the gas supply branch are regulated by adjusting the heating power and the opening of the electric regulating valve to meet the set gas-liquid ratio.

[0056] After adjusting the foam liquid and water mixing ratio to meet the deviation requirements by adjusting the conductivity, the foam liquid and compressed gas are then mixed in the gas-liquid mixer. The gas-liquid ratio is then adjusted again after 25% liquid separation time, thereby achieving precise control of the two-phase flow to meet the fire extinguishing performance requirements of compressed air foam.

[0057] The 25% precipitation time is the time required for 25% of the liquid by mass to precipitate from the foam.

[0058] Furthermore, in order to more accurately control the gas-liquid ratio and fit the relationship between gas temperature and flow rate, the specific control steps for the gas-liquid ratio are as follows:

[0059] Step a: Measure the flow rate, pressure, and dew point temperature of the compressed gas output from the gas supply branch under low-temperature operating conditions.

[0060] Step b: Heat the compressed air to a temperature higher than the pressure dew point and keep it constant.

[0061] Step c: Adjust the compressed gas flow rate output from the gas supply branch at different heating temperatures.

[0062] Step d involves obtaining the relationship between compressed gas and gas flow rate at different temperatures, and then adjusting the gas-liquid ratio accordingly.

[0063] The low-temperature operating condition refers to the temperature of the compressed air and foam mixture being within the range of -30℃ to 5℃.

[0064] Furthermore, in order to control the mixing ratio more precisely, the liquid flow rate is adjusted by utilizing the relationship between conductivity and mixing ratio. The specific control steps for the mixing ratio are as follows:

[0065] Step e: Measure the electrical conductivity of foam mixtures with different mixing ratios under normal temperature conditions.

[0066] Step f involves performing a low-temperature correction to the relationship between conductivity and mixing ratio.

[0067] Step g: Measure the conductivity and mixing ratio of the foam mixture under low-temperature conditions.

[0068] Step h: Adjust the mixing ratio of foam liquid and water according to the conductivity deviation.

[0069] The normal temperature condition refers to the temperature of the compressed air and foam mixture being 10℃ to 30℃, and the low temperature condition refers to the temperature of the compressed air and foam mixture being within the range of -30℃ to 5℃.

[0070] Furthermore, in order to accurately obtain the gas flow rate and temperature at the outlet side of the gas supply branch, this invention utilizes a gas flow meter and a temperature transmitter at the outlet side of the gas supply branch to measure the compressed gas flow rate and temperature output under low-temperature conditions, respectively.

[0071] Furthermore, in order to obtain the temperature of the heated gas in a timely manner when it is higher than the pressure dew point value, the pipeline is heated by electric heat tracing until the temperature of the compressed air detected by the temperature transmitter is higher than the pressure dew point value and constant. The heating power of the electric heat tracing and the corresponding output gas flow rate and temperature value are recorded at this time.

[0072] Furthermore, in order to obtain the correlation between gas flow rate and temperature so as to adjust the gas-liquid ratio and keep the heating temperature of the electric heat tracing constant, the flow rate is adjusted by the electric regulating valve on the gas supply branch, and the opening degree of the electric regulating valve and the corresponding output gas flow rate are recorded at this time.

[0073] Furthermore, the heating power of the electric heat tracing is adjusted and kept constant, the flow rate is adjusted by the electric regulating valve on the gas supply branch, and the opening degree of the electric regulating valve and the corresponding output gas flow rate are recorded at different temperatures. The correspondence between the actual output gas volume and gas temperature of the gas supply branch is obtained. By adjusting the heating temperature of the electric heat tracing and the opening degree of the electric regulating valve, the gas flow rate is controlled to meet the set gas-liquid ratio.

[0074] Furthermore, to make the structure more reasonable, the dew point temperature meter is a mirror sensor or a capacitive sensor.

[0075] Furthermore, the gas-liquid ratio is the ratio of the volume of compressed air entering the gas-liquid mixer to the volume of foam mixture, and the gas-liquid ratio ranges from 7:1 to 10:1.

[0076] Furthermore, in order to determine the relationship between the conductivity of the foam mixture and the mixing ratio, in step e, a conductivity meter installed on the pipeline connecting the liquid-liquid mixer and the gas-liquid mixer calibrates the conductivity σ of the foam mixture at different mixing ratios under normal temperature conditions. 25℃ Using numerical analysis, the relationship between the conductivity of the foam mixture and the mixing ratio was obtained by fitting:

[0077] σ 25℃ =σ(R)

[0078] The mixing ratio is in the range of 0.1% ≤ R ≤ 6%.

[0079] Furthermore, in step f, the relationship between conductivity and mixing ratio is corrected at low temperature:

[0080] σ t =σ 25℃·(1+α·(t-25))

[0081] Calculate the conductivity σ of the mixture at the target mixing ratio R0. t (R0), where t is the temperature of the foam mixture under low temperature conditions, R is the mixing ratio, and α is the temperature coefficient.

[0082] Furthermore, in step g, the liquid supply branch is operated, and the conductivity σ of the mixture delivered from the outlet of the liquid-liquid mixer is measured in real time by a conductivity meter. The measured conductivity σ of the mixture and the target conductivity σ are then calculated. t (R0) Deviation:

[0083]

[0084] Where a0 is the allowable deviation of conductivity;

[0085] When a < 0, it is determined that the actual mixing ratio R is less than the target mixing ratio R0. The electric regulating valves on the liquid supply branch and the water supply branch are adjusted to increase the foam liquid flow rate and decrease the water flow rate until 0 ≤ a ≤ a0. At this time, the mixing ratio meets the system deviation requirements.

[0086] When a > a0, it is determined that the actual mixing ratio R is greater than the target mixing ratio R0. The electric regulating valves on the liquid supply branch and the water supply branch are adjusted to increase the water flow and decrease the foam liquid flow until 0 ≤ a ≤ a0. At this time, the mixing ratio meets the system deviation requirements.

[0087] When 0 ≤ a ≤ a0, the mixing ratio meets the system deviation requirement. At this time, the foam mixture and compressed gas are mixed at the set gas-liquid ratio.

[0088] If the 25% separation time is ≥3.5 min, then the compressed air foam liquid meets the fire extinguishing performance requirements, and the system can continue to operate at the current flow rate.

[0089] If the 25% separation time is less than 3.5 minutes, keep the flow rate and mixing ratio of the foam mixture unchanged, adjust the flow rate of compressed gas output from the gas supply branch, and change the gas-liquid ratio until the 25% separation time is greater than or equal to 3.5 minutes.

[0090] Furthermore, in order to achieve precise control of the mixing ratio, the allowable deviation of conductivity a0 is in the range of 0 to 0.3.

[0091] Furthermore, such as Figure 2As shown, to make the structure of the compressed air foam system of the present invention more reasonable, the air supply branch includes an air compressor 100. The air compressor 100 is connected to the corresponding input end pipeline of the gas-liquid mixer 500 through an air pipe. The air pipe is sequentially equipped with a first gas flow meter 101, a first electric regulating valve 102, a check valve 103, a second gas flow meter 104, a dew point temperature meter 105, an electric heat tracing device 106, a temperature transmitter 107, and a third gas flow meter 108.

[0092] The liquid supply branch includes a foam liquid tank 200, which is connected to the corresponding input pipe of the liquid-liquid mixer 400 via a foam liquid pipe. A second electric regulating valve 201 and a first liquid flow meter 202 are sequentially installed on the foam liquid pipe.

[0093] The water supply branch includes a water tank 300, which is connected to the corresponding input pipe of the liquid-liquid mixer 400 via a water pipe. A third electric regulating valve 301 and a second liquid flow meter 302 are sequentially installed on the water pipe.

[0094] The liquid-liquid mixer 400 is connected to the corresponding input end of the gas-liquid mixer 500 through a water-liquid mixing pipe. The water-liquid mixing pipe is equipped with a conductivity meter 601, a fourth regulating valve 602 and a third liquid flow meter 603.

[0095] This invention measures the output gas flow rate and dew point temperature of an air compressor under low-temperature conditions. By using electric heating and an electric regulating valve to change the gas temperature and flow rate, it obtains the correlation between the actual output gas flow rate and temperature, thereby controlling the gas-liquid ratio. It also measures the conductivity of the foam mixture under normal temperature conditions, corrects the correlation between the conductivity and mixing ratio at low temperatures, and adjusts the mixing ratio based on the conductivity deviation. This invention can regulate both the gas and liquid streams. By controlling the gas-liquid ratio and the mixing ratio, it controls the two-phase flow rates of gas, water, and foam liquid. This effectively solves problems such as the easy condensation of compressed gas below the dew point temperature in low-temperature environments, inaccurate mixing ratio control, and the actual liquid separation time of compressed air foam not meeting requirements. It achieves precise control of the two-phase flow rates of the compressed air foam system, enabling firefighters to use compressed air foam for targeted and precise firefighting in low-temperature areas.

[0096] Example 2

[0097] This invention relates to the method of outputting 6m³ ​​of gas from an air compressor at a pressure of 0.8MPa in an environment of -5℃. 3 Taking a planned compressed air foam generation of 600 L / min as an example, the preset gas-liquid ratio is 10:1 and the mixing ratio is 3%.

[0098] The flow rate and temperature of the air compressor output gas in a low-temperature environment were measured using a gas flow meter and temperature transmitter on the outlet side of the air compressor. The pressure dew point temperature value was directly obtained using a dew point thermometer at a pressure of 0.8 MPa. Then, the pipeline was heated by electric heat tracing until the temperature transmitter detected that the compressed air temperature was stable and 3-10°C higher than the pressure dew point value. The changes in gas flow rate before and after electric heat tracing were recorded.

[0099] The adjustment range is determined based on the recorded changes in gas flow rate before and after electric heating. The flow rate is adjusted using an electric regulating valve, and the actual output gas flow rate and corresponding temperature at different temperatures are recorded to obtain the correspondence between the actual output gas volume and gas temperature of the air compressor. The opening degree of the corresponding electric regulating valve is also recorded.

[0100] The conductivity meter measures the conductivity σ25℃ of foam mixture under normal operating conditions (25℃) and the relationship between different mixing ratios, and fits a linear relationship. The conductivity relationship of foam mixture under low temperature conditions of -5℃ is corrected and the target conductivity of 3% corresponding mixing ratio is calculated.

[0101] The compressed air foam preparation system is operated, and the conductivity meter measures the conductivity σ of the liquid mixture at the outlet of the liquid mixer in real time. The deviation a between the measured conductivity σ and the target conductivity σt (3%) is calculated.

[0102] At this point, a > 0.3, indicating the actual mixing ratio R is 3% greater than the target mixing ratio. The electric regulating valves on the liquid supply branch and water supply branch are adjusted to increase water flow and decrease foam liquid flow until 0 ≤ a ≤ 0.3. The foam mixer is then mixed with compressed air at a preset gas-liquid ratio of 10:1. The measured 25% liquid separation time is 3.2 minutes, less than 3.5 minutes, failing to meet the fire extinguishing performance requirements. A feedback signal is sent to the control system, which then readjusts the gas supply branch. Based on the relationship between gas flow and temperature, the system adjusts the electric heating power and the opening of the electric regulating valve, adjusting the actual output gas flow to 5.8 m³ / s. 3 / min, at which point the gas and foam mixture were remixed, and the time for 25% liquid separation was measured to be 3.6min, indicating that the compressed air foam met the fire extinguishing performance requirements.

[0103] In summary, the control method of this invention is not only rationally designed but also easy to operate. In low-temperature environments, the compressed air is prone to high moisture content, and even condensate freezing can occur, directly affecting the actual gas-liquid ratio of the compressed air foam. Furthermore, the liquid separation time of compressed air foam is highly correlated with the mixing ratio of foam liquid and water; in low-temperature environments, it is difficult to precisely control the mixing ratio to achieve the expected liquid separation time. This invention regulates the gas-liquid ratio by adjusting both the temperature and flow rate of the compressed air, and fits the relationship between gas temperature and flow rate. Simultaneously, it utilizes the correlation between conductivity and mixing ratio to adjust the liquid flow rate, enabling precise control of the two-phase flow of the compressed air foam system. This facilitates the acquisition of compressed air foam with target fire extinguishing performance in low-temperature environments.

[0104] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A two-phase flow control method for a compressed air foam system under low-temperature conditions, comprising a compressed air foam system, wherein the compressed air foam system includes an air supply branch, a liquid supply branch, and a water supply branch, the liquid supply branch and the water supply branch are connected to the corresponding input terminals of a liquid-liquid mixer (400), and the output terminals of the air supply branch and the liquid-liquid mixer (400) are respectively connected to the corresponding input terminals of a gas-liquid mixer (500), wherein the compressed air foam is a homogeneous gas-liquid mixture formed by injecting compressed air into the gas-liquid mixer via the air supply branch and mixing it with water and foam liquid output from the liquid-liquid mixer, characterized in that: The specific two-phase flow control steps are as follows: When the flow rate of the foam mixture output by the liquid-liquid mixer (400) is maintained at the set value, the gas temperature and flow rate output by the gas supply branch are controlled by adjusting the heating power and the opening of the electric regulating valve to meet the set gas-liquid ratio. After adjusting the mixing ratio of foam liquid and water to meet the deviation requirements by adjusting the conductivity, the foam liquid is then mixed with compressed gas in the gas-liquid mixer. The gas-liquid ratio is then adjusted again after 25% liquid separation time, thereby achieving precise control of the two-phase flow to meet the fire extinguishing performance requirements of compressed air foam.

2. The two-phase flow control method for a compressed air foam system under low-temperature conditions according to claim 1, characterized in that: The specific steps for controlling the gas-liquid ratio are as follows: Step a: Measure the flow rate, pressure dew point temperature, and pressure of the compressed gas output from the supply branch under low-temperature conditions. Step b: Heat the compressed air until the temperature is above the pressure dew point value and remains constant. Step c: Adjust the compressed gas flow rate output from the gas supply branch at different heating temperatures. Step d involves obtaining the relationship between compressed gas and gas flow rate at different temperatures, and then adjusting the gas-liquid ratio accordingly. The low-temperature operating condition refers to the temperature of the compressed air and foam mixture being within the range of -30℃ to 5℃.

3. The two-phase flow control method for a compressed air foam system under low-temperature conditions according to claim 1, characterized in that: The specific steps for controlling the mixing ratio are as follows: Step e: Measure the conductivity of foam mixtures with different mixing ratios under normal temperature conditions; Step f: Perform low-temperature correction on the relationship between conductivity and mixing ratio. Step g: Measure the conductivity and mixing ratio of the foam mixture under low-temperature conditions. Step h: Adjust the mixing ratio of foam liquid and water according to the conductivity deviation. The normal temperature condition refers to the temperature of the compressed air and foam mixture being 10℃ to 30℃, and the low temperature condition refers to the temperature of the compressed air and foam mixture being within the range of -30℃ to 5℃.

4. The two-phase flow control method for a compressed air foam system under low-temperature conditions according to claim 2, characterized in that: The flow rate and temperature of the compressed gas output under low-temperature conditions are measured using a gas flow meter and a temperature transmitter on the outlet side of the gas supply branch.

5. The two-phase flow control method for a compressed air foam system under low-temperature conditions according to claim 2, characterized in that: The dew point temperature value is directly obtained by using the dew point temperature meter installed on the gas supply branch at a pressure of 0.8 to 1.0 MPa. Then, the pipeline is heated by electric heat tracing until the temperature of the compressed air detected by the temperature transmitter is higher than the pressure dew point value and constant. The heating power of the electric heat tracing and the corresponding output gas flow rate and temperature value are recorded at this time.

6. The two-phase flow control method for a compressed air foam system under low-temperature conditions according to claim 5, characterized in that: Keep the heating temperature of the electric heat tracing constant, adjust the flow rate through the electric regulating valve on the gas supply branch, and record the opening degree of the electric regulating valve and the corresponding output gas flow rate at this time.

7. The two-phase flow control method for a compressed air foam system under low-temperature conditions according to claim 5, characterized in that: Adjust the heating power of the electric heat tracing and keep it constant. Adjust the flow rate through the electric regulating valve on the gas supply branch and record the opening degree of the electric regulating valve and the corresponding output gas flow rate at different temperatures. Obtain the correspondence between the actual output gas volume and gas temperature of the gas supply branch. By adjusting the heating temperature of the electric heat tracing and the opening degree of the electric regulating valve, control the gas flow rate to meet the set gas-liquid ratio.

8. The two-phase flow control method for a compressed air foam system under low-temperature conditions according to claim 5, characterized in that: The dew point temperature meter is either a mirror sensor or a capacitive sensor.

9. The two-phase flow control method for a compressed air foam system under low-temperature conditions according to claim 1, characterized in that: The gas-liquid ratio is the ratio of the volume of compressed air entering the gas-liquid mixer to the volume of foam mixture, and the gas-liquid ratio ranges from 7:1 to 10:

1.

10. The two-phase flow control method for a compressed air foam system under low-temperature conditions according to claim 3, characterized in that: In step e, a conductivity meter installed on the pipeline connecting the liquid-liquid mixer and the gas-liquid mixer calibrates the conductivity σ of the foam mixture under different mixing ratios at room temperature. 25℃ Using numerical analysis, the relationship between the conductivity of the foam mixture and the mixing ratio was obtained by fitting: s 25℃ =σ(R) The mixing ratio is in the range of 0.1% ≤ R ≤ 6%.

11. The two-phase flow control method for a compressed air foam system under low-temperature conditions according to claim 10, characterized in that: In step f, the relationship between conductivity and mixing ratio is corrected at low temperature: s t =s 25℃ ·(1+α·(t-25)) Calculate the conductivity σ of the mixture at the target mixing ratio R0. t (R0), where t is the temperature of the foam mixture under low temperature conditions, R is the mixing ratio, and α is the temperature coefficient.

12. The two-phase flow control method for a compressed air foam system under low-temperature conditions according to claim 11, characterized in that: In step g, the liquid supply branch is operated, and the conductivity σ of the mixture delivered from the outlet of the liquid-liquid mixer is measured in real time by a conductivity meter. The measured conductivity σ of the mixture and the target conductivity σ are then calculated. t (R0) Deviation: Where a0 is the allowable deviation of conductivity; When a < 0, it is determined that the actual mixing ratio R is less than the target mixing ratio R0. The electric regulating valves on the liquid supply branch and the water supply branch are adjusted to increase the foam liquid flow rate and decrease the water flow rate until 0 ≤ a ≤ a0. At this time, the mixing ratio meets the system deviation requirements. When a > a0, it is determined that the actual mixing ratio R is greater than the target mixing ratio R0. The electric regulating valves on the liquid supply branch and the water supply branch are adjusted to increase the water flow and decrease the foam liquid flow until 0 ≤ a ≤ a0. At this time, the mixing ratio meets the system deviation requirements. When 0 ≤ a ≤ a0, the mixing ratio meets the system deviation requirement. At this time, the foam mixture and compressed gas are mixed at the set gas-liquid ratio. If the 25% separation time is ≥3.5 min, then the compressed air foam liquid meets the fire extinguishing performance requirements, and the system can continue to operate at the current flow rate. If the 25% separation time is less than 3.5 minutes, keep the flow rate and mixing ratio of the foam mixture unchanged, adjust the flow rate of compressed gas output from the gas supply branch, and change the gas-liquid ratio until the 25% separation time is greater than or equal to 3.5 minutes.

13. The two-phase flow control method for a compressed air foam system under low-temperature conditions according to claim 12, characterized in that: The permissible deviation of conductivity a0 is in the range of 0 to 0.

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14. The two-phase flow control method for a compressed air foam system under low-temperature conditions according to claim 1, characterized in that: The gas supply branch includes an air compressor (100), which is connected to the corresponding input end pipeline of the gas-liquid mixer (500) via a gas pipe. The gas pipe is sequentially equipped with a first gas flow meter (101), a first electric regulating valve (102), a check valve (103), a second gas flow meter (104), a dew point temperature meter (105), an electric heat tracing device (106), a temperature transmitter (107), and a third gas flow meter (108). The liquid supply branch includes a foam liquid tank (200), which is connected to the corresponding input end pipe of the liquid-liquid mixer (400) via a foam liquid pipe. A second electric regulating valve (201) and a first liquid flow meter (202) are sequentially installed on the foam liquid pipe. The water supply branch includes a water tank (300), which is connected to the corresponding input pipe of the liquid-liquid mixer (400) via a water pipe. A third electric regulating valve (301) and a second liquid flow meter (302) are sequentially installed on the water pipe. The liquid-liquid mixer (400) is connected to the corresponding input end of the gas-liquid mixer (500) through a water-liquid mixing pipe. The water-liquid mixing pipe is equipped with a conductivity meter (601), a fourth regulating valve (602) and a third liquid flow meter (603).

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