A salt water experimental method to simulate the movement of fire smoke in the low gravity of the moon

Abstract

The present invention discloses a salt water experiment method for simulating the movement of fire smoke under low gravity on the moon. First, an analogy relationship between salt water and fire smoke under a microgravity / low gravity environment is established; then, a salt water experiment is used to simulate the smoke spread scene of a building fire under a microgravity / low gravity environment. The salt water experiment method for simulating the movement of fire smoke under low gravity on the moon can simulate the smoke spread scene of a building fire under a microgravity / low gravity environment at a low research cost. The simulated microgravity / low gravity environment has stable numerical values, a clear smoke spread simulation process, and data can be quantitatively obtained without contact. It can provide a theoretical basis and data support for studying the smoke spread characteristics of building fires under microgravity / low gravity environments.

Description

Technical Field

[0001] The invention relates to an experimental method for simulating the spread of smoke from a building fire, in particular to a salt water experimental method for simulating the movement of smoke from a fire under low gravity on the moon, belonging to the technical field of simulated fire experiments. Background Art

[0002] Scientific experimental facilities or spacecraft such as the International Lunar Research Station and the Space Station (also known as: space station, aerospace station) that can allow astronauts to work and live in a microgravity / low gravity environment are the carriers and basis for multidisciplinary and multi-objective scientific research activities such as space observation, scientific experiments and technology verification. They can promote mankind's in-depth understanding of space and provide important support for future deep space exploration and space resource development.

[0003] In a microgravity / low-gravity environment, due to the lack of gravity and air flow, air convection, heat convection, etc. will slow down, and flame combustion will present a phenomenon that is completely different from surface flame combustion. Therefore, space fires that may occur in space capsules, space stations, spacecraft or space equipment have the characteristics of rapid fire spread, difficulty in rescue and high risk. Studying the smoke spread characteristics of building fires in microgravity / low-gravity environments is of great significance for revealing the behavior characteristics of fires in microgravity / low-gravity environments and enhancing the disaster prevention and mitigation capabilities of space engineering.

[0004] At present, the fire and smoke spread in buildings under low gravity are mainly tested and analyzed by creating a microgravity / low gravity environment, such as using drop tower experiments, parabolic aircraft, and orbital vehicles. Drop tower experiments are limited by the height of the drop tower, and the microgravity / low gravity environment created is extremely short. The research cost of parabolic aircraft and orbital vehicles is very expensive, and it is not suitable for studying the whole process of flame and smoke spread in the experimental process. Therefore, how to study the smoke spread characteristics of building fires in a microgravity / low gravity environment at a low research cost is an urgent problem to be solved in the industry. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a salt water experimental method for simulating the movement of fire smoke under low gravity on the moon, which can simulate the spread of smoke from building fires in microgravity / low gravity environments at low research costs, and can provide a theoretical basis and data support for studying the spread characteristics of smoke from building fires in microgravity / low gravity environments.

[0006] To achieve the above purpose, the salt water experiment method for simulating the movement of fire smoke under low gravity on the moon specifically includes the following steps:

[0007] Step 1: Determine the gravity level corresponding to the density of the salt water in the experiment, and use the salt water with a salt concentration of 10% as the reference of the earth's constant gravity level. When unchanged, assuming the same fire source power Corresponding to the mass flow rate of saline in microgravity / low gravity same;

[0008] Step 2, determine the relationship between the fire source power and the density of the salt solution under different gravity conditions. The relationship between the fire source power and the density of the salt solution under different gravity conditions is as follows:

[0009]

[0010] Where: m is the density of salt water; ρ 0 is the density of water; ΔT is the flue gas temperature rise; T f is the maximum temperature of flue gas; g f is the gravitational acceleration in the actual fire scene; g m is the gravity acceleration of the model scene; H is the actual fire scene height; h is the model scene height; v m is the dynamic viscosity of water; v f is the dynamic viscosity of air;

[0011] Step 3, determine the time ratio between the model scene and the actual fire scene. The time ratio between the model scene and the actual fire scene is expressed as follows:

[0012]

[0013] Where: n v is the velocity ratio between the model scenario and the actual fire scenario; n L is the length ratio between the model scene and the actual fire scene; n t is the time ratio between the model scenario and the actual fire scenario; B is the buoyancy flux;

[0014] Step 4: Based on the required microgravity / low gravity environment, conduct a salt water experiment according to the calculation results of Step 2 and Step 3 to simulate the smoke spread scenario of a building fire in a microgravity / low gravity environment.

[0015] Furthermore, when the salt water experiment is performed in Step 4, the salt water experiment device includes a measuring cylinder, a peristaltic pump, a water tank, a backlight panel and a camera. The measuring cylinder is connected to the input end of the peristaltic pump through a pipeline, the output end of the peristaltic pump is connected to the input end of the silicone tube through a water inlet valve, the output end of the silicone tube is connected to the set simulated ignition point of the building model, the backlight panel is located on one side of the water tank made of transparent material, and the camera corresponding to the backlight panel is set on the other side of the water tank;

[0016] Before the experiment, the building model was immersed and positioned below the level of the clean water in the water tank, the power switch of the backlight panel was turned on to make it a single uniform light source and a calibration pre-experiment was carried out; after the experiment began, the total volume of the red salt solution in the measuring cylinder was recorded, the automatic shooting frequency of the camera was adjusted, the water inlet valve was opened, and the peristaltic pump was adjusted to steadily inject the red salt water into the building model at a set flow rate. After the required simulation time was reached, the water inlet valve and the peristaltic pump were closed, the flow rate and volume displayed on the peristaltic pump interface were recorded, and the remaining volume of the red salt solution in the measuring cylinder was observed and recorded; the photos taken by the camera were imported into the computer for grayscale processing. First, the corresponding relationship between grayscale and concentration was calculated based on the photos taken in the calibration pre-experiment, and then the grayscale of the photos taken during the formal experiment was processed and marked. According to the corresponding relationship between grayscale and concentration obtained in the experiment, the concentration of each point in the building model was obtained to simulate the spread of smoke in the building model under microgravity / low gravity environment conditions.

[0017] Compared with the existing technology, the salt water experiment method for simulating the movement of fire smoke in low gravity on the moon establishes an analogous relationship between salt water and fire smoke in microgravity / low gravity environment, and uses salt water experiment to simulate the smoke spread scene of building fire in microgravity / low gravity environment. The experimental method is simple to operate and has low experimental cost. The simulated microgravity / low gravity environment has stable numerical values, the smoke spread simulation process is clear, and the data can be obtained quantitatively and contactlessly. It can provide a theoretical basis and data support for studying the smoke spread characteristics of building fires in microgravity / low gravity environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a graph showing the relationship between the density of the salt solution and the model gravity in an embodiment of the present invention;

[0019] Figure 2 It is a structural schematic diagram of the salt water experimental device of the present invention.

[0020] In the picture: 1. Silicone tube; 2. Water inlet valve; 3. Drain valve; 4. Measuring cylinder; 5. Peristaltic pump; 6. Lunar research station model; 7. Water tank; 8. Camera; 9. Backlight panel. DETAILED DESCRIPTION

[0021] Salt water experiment is one of the important means to study the movement of fire smoke. It can simulate fires of different scales by adjusting the density and flow rate of salt water. However, the traditional salt water experiment method usually uses the movement of salt water to analogize the movement of fire smoke in the earth's gravity field. Based on the traditional salt water experiment analogy method, the present invention establishes an analogy relationship between salt water and fire smoke in a microgravity / low gravity environment to study the smoke spread characteristics of building fires in a microgravity / low gravity environment.

[0022] The present invention will be further described below in conjunction with the accompanying drawings.

[0023] The salt water experiment method for simulating the movement of fire smoke under low gravity on the moon specifically includes the following steps:

[0024] Step 1, determine the gravity level corresponding to each salt water density in the experiment. Take the salt water with a salt concentration of 10% as the reference of the earth's constant gravity level (9.8m / s 2 ), while the fire source power When unchanged, assuming the same fire source power Corresponding to the mass flow rate of saline in microgravity / low gravity same.

[0025] Step 2, determine the relationship between the fire source power and the density of the salt solution under different gravity conditions.

[0026] The initial fire in space can be considered as a low-intensity ignition source, and the chemical reaction and radiation heat transfer in the gas are ignored in the calculation process. At the same time, the hot smoke flow in the fire is a buoyancy-driven flow, while the movement of the salt water in the salt water experiment is an anti-buoyancy-driven flow. The two are similar in the control equation, so the two scenarios (the salt water experiment model scenario on Earth and the actual microgravity / low gravity environment fire scenario corresponding to the microgravity / low gravity level) can be established according to the Froude similarity criterion. The equation relationship is as follows:

[0027]

[0028] Where: V is the characteristic velocity; h and H are the model scene height and the actual fire scene height respectively; g is the gravitational acceleration; Δρ is the density difference between the salt solution and the clean water; ρ 0 is the density of water; m , f They represent the model scenario and the actual fire scenario respectively.

[0029] After rearranging the above formula, we get the characteristic velocity relationship as follows:

[0030]

[0031] The characteristic velocity is solved because the movement of salt water in water is caused by the density difference between the two. Similarly, the movement of smoke in air is also driven by the density difference between smoke and air. The dimensionless control equations of the two are similar, and a relationship can be established to finally obtain the characteristic relationship and buoyancy flux as follows:

[0032]

[0033]

[0034] Where: is the heat release rate of the fire source, in KW; is the mass flow rate of brine, in kg / s; C p is the specific heat capacity at constant pressure, in kJ / kg·K; ρ a is the air density, in kg / m 3 ; T 0 is the ambient temperature.

[0035] The corresponding relationship between the fire source power and the brine mass flow rate under constant gravity is solved. The corresponding relationship between the fire source power and the brine mass flow rate under constant gravity can be obtained by using the Reynolds similarity criterion as follows:

[0036]

[0037] Substituting Formula 3, Formula 4 and Formula 5 into Formula 2, we can get

[0038]

[0039] Further sorting can be obtained

[0040]

[0041] Finally, by substituting Formula 5 into Formula 7, we can obtain the following relationship between the fire source power and the density of the salt solution under different gravity conditions:

[0042]

[0043] Where: m is the density of salt water; ρ 0 is the density of water; ΔT is the flue gas temperature rise; T f is the maximum temperature rise of flue gas; g f is the gravitational acceleration in the actual fire scene; g m is the gravity acceleration of the model scene; H is the actual fire scene height; h is the model scene height; v m is the dynamic viscosity of water; v f is the dynamic viscosity of air.

[0044] For example, when the smoke temperature is 623K, the ambient temperature is 293K, and the ratio of the actual fire scene to the model scene is 50:1, 40:1, and 30:1, respectively, the relationship between the required salt solution density and the model gravity is as follows: Figure 1 shown.

[0045] Step 3, determine the time ratio between the model scene and the actual fire scene.

[0046] Similarity between time and flue gas temperature rise

[0047]

[0048] The flue gas temperature rise ΔT can be expressed as follows:

[0049]

[0050] At the same time, according to the definition of Froude number Fr It can be concluded that

[0051]

[0052] Also know but

[0053]

[0054] Where: n v is the velocity ratio between the model scenario and the actual fire scenario; n L is the length ratio between the model scene and the actual fire scene; n t is the time ratio between the model scene and the actual fire scene; B is the buoyancy flux.

[0055] Step 4, conduct salt water experiment.

[0056] like Figure 2 As shown, the salt water experiment device includes a measuring cylinder 4, a peristaltic pump 5, a water tank 7, a backlight panel 9 and a camera 8. The measuring cylinder 4 is connected to the input end of the peristaltic pump 5 through a pipeline, the output end of the peristaltic pump 5 is connected to the input end of the silicone tube 1 through the water inlet valve 2, the output end of the silicone tube 1 is connected to the set simulated ignition point of the building model, the backlight panel 9 is located on one side of the water tank 7 made of transparent material, and the camera 8 corresponding to the backlight panel 9 is arranged on the other side of the water tank 7.

[0057] When simulating the fire at the lunar research station, after installing and connecting the experimental equipment such as the measuring cylinder 4, peristaltic pump 5, water tank 7, backlight board 9, and camera 8, the lunar research station model 6 is immersed and positioned below the clean water level of the water tank 7; before the experiment begins, all lights in the laboratory are turned off to ensure that there is no environmental or other lighting influence in the laboratory, and then the power switch of the backlight board 9 is turned on to make it a single uniform light source and perform a calibration pre-experiment; at the beginning of the formal experiment, the total volume of the red salt solution in the measuring cylinder 4 is recorded, and the automatic shooting frequency of the camera 8 is adjusted to 0. The frequency of shooting is 25 seconds / frame, the water inlet valve 2 is opened, and the peristaltic pump 5 is adjusted to stably inject the red salt water into the lunar research station model 6 at the set flow rate. After reaching the required simulation time (after similarity conversion), the water inlet valve 2 and the peristaltic pump 5 are closed, and the flow rate and volume displayed on the interface of the peristaltic pump 5 are recorded, and the remaining volume of the red salt solution in the measuring cylinder 4 is observed and recorded. At this time, one experiment is completed, and the drain valve 3 is opened to discharge all the mixed solutions in the water cylinder 7, and the inside is cleaned to avoid causing errors in the next experiment. If the experiment needs to be repeated, the above steps can be repeated to conduct the experiment. The photos taken by the camera 8 are imported into the computer matlab software for grayscale processing. First, the corresponding relationship between grayscale and concentration is calculated based on the photos taken by the calibration pre-experiment, and then the grayscale of the photos taken during the formal experiment is processed and marked. According to the corresponding relationship between grayscale and concentration obtained in the pre-experiment, the concentration of each point in the lunar research station model 6 is obtained, so as to simulate the spread of smoke in the lunar research station under microgravity / low gravity environment conditions.

Claims

1. A salt water experiment method for simulating the movement of fire smoke under low gravity on the moon, characterized in that: The specific steps include: Step 1: Determine the gravity level corresponding to the density of the salt water in the experiment, and use the salt water with a salt concentration of 10% as the reference of the earth's constant gravity level. When unchanged, assuming the same fire source power Corresponding to the mass flow rate of saline in microgravity / low gravity same; Step 2, determine the relationship between the fire source power and the density of the salt solution under different gravity conditions. The relationship between the fire source power and the density of the salt solution under different gravity conditions is as follows: Where: m is the density of salt water; ρ0 is the density of water; ΔT is the flue gas temperature rise; T f is the maximum temperature of flue gas; g f is the gravity acceleration in the actual fire scene; g m is the gravity acceleration of the model scene; H is the actual fire scene height; h is the model scene height; v m is the dynamic viscosity of water; v f is the dynamic viscosity of air; Step 3, determine the time ratio between the model scene and the actual fire scene. The time ratio between the model scene and the actual fire scene is expressed as follows: Where: n v is the velocity ratio between the model scenario and the actual fire scenario; n L is the length ratio between the model scene and the actual fire scene; n t is the time ratio between the model scenario and the actual fire scenario; B is the buoyancy flux; Step 4: Based on the required microgravity / low gravity environment, conduct a salt water experiment according to the calculation results of Step 2 and Step 3 to simulate the smoke spread scenario of a building fire in a microgravity / low gravity environment.

2. The salt water experiment method for simulating the movement of fire smoke under low gravity on the moon according to claim 1, characterized in that: When the salt water experiment is carried out in Step 4, the salt water experiment device includes a measuring cylinder (4), a peristaltic pump (5), a water tank (7), a backlight panel (9) and a camera (8); the measuring cylinder (4) is connected to the input end of the peristaltic pump (5) through a pipeline; the output end of the peristaltic pump (5) is connected to the input end of the silicone tube (1) through a water inlet valve (2); the output end of the silicone tube (1) is connected to the set simulated ignition point of the building model; the backlight panel (9) is located on one side of the water tank (7) made of transparent material; and the camera (8) corresponding to the backlight panel (9) is arranged on the other side of the water tank (7); Before the experiment begins, the building model is immersed and positioned below the level of the clean water in the water tank (7), the power switch of the backlight panel (9) is turned on to make it a single uniform light source and a calibration pre-experiment is carried out; after the experiment begins, the total volume of the red salt solution in the measuring cylinder (4) is recorded, the automatic shooting frequency of the camera (8) is adjusted, the water inlet valve (2) is opened, and the peristaltic pump (5) is adjusted to steadily inject the red salt water into the building model at a set flow rate. After the required simulation time is reached, the water inlet valve (2) and the peristaltic pump (5) are closed. The flow rate and volume displayed on the interface of the peristaltic pump (5) are recorded, and the remaining volume of the red salt solution in the measuring cylinder (4) is observed and recorded; the photos taken by the camera (8) are imported into the computer for grayscale processing, and the corresponding relationship between grayscale and concentration is first calculated based on the photos taken in the calibration pre-experiment, and then the grayscale of the photos taken during the formal experiment is processed and marked, and the concentration of each point in the building model is obtained based on the corresponding relationship between grayscale and concentration obtained in the experiment, so as to simulate the spread of smoke in the building model under microgravity / low gravity environment conditions.

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