A mass transfer visualization measurement device and method for simulating seawater intrusion into groundwater

Abstract

The present invention discloses a mass transfer visualization measurement device and method for simulating seawater intrusion into groundwater. The device includes a plexiglass water tank, a fresh water and seawater delivery system, a tide generation system, a base flow generation system, and a visualization observation system. The plexiglass water tank is made of transparent acrylic material; the fresh water and seawater delivery system is used to deliver fresh water and salt water into the water tank; the tide generation system generates a specified waveform and inputs it into the water tank to simulate the tidal action of seawater; the base flow simulation system is used to simulate the base flow action of groundwater; the visualization observation system can visualize the refractive index change caused by the density difference between fresh water and salt water. The present invention can visualize the mass transfer process between seawater and fresh water, and accurately reproduce the mass transfer process between groundwater and seawater under tidal action on near-island reefs through experiments. In addition, the experimental device and method of the present invention can also be used to study the mass transfer laws under different water heads, tidal waveforms, and sandy soil media.

Description

Technical Field

[0001] The present invention relates to a mass transfer process visualization device, and particularly to a mass transfer visualization measurement device and method for simulating seawater intrusion into groundwater. Background Art

[0002] Due to the widespread use of plastics worldwide, plastics inevitably enter the marine environment. The stability of plastic materials causes plastic particles to accumulate in the ocean for a long time and degrade into tiny sizes through biological and abiotic processes. These plastic particles may enter groundwater through tidal action and seawater-freshwater mass transfer, posing a potential threat to human health.

[0003] Understanding the migration of plastic particles at the interface between groundwater and seawater in coastal areas can provide technical support for groundwater protection and filtration. Studying the influence of mass transfer processes on the migration of plastic particles and understanding the real-time changes in the content of plastic particles in groundwater under tidal action are crucial for protecting the safety of groundwater resources.

[0004] Currently, there are also methods for studying seawater intrusion into groundwater. Among them, the main research method for intrusion is the high-density resistivity observation method. However, this method has the following deficiencies:

[0005] ①. Since the seawater migration process is quite complex and cannot be clearly described by only analyzing the solutes in water at the beginning and end stages, the current methods for seawater intrusion into groundwater lack visual process research and experimental methods for observing the process between seawater and freshwater.

[0006] ②. Studying seawater intrusion by the high-density resistivity method is based on the principle that the resistivity changes due to the density difference. However, the resistivity change caused by plastic particles in seawater is almost negligible. Therefore, this method cannot study the migration of plastic particles during seawater intrusion.

[0007] Therefore, there is an urgent need to study a device for visualizing the mass transfer process of groundwater intrusion into seawater to accurately describe the influence law of seawater-freshwater mass transfer on the migration of plastic particles under seawater intrusion conditions. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a mass transfer visualization measurement device and method for simulating seawater intrusion into groundwater in view of the above-mentioned deficiencies of the prior art.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A mass transfer visualization measurement device for simulating seawater intrusion into groundwater includes an organic glass water tank, a fresh water delivery system, and a seawater delivery system;

[0011] On one side of the plexiglass water tank, there is a water baffle, two water passing baffles, and a water baffle in sequence from one side to the other side, successively forming a seawater inlet area, a seawater area, a gravel area, a fresh water area, and a fresh water inlet area. The water baffle is lower than the water passing baffle. The gravel area is filled with gravel, and gravel is laid at the bottom of the seawater area and the bottom of the fresh water area respectively. Setting the seawater inlet area and the fresh water inlet area can keep the flow velocity of the water entering the seawater area and the fresh water area stable;

[0012] The fresh water delivery system includes a fresh water tank and a fresh water pipe. The fresh water tank is connected to the fresh water inlet area through the fresh water pipe, and a second water storage tank, a second water valve, and a second water pump are provided on the fresh water pipe;

[0013] The seawater delivery system includes a first seawater tank and a seawater pipe. The first seawater tank is connected to the seawater inlet area through the seawater pipe, and a first water pump, a first water storage tank, and a first water valve are provided on the seawater pipe. A plastic particle box is also provided on the first water storage tank.

[0014] As a further preferred solution, the device further includes a base flow generation system, including a base flow hole, a third rotor flowmeter, and a third water valve. The base flow hole is opened at the bottom of the gravel area of the plexiglass water tank. There is a base flow pipe on the base flow hole, and the third rotor flowmeter and the third water valve are installed on the base flow pipe.

[0015] As a further preferred solution, the device further includes a tide generation system, including a second seawater tank and a wave maker. The wave maker pumps out the seawater in the second seawater tank and outputs the seawater in a specified waveform. The wave maker penetrates the seawater inlet area, and the perforation is sealed.

[0016] As a further preferred solution, a second rotor speedometer and a second lifting nut are also provided on the fresh water pipe.

[0017] As a further preferred solution, a first rotor speedometer and a first lifting nut are also provided on the seawater pipe.

[0018] As a further preferred solution, the plexiglass water tank is made of transparent acrylic material.

[0019] As a further preferred solution, the device further includes a visualization observation system, which includes a first high-precision concave mirror, a second high-precision concave mirror, a blade, a high-speed camera, an observation area of an acrylic water tank, and a point light source. The acrylic water tank is placed in the observation area of the acrylic water tank. The first high-precision concave mirror and the second high-precision concave mirror are respectively arranged on both sides of the observation area of the acrylic water tank. The first high-precision concave mirror and the second high-precision concave mirror are arranged obliquely relative to the acrylic water tank. The first high-precision concave mirror and the second high-precision concave mirror are parallel to each other. The point light source emits light towards the first high-precision concave mirror, and the high-speed camera obtains images towards the second high-precision concave mirror. The blade is used to block part of the focus.

[0020] A measurement method for a mass transfer visualization measurement device for simulating seawater intrusion into groundwater includes the following steps:

[0021] (1) Disconnect the diversion pipe between the fresh water and seawater supply systems and the transparent acrylic water tank. After pasting filter paper on both sides of the partition, add sand samples into the water tank. The space between the two partitions of the water tank is filled with sand samples. The sand samples added on both sides of the water tank are lower than the liquid level to simulate the seawater and fresh water interface environment.

[0022] (2) Open the fresh water supply system, adjust the nut to control the water head position, start the water pump to pump fresh water, and open the valve to control the water level to meet the test requirements.

[0023] (3) Open the seawater supply system, adjust the nut to control the water head position, start the water pump to pump fresh water, and open the valve to control the water level to meet the test requirements.

[0024] (4) Add plastic particles dyed with fluorescent agent into the brine tank, and use PIV and PTV technologies to measure the velocity and track the plastic particles.

[0025] (5) Open the visualization observation system, adjust the brightness of the point light source, the light-blocking area of the blade, and the parameters of the high-speed camera to simulate the migration law of plastic particles during the mass transfer process of seawater and fresh water under a non-tidal environment.

[0026] The principle of the visualization observation system is: In a homogeneous medium, the propagation of light is uniform. For example, in a clean space, the propagation of starlight is unperturbed. If the Earth's atmosphere were as uniform as a clean space, starlight would propagate like perfectly parallel rays. The starlight would converge at an almost perfect diffraction point without twinkling.

[0027] However, the atmosphere is not uniform. Due to reasons such as turbulence, thermal convection, and weather phenomena, the atmosphere is disturbed, making it non-uniform. Moreover, these disturbances can slightly change the atmospheric density and refractive index, causing the starlight rays to bend, resulting in the twinkling of starlight in our field of view.

[0028] Using the same principle, when there is a density difference in the solution through which the light of a point source passes, the propagation path of the light will be changed due to the different refractive indices, thus enabling the observation of the mass transfer process of solutions with different densities.

[0029] The formula derivation regarding the refractive index and the principle of light bending is as follows:

[0030] It is considered that at the initial moment, the plane wave passing through z1 has a wavefront perpendicular to the horizontal optical axis z-axis. When the wavefront passes through the object under test, that is, from z1 to z2, different differential times Δt correspond to differential distances Δz, and the deflection angle of refraction is Δε. Since the light is always perpendicular to the wavefront, the horizontal light passing through z1 is also refracted by Δε.

[0031] Define n0 = c0 / cn0: refractive index of the medium; c0: speed of light in vacuum; c: local speed of light.

[0032]

[0033] At different times Δt, there is

[0034]

[0035] Combining them gives

[0036]

[0037] When Δy approaches zero infinitely, the in the equation can be simplified to Letting all micro-elements approach zero, we can obtain

[0038]

[0039] Substituting it into the derivative, we can get

[0040]

[0041] In the x-axis direction, integrating gives

[0042]

[0043] It can thus be proved that the deflection angle ε x is proportional to the optical path length L and to the refractive index gradient It is directly proportional. Therefore, due to the density difference between seawater and fresh water, there is a refractive index gradient in the visualization system. By selecting the focal length of the concave mirror in the visualization system to change the optical path length L, the deflection angle size suitable for visual observation can be obtained, and thus the mass transfer process of seawater and fresh water can be observed. The plastic particles stained with fluorescent agent will emit light under the illumination of the light source and are easily captured by the camera. Therefore, the migration law of plastic particles during the mass transfer process of seawater and fresh water can be obtained by taking photos with a high-speed camera.

[0044] (6) Connect the wave maker and the water tank, and turn on the wave maker switch to simulate different seawater intrusion environments.

[0045] (7) Use the visualization observation system to observe the migration law of plastic particles during the mass transfer process of seawater and fresh water under tidal action.

[0046] (8) After the test, turn off all devices and clean the sand samples in the plexiglass water tank.

[0047] We use the visualization observation system to observe the mass transfer phenomenon during the seawater intrusion process. Then, fluorescently stained plastic particles are added to the seawater tank. These particles have good randomness and can emit light when illuminated by a point light source. The migration of fluorescent plastic particles can be captured by a high-speed camera while capturing the solute migration process. Then, the collected migration of fluorescent particles and solute migration are analyzed. Finally, the flow velocity and flow field state during the seawater intrusion process are obtained, and at the same time, the mutual relationship between the solute migration law and the plastic particle migration law is obtained. Description of the Drawings

[0048] Figure 1 It is a schematic diagram of the seawater intrusion into the groundwater system of the present invention;

[0049] Figure 2 It is a schematic diagram of the visualization observation system;

[0050] Figure 3 It is a schematic diagram of the structure of the water passing partition;

[0051] Figure 4 It is a schematic diagram of solute migration;

[0052] Figure 5 It is a schematic diagram of the flow field and flow velocity distribution. Detailed Embodiment

[0053] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0054] As Figure 1As shown in the figure, a mass transfer visualization measurement device for simulating seawater intrusion into groundwater in the present invention can accurately reflect the process change of seawater intrusion into groundwater by using the different refractive indices of light when the optical path passes through seawater and fresh water. In addition, this experimental device and method can also be used to study the effects of different water head heights, different sand samples, different tidal action waveforms, different plastic particles, different seawater concentrations, and base flow on seawater intrusion, and realize visual observation of the solute and plastic particle migration during the seawater intrusion process;

[0055] This device includes a plexiglass water tank, a fresh water and seawater delivery system, a tide generation system, a base flow generation system, and a visualization observation system.

[0056] The fresh water and seawater delivery system is used to convey water into the plexiglass water tank, add fluorescent particles to the seawater, and a water head control nut is added to the fresh water and seawater delivery system.

[0057] The tide generation system is connected to the seawater tank, generates waves for the seawater by inputting a specified waveform, and inputs the generated waves into the plexiglass water tank.

[0058] The base flow simulation system is located at the bottom of the plexiglass water tank. A rotor flowmeter is installed in the base flow simulation system to measure the velocity of the base flow, which is used to simulate the base flow effect in groundwater.

[0059] The visualization observation system includes a point light source, a high-precision concave mirror, a high-speed camera, and a blade, obtains the refractive index change caused by the density difference between fresh water and salt water, visualizes the mass transfer process, and the visualization observation system is arranged in front of and behind the plexiglass water tank.

[0060] In the seawater supply component, a sodium chloride solution with a certain concentration is configured to simulate seawater. In the seawater tank 1 of the seawater supply system, water is pumped into the first water storage tank 4 by the first water pump 2, and the water head height of the water storage tank 4 is controlled by using the lifting nut 6. It is connected to the plexiglass water tank through the first water stop valve 5 and the first rotor flowmeter 6. The salt water in the first seawater tank 1 is conveyed to the first water storage tank 4 by the first water pump 2, and the outflow of the water flow is controlled by the first water valve 5. The first lifting nut 7 is installed outside the water pipe connected to the plexiglass water tank, and the height of the water storage tank is controlled by rotating the nut.

[0061] An external plastic particle box 3 is installed at the upper end of the first water storage tank 4 to simulate plastic particle pollutants in seawater. The size of the plexiglass water tank device is 0.6m×0.2m×0.4m. The left end of the water tank forms a seawater area through the water retaining partition 10.

[0062] The second seawater tank 9 is located on the ground, pumps water and generates waves through the wave generator 8 and enters the plexiglass water tank to simulate the tidal action of seawater. The wave generator can change parameters to adjust the waveform and frequency.

[0063] The fresh water tank 20 of the fresh water supply system is located on the ground. The second water pump 19 pumps water into the second storage tank 14. The lifting nut 17 is used to control the water head height of the second storage tank 14, and it is connected to the plexiglass water tank through the second water stop valve 15 and the second rotor flowmeter 16.

[0064] Two perforated partitions 11 are installed in the middle of the plexiglass water tank. Two layers of filters are installed on the partitions. The aperture of the filter is less than 0.1 mm, which can prevent sand particles from leaking out while not affecting the water seepage performance. The sand layer simulates the sandy soil transition zone in the contact area between fresh water and sea water.

[0065] The plexiglass water tank includes a water passing partition 11 and a water retaining partition 10. The water passing partition 11 prevents sand particles from overflowing, and the water retaining partition 10 is used to control the water level line inside the plexiglass.

[0066] The base flow simulation component is located at the bottom of the water tank. A filter is installed at the entrance of the base flow hole, which is connected to the third rotor flowmeter 12 and the third water stop valve 13 in sequence, and the base flow is simulated through bottom drainage.

[0067] The plexiglass water tank is made of high-transparency acrylic board. The material has a low refractive index and high transparency. Through an Abbe refractometer, the refractive index of the plexiglass water tank made of acrylic material is measured to be 1.45.

[0068] As Figure 2 shown, a visualization component includes a point light source, a high-precision concave mirror, a blade and a high-speed camera.

[0069] The point light source is an LED coaxial point light source, with a lamp diameter of 6 mm, a power of 5 W, and a luminous color of white light.

[0070] The high-precision concave mirror has a diameter of 203 mm and a focal length of 750 mm.

[0071] The light path of the point light source 21 is converted into a parallel light path by the first high-precision concave mirror 22 and passes through the observation area 26 of the plexiglass water tank. The parallel light path is focused after passing through the second high-precision concave mirror 23. The blade 24 is used to block part of the focus, and it is imaged by the high-speed camera 25.

[0072] Turn on the point light source. The point light source enters the first concave mirror according to the pre-designed light path. After being reflected by the concave mirror into parallel light, it passes through the plexiglass container. Passing through media with different densities will cause different refractive indexes of light. The light path after passing through the plexiglass water tank reaches the second concave mirror and is focused. A blade is set at the focus where the second concave mirror is focused to block half of the light path to further increase the contrast, and the other half of the unobstructed light path enters the high-speed camera.

[0073] A mass transfer visualization method for seawater intrusion into groundwater includes the following steps:

[0074] (1) Disconnect the diversion pipe between the plexiglass water tank and the seawater and fresh water delivery components, and attach the filter paper to the perforated partition to prevent the sand particles from flowing out;

[0075] (2) Pour the sand particles required for the test into the plexiglass water tank in layers, and vibrate them layer by layer to reach the required compactness for the test;

[0076] (3) Connect the diversion pipe between the seawater and fresh water delivery components and the plexiglass, use a water pump to extract fresh water, open the valve, measure the flow rate through the rotor flowmeter, and control the flow rate through the valve until the water level reaches the test requirements;

[0077] (4) Open the water pump of the seawater delivery component, extract the brine in the first seawater tank and inject it into the water isolation area on the left side of the water tank until it reaches the specified water level height for the test;

[0078] (5) Open the plastic particle box of the seawater delivery component to mix the plastic particles with the seawater in the water isolation area;

[0079] (6) Turn on the point light source of the visualization component, start the camera and adjust the camera parameters, adjust the placement positions of the two concave mirrors so that the image is clearly displayed, and then set a blade at the intersection to increase the image contrast;

[0080] (7) Turn on the wave maker, set the parameters of the wave maker, adjust the waveform and frequency, connect the wave maker to the second seawater tank, pump water from the second seawater tank, and input the specified waveform into the plexiglass water tank;

[0081] (8) Use a high-speed camera to record the mass transfer process between seawater and fresh water under tidal action;

[0082] (9) Take samples from the left and right sides of the plexiglass water tank at different times, and record the concentration and plastic particle content;

[0083] (10) Study the influence of the base flow on seawater-fresh water mass transfer and plastic particle migration: In step 5, open the valve of the base flow component and control the flow rate of the base flow, and repeat steps 1-11;

[0084] (11) After the test, clean the plexiglass water tank;

[0085] Capture and analyze the solute migration and plastic particle movement trajectories during the test by using particle image velocimetry (PIV) and particle tracking velocimetry (PTV).

[0086] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the protection scope of the present invention.

Claims

1. A mass transfer visualization measurement device for simulating seawater intrusion into groundwater, characterized in that: It includes a plexiglass water tank, a fresh water delivery system, and a seawater delivery system; On one side of the plexiglass water tank, a water baffle (10), two water passing baffles (11), and a water baffle (10) are successively arranged from one side to the other, successively forming a seawater inlet area, a seawater area, a gravel area, a fresh water area, and a fresh water inlet area. The water baffle (10) is lower than the water passing baffle (11). The gravel area is filled with gravel, and gravel is laid at the bottom of the seawater area and the bottom of the fresh water area respectively; The fresh water delivery system includes a fresh water tank (20) and a fresh water pipe. The fresh water tank (20) is connected to the fresh water inlet area through the fresh water pipe. A second water storage tank (14), a second water valve (15), and a second water pump (19) are arranged on the fresh water pipe; The seawater delivery system includes a first seawater tank (1) and a seawater pipe. The first seawater tank (1) is connected to the seawater inlet area through the seawater pipe. A first water pump (2), a first water storage tank (4), and a first water valve (5) are arranged on the seawater pipe. A plastic particle box (3) is also arranged on the first water storage tank (4); The plexiglass water tank is made of transparent acrylic material; The device further includes a visual observation system, which includes a first high-precision concave mirror (22), a second high-precision concave mirror (23), a blade (24), a high-speed camera (25), an observation area of the plexiglass water tank (26), and a point light source (21). The plexiglass water tank is placed in the observation area of the plexiglass water tank (26). The first high-precision concave mirror (22) and the second high-precision concave mirror (23) are respectively arranged on both sides of the observation area of the plexiglass water tank (26). The first high-precision concave mirror (22) and the second high-precision concave mirror (23) are arranged obliquely relative to the plexiglass water tank. The first high-precision concave mirror (22) and the second high-precision concave mirror (23) are parallel to each other. The point light source (21) emits light towards the first high-precision concave mirror (22), and the high-speed camera (25) obtains images towards the second high-precision concave mirror (23). The blade (24) is used to block part of the focus; Due to the density difference between seawater and fresh water, there is a refractive index gradient in the visualization system. By selecting the focal length of the concave mirror in the visualization system to change the optical path length L, the deflection angle size suitable for visual observation is obtained, that is, the mass transfer process of seawater and fresh water is observed; the fluorescent dye-stained plastic particles will emit light under the illumination of the light source and are easily captured by the camera; the movement law of plastic particles in the mass transfer process of seawater and fresh water is obtained by taking pictures with a high-speed camera.

2. The mass transfer visualization measurement device for simulating seawater intrusion into groundwater according to claim 1, wherein: It further includes a base flow generation system, which includes base flow holes, a third rotor flowmeter (12), and a third water valve (13). The base flow holes are opened at the bottom of the gravel area of the plexiglass water tank. A base flow pipeline is provided on the base flow holes. The third rotor flowmeter (12) and the third water valve (13) are installed on the base flow pipeline.

3. The mass transfer visualization measurement device for simulating seawater intrusion into groundwater according to claim 1, characterized in that: It further includes a tide generation system, which includes a second seawater tank (9) and a wave maker (8). The wave maker (8) pumps out the seawater in the second seawater tank (9) and outputs the seawater in a specified waveform.

4. A mass transfer visualization measurement device for simulating seawater intrusion into groundwater according to claim 1, characterized in that: A second rotor speedometer (16) and a second lifting nut (17) are also arranged on the fresh water pipe.

5. A mass transfer visualization measurement device for simulating seawater intrusion into groundwater according to claim 1, characterized in that: A first rotor speedometer (6) and a first lifting nut (7) are also provided on the seawater water pipe.

6. The measurement method of a mass transfer visualization measurement device for simulating seawater intrusion into groundwater according to any one of claims 1-5, characterized in that: It includes the following steps: (1) Disconnect the diversion pipe between the fresh water and seawater supply systems and the transparent plexiglass water tank. After pasting filter paper on both sides of the partition board, add sand samples into the water tank. The space between the two partition boards of the water tank is filled with sand samples, and the sand samples added on both sides of the water tank are lower than the liquid level to simulate the seawater and fresh water interface environment; (2) Open the fresh water supply system, adjust the nut to control the water head position, start the water pump to pump fresh water, open the valve, and control the water level to meet the test requirements; (3) Open the seawater supply system, adjust the nut to control the water head position, start the water pump to pump fresh water, open the valve, and control the water level to meet the test requirements; (4) Add plastic particles dyed with fluorescent agent into the brine tank, and use PIV and PTV technologies to measure the speed and track the plastic particles; (5) Open the visualization observation system, adjust the brightness of the point light source, the light blocking area of the blade, and the parameters of the high-speed camera to simulate the migration law of plastic particles during the mass transfer process of seawater and fresh water in a non-tidal environment; (6) Connect the wave maker and the water tank, turn on the wave maker switch, and simulate different seawater intrusion environments; (7) Use the visualization observation system to observe the migration law of plastic particles during the mass transfer process of seawater and fresh water under the action of tides; (8) After the test is completed, turn off all devices and clean the sand samples in the plexiglass water tank.

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