Particle sedimentation dynamic test method under thermal stratification effect

Abstract

The invention discloses a particle sedimentation dynamic test method under a thermal stratification effect. The method comprises the following steps: collecting a thermal stratification water sample of a field deep water reservoir; separating particulate matters in the water sample, and analyzing to obtain particle sizes and morphological characteristics of the particulate matters; building a particle sedimentation behavior test device; preparing a particle sample for a particle sedimentation dynamic test; putting the prepared particle sample into a particle sedimentation behavior test device to carry out a particle sedimentation test under the thermal stratification effect of the reservoir; a camera device is adopted to record particle sedimentation dynamic behaviors. Aiming at the water quality problem caused by delayed sedimentation of thermocline particles of the deep and large reservoir, a thermocline interface of the deep and large reservoir is used as a key research area, and the vertical differentiation characteristics of the particles under the thermal stratification effect of the deep and large reservoir are disclosed through an in-situ high-frequency monitoring technology; a high-precision indoor control test is combined to detect and analyze sedimentation behaviors of particles with different sizes, shapes and porosities in a thermal stratification water body, and a sedimentation dynamic mechanism of thermal stratification on particle aggregation is disclosed.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal stratification particle movement in deepwater reservoirs, and in particular relates to a particle sedimentation dynamics test method under thermal stratification. Background Art

[0002] Nearly 90% of the world's surface fresh water is stored in lakes and reservoirs. Lake-reservoir water sources account for 40.6% of my country's centralized drinking water sources, serving 47.2% of the population, and are an important cornerstone for ensuring drinking water safety. Under the thermal stratification of deep-water reservoirs, organic particles such as algae debris gather in large quantities in the thermocline, and organic matter decomposes rapidly, accompanied by phenomena such as thermocline hypoxia, fish deaths, and large-scale release of greenhouse gases, causing serious deterioration of the water quality of the upper water bodies of the reservoirs, threatening the water supply safety and water ecological safety of the reservoirs.

[0003] The deceleration behavior of organic particles settling at the thermocline interface plays a vital role in the vertical transport of nutrients in the reservoir. However, most of the current research on deep and large reservoirs focuses on biochemical processes such as thermal stratification of reservoirs and decomposition of dead algae debris in the thermocline leading to hypoxia. There is little research on physical mechanisms such as the settling movement that controls the vertical heterogeneity of organic particles. Related research mainly focuses on the density stratification interface caused by vertical salinity changes in the ocean. Related studies on marine salinity stratified waters have shown that vertical density stratification of water bodies has a significant deceleration effect on particle settling, causing 70% to 90% of organic particles to mineralize and decompose in waters with density stratification or above. However, there are large differences in the diffusion coefficients of water body heat and salinity, and there are differences in the effects of thermal stratification and salinity stratification on particle settling behavior. At present, there is little research on the particle settling behavior under the action of thermal stratification in deepwater reservoirs, and there is insufficient understanding of the potential impact of thermal stratification on particle settling behavior.

[0004] Particles are widely present in natural water bodies, mainly including debris, fecal particles, plankton, minerals and microplastics, among which organic particles are considered to be important carriers of nutrients in water bodies, and the sedimentation of organic particles plays a vital role in the transport of nutrients in lakes, reservoirs, oceans and other water bodies. The definition of organic particles in water bodies belongs to the category of chemical particle size classification. Organic matter filtered through a 0.5μm membrane is usually considered to be organic particles, and those below 0.5μm are considered to be dissolved organic matter. Previous studies on particulate matter in water bodies have found that they vary in size, from micron particles to aggregates visible to the naked eye, with irregular geometric shapes, mostly disc-shaped, floc-shaped and other structures. For example, diatoms and fecal particles are disc-shaped, while flocculent particles widely present in water bodies are irregular in shape and usually have a porosity of more than 95%.

[0005] At present, the research on the vertical distribution characteristics of particles under the effect of water density stratification is mainly concentrated in the marine estuary area, and there are few research results on the freshwater bodies of inland lakes. The phenomenon of particle aggregation under the effect of marine salinity stratification is called "marine snow". This phenomenon is widespread and has also been the focus of research on marine material circulation in recent years. Studies have shown that "marine snow" is mostly aggregates of organic particles distributed in marine salinity stratified waters, and the density stratification of water bodies is the main reason for the aggregation of these particles. The large-scale aggregation of organic particles such as detrital materials in density stratified waters and the rapid decomposition of organic matter have greatly reduced their sinking flux and accelerated the circulation of nutrients in the upper water body, causing the water quality of this layer of water to deteriorate. These organic particles are usually associated with major elements such as organic carbon, nitrogen, phosphorus, and sulfur in the water body, as well as metal elements such as iron and manganese. The sedimentation of particles is accompanied by the transport flux of these elements. Therefore, understanding the mechanism of the influence of water density stratification on particle sedimentation behavior is the basis for understanding the biogeochemical cycle of water bodies.

[0006] In general, the research on the aggregation of organic particles in the thermocline of deepwater reservoirs is mostly the description of phenomena and the analysis of biochemical processes, and there is little research on the physical mechanisms such as the vertical movement of organic particles under thermal stratification. Summary of the invention

[0007] The purpose of the present invention is to provide a particle sedimentation dynamics test method under thermal stratification to address the above-mentioned deficiencies in the prior art, so as to solve the problem that there are few studies on the physical mechanisms such as vertical movement of organic particles under thermal stratification in deep-water reservoirs.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for testing particle settling kinetics under thermal stratification, comprising the following steps:

[0010] S1. Collect thermally stratified water samples from deep water reservoirs in the field;

[0011] S2. Separate the particles in the water sample and analyze and obtain the particle size and morphology characteristics of the particles;

[0012] S3. Build a particle settling behavior test device;

[0013] S4, preparing particle samples for particle settling kinetics test according to the particle size and morphology characteristics of the particles in S2;

[0014] S5, placing the prepared particle sample into a particle settling behavior test device to conduct a particle settling test under the action of reservoir thermal stratification;

[0015] S6. Use a camera to record the particle settling dynamics behavior.

[0016] Furthermore, S1 includes the following sub-steps:

[0017] S11. Use a portable water quality monitor to conduct vertical water quality monitoring at monitoring points in a deepwater reservoir in the field to obtain reservoir thermal stratification information;

[0018] S12. Carry out vertical sampling according to the thermal stratification information of the reservoir. Collect a water sample every 3m in the mixed layer on the reservoir surface, a water sample every 2m in the thermocline, and a water sample every 5m in the stagnation layer.

[0019] Furthermore, S2 includes the following sub-steps:

[0020] S21, passing the water sample obtained in S1 through filter membranes with different pore sizes in sequence to obtain particles with different particle size ranges;

[0021] S22, particle size and shape physical parameters measured using a high-speed camera.

[0022] Furthermore, S3 includes the following sub-steps:

[0023] S31, build a rectangular structure box with a height of 2.0m and a length and width of 0.09m;

[0024] S32. Install temperature control plates with small holes on the horizontal planes 0.020m and 1.180m from the bottom of the box, and pour the lower temperature constant temperature water solution under the constant temperature plate until the water level reaches the height of the constant temperature plate;

[0025] S33. The low-temperature constant-temperature aqueous solution is slowly injected into the test device using a diffuser made of sponge. When the water tank is filled with the required volume of low-temperature constant-temperature water, the high-temperature constant-temperature aqueous solution is injected again until the height of the water column reaches 0.80m; that is, two layers of water columns are formed in the rectangular structure box, the lower layer is the low-temperature water layer, and the upper layer is the high-temperature water layer. The initial density interface is located at 0.80m from the bottom, and the vertical coordinate is set so that the coordinate zero point corresponds to the position of the stratification interface of the theoretical low-temperature water layer and the high-temperature water layer;

[0026] S34. Temperature sensors are arranged at monitoring holes spaced 0.020 m apart in the vertical direction of the rectangular structural box.

[0027] Furthermore, S4 includes the following sub-steps:

[0028] S41, preparation of disc particles; preparing ABS acetone solution, dropping droplets of the ABS acetone solution onto a polished glass plate, and forming a thin sheet after evaporation of the acetone, and selecting two groups of disc particles with different diameter-to-thickness ratios according to the morphological characteristics of the particles in S2, namely, thin discs and thick discs;

[0029] S42, preparation of porous particles; porous particle samples were prepared using agarose spheres, the agarose spheres were prepared by gelling an agarose solution in deionized water, the agarose dry density was 1.640 g / mL, and during the gelation of the agarose solution, the agarose formed a fibrous microstructure with a porosity of about 95%;

[0030] S43, using an inverted fluorescence microscope to observe and measure the particle size, and selecting particles with a particle size and thickness similar to those of the particles in S2 as particle samples;

[0031] S44, estimate the density of the particle sample by measuring the sedimentation velocity of the particle sample in distilled water at a constant temperature of 20°C;

[0032] S45. Calculate the porosity of the particle sample.

[0033] Furthermore, the particle sample density is estimated in S44, including:

[0034] A single particle sample is transferred to the particle sedimentation behavior test device through a pipette with a cut-off tip. The sedimentation velocity of the particle sample is calculated from the recorded vertical displacement. The average sedimentation velocity is calculated over at least 3 consecutive seconds to obtain the sedimentation velocity after the particle sedimentation is uniform. The particle density is estimated based on the obtained average sedimentation velocity. The relationship between the average sedimentation velocity and the particle density is:

[0035]

[0036] Where u is the average sedimentation velocity of the particles after uniform sedimentation; g is the gravitational acceleration, ρ T is the water density; C D is the drag coefficient; d is the equivalent particle diameter; ρ a To estimate particle density;

[0037] Drag coefficient C D for:

[0038]

[0039] Water density ρ T for:

[0040] ρ T =a0+a1T+a2T 2 +a3T 3 +a4T 4 +a5T 5

[0041] Among them, T is the water temperature, and a0, a1, a2, a3, a4, and a5 are constants.

[0042] Furthermore, the porosity of the particle sample is calculated in S45, including:

[0043]

[0044] Where P is the porosity of the particle; W is the mass of the particle, and V is the volume of the particle.

[0045] Furthermore, S5 specifically includes:

[0046] Image acquisition of particle settling kinetics experiments was performed using two cameras equipped with macro lenses;

[0047] The bottom layer temperature of the particle settling behavior test device was kept constant, and the upper layer temperature was set based on monitoring experience, so that the surface and bottom temperature differences were ΔT, 2ΔT, and 3ΔT, respectively;

[0048] The particle size of the test particles is determined according to the measured particle size. Disc particles and porous particles are set up with different particle size control groups for particle sedimentation tests. Disc particles are divided into two groups: thick disc and thin disc. The diameter-thickness ratio χ is set according to the monitoring records.

[0049] In the particle sedimentation behavior test device, a single particle is released below the water surface with tweezers in the center to allow the particle to settle freely in the stratified water column; 20 particles of the same type are used in each group of experiments, and 5 repeated experiments are carried out for each particle. The sedimentation trajectories and particle directions of all types of particles are collected during the experiment.

[0050] The particle settling kinetics test method under thermal stratification provided by the present invention has the following beneficial effects:

[0051] This invention takes the thermocline interface of deep and large reservoirs as the key research area, and deeply studies the scientific problem of the influence mechanism of thermal stratification of reservoirs on particle sedimentation behavior, revealing the vertical transport mechanism of substances under the action of thermal stratification of deep and large reservoirs, which is of great significance for formulating reservoir water environment protection and management strategies and ensuring reservoir water quality and water supply safety.

[0052] The present invention aims at the water quality problem caused by delayed sedimentation of thermocline particles in deep and large reservoirs. The thermocline interface of deep and large reservoirs is taken as the key research area. The vertical differentiation characteristics of particles under the action of thermal stratification in deep and large reservoirs are revealed through in-situ high-frequency monitoring technology. Combined with high-precision indoor control experiments, the sedimentation behavior of particles of different sizes, shapes and porosities in thermally stratified water bodies is explored, and the sedimentation dynamics mechanism of thermal stratification on particle aggregation is revealed. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 The figure is a flow chart of the particle settling kinetics test method under the action of thermal stratification of the present invention.

[0054] Figure 2 It is a particle sedimentation behavior test device of the present invention. DETAILED DESCRIPTION

[0055] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0056] Example 1

[0057] The particle settling kinetics test method under the action of thermal stratification in this embodiment focuses on the hydrodynamic mechanism of the particle settling movement in the thermocline of a large thermally stratified reservoir, constructs a particle settling kinetics test under the action of thermal stratification, develops a high-precision test device that can reflect the particle settling movement process in thermally stratified water bodies, conducts settling behavior tests on particles of different particle sizes, shapes, and porosities, monitors the settling movement trajectory of particles, and refers to Figure 1 , which specifically includes the following:

[0058] Step S1, collecting thermal stratified water samples from a field deepwater reservoir, which specifically includes the following contents:

[0059] Step S11, using a portable water quality monitor to perform vertical water quality monitoring at a monitoring point of a deep-water reservoir in the field to obtain reservoir thermal stratification information;

[0060] Specifically, this embodiment conducts vertical stratified water quality monitoring in the thermal stratification stabilization period of June to September in the Panjiakou Reservoir. Monitoring points such as Panjiakou and dam front in the Panjiakou Reservoir area are selected, and a portable water quality monitor is used for vertical water quality monitoring. The main indicators include water depth, water temperature, dissolved oxygen, chlorophyll a, soluble organic matter, etc., and data is recorded vertically every 0.25s.

[0061] Step S12: after determining the water depth of the vertical sampling point of the reservoir according to the thermal stratification information of the reservoir, use a card-covered stratified water sampler to collect water samples in layers at the set water depth. The water samples are collected and preserved in accordance with the "Technical Specifications for Surface Water and Sewage Monitoring"; specifically, a water sample is collected every 3m in the mixed layer on the reservoir surface, a water sample is collected every 2m in the thermocline, and a water sample is collected every 5m in the stagnation layer.

[0062] Step S2: Separate the particles in the water sample and analyze and obtain the particle size and morphology characteristics of the particles, which specifically includes the following contents:

[0063] Step S21, passing the water sample obtained in step S1 through filter membranes with different pore sizes in sequence to obtain particles with different particle size ranges;

[0064] Specifically, 5L of water sample was taken and filtered through filter membranes with pore sizes of 20μm, 10μm, 5μm, 3μm, 0.8μm, and 0.45μm, respectively, to obtain 6 types of particles with different particle sizes (>20μm, 10-20μm, 5-10μm, 3-5μm, 0.8-3μm, and 0.45-0.8μm). The filtration speed was kept low during the filtration process, and the filter membrane should be replaced in time to prevent clogging.

[0065] Step S22, using a high-speed camera to measure the particle size, shape, and other physical parameters;

[0066] This embodiment measures the weight of organic particles according to "Reference GB11901-89 for determination of suspended particles" (GB11901-89); uses a high-speed camera to measure the size, morphology, etc. of particles, the objective lens magnification is 10X, the eyepiece magnification is 4X and 10X respectively, where the 4X eyepiece has a particle size range of 25 to 300μm, and the 10X eyepiece has a particle size range of 4 to 100μm, and the measurements are made after passing through 300μm and 80μm filter membranes respectively. In this way, the abundance, particle size, shape, etc. of particles in each vertical water sample can be obtained.

[0067] Step S3: Build a particle settling behavior test device, refer to Figure 2 , which specifically includes the following:

[0068] Step S31, build a rectangular structure box with a height of 2.0m and a length and width of 0.09m;

[0069] Specifically, the side walls of the rectangular structure box are vacuum insulation panels, and compared with the particle size, the device is wide enough to eliminate the influence of the wall surface.

[0070] Step S32, in order to form a temperature stratification interface, temperature control plates with small holes are installed on the horizontal planes 0.020m and 1.180m away from the bottom of the box, respectively, and a constant temperature aqueous solution with a lower temperature is poured under the constant temperature plate until the water level reaches the height of the constant temperature plate;

[0071] Step S33, the low-temperature constant-temperature aqueous solution is slowly injected into the test device using a diffuser made of sponge. When the water tank is filled with the required volume of low-temperature constant-temperature water, the high-temperature constant-temperature aqueous solution is injected again until the height of the water column reaches 0.80m; that is, two layers of water columns are formed in the rectangular structure box, the lower layer is the low-temperature water layer, and the upper layer is the high-temperature water layer. The initial density interface is located at 0.80m from the bottom, and the vertical coordinate is set so that the coordinate zero point corresponds to the position of the stratification interface of the theoretical low-temperature water layer and the high-temperature water layer;

[0072] Before the test, the sponge diffuser was soaked in constant temperature water of corresponding temperature, and the solution was slowly filled, and the filling speed was controlled to prevent the formation of bubbles.

[0073] Step S34: In order to determine the vertical change of the temperature in the device, temperature sensors are arranged at monitoring holes spaced 0.020 m apart in the vertical direction of the rectangular structure box.

[0074] Step S4, preparing a particle sample for a particle settling kinetics test according to the particle size and morphology characteristics of the particles in step S2;

[0075] Step S41, preparation of disc particles; preparing acrylonitrile-butadiene-styrene ABS acetone solution, with a density of 1.050 g / mL; dropping droplets formed by the ABS acetone solution onto a polished glass plate, and forming a thin sheet after the acetone evaporates, and selecting two groups of disc particles with different diameter-thickness ratios according to the morphological characteristics of the particles in S2, namely thin discs and thick discs;

[0076] Step S42, preparation of porous particles; porous particle samples are made using agarose spheres, the agarose spheres are prepared by gelling an agarose solution in deionized water, the dry density of agarose is 1.640 g / mL, and during the gelation of the agarose solution, the agarose forms a fibrous microstructure with a porosity of approximately 95%; before the test, the porous particles are washed three times with constant temperature water on the upper layer of the test device.

[0077] Step S43, using an inverted fluorescence microscope to observe and measure the particle size, and selecting particles with a particle size and thickness similar to those of the particles in S2 as particle samples;

[0078] Step S44, estimating the density of the particle sample by measuring the sedimentation velocity of the particle sample in 20° C. constant temperature distilled water;

[0079] The density of the particles was estimated by measuring the sedimentation velocity of the particles in distilled water at a constant temperature of 20°C. After measuring the particle size, the individual particles were gently transferred to the sedimentation behavior test device through a pipette with a cut-off tip. The particle sedimentation velocity was calculated from the recorded vertical displacement, and then the average sedimentation velocity was calculated over at least 3 consecutive seconds to obtain the sedimentation velocity u after the particles settled at a uniform speed, which was used to estimate the particle density ρ a , the particle density is estimated based on the average sedimentation velocity, and the relationship between the average sedimentation velocity and the particle density is obtained. The specific formula is:

[0080]

[0081] Where u is the average sedimentation velocity of the particles after uniform sedimentation; g is the gravitational acceleration, ρ T is the water density; C D is the drag coefficient; d is the particle equivalent diameter; ρ a To estimate particle density;

[0082] Drag coefficient C D for:

[0083]

[0084] Water density ρ T for:

[0085] ρ T =a0+a1T+a2T 2 +a3T 3 +a4T 4 +a5T 5

[0086] Among them, T is the water temperature, and a0, a1, a2, a3, a4, and a5 are constants.

[0087] Step S45, calculating the porosity of the particle sample, comprising:

[0088]

[0089] Where P is the porosity of the particle; W is the mass of the particle, and V is the volume of the particle.

[0090] Step S5, placing the prepared particle sample into a particle settling behavior test device to conduct a particle settling test under the action of reservoir thermal stratification, which specifically includes:

[0091] Image acquisition of particle settling kinetics experiments was performed using two cameras equipped with macro lenses;

[0092] The bottom layer temperature of the particle settling behavior test device was kept constant, and the upper layer temperature was set based on monitoring experience, so that the surface and bottom temperature differences were ΔT, 2ΔT, and 3ΔT, respectively;

[0093] The particle size of the test particles is determined according to the measured particle size. Disc particles and porous particles are set up with different particle size control groups for particle sedimentation tests. Disc particles are divided into two groups: thick disc and thin disc. The diameter-thickness ratio χ is set according to the monitoring records.

[0094] In the particle sedimentation behavior test device, a single particle is released below the water surface with tweezers in the center to allow the particle to settle freely in the stratified water column; 20 particles of the same type are used in each group of experiments, and 5 repeated experiments are carried out for each particle. The sedimentation trajectories and particle directions of all types of particles are collected during the experiment.

[0095] Step S6: Use a camera to record the particle settling dynamics behavior, and record the particle movement trajectory based on the collected images and videos of the particle settling movement.

[0096] Although the specific implementation of the invention is described in detail in conjunction with the drawings, it should not be understood as limiting the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A method for testing particle settling kinetics under thermal stratification, characterized in that: The following steps are involved: S1. Collect thermally stratified water samples from deep water reservoirs in the field; S2. Separate the particles in the water sample and analyze and obtain the particle size and morphology characteristics of the particles; S3. Build a particle settling behavior test device; S4, preparing particle samples for particle settling kinetics test according to the particle size and morphology characteristics of the particles in S2; S5, placing the prepared particle sample into a particle settling behavior test device to conduct a particle settling test under the action of reservoir thermal stratification; S6. Use a camera to record the particle settling dynamics behavior.

2. The particle settling kinetics test method under thermal stratification according to claim 1, characterized in that: The S1 comprises the following sub-steps: S11. Use a portable water quality monitor to conduct vertical water quality monitoring at monitoring points in a deepwater reservoir in the field to obtain reservoir thermal stratification information; S12. Carry out vertical sampling according to the thermal stratification information of the reservoir. Collect a water sample every 3m in the mixed layer on the reservoir surface, a water sample every 2m in the thermocline, and a water sample every 5m in the stagnation layer.

3. The particle settling kinetics test method under thermal stratification according to claim 1, characterized in that: The S2 comprises the following sub-steps: S21, passing the water sample obtained in S1 through filter membranes with different pore sizes in sequence to obtain particles with different particle size ranges; S22, particle size and shape physical parameters measured using a high-speed camera.

4. The particle settling kinetics test method under thermal stratification according to claim 1, characterized in that: The S3 comprises the following sub-steps: S31, build a rectangular structure box with a height of 2.0m and a length and width of 0.09m; S32. Install temperature control plates with small holes on the horizontal planes 0.020m and 1.180m from the bottom of the box, and pour the lower temperature constant temperature water solution under the constant temperature plate until the water level reaches the height of the constant temperature plate; S33. The low-temperature constant-temperature aqueous solution is slowly injected into the test device using a diffuser made of sponge. When the water tank is filled with the required volume of low-temperature constant-temperature water, the high-temperature constant-temperature aqueous solution is injected again until the height of the water column reaches 0.80m; that is, two layers of water columns are formed in the rectangular structure box, the lower layer is the low-temperature water layer, and the upper layer is the high-temperature water layer. The initial density interface is located at 0.80m from the bottom, and the vertical coordinate is set so that the coordinate zero point corresponds to the position of the stratification interface of the theoretical low-temperature water layer and the high-temperature water layer; S34. Temperature sensors are arranged at monitoring holes spaced 0.020 m apart in the vertical direction of the rectangular structural box.

5. The particle settling kinetics test method under thermal stratification according to claim 1, characterized in that: The S4 comprises the following sub-steps: S41, preparation of disc particles; preparing ABS acetone solution, dropping droplets of the ABS acetone solution onto a polished glass plate, and forming a thin sheet after evaporation of the acetone, and selecting two groups of disc particles with different diameter-to-thickness ratios according to the morphological characteristics of the particles in S2, namely, thin discs and thick discs; S42, preparation of porous particles; porous particle samples were prepared using agarose spheres, the agarose spheres were prepared by gelling an agarose solution in deionized water, the agarose dry density was 1.640 g / mL, and during the gelation of the agarose solution, the agarose formed a fibrous microstructure with a porosity of about 95%; S43, using an inverted fluorescence microscope to observe and measure the particle size, and selecting particles with a particle size and thickness similar to those in S2 as particle samples; S44, estimate the density of the particle sample by measuring the sedimentation velocity of the particle sample in distilled water at a constant temperature of 20°C; S45. Calculate the porosity of the particle sample.

6. The particle settling kinetics test method under thermal stratification according to claim 5, characterized in that: The step S44 of estimating the density of the particle sample comprises: A single particle sample is transferred to the particle sedimentation behavior test device through a pipette with a cut-off tip. The sedimentation velocity of the particle sample is calculated from the recorded vertical displacement. The average sedimentation velocity is calculated over at least 3 consecutive seconds to obtain the sedimentation velocity after the particle sedimentation is uniform. The particle density is estimated based on the obtained average sedimentation velocity. The relationship between the average sedimentation velocity and the particle density is: Where u is the average sedimentation velocity of the particles after uniform sedimentation; g is the gravitational acceleration, ρ T is the water density; C D is the drag coefficient; d is the particle equivalent diameter; ρ a To estimate particle density; Drag coefficient C D for: Water density ρ T for: ρ T =a0+a1T+a2T 2 +a3T 3 +a4T 4 +a5T 5 Among them, T is the water temperature, and a0, a1, a2, a3, a4, and a5 are constants.

7. The particle settling kinetics test method under thermal stratification according to claim 6, characterized in that: The porosity of the particle sample is calculated in S45, including: Where P is the porosity of the particle; W is the mass of the particle, and V is the volume of the particle.

8. The particle settling kinetics test method under thermal stratification according to claim 1, characterized in that: The S5 specifically includes: Image acquisition of particle settling kinetics experiments was performed using two cameras equipped with macro lenses; The bottom layer temperature of the particle settling behavior test device was kept constant, and the upper layer temperature was set based on monitoring experience, so that the surface and bottom temperature differences were ΔT, 2ΔT, and 3ΔT, respectively; The particle size of the test particles is determined according to the measured particle size. Disc particles and porous particles are set up with different particle size control groups for particle sedimentation tests. Disc particles are divided into two groups: thick disc and thin disc. The diameter-thickness ratio χ is set according to the monitoring records. In the particle sedimentation behavior test device, a single particle is released below the water surface with tweezers in the center to allow the particle to settle freely in the stratified water column; 20 particles of the same type are used in each group of experiments, and 5 repeated experiments are carried out for each particle. The sedimentation trajectories and particle directions of all types of particles are collected during the experiment.

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