Analysis method for sedimentation behavior of spherical particles in layered water body

Abstract

The invention discloses a method for analyzing the settlement behavior of spherical particles in layered water, which comprises the following steps: building a particle settlement behavior test device, and carrying out a particle settlement test under the action of reservoir thermal stratification to obtain the dynamic behavior of particle settlement in the thermal stratification motion of a deepwater reservoir; obtaining the stress information of the particles in the sedimentation motion according to the sedimentation dynamic behavior of the thermal stratification motion particles of the deepwater reservoir; according to the stress information of the particles in the sedimentation motion, the corrected particle sedimentation velocity is obtained through calculation; and calculating key kinetic parameters of the particle sedimentation behavior according to the corrected particle sedimentation velocity. According to the method, the vertical transportation process of the particles under the thermal stratification effect of the water body can be deeply understood, and the obtained scientific data and cognition are helpful for perfecting a basic theory system for ecological protection and restoration of lake and reservoir water and water safety guarantee of a water source.

Description

Technical Field

[0001] The invention belongs to the technical field of particle movement behavior analysis under thermal stratification in deep-water reservoirs, and specifically relates to an analysis method for the sedimentation behavior of spherical particles in stratified water bodies. Background Art

[0002] The sedimentation deceleration behavior of organic particles at the thermocline interface under the thermal stratification of deep-water reservoirs 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 sedimentation movement that controls the vertical heterogeneity of organic particles. Relevant research mainly focuses on the density stratification interface caused by vertical salinity changes in the ocean. Relevant studies on marine salinity stratified waters have shown that the vertical density stratification of water bodies has a significant deceleration effect on particle sedimentation, 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 sedimentation behavior. At present, there is little research on the sedimentation behavior of particles under thermal stratification in deep-water reservoirs, and the potential impact of thermal stratification on particle sedimentation behavior is not well understood.

[0003] At present, the research on particle sedimentation in stratified water bodies mainly focuses on spherical particles. However, the geometric shapes of particles in natural water bodies are mostly disc-shaped, flocculent and other structural forms. There are few studies on non-spherical particles, and the related mechanism is still unclear. Through observations of indoor control experiments, it is found that in addition to the additional resistance generated by the "entrainment" mechanism in the sedimentation of spherical particles, the particle torque caused by the density stratification of the water body causes the particles to redirect during the sedimentation process. This redirection makes its sedimentation mechanism more complicated. Non-spherical particles are subjected to complex forces when settling in stratified water bodies. The particle morphology significantly affects their sedimentation behaviors such as sedimentation rate and sedimentation direction. The mechanism of this process is still being explored. The natural particle sedimentation process calculated based on the sedimentation formula determined by spherical particles is inaccurate and has large errors. Summary of the invention

[0004] The purpose of the present invention is to address the above-mentioned deficiencies in the prior art and to provide an analysis method for the sedimentation behavior of spherical particles in stratified water bodies, so as to solve the problem of inaccurate natural particle sedimentation process and large errors in the existing sedimentation calculation method when particles settle in thermal stratified water bodies in deepwater reservoirs.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for analyzing the sedimentation behavior of spherical particles in stratified water comprises the following steps:

[0007] S1. Build a particle settling behavior test device, conduct a particle settling test under the effect of thermal stratification in the reservoir, and obtain the particle settling dynamics behavior under the effect of thermal stratification in the deepwater reservoir;

[0008] S2. Obtain the force information of particles in the sedimentation movement according to the particle sedimentation dynamics behavior under the thermal stratification of deep-water reservoirs;

[0009] S3, calculating the corrected particle settling velocity according to the force information of the particles during the settling motion;

[0010] S4. Calculate the key kinetic parameters of particle settling behavior based on the corrected particle settling velocity.

[0011] Furthermore, the S1 comprises the following sub-steps:

[0012] S11. Monitor the vertical thermal stratification of the reservoir and collect thermal stratified water samples from field deepwater reservoirs;

[0013] S12, separate the particles in the water sample, and analyze and obtain the particle size and morphology characteristics of each layer of particles;

[0014] S13. Build a test device for particle settling behavior in stratified water;

[0015] S14, preparing particle samples for particle settling kinetics test according to particle size and morphology characteristics;

[0016] S15, placing the prepared particle sample into a stratified water particle settling behavior test device to conduct a particle settling test under the action of reservoir thermal stratification;

[0017] S16. Use a camera to record the particle settling dynamics behavior.

[0018] Furthermore, the force information of the particles in S2 during the sedimentation movement in the stratified water body includes: gravity, buoyancy, resistance and additional mass force exerted on the particles.

[0019] Furthermore, the gravity on the spherical particles is:

[0020]

[0021] Among them, F g is the gravity of the particle, g is the acceleration due to gravity, d is the particle diameter, ρ a is the estimated particle density, ρ T (z0) is the density of the water body where the particle has a smaller density in the upper layer, V L is the volume of water attached to the tail of the particle.

[0022] Furthermore, the buoyancy of the spherical particles is:

[0023]

[0024] Among them, F f is the buoyancy of the particle, ρ T (z) is the water density of the particle at depth z.

[0025] Furthermore, the resistance of the spherical particles is:

[0026]

[0027] Among them, F d is the resistance of the particle, u(z) is the settling velocity of the particle at depth z, C D is the resistance coefficient.

[0028] Furthermore, the additional mass force on the spherical particle is:

[0029]

[0030] Among them, F m is the additional mass force on the particle, and k is the particle shape coefficient.

[0031] Furthermore, the corrected particle settling velocity calculated in S3 includes:

[0032] When the gravity, buoyancy, drag and additional mass force on the spherical particles reach equilibrium, the particle sedimentation velocity is:

[0033]

[0034] Wherein, u is the corrected particle settling velocity, Re is the Reynolds number, and v is the kinematic viscosity of water. Further, the key dynamic parameters for calculating the particle settling behavior in S4 include: the water density ρ of the particle at the depth z T (z) is:

[0035]

[0036] Among them, ρ ul is the density of the upper water layer, ρ ll is the density of the lower water layer, z m , p is the fitting parameter; Brunt-Vaisala buoyancy frequency N of stratified water b for:

[0037]

[0038] The Froude number Fr(z) is:

[0039]

[0040] Among them, N b (z) is the buoyancy frequency at depth z;

[0041] The Reynolds number Re(z) is:

[0042]

[0043] The ratio of the Reynolds number to the Froude number is:

[0044]

[0045] The Prandtl number Pr is:

[0046]

[0047] Where κ is the diffusion coefficient of the water body;

[0048] The Archimedean number is:

[0049]

[0050] Among them, Ar is the Archimedean number, which is used to measure the ratio of gravity and viscosity.

[0051] The method for analyzing the sedimentation behavior of spherical particles in stratified water provided by the present invention has the following beneficial effects:

[0052] The present invention constructs a particle sedimentation kinetics test under the action of thermal stratification, develops a high-precision test device that can reflect the sedimentation movement process of particles in thermally stratified water bodies, carries out sedimentation behavior tests on particles of different particle sizes, shapes, and porosities, monitors the sedimentation movement trajectory of particles, and analyzes the behavioral characteristics of particle sedimentation movement. This can help to more deeply understand the vertical transport process of particles under the action of thermal stratification of water bodies. The scientific data and cognition obtained will help to improve the basic theoretical system for lake and reservoir water ecological protection and restoration and water source water security. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 The present invention is a flow chart of the method for analyzing the sedimentation behavior of spherical particles in stratified water.

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

[0055] Figure 3 It is the force of a single spherical particle of the present invention. DETAILED DESCRIPTION

[0056] 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.

[0057] Example 1

[0058] The analysis method of the settling behavior of spherical particles in stratified water of this embodiment specifically includes the following contents:

[0059] Step S1: Build a particle settling behavior test device to conduct a particle settling test under the action of thermal stratification in the reservoir to obtain the dynamic behavior of particle settling in thermal stratification in deepwater reservoirs. Figure 1 , which specifically includes the following:

[0060] 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;

[0061] 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.

[0062] After determining the water depth of the vertical sampling point in the reservoir based on the thermal stratification information of the reservoir, a card-covered stratified water sampler is used 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.

[0063] Step S12, separating the particles in the water sample and analyzing and obtaining the particle size and morphology characteristics of each layer of particles, which specifically includes the following contents:

[0064] The obtained water samples are sequentially passed through filter membranes with different pore sizes to obtain particles with different particle size ranges;

[0065] 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.

[0066] Physical parameters such as particle size and shape measured by high-speed cameras;

[0067] This embodiment measures the weight of organic particles according to "Reference GB11901-89 for determination of suspended particles" (GB11901-89); uses a laser particle size analyzer to measure the particle size distribution; uses a high-speed camera to measure the size, morphology, etc. of the 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.

[0068] Step S13: construct a stratified water particle sedimentation behavior test device, refer to Figure 2 , which specifically includes the following:

[0069] Build a rectangular structural box with a height of 2.0m and a length and width of 0.09m;

[0070] 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.

[0071] 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 from the bottom of the box, and a constant temperature water solution with a lower temperature is poured under the constant temperature plate until the water level reaches the height of the constant temperature plate;

[0072] 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;

[0073] 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.

[0074] In order to determine the vertical change of temperature in the device, temperature sensors are arranged at monitoring holes every 0.020m in the vertical direction of the rectangular structure box.

[0075] Step S14, preparing particle samples for particle settling kinetics test according to particle size and morphology characteristics;

[0076] Preparation of spherical particles: prepare acrylonitrile-butadiene-styrene ABS acetone solution with a density of 1.050 g / mL; drop the droplets formed by the ABS acetone solution onto a polished glass plate, and after the acetone evaporates, a thin sheet is formed. Two groups of spherical particles with different diameter-to-thickness ratios are selected according to the morphological characteristics of the particles;

[0077] An inverted fluorescence microscope is used to observe and measure the particle size, and particles with a size similar to that of the sampled particles are selected as particle samples;

[0078] The density of the particle sample was estimated by measuring the sedimentation velocity of the particle sample in distilled water at a constant temperature of 20°C;

[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 density of spherical particles 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 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] Calculate the porosity of granular samples, including:

[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 S15, placing the prepared particle sample into a stratified water 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 S16: 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] Step S2: Reference Figure 3 , according to the sedimentation dynamics of particles in thermal stratification movement in deep-water reservoirs, the force information of particles in sedimentation movement is obtained;

[0097] The force information includes: gravity, buoyancy, drag and additional mass force on the particles.

[0098] When a spherical particle settles in a layered water body, the tail of the particle "entrains" the upper layer of water. The volume of water attached to the tail of the particle is V. L , therefore, the gravity acting on the particle is:

[0099]

[0100] Among them, F g is the gravity of the particle, g is the acceleration due to gravity, d is the particle diameter, ρ a is the estimated particle density, ρ T (z0) is the density of the water body where the particle has a smaller density in the upper layer, V L is the volume of water attached to the tail of the particle.

[0101] The buoyancy force on the particle is:

[0102]

[0103] Among them, F f is the buoyancy of the particle, ρ T (z) is the water density of the particle at depth z.

[0104] The resistance to particle settling is not only related to the Reynolds number of the particle, but also to the water temperature, particle shape (projected area), etc. The resistance calculation formula obtained from the spherical particle settling test is:

[0105]

[0106] Among them, F d is the resistance of the particle, u(z) is the settling velocity of the particle at depth z, C D is the resistance coefficient.

[0107] The additional mass force is the additional mass force that is added when the particle settles in the still water body and accelerates or decelerates. When the particle settles in the water body, it pushes the surrounding water body. Due to the inertia of the water body, the reaction force of the particle is shown. The calculation formula of this additional mass force is:

[0108]

[0109] Among them, F m is the additional mass force on the particle, k is the particle shape coefficient

[0110] Step S3, calculating a corrected particle settling velocity according to the force information of the particles during the settling motion;

[0111] The sedimentation of spherical particles in static water can be roughly divided into two stages, namely the acceleration stage and the stabilization stage. The resistance encountered by the particle sedimentation is proportional to the square of the sedimentation velocity u(z). When the particle sedimentation velocity increases to a certain extent, the force balance is achieved and the particle sedimentation velocity tends to be stable. At this time, the calculation formula of the particle sedimentation velocity is:

[0112]

[0113] According to the formula for calculating the resistance during particle sedimentation given by Stocks:

[0114] F d =3πduv

[0115] The corrected particle settling velocity is obtained as follows:

[0116]

[0117] Where, u is the corrected particle settling velocity, Re is the Reynolds number; ν is the kinematic viscosity of water;

[0118] It should be noted that the sedimentation velocity of non-spherical particles needs to be corrected according to the relevant parameters of this experiment.

[0119] Step S4, calculating key kinetic parameters of particle settling behavior according to the corrected particle settling velocity;

[0120] Specifically, the key kinetic parameters of particle settling behavior include:

[0121] The water density of the particle at depth z is ρ T (z) is:

[0122]

[0123] Among them, ρ ul is the density of the upper water layer, ρ ll is the density of the lower water layer, z m , p is the fitting parameter;

[0124] Brunt-Vaisala buoyancy frequency N in stratified water b for:

[0125]

[0126] The Froude number Fr(z) is:

[0127]

[0128] Among them, N b (z) is the buoyancy frequency at depth z;

[0129] The Reynolds number Re(z) is:

[0130]

[0131] The ratio of the Reynolds number to the Froude number is:

[0132]

[0133] The Prandtl number Pr is:

[0134]

[0135] Where κ is the diffusion coefficient of the water body;

[0136] The Archimedean number is:

[0137]

[0138] Among them, Ar is the Archimedean number, which is used to measure the ratio of gravity and viscosity.

[0139] The present invention considers the influence of particle morphology indicators such as particle size, shape (diameter-thickness ratio), porosity, etc. on the sedimentation velocity, obtains the sedimentation velocity through experiments, and calculates the resistance coefficient C D , Reynolds number and other parameters, and analyze the response relationship between these parameters and particle morphology indicators. Referring to the classic formula of particle settling velocity, the particle size, volume, porosity and other morphology index parameters in the formula are corrected using the experimental data of the present invention to obtain the velocity formula of different particle settling.

[0140] 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 analyzing the sedimentation behavior of spherical particles in stratified water, characterized in that: The following steps are involved: S1. Build a particle settling behavior test device to conduct a particle settling test under the action of thermal stratification in the reservoir to obtain the dynamic behavior of particle settling in thermal stratification in deepwater reservoirs; S2. Obtain the force information of particles in the sedimentation motion according to the sedimentation dynamics behavior of particles in thermal stratification motion in deep-water reservoirs; S3, calculating the corrected particle settling velocity according to the force information of the particles during the settling motion; S4. Calculate the key kinetic parameters of particle settling behavior based on the corrected particle settling velocity.

2. The method for analyzing the sedimentation behavior of spherical particles in stratified water according to claim 1, characterized in that: The S1 comprises the following sub-steps: S11. Monitor the vertical thermal stratification of the reservoir and collect thermal stratified water samples from field deepwater reservoirs; S12, separate the particles in the water sample, and analyze and obtain the particle size and morphology characteristics of each layer of particles; S13. Build a test device for particle settling behavior in stratified water; S14, preparing particle samples for particle settling kinetics test according to particle size and morphology characteristics; S15, placing the prepared particle sample into a stratified water particle settling behavior test device to conduct a particle settling test under the action of reservoir thermal stratification; S16. Use a camera to record the particle settling dynamics behavior.

3. The method for analyzing the sedimentation behavior of spherical particles in stratified water according to claim 1, characterized in that: The force information of the particles in S2 during the sedimentation movement of the stratified water body includes: gravity, buoyancy, resistance and additional mass force exerted on the particles.

4. The method for analyzing the sedimentation behavior of spherical particles in stratified water according to claim 3, characterized in that: The gravitational force on the particle is: Among them, F g is the gravity of the particle, g is the acceleration due to gravity, d is the particle diameter, ρ a is the estimated particle density, ρ T (z0) is the density of the water body where the particle has a smaller density in the upper layer, V L is the volume of water attached to the tail of the particle.

5. The method for analyzing the sedimentation behavior of spherical particles in stratified water according to claim 4, characterized in that: The buoyancy force on the particle is: Among them, F f is the buoyancy of the particle, ρ T (z) is the water density of the particle at depth z.

6. The method for analyzing the sedimentation behavior of spherical particles in stratified water according to claim 4, characterized in that: The resistance force on the particle is: Among them, F d is the resistance of the particle, u(z) is the settling velocity of the particle at depth z, C D is the resistance coefficient.

7. The method for analyzing the sedimentation behavior of spherical particles in stratified water according to claim 4, characterized in that: The additional mass force on the particle is: Among them, F m is the additional mass force on the particle, and k is the particle shape coefficient.

8. The method for analyzing the sedimentation behavior of spherical particles in stratified water according to claim 6, characterized in that: The corrected particle settling velocity calculated in S3 includes: When the gravity, buoyancy, drag and additional mass force on the spherical particles reach equilibrium, the settling velocity of the spherical particles is: Where u is the corrected particle settling velocity, Re is the Reynolds number, and v is the kinematic viscosity of water.

9. The method for analyzing the sedimentation behavior of spherical particles in stratified water according to claim 8, characterized in that: The key kinetic parameters of particle settling behavior calculated in S4 include: The water density of the particle at depth z is ρ T (z) is: Among them, ρ ul is the density of the upper water layer, ρ ll is the density of the lower water layer, z m , p is the fitting parameter; Brunt-Vaisala buoyancy frequency N in stratified water n for: The Froude number Fr(z) is: Among them, N b (z) is the buoyancy frequency at depth z; The Reynolds number Re(z) is: The ratio of the Reynolds number to the Froude number is: The Prandtl number Pr is: Where κ is the diffusion coefficient of the water body; The Archimedean number is: Among them, Ar is the Archimedean number, which is used to measure the ratio of gravity and viscosity.

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