CN111323344B - Simulation device and experimental method for three-dimensional solute transport in porous medium - Google Patents
Simulation device and experimental method for three-dimensional solute transport in porous medium Download PDFInfo
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- CN111323344B CN111323344B CN202010303042.8A CN202010303042A CN111323344B CN 111323344 B CN111323344 B CN 111323344B CN 202010303042 A CN202010303042 A CN 202010303042A CN 111323344 B CN111323344 B CN 111323344B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/0806—Details, e.g. sample holders, mounting samples for testing
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/082—Investigating permeability by forcing a fluid through a sample
- G01N15/0826—Investigating permeability by forcing a fluid through a sample and measuring fluid flow rate, i.e. permeation rate or pressure change
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N2015/0023—Investigating dispersion of liquids
- G01N2015/0034—Investigating dispersion of liquids in solids
Abstract
A simulation device and an experimental method for three-dimensional solute migration in porous media are provided, wherein the simulation device comprises a sand tank, an injection mode adjusting device, a liquid supply device, a penetrating fluid collector, a water-stop sheet, a well pipe, a conductivity measuring electrode, a data acquisition unit and a data processing system. The sand tank is horizontally arranged, the interior of the sand tank is divided into three subchambers from left to right, the subchambers are separated by a baffle plate, a plurality of water permeable holes are uniformly and densely distributed on the baffle plate, the left chamber is connected with the liquid supply device, the middle subchamber is used for filling porous media, and the right chamber is vacant and connected with the penetrating fluid collector; the well pipes are uniformly distributed in the porous medium in the sand tank, the side walls of the whole body of the well pipes are provided with dense water-permeable holes, and each cavity chamber is internally provided with a conductivity measuring electrode. The invention can simulate and observe the three-dimensional solute transport condition in the porous medium, and is favorable for researching the influence of the heterogeneity of the medium on the migration of pollutants.
Description
Technical Field
The invention relates to the field of soil physics research, in particular to a simulation device and an experimental method for three-dimensional solute migration in a porous medium.
Background
With the continuous development of the scientific and technical level, the contradiction between human production activities and the natural ecological environment becomes more acute, the use of a large amount of pesticide reagents and the discharge of sewage of enterprises cause serious water pollution, the pollutants can be continuously migrated and diffused along with the flow of underground water, the productivity of soil is damaged, and meanwhile, the health of human bodies is seriously threatened, so that the migration rule of solute migration in a porous medium is very important to disclose.
The traditional method for observing the solute transport process mainly comprises a horizontal soil column method, a vertical soil column method and a field tracing test method. However, in both the horizontal soil column method and the vertical soil column method, the water flow is only forced to move in a near-one dimension due to the limitation of the side wall of the column, and in nature, the movement of the water flow is often three-dimensional due to the heterogeneity of the porous medium, and the difference of the movement forms can greatly affect the experimental result, thereby causing observation errors. The field tracing test method well maintains the motion form of water flow, but a large number of observation well pipes are often needed for observing pollutant dispersion plumes, the observation precision is influenced by too few observation wells, and huge economic pressure is caused by increasing the number of the observation wells.
Disclosure of Invention
The invention provides a simulation device for three-dimensional solute transport in a porous medium.
A three-dimensional solute migration simulation device in porous media comprises a sand tank, an injection mode adjusting device, a liquid supply device, a penetrating fluid collector, a water-stop sheet, a well pipe, a conductivity measuring electrode, a data collector and a data processing system, wherein the three-dimensional solute migration simulation device comprises a sand tank, a liquid supply device, a penetrating fluid collector, a water-stop sheet, a well pipe, a conductivity measuring electrode:
the liquid supply device comprises a tracer liquid supply tank, a distilled water liquid supply tank and a peristaltic pump; the sand tank left chamber, the suspended sub-chamber, the water-stop plate, the first baffle plate and the third baffle plate densely distributed with the water-permeable holes of the sand tank form an injection mode adjusting device;
the sand tank is horizontally arranged, the interior of the sand tank is divided into a left sand tank chamber, a middle part chamber and a right sand tank chamber from left to right, and a suspended chamber is arranged in the left sand tank chamber;
the middle part sub-chamber occupies the largest volume, the middle part sub-chamber is filled with porous media, the right sand tank chamber is vacant, the right sand tank chamber is connected with a penetrating fluid collector, the left sand tank chamber and the middle part sub-chamber are divided by two first baffles, a plurality of water permeable holes are uniformly and densely distributed on the first baffles, a gap is reserved between the two first baffles and used for placing a water-stop plate, the water-stop plate plays a role of opening and closing, when an experiment is started, the water-stop plate is drawn out to enable water flow to flow, when the experiment is suspended, the water-stop plate is inserted to stop flowing, and the middle part sub-chamber and the right sand tank chamber are separated by a second baffle densely distributed with the water permeable holes; the suspended sub-chamber is internally provided with a third baffle plate densely covered with water permeable holes, and the third baffle plate densely covered with the water permeable holes penetrates through the suspended sub-chamber to relieve liquid level disturbance caused during water injection.
A plurality of first water inlet holes, second water inlet holes, first water outlet holes and second water outlet holes are distributed on the left side wall of the sand tank in a staggered manner; the first water inlet hole and the second water outlet hole are communicated with the suspended sub-chambers, and the second water inlet hole and the first water outlet hole are communicated with the left chamber of the sand tank; the first water inlet hole and the second water inlet hole are in the same horizontal height; the first water outlet hole and the second water outlet hole are at the same horizontal height; the horizontal heights of the first water inlet hole and the second water inlet hole are higher than the horizontal heights of the first water outlet hole and the second water outlet hole.
A plurality of groups of third water outlet holes are distributed on the side wall of the right side of the sand tank at different heights, each group of the third water outlet holes consists of two water outlet holes with the same horizontal height, and the height of each third water outlet hole is lower than that of the first water outlet hole and that of the second water outlet hole, so that a water head difference is formed to form seepage;
the device comprises a sand tank, a plurality of sand inlet pipes, a plurality of water outlet pipes, a plurality of water inlet holes, a plurality of water outlet pipes and a plurality of water outlet pipes, wherein the porous medium in the sand tank is provided with a plurality of well pipes, the bottom ends of the well pipes are deep into the bottom of the sand tank, the well pipes penetrate through the whole porous medium aquifer; the chamber number is set according to individual requirement, and the chamber number is more, and the position that can measure in same well casing is just more, in addition, except that will placing the conductivity measuring electrode in every cavity, other part will be filled with porous medium, and the solution of avoiding different degree of depth department is mixed and dissolved in the well casing, and then causes experiment observation error.
A tracer liquid supply tank of the liquid supply device is communicated with the first water inlet hole through a peristaltic pump and a water guide pipe; a distilled water supply tank of the liquid supply device is communicated with the second water inlet hole through a peristaltic pump and a water guide pipe; the tracer liquid supply tank is used for storing tracer solution, the distilled water liquid supply tank is used for supplying distilled water,
one end of the data acquisition unit is connected with the conductivity measuring electrode, the other end of the data acquisition unit is connected with the data processing system, the conductivity measuring electrode can detect the change condition of the conductivity in the aqueous solution and transmit the information to the data acquisition unit, the data acquisition unit can automatically record the measuring information of the electrode in real time and transmit the data to the data processing system, and the data processing system can convert the received conductivity information into the concentration information of the solution so as to realize the real-time observation of the solute transport condition.
In the invention, the porous medium in the middle sub-chamber is soil or sand, and is selected according to the experiment requirement; the manufacturing material of the sand tank can be organic glass, the thickness of the glass plate can be set to be 1.5cm, the volume of the sand tank can be set to be 155 multiplied by 60cm, the left chamber of the sand tank is 10cm, the middle part sub-chamber is 140cm, and the right chamber of the sand tank is 5 cm; the thickness of the first baffle, the second baffle and the third baffle is 8mm, and the thickness of the water-stop plate is 4 mm; the inner diameters of the first water inlet hole, the second water inlet hole, the first water outlet hole, the second water outlet hole and the third water outlet hole are all 8mm, and the outer diameters of the first water inlet hole, the second water inlet hole, the first water outlet hole, the second water outlet hole and the third water outlet hole are all 12 mm; the volume of the suspended sub-chamber is 10 multiplied by 8cm, and the thickness of the side wall of the suspended sub-chamber is 8 mm; the tracer liquid supply tank, the distilled water liquid supply tank and the penetrating fluid collector are made of PVC plastics; the water guide pipe is a rubber pipe with the inner diameter of 10 mm; the well pipe is made of organic glass material, the inner diameter of the well pipe is 4cm, and the well pipe is divided into three sub-chambers; the conductivity measuring electrode is a platinum electrode, the platinum electrode is composed of two platinum sheets, the two platinum sheets are arranged in parallel with the water flow direction, and the diameter of the conductivity measuring electrode is controlled within 1 cm; the filling material in the well pipe can be glass beads with the diameter of 3 mm.
An experimental method of a three-dimensional solute transport simulation device in a porous medium comprises the following steps:
1) filling materials: wrapping a first baffle and a second baffle on the left side and the right side of a middle subchamber of the sand tank by gauze to prevent medium particles from blocking a permeable hole, selecting a porous medium required by an experiment according to requirements, performing well pipe laying work when the filling thickness of the medium reaches 20-30 CM, continuously filling the porous medium after well pipe laying is completed, selecting whether to cover a clay layer above the porous medium according to the requirements of a simulation object, and setting an upper clay layer for a diving aquifer without setting the upper clay layer and an upper clay layer for a pressure-bearing aquifer;
2) well pipe laying: wrapping the side wall of the well pipe by gauze to prevent medium particles from blocking a third water inlet hole in the side wall of the well pipe, wherein the length of the well pipe is larger than the thickness of the porous medium, the well pipe is arranged when the material filling thickness reaches 20-30 cm (the well pipe can be well fixed in the medium), one end of the well pipe is blocked, the blocking end is inserted into a preset hole distribution position, and the material filling is continued after the hole distribution is finished;
3) and (3) electrode layout: connecting all the conductivity measuring electrodes with a data collector, calibrating, wrapping the front edges of the conductivity measuring electrodes with gauze, preventing medium particles from being clamped between electrode platinum sheets after being saturated with water, presetting the arrangement depth of each chamber conductivity measuring electrode, filling the rest part of the chamber with glass beads with the diameter of 3mm after the conductivity measuring electrodes are arranged, and preventing solutions with different depths from being mixed and dissolved in a well pipe chamber so as to cause measurement errors;
4) sand tank water supply: connecting a sand tank with a tracer liquid supply tank, a distilled water liquid supply tank and a penetrating fluid collector 17, under the condition that the heights of a first water outlet and a second water outlet on the left side of the sand tank are fixed, the lower the height of a third water outlet on the right side of the sand tank is, the higher the seepage speed is, selecting the height of the third water outlet on the right side of the sand tank according to experiments, butting the penetrating fluid collector with the third water outlet on the right side of the sand tank, starting a peristaltic pump connected with the distilled water liquid supply tank, injecting distilled water into the left chamber of the sand tank, not injecting distilled water into a suspended subchamber, wherein the whole injection process needs to be slow, further removing the penetrating fluid sealed in a porous medium, and continuing until the distilled water is collected by the collector;
5) medium washing: the method comprises the following steps of (1) washing the porous medium to avoid the influence of ions carried by the medium on an observation result, wherein the washing process is to continuously supply distilled water, the flow rate of a peristaltic pump is properly increased, and the first water outlet and the second water outlet on the left side of a sand tank are required to form continuous and slow overflow;
6) injecting a tracer: the tracer takes NaCl as an example, NaCl solution with proper concentration is prepared before the experiment, the injection form (point source/area source) of the tracer is selected according to the experiment requirement, the water-stop plate is inserted into the set position to stop the water from flowing to the input of the porous medium, if the injection mode is point source injection, the distilled water in the suspended seed chamber is replaced by prepared NaCl solution, connecting the first water inlet hole corresponding to the suspended sub-chamber with the tracer liquid supply tank, opening a peristaltic pump connected with the tracer liquid supply tank, if the injection mode is non-point source injection, the distilled water in the whole suspended sub-chamber including the suspended sub-chamber and the left chamber of the sand tank is replaced by the prepared NaCl solution, connecting all first water inlet holes on the left side of the sand tank with the tracer liquid supply tank, opening a peristaltic pump connected with the tracer liquid supply tank, removing the water-stop sheet after the operation is finished, and continuously conveying the solution in the porous medium;
7) observing and recording experimental data: when the water-stop sheet is removed, observation and recording of experimental data are started, the recorded time interval can be selected according to the seepage velocity, the seepage velocity can be obtained through flow calculation of the third water outlet hole on the right side of the sand tank, if the velocity is high, the overall duration of the experiment is relatively short, the recorded time interval can be a small value, and vice versa, concentration conditions of different positions at the same moment can be observed through the data processing system, an isoconcentration curve is drawn by utilizing an interpolation method, and the migration condition and the dispersion feather form of the tracer can be observed more visually;
in the method, the tracer is selected as NaCl solution, and the concentration can be set to be 500 mg/L; the mesh number of the gauze can be selected from 100 meshes; for the confined aquifer simulation, the overlying clay layer thickness can be set to 15 cm; the arrangement of the conductivity measuring electrode is shown in figure 1; the water head difference between the left and the right of the sand tank 5 can be set according to the requirement; the recording time interval may be set to 30 seconds; the experiment can be repeated three times for the same medium to ensure the reliability of the results.
The invention has the beneficial effects that:
1. through the design of the well pipe structure, the observation of the three-dimensional solute migration condition in the porous medium is realized under the relatively economic condition.
2. Through the design of injection mode adjusting device, can realize the simulation to point source pollution and surface source pollution.
3. The simulation of the two aquifer conditions of the diving aquifer and the confined aquifer can be realized respectively.
4. The experimental method is convenient and fast, the data observation is automatic, the labor cost is saved, the experimental process can be repeated, the results can be compared with each other, and the reliability is high.
Drawings
FIG. 1 is a schematic structural diagram of the present invention.
Fig. 2 is a first structural schematic diagram of the injection mode adjusting device of the present invention.
Fig. 3 is a schematic structural diagram of an injection mode adjusting device according to the present invention.
Figure 4 is a schematic view of a well tubular structure according to the invention.
In the figure: a-a liquid supply device; b, an injection mode adjusting device; 1-tracer liquid supply tank; 2-distilled water supply tank; 3-a peristaltic pump; 4-a water guide pipe; 5, a sand tank; 6-a first water outlet; 7-a first water inlet hole; 8-a second water inlet hole; 9-a second water outlet; 10-suspended subchambers; 11-left chamber of sand tank; 12-a water-stop sheet; 13-electrode lead; 14-well tubing; 141-third water inlet hole; 15-data collector; 16-a data processing system; 17-a permeate collector; 18 — a first baffle; 19-a third water outlet; 20-water permeable holes; 21-conductivity measuring electrodes; 22-middle subchamber; 23-sand tank right chamber; 24-second baffle plates densely distributed with water permeable holes; 25-a third baffle plate densely covered with water permeable holes.
Detailed Description
As shown in fig. 1 to 4, a three-dimensional solute transport simulation device in a porous medium includes a sand tank 5, an injection mode adjusting device B, a liquid supply device a, a permeate collector 17, a water-stop sheet 12, a well pipe 14, a conductivity measuring electrode 21, a data collector 15, and a data processing system 16:
the liquid supply device A comprises a tracer liquid supply tank 1, a distilled water liquid supply tank 2 and a peristaltic pump 3; the sand tank left chamber 11, the suspended sub-chamber 10, the water stop sheet 12, the first baffle plate 18 and the third baffle plate 25 densely distributed with the water permeable holes of the sand tank 5 form an injection mode adjusting device B;
the sand tank 5 is horizontally arranged, the interior of the sand tank 5 is divided into a sand tank left chamber 11, a middle subchamber 22 and a sand tank right chamber 23 from left to right, and the sand tank left chamber 11 is internally provided with a suspended subchamber 10;
the volume occupied by the middle part sub-chamber 22 is the largest, the middle part sub-chamber 22 is filled with porous media, the sand tank right chamber 23 is empty, the sand tank right chamber 23 is connected with the penetrating fluid collector 17, the sand tank left chamber 11 and the middle part sub-chamber 22 are divided by two first baffles 18, a plurality of water permeable holes 20 are uniformly and densely distributed on the first baffles 18, a gap is reserved between the two first baffles 18 and used for placing a water baffle 12, the water baffle 12 plays a role of opening and closing, when an experiment starts, the water baffle 12 is drawn out to enable water flow, when the experiment pauses, the water baffle 12 is inserted to stop flowing, and the middle part sub-chamber 22 and the sand tank right chamber 23 are separated by a second baffle 24 densely distributed with the water permeable holes; and a third baffle 25 densely distributed with water permeable holes is arranged in the suspended sub-chamber 10, and the third baffle 25 densely distributed with the water permeable holes penetrates through the suspended sub-chamber 10 to relieve the disturbance of the liquid level caused by water injection.
A plurality of first water inlet holes 7, second water inlet holes 8, first water outlet holes 6 and second water outlet holes 9 are distributed on the left side wall of the sand tank 5 in a staggered manner; the first water inlet hole 7 and the second water outlet hole 9 are communicated with a suspended sub-chamber 10, and the second water inlet hole 8 and the first water outlet hole 6 are communicated with a sand tank left chamber 11; the first water inlet hole 7 and the second water inlet hole 8 are at the same horizontal height; the first water outlet hole 6 and the second water outlet hole 9 are at the same horizontal height; the level of the first inlet opening 7 and the second inlet opening 8 is higher than the level of the first outlet opening 6 and the second outlet opening 9.
A plurality of groups of third water outlet holes 19 are distributed on the right side wall of the sand tank 5 at different heights, each group of third water outlet holes 19 consists of two water outlet holes with the same horizontal height, and the heights of the third water outlet holes 19 are all lower than the first water outlet hole 6 and the second water outlet hole 9 so as to form a water head difference to form seepage;
a plurality of well pipes 14 are distributed in the porous medium in the sand tank 5, the bottom ends of the well pipes 14 extend into the bottom of the sand tank 5, the well pipes 14 penetrate through the whole porous medium aquifer, the well pipes 14 are hollow cylindrical, third water inlet holes 141 are distributed on the side wall of the whole body, the well pipes 14 are divided into a plurality of cavity chambers, a conductivity measuring electrode 21 is distributed in each cavity chamber, and the conductivity measuring electrodes 21 are connected with a data collector 15 through electrode leads 13; the number of the chambers is set according to personal requirements, the more the number of the chambers is, the more the positions which can be measured in the same well pipe are, besides the conductivity measuring electrode 21 is placed in each cavity, the rest part is filled with porous media, and the solution at different depths is prevented from being mixed and dissolved in the well pipe, so that experimental observation errors are caused.
A tracer liquid supply tank 1 of the liquid supply device A is communicated with a first water inlet hole 7 through a peristaltic pump 3 and a water guide pipe; a distilled water liquid supply tank 2 of the liquid supply device A is communicated with a second water inlet hole 8 through a peristaltic pump 3 and a water guide pipe; the tracer liquid supply tank 1 is used for storing tracer solution, the distilled water liquid supply tank 2 is used for supplying distilled water,
one end of the data acquisition unit 15 is connected with the conductivity measuring electrode 21, the other end of the data acquisition unit 15 is connected with the data processing system 16, the conductivity measuring electrode 21 can detect the change condition of the conductivity in the aqueous solution and transmit the information to the data acquisition unit 15, the data acquisition unit 15 can automatically record the measurement information of the electrode in real time and transmit the data to the data processing system 16, and the data processing system 16 can convert the received conductivity information into the concentration information of the solution, thereby realizing the real-time observation of the solute transport condition.
In the invention, the porous medium in the middle sub-chamber 22 is soil or sand, and is selected according to the experiment requirement; the manufacturing material of the sand tank 5 can be organic glass, the thickness of the glass plate can be set to be 1.5cm, the volume of the sand tank 5 can be set to be 155 multiplied by 60cm, the left chamber 11 of the sand tank is 10cm, the middle part sub-chamber 22 is 140cm, and the right chamber 23 of the sand tank is 5 cm; the thicknesses of the first baffle plate 18, the second baffle plate 24 and the third baffle plate 25 are 8mm, and the thickness of the water-stop plate 12 is 4 mm; the inner diameters of the first water inlet hole 7, the second water inlet hole 8, the first water outlet hole 6, the second water outlet hole 9 and the third water outlet hole 19 are all 8mm, and the outer diameters thereof are all 12 mm; the volume of the suspended sub-chamber 10 is 10 multiplied by 8cm, and the thickness of the side wall of the suspended sub-chamber 10 is 8 mm; the tracer liquid supply tank 1, the distilled water liquid supply tank 2 and the penetrating fluid collector 17 are made of PVC plastics; the water guide pipe 4 is a rubber pipe with the inner diameter of 10 mm; the well pipe 14 is made of organic glass material, the inner diameter of the well pipe 14 is 4cm, and the well pipe is divided into three sub-chambers; the conductivity measuring electrode 21 is a platinum electrode which consists of two platinum sheets which are arranged in parallel with the water flow direction, and the diameter of the conductivity measuring electrode 21 is controlled within 1 cm; the packing material in the wellbore tubular 14 may be glass beads having a diameter of 3 mm.
An experimental method of a three-dimensional solute transport simulation device in a porous medium comprises the following steps:
1) filling materials: wrapping first baffles 18 and second baffles 24 at the left side and the right side of a middle subchamber 22 of a sand tank 5 by gauze to prevent medium particles from blocking a water permeable hole 20, selecting a porous medium required by an experiment according to requirements, laying a well pipe 14 when the filling thickness of the medium reaches 20-30 CM, continuously filling the porous medium after laying the well pipe 14, selecting whether to cover a clay layer above the porous medium according to the requirements of a simulation object, and arranging an upper clay layer for a diving aquifer without arranging an upper clay layer and an upper clay layer for a pressure-bearing aquifer;
2) well pipe laying: wrapping the side wall of the well pipe 14 by gauze to prevent medium particles from blocking the third water inlet hole 141 on the side wall of the well pipe 14, wherein the length of the well pipe 14 is larger than the thickness of the porous medium, the well pipe 14 is arranged when the material filling thickness reaches 20-30 cm (the well pipe can be well fixed in the medium), one end of the well pipe 14 is blocked, the blocking end is inserted into a preset hole distribution position, and the material filling is continued after the hole distribution is finished;
3) and (3) electrode layout: connecting all the conductivity measuring electrodes 21 with the data collector 15, calibrating, wrapping the front edges of the conductivity measuring electrodes 21 with gauze, preventing medium particles from being clamped between electrode platinum sheets after being saturated with water, setting the arrangement depth of each chamber conductivity measuring electrode 21 in advance, filling the rest part of the chamber with glass beads with the diameter of 3mm after arranging the conductivity measuring electrodes 21, and preventing the solution with different depths from being mixed and dissolved in the chamber of the well pipe 14 so as to cause measurement errors;
4) sand tank water supply: connecting a sand tank 5 with a tracer liquid supply tank 1, a distilled water liquid supply tank 2 and a penetrating fluid collector 17, under the condition that the heights of a first water outlet 6 and a second water outlet 9 on the left side of the sand tank 5 are fixed, the lower the height of a third water outlet 19 on the right side of the sand tank 5 is, the higher the seepage speed is, selecting the height of the third water outlet 19 on the right side of the sand tank 5 according to experiments, butting the penetrating fluid collector 17 with the third water outlet 19 on the right side of the sand tank 5, starting a peristaltic pump 3 connected with the distilled water liquid supply tank 2, injecting distilled water into a left chamber 11 of the sand tank, not injecting distilled water into a suspended sub-chamber 10, wherein the whole injection process needs to be slow, further removing bubbles sealed in a porous medium, and continuing until the penetrating fluid collector 17 collects distilled water;
5) medium washing: the porous medium is washed to avoid the influence of ions carried by the medium on an observation result, distilled water is continuously supplied in the washing process, the flow rate of the peristaltic pump 3 is properly increased, and the first water outlet 6 and the second water outlet 9 on the left side of the sand tank 5 are required to form continuous slow overflow, the observation data of the conductivity measuring electrode 21 is used as a judgment basis in the washing process, and when the data of the data processing system 16 are not obviously changed any more, the washing process is finished;
6) injecting a tracer: taking NaCl as an example of the tracer, preparing a NaCl solution with a proper concentration before an experiment, selecting a tracer injection form (point source/surface source) according to the experiment requirement, inserting a water-stop plate 12 into a set position to block water from flowing to the input of a porous medium, if the injection form is point source injection, replacing distilled water in a suspended sub-chamber 10 with the prepared NaCl solution, connecting a first water inlet 7 corresponding to the suspended sub-chamber 10 with a tracer liquid supply tank 1, and opening a peristaltic pump 3 connected with the tracer liquid supply tank 1, if the injection form is surface source injection, replacing distilled water in the whole suspended sub-chamber 10 including the suspended sub-chamber 10 and a sand tank left chamber 11 with the prepared NaCl solution, connecting all first water inlet 7 on the left side of a sand tank 5 with the tracer liquid supply tank 1, opening the peristaltic pump 3 connected with the tracer liquid supply tank 1, and completing the operation, removing the water-stop sheet 12, and continuing to convey the solution in the porous medium;
7) observing and recording experimental data: when the water-stop sheet 12 is removed, observation and recording of experimental data are started, the recorded time interval can be selected according to the seepage velocity, the seepage velocity can be obtained by calculating the flow of the third water outlet 19 on the right side of the sand tank 5, if the velocity is high, the overall duration of the experiment is relatively short, the recorded time interval can be a small value, and vice versa, concentration conditions of different positions at the same moment can be observed through the data processing system, and an isoconcentration curve is drawn by utilizing an interpolation method, so that the migration condition and the dispersion feather form of the tracer can be observed more intuitively;
in the method, the tracer is selected as NaCl solution, and the concentration can be set to be 500 mg/L; the mesh number of the gauze can be selected from 100 meshes; for the confined aquifer simulation, the overlying clay layer thickness can be set to 15 cm; the conductivity measuring electrode 21 is arranged as shown in fig. 1; the water head difference between the left and the right of the sand tank 5 can be set according to the requirement; the recording time interval may be set to 30 seconds; the experiment can be repeated three times for the same medium to ensure the reliability of the results.
Claims (6)
1. A simulation device for three-dimensional solute transport in porous media is characterized in that: the device comprises a sand tank (5), an injection mode adjusting device (B), a liquid supply device (A), a penetrating fluid collector (17), a water-stop plate (12), a well pipe (14), a conductivity measuring electrode (21), a data collector (15) and a data processing system (16):
the liquid supply device (A) comprises a tracer liquid supply box (1), a distilled water liquid supply box (2) and a peristaltic pump (3); a sand tank left chamber (11), a suspended sub-chamber (10), a water-stop plate (12), a first baffle plate (18) and a third baffle plate (25) densely distributed with water permeable holes of the sand tank (5) form an injection mode adjusting device (B);
the sand tank (5) is horizontally arranged, the interior of the sand tank (5) is divided into a sand tank left chamber (11), a middle sub chamber (22) and a sand tank right chamber (23) from left to right, and a suspended sub chamber (10) is arranged in the sand tank left chamber (11);
the middle part sub-chamber (22) is filled with porous media, the sand groove right chamber (23) is vacant, the sand groove right chamber (23) is connected with the penetrating fluid collector (17), the sand groove left chamber (11) and the middle part sub-chamber (22) are divided by two first baffles (18), a plurality of water permeable holes (20) are uniformly and densely distributed on the first baffles (18), a gap is reserved between the two first baffles (18) and used for placing the water stop plate (12), the water stop plate (12) plays a role of opening and closing, when an experiment is started, the water stop plate (12) is drawn out to enable water flow, when the experiment is paused, the water stop plate (12) is inserted to stop flowing, and the middle part sub-chamber (22) and the sand groove right chamber (23) are divided by a second baffle (24) densely distributed with the water permeable holes; third baffles (25) densely distributed with water permeable holes are arranged in the suspended sub-chambers (10), and the third baffles (25) densely distributed with the water permeable holes penetrate through the suspended sub-chambers (10) to relieve liquid level disturbance caused by water injection;
a plurality of first water inlet holes (7), second water inlet holes (8), first water outlet holes (6) and second water outlet holes (9) are distributed on the left side wall of the sand tank (5) in a staggered manner; the first water inlet hole (7) and the second water outlet hole (9) are communicated with the suspended sub-chamber (10), and the second water inlet hole (8) and the first water outlet hole (6) are communicated with the sand tank left chamber (11); the first water inlet hole (7) and the second water inlet hole (8) are at the same horizontal height; the first water outlet hole (6) and the second water outlet hole (9) are at the same horizontal height; the horizontal heights of the first water inlet hole (7) and the second water inlet hole (8) are higher than the horizontal heights of the first water outlet hole (6) and the second water outlet hole (9);
a plurality of groups of third water outlet holes (19) are distributed on the side wall of the right side of the sand tank (5) at different heights, each group of third water outlet holes (19) consists of two water outlet holes with the same horizontal height, and the heights of the third water outlet holes (19) are all lower than the first water outlet hole (6) and the second water outlet hole (9) so as to form water head difference to form seepage;
a plurality of well pipes (14) are distributed in a porous medium in the sand tank (5), the bottom ends of the well pipes (14) extend into the bottom of the sand tank (5), the well pipes (14) penetrate through a whole porous medium aquifer, the well pipes (14) are hollow cylindrical, third water inlet holes (141) are distributed on the side wall of the whole body, the well pipes (14) are equally divided into a plurality of cavity chambers, a conductivity measuring electrode (21) is distributed in each cavity chamber, and the conductivity measuring electrodes (21) are connected with a data collector (15) through electrode leads (13); the rest parts except for the conductivity measuring electrode (21) to be placed in each cavity are filled with porous media;
a tracer liquid supply box (1) of the liquid supply device (A) is communicated with a first water inlet hole (7) through a peristaltic pump (3) and a water guide pipe; a distilled water liquid supply box (2) of the liquid supply device (A) is communicated with a second water inlet hole (8) through a peristaltic pump (3) and a water guide pipe; the tracer liquid supply tank (1) is used for storing tracer solution, the distilled water liquid supply tank (2) is used for supplying distilled water,
one end of the data collector (15) is connected with the conductivity measuring electrode (21), and the other end of the data collector (15) is connected with the data processing system (16).
2. The apparatus according to claim 1, wherein the apparatus comprises: the porous medium in the middle sub-chamber (22) is soil or sand.
3. The apparatus according to claim 1, wherein the apparatus comprises: the sand tank (5) is made of organic glass, the thickness of the glass plate is 1.5cm, the volume of the sand tank (5) is 155 multiplied by 60cm, the left chamber (11) of the sand tank is 10cm, the middle subchamber (22) is 140cm, and the right chamber (23) of the sand tank is 5 cm; the thickness of the first baffle (18), the second baffle (24) and the third baffle (25) is 8mm, and the thickness of the water-stop sheet (12) is 4 mm; the inner diameters of the first water inlet hole (7), the second water inlet hole (8), the first water outlet hole (6), the second water outlet hole (9) and the third water outlet hole (19) are all 8mm, and the outer diameters thereof are all 12 mm; the volume of the suspended sub-chamber (10) is 10 multiplied by 8cm, and the thickness of the side wall of the suspended sub-chamber (10) is 8 mm.
4. The apparatus according to claim 1, wherein the apparatus comprises: the tracer liquid supply tank (1), the distilled water liquid supply tank (2) and the penetrating fluid collector (17) are made of PVC plastics; the water guide pipe 4 is a rubber pipe with the inner diameter of 10 mm; the well pipe (14) is made of organic glass material, and the inner diameter of the well pipe (14) is 4 cm; the conductivity measuring electrode (21) is a platinum electrode, the platinum electrode is composed of two platinum sheets, the two platinum sheets are arranged in parallel with the water flow direction, and the diameter of the conductivity measuring electrode (21) is smaller than 1 cm; the filling material in the well pipe (14) is glass beads with the diameter of 3 mm.
5. An experimental method of a simulator for the three-dimensional migration of solutes in a porous medium according to claim 1, characterized in that: the method comprises the following steps:
1) filling materials: wrapping a first baffle (18) and a second baffle (24) at the left side and the right side of a middle subchamber (22) of a sand tank (5) by gauze to prevent medium particles from blocking a permeable hole (20), selecting a porous medium required by an experiment according to requirements, laying a well pipe (14) when the medium filling thickness reaches 20-30 cm, continuously filling the porous medium after laying the well pipe (14), selecting whether to cover a clay layer above the porous medium according to the requirement of a simulation object, not needing to arrange an overlying clay layer for a diving aquifer, and arranging an overlying clay layer for a pressure-bearing aquifer;
2) well pipe laying: wrapping the side wall of the well pipe (14) by gauze to prevent medium particles from blocking a third water inlet hole (141) in the side wall of the well pipe (14), wherein the length of the well pipe (14) is larger than the thickness of a porous medium, the well pipe (14) is arranged when the material filling thickness reaches 20-30 cm, one end of the well pipe (14) is blocked, the blocked end is inserted into a preset hole distribution position, and the material filling is continued after the hole distribution is finished;
3) and (3) electrode layout: connecting all the conductivity measuring electrodes (21) with a data collector (15), calibrating, wrapping the front edges of the conductivity measuring electrodes (21) by gauze, preventing medium particles from being clamped between electrode platinum sheets after being saturated with water, presetting the arrangement depth of each chamber conductivity measuring electrode (21), filling the rest part of the chamber with glass beads with the diameter of 3mm after arranging the conductivity measuring electrodes (21), and preventing solutions with different depths from being mixed and dissolved in a well pipe (14) chamber so as to cause measuring errors;
4) sand tank water supply: the sand tank (5) is connected with the tracer liquid supply tank (1), the distilled water liquid supply tank (2) and the penetrating fluid collector (17), under the condition that the heights of the first water outlet hole (6) and the second water outlet hole (9) on the left side of the sand tank (5) are fixed, the lower the height of the third water outlet hole (19) on the right side of the sand tank (5), the higher the seepage speed, the height of the third water outlet hole (19) at the right side of the sand tank (5) is selected according to experiments, and the penetrating fluid collector (17) is butted with a third water outlet hole (19) on the right side of the sand tank (5), a peristaltic pump (3) connected with the distilled water supply tank (2) is started, the distilled water is injected into the left chamber (11) of the sand tank, distilled water is not required to be injected into the suspended subchamber (10), the whole injection process needs to be slow, thereby removing the air bubbles enclosed in the porous medium, and the process is continued until the permeate collector (17) collects the distilled water;
5) medium washing: the method comprises the following steps of washing the porous medium to avoid the influence of ions carried by the medium on an observation result, wherein the washing process is to continuously supply distilled water, the flow rate of a peristaltic pump (3) is properly increased, and continuous and slow overflow is required to be formed in a first water outlet (6) and a second water outlet (9) on the left side of a sand tank (5), the washing process takes observation data of a conductivity measuring electrode (21) as a judgment basis, and when the data of a data processing system (16) are not obviously changed any more, the washing process is finished;
6) injecting a tracer: taking NaCl as an example of the tracer, preparing NaCl solution with proper concentration before experiments, selecting a tracer injection form to be a point source or a surface source according to experiment needs, inserting a water-stop plate (12) into a set position to block water from flowing to the input of a porous medium, if the injection mode is point source injection, replacing distilled water in a suspended sub-chamber (10) with the prepared NaCl solution, connecting a first water inlet (7) corresponding to the suspended sub-chamber (10) with a tracer liquid supply tank (1), opening a peristaltic pump (3) connected with the tracer liquid supply tank (1), if the injection mode is surface source injection, replacing distilled water in the whole suspended sub-chamber (10) including the suspended sub-chamber (10) and a sand tank left chamber (11) with the prepared NaCl solution, and connecting all first water inlets (7) on the left side of a sand tank (5) with the tracer liquid supply tank (1), opening a peristaltic pump (3) connected with the tracer liquid supply tank (1), removing the water-stop sheet (12) after the tracer injection operation is finished, and continuously conveying the solution in the porous medium;
7) observing and recording experimental data: when the water-stop sheet (12) is removed, observation and recording of experimental data are started, the recorded time interval is selected according to the seepage velocity, the seepage velocity can be obtained through flow calculation of the third water outlet hole (19) on the right side of the sand tank (5), if the velocity is high, the overall duration of the experiment is relatively short, the recorded time interval is small, and vice versa, concentration conditions of different positions at the same moment can be observed through the data processing system, and an equal concentration curve is drawn by utilizing an interpolation method, so that the migration condition and the dispersion feather form of the tracer can be observed more intuitively.
6. The experimental method of the simulation apparatus for three-dimensional solute transport in porous media according to claim 5, wherein: the tracer is selected to be NaCl solution with the concentration of 500 mg/L; the mesh number of the gauze is 100 meshes; for the simulation of the confined aquifer, the overlying clay layer was 15cm thick.
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