Sludge dewatering and decontamination test device and method for simulating freeze thawing-electroosmosis

Abstract

The invention belongs to the technical field of polluted sludge treatment, and particularly relates to a sludge dewatering and decontamination test device and method for simulating freeze thawing-electroosmosis, and the device comprises a model box module which is used for accommodating a sludge sample; the electroosmosis module is arranged in the model box module, and the electroosmosis module is used for applying an electric field to the sludge sample and discharging moisture and heavy metal pollutants in the model box module in an electroosmosis stage; the freezing and thawing module, the model box module and the electroosmosis module are both placed in the freezing and thawing module, and the freezing and thawing module is used for discharging moisture and heavy metal pollutants in sludge in the freezing and thawing stage and adjusting the environment temperature in the model box module in the electroosmosis stage; and the acquisition module is used for acquiring temperature data in the model box module, electric field data applied by the electroosmosis module, water sample data of moisture and heavy metal pollutants and crack change information of the sludge sample. The invention further provides a sludge dewatering and decontamination simulation test method using the device. The device can significantly improve the test efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of polluted sludge treatment, and in particular relates to a sludge dehydration and pollution removal test device and method for simulating freeze-thaw-electroosmosis. Background Art

[0002] In recent years, in order to change the water quality of lakes, ensure the normal flood discharge capacity of rivers, and improve the navigation capacity of ports and waterways, my country has begun to carry out large-scale dredging and desilting of some lakes, rivers, ports and waterways in a planned manner. The disposal method of on-site stacking is usually adopted, which will cause the following environmental problems: First, silt has the characteristics of high clay content and high water content, and simple stacking will cause waste of land resources; second, silt often contains a large amount of heavy metal pollutants, which is easy to cause secondary pollution to the surrounding soil and groundwater if not treated. Therefore, it is particularly important to dehydrate and reduce the volume of silt and simultaneously remove pollution.

[0003] Electroosmosis is an electrochemical method that uses electric field as a driving force to induce directional migration of water molecules and heavy metal ions. It has a fast dehydration speed and is suitable for low-permeability soils. It has gradually shown great potential in sludge dehydration and simultaneous pollution removal. However, this technology also has obvious defects: the soil body cracks severely in the later stage of electroosmosis, resulting in low efficiency and high energy consumption, which to a certain extent limits the application of this technology in practice.

[0004] As an environmentally friendly technology, freeze-thaw method has received extensive attention in recent years. This technology has the advantages of being economical and capable of dehydrating and removing pollutants simultaneously. However, when the water content of sludge is low, the effect is often poor. It is difficult to achieve deep dehydration and pollution removal of sludge by the simple freeze-thaw method.

[0005] Combining freeze-thaw and electroosmosis may be a more effective method for sludge dewatering and pollution removal. Some scholars have done some exploratory work through some simple test devices, such as repeatedly pre-freezing and thawing the sludge in a refrigerator to enhance the mobility of heavy metal ions in the sludge, then stirring the frozen and thawed sludge evenly, and finally placing the sludge in a simple electroosmosis test device for electroosmosis pollution removal, which effectively improves the pollution removal efficiency of the sludge, but there are still the following shortcomings:

[0006] ① The main goal is to remove heavy metal pollutants in sludge, and it is impossible to achieve integrated sludge dewatering and pollution removal.

[0007] ② Freeze-thaw and electroosmosis were carried out in two sets of experimental devices, which were inefficient and could not simulate the freeze-thaw process under complex temperature boundaries.

[0008] ③During the test, it is impossible to monitor the test data in real time.

[0009] ④ Artificially setting the freezing temperature and electroosmosis intervention time cannot maximize the efficiency of sludge dewatering and pollution removal.

[0010] ⑤ During the electroosmosis process, fine particles migrate, and clogging is likely to occur near the cathode electrode plate in the later stage, resulting in low drainage and pollution removal efficiency.

[0011] Therefore, the development of an intelligent and integrated test device and test method for sludge dewatering and pollution removal with high efficiency, strong economy and the ability to simulate freeze-thaw electroosmosis coupling has significant engineering value and practical significance. Summary of the invention

[0012] The purpose of the present invention is to provide a sludge dewatering and decontamination test device and method simulating freeze-thaw-electroosmosis to solve the above problems.

[0013] To achieve the above object, the present invention provides the following solutions:

[0014] A sludge dewatering and decontamination test device simulating freeze-thaw-electroosmosis, comprising:

[0015] A model box module, wherein the model box module is used to accommodate a sludge sample;

[0016] An electroosmosis module is arranged in the model box module, and is used to apply an electric field to the sludge sample and to discharge water and heavy metal pollutants in the model box module during the electroosmosis stage;

[0017] A freeze-thaw module, wherein the model box module and the electroosmosis module are both placed in the freeze-thaw module, and the freeze-thaw module is used to remove moisture from the sludge and heavy metal pollutants during the freeze-thaw stage and to adjust the ambient temperature inside the model box module during the electroosmosis stage;

[0018] The acquisition module is used to acquire the temperature data inside the model box module, the electric field data applied by the electroosmosis module, the water sample data of the moisture and heavy metal pollutants, and the crack change information of the sludge sample.

[0019] Optionally, the model box module includes:

[0020] Box;

[0021] A sludge sample box, fixedly connected to the box body, used to contain sludge samples, and provided with a window for observation;

[0022] A water collection area is formed by one side of the sludge sample box and the inner wall of the box. The water collection area is connected to the sludge sample box. The electroosmosis module is arranged in the sludge sample box. The water collection area is used to temporarily store water and heavy metal pollutants discharged from the sludge. A drainage hole is opened on one side of the bottom of the water collection area.

[0023] The water inlet of the reverse filtration module is connected with the water outlet of the sludge sample box, and the water outlet of the reverse filtration module is connected with the water collection area. The reverse filtration module prevents the water outlet of the sludge sample box from being blocked.

[0024] Optionally, the sides and bottom of the sludge sample box are made of double-layer hollow transparent organic glass, and grid lines are engraved on the front panel of the sludge sample box.

[0025] Optionally, the electroosmosis module comprises:

[0026] The freezing electrode plate 1 and the freezing electrode plate 2 are installed in the sludge sample box, the freezing electrode plate 1 is located on the side close to the water collection area, and the freezing electrode plate 1 is provided with a channel for fluid flow; the freezing electrode plate 1 and the freezing electrode plate 2 are electrically connected to the acquisition module, and the acquisition module is used to provide electrical energy.

[0027] Optionally, the first freezing electrode plate comprises:

[0028] An outer heat insulation board 1; the outer heat insulation board 1 is provided with a channel for fluid to pass through;

[0029] An inner metal plate 1 is fixedly connected to the outer heat insulation plate 1, and the structure of the inner metal plate 1 matches the structure of the outer heat insulation plate 1; the inner metal plate 1 is used to contact the sludge sample;

[0030] A refrigerant flow channel 1, fixedly connected between the outer heat insulation plate 1 and the inner metal plate 1, the refrigerant enters through a refrigerant inlet 1 of the refrigerant flow channel 1 and is discharged through a refrigerant outlet 1 of the refrigerant flow channel 1;

[0031] A semi-cylindrical sealing protrusion and groove is arranged between the outer insulation board and the inner metal plate, and is used for sealing the edge of the gap between the outer insulation board and the inner metal plate after the outer insulation board and the inner metal plate are assembled.

[0032] Optionally, the second freezing electrode plate comprises:

[0033] Outer insulation board 2;

[0034] The second inner metal plate is fixedly connected to the second outer heat insulation plate. The second outer heat insulation plate and the second inner metal plate have matching structures. The second inner metal plate is used to contact the sludge sample. The surface of the second inner metal plate is coated with an anti-electro-corrosion coating.

[0035] A second refrigerant flow channel is fixedly connected between the second outer heat insulation board and the second inner metal plate, and the refrigerant enters through a second refrigerant inlet of the second refrigerant flow channel and is discharged through a second refrigerant outlet of the second refrigerant flow channel;

[0036] The semi-cylindrical sealing protrusion and groove are arranged between the outer insulation board 2 and the inner metal board 2, and are used for sealing the edge of the gap between the outer insulation board 2 and the inner metal board 2 after the outer insulation board 2 and the inner metal board 2 are spliced ​​together.

[0037] Optionally, the anti-filtration module includes:

[0038] A high-strength nylon plate outer frame, wherein the high-strength nylon plate outer frame is filled with a sand cushion layer, and the particle size of the sand cushion layer increases sequentially along the flow direction of the fluid;

[0039] A plurality of PVC drainage flower pipes are buried in the sand cushion layer, and the plurality of PVC drainage flower pipes are arranged in a matrix;

[0040] A large-aperture geotextile is fixed to the high-strength nylon plate outer frame on one side close to the sludge sample box;

[0041] The small-aperture geotextile is fixedly connected to the high-strength nylon plate outer frame on one side close to the water collection area.

[0042] Optionally, the freeze-thaw module comprises:

[0043] Constant temperature room;

[0044] A movable platform is slidably arranged at the bottom of the inner side of the constant temperature chamber through a horizontal telescopic guide rail, and the model box module is placed in the movable platform. The horizontal telescopic guide rail is located at one end outside the constant temperature chamber and is detachably connected to the top of the vertical bracket through a movable latch. The vertical bracket is vertically arranged with the horizontal telescopic guide rail;

[0045] An LED cold light lamp is fixed on the top of the inner side of the constant temperature chamber;

[0046] A temperature-controlled cold bath box 1 is located outside the constant temperature chamber, and the inlet and outlet of the temperature-controlled cold bath box 1 are respectively connected to the freezing liquid outlet 1 and the freezing liquid inlet 1 through the freezing electrode plate liquid inlet and outlet bellows 1;

[0047] The second temperature-controlled cold bath box is located outside the constant temperature chamber, and the inlet and outlet ends of the second temperature-controlled cold bath box are respectively connected to the second freezing liquid outlet and the second freezing liquid inlet through the second freezing electrode plate liquid inlet and outlet bellows.

[0048] A sludge dehydration and decontamination test method simulating freeze-thaw-electroosmosis, using the above-mentioned sludge dehydration and decontamination test device simulating freeze-thaw-electroosmosis, comprises the following steps:

[0049] Filling the sludge sample containing the pollution source into the model box module;

[0050] Controlling the freeze-thaw module to adjust the temperature boundaries at both ends of the sludge sample in the model box module and the ambient temperature, carrying out sludge dehydration and decontamination tests with different freezing temperature gradients and different freezing-thaw cycle times, and using a multi-objective algorithm to determine the optimal freezing temperature gradient and freezing-thaw cycle times;

[0051] After the freeze-thaw cycle test under the optimal freeze-thaw conditions determined above, controlling the electroosmosis module to perform an electroosmosis test to continue to discharge water and heavy metal pollutants;

[0052] The acquisition module is used to acquire water sample data of water content and heavy metal pollutants in the freeze-thaw stage and the electroosmosis stage, and to calculate the dehydration efficiency of the sludge and the removal efficiency of the heavy metal ions.

[0053] Optionally, the step of determining the optimal freezing temperature gradient and the number of freeze-thaw cycles by the multi-objective algorithm includes:

[0054] According to the image data captured by the front high-definition digital camera in the acquisition module, the image processing technology is used to analyze the changes in the settlement of the front n grid line intersections of the sludge sample after N freeze-thaw cycles under different freezing temperature gradients, and the first objective optimization function is constructed with the settlement as the independent variable;

[0055] The surface images of the sludge sample taken by the high-definition digital camera on the top of the acquisition module after N freeze-thaw cycles at different freezing temperature gradients are processed, the area of ​​the cracks is calculated by counting the number of pixels, and the second objective optimization function is constructed with the crack area as the independent variable;

[0056] By combining the first objective function and the second objective function, a unified multi-objective optimization function can be established. When this function reaches a minimum value, the optimal freezing temperature gradient and the number of freeze-thaw cycles can be obtained. Compared with the prior art, the present invention has the following advantages and technical effects:

[0057] When in use, a sludge sample is placed in the model box module, and the model box module is placed in the freeze-thaw module. The sludge sample placed in the model box module is subjected to freeze-thaw cycles through the freeze-thaw module. At the same time, an electric field can be applied to the sludge sample through the electroosmosis module to produce electroosmosis. By setting freeze-thaw conditions and electroosmosis conditions, freeze-thaw and electroosmosis can be combined to realize sludge dehydration and pollution removal test, which facilitates finding the optimal freeze-thaw conditions. Compared with traditional technologies, this device can realize the removal of pollutants and water in sludge in an integrated manner. The electroosmosis module and freeze-thaw module are integrated in one device to avoid sample transfer and improve test efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative labor:

[0059] Figure 1 It is a schematic diagram of the structure of the present invention;

[0060] Figure 2 It is a structural schematic diagram of a freezing electrode plate 1 of the present invention;

[0061] Figure 3 It is a structural schematic diagram of the second freezing electrode plate of the present invention;

[0062] Figure 4 It is a structural schematic diagram of the constant temperature chamber of the present invention;

[0063] Figure 5 It is a schematic diagram of the overall structure of the reverse filtration module of the present invention;

[0064] Figure 6 It is a schematic diagram of the longitudinal section structure of the reverse filtration module of the present invention;

[0065] Figure 7 A schematic diagram of the processing process of the crack image on the surface of the sludge sample obtained by the sludge dehydration and decontamination test device simulating freeze-thaw-electroosmosis of the present invention;

[0066] Figure 8 A schematic diagram of the processing process of a sludge sample side image obtained by a sludge dehydration and decontamination test device simulating freeze-thaw-electroosmosis of the present invention;

[0067] Among them, 11, sludge sample box; 111, grid line; 12, water collection area; 121, drainage hole; 21, freezing electrode plate one; 211, outer insulation board one; 212, inner metal plate one; 213, refrigerant flow channel one; 214, refrigerant inlet one; 215, refrigerant outlet one; 216, semi-cylindrical sealing protrusion and groove one; 217, fixing nut one; 22, freezing electrode plate two; 221, outer insulation board two; 222, inner metal plate two; 223, refrigerant flow channel two; 224, refrigerant inlet two; 225, refrigerant outlet two; 226, anti-electrocorrosion coating; 227, semi-cylindrical sealing protrusion and groove two; 228, fixing nut two; 2 3. Adjustable telescopic rod; 31. One temperature-controlled cold bath box; 311. One bellows for inlet and outlet of the freezing electrode plate; 32. Two temperature-controlled cold bath boxes; 321. Two bellows for inlet and outlet of the freezing electrode plate; 33. Constant temperature chamber; 34. LED cold light; 35. Movable platform; 36. Horizontal telescopic guide rail; 37. Vertical bracket; 38. Movable latch; 41. DC power supply; 42. Wire; 43. Wide-mouth bottle; 44. Electronic balance; 45. Collection box; 46. Collection computer; 47. Front high-definition digital camera; 48. Top high-definition digital camera; 61. High-strength nylon board frame; 62. Sand cushion layer; 63. PVC drainage flower pipe; 64. Large-aperture geotextile; 65. Small-aperture geotextile. DETAILED DESCRIPTION

[0068] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0069] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0070] Reference Figures 1 to 8 The present invention discloses a sludge dehydration and decontamination test device simulating freeze-thaw-electroosmosis, comprising:

[0071] A model box module, the model box module is used to contain the sludge sample;

[0072] An electroosmosis module is arranged in the model box module, and is used to apply an electric field to the sludge sample and to discharge water and heavy metal pollutants in the model box module during the electroosmosis stage;

[0073] The freeze-thaw module, the model box module and the electroosmosis module are all placed in the freeze-thaw module, and the freeze-thaw module is used to remove moisture and heavy metal pollutants from the sludge during the freeze-thaw stage and to adjust the ambient temperature inside the model box module during the electroosmosis stage;

[0074] The acquisition module is used to obtain the temperature data inside the model box module, the electric field data applied by the electroosmosis module, the water sample data of moisture and heavy metal pollutants, and the crack change information of the sludge sample.

[0075] When in use, a sludge sample is placed in the model box module, and the model box module is placed in the freeze-thaw module. The sludge sample placed in the model box module is subjected to freeze-thaw cycles through the freeze-thaw module. At the same time, an electric field can be applied to the sludge sample through the electroosmosis module to produce electroosmosis. By setting freeze-thaw conditions and electroosmosis conditions, freeze-thaw and electroosmosis can be combined to realize sludge dehydration and pollution removal test, which facilitates finding the optimal freeze-thaw conditions. Compared with traditional technologies, this device can realize the removal of pollutants and water in sludge in an integrated manner. The electroosmosis module and freeze-thaw module are integrated in one device to avoid sample transfer and improve test efficiency.

[0076] As an optional implementation, the model box module includes:

[0077] Box;

[0078] The sludge sample box 11 is fixedly connected to the box body. The sludge sample box 11 is used to contain the sludge sample. The sludge sample box 11 is provided with a window for observation;

[0079] The water collection area 12 is formed by one side of the sludge sample box 11 and the inner wall of the box. The water collection area 12 is connected to the sludge sample box 11. The electroosmosis module is arranged in the sludge sample box 11. The water collection area 12 is used to temporarily store water and heavy metal pollutants discharged from the sludge. A drainage hole 121 is opened at one side of the bottom of the water collection area 12.

[0080] The water inlet of the reverse filtration module is connected to the water outlet of the sludge sample box 11 , and the water outlet of the reverse filtration module is connected to the water collection area 12 . The reverse filtration module prevents the water outlet of the sludge sample box 11 from being blocked.

[0081] As an optional implementation, the sides and bottom of the sludge sample box 11 are made of double-layer hollow transparent organic glass, and grid lines 111 are engraved on the front panel of the sludge sample box 11.

[0082] The model box module includes a sludge sample box 11 and a water collection area 12. The sludge sample box 11 is used to hold sludge samples, and the water collection area 12 is used to temporarily store water and heavy metal pollutants discharged from the sludge. The sludge sample box 11 is open at the top, and the sides and bottom are made of double-layer hollow transparent organic glass, which can effectively reduce heat loss during the test; the front panel of the model box is drawn with grid lines 111, which is convenient for subsequent processing by digital image technology to obtain the settlement of n grid line intersections.

[0083] As an optional embodiment, the electroosmosis module includes:

[0084] The freezing electrode plate 1 21 and the freezing electrode plate 2 22 are installed in the sludge sample box 11, and the freezing electrode plate 1 21 is located on the side close to the water collection area 12. The freezing electrode plate 1 21 is provided with a channel for fluid flow; the freezing electrode plate 1 21 and the freezing electrode plate 2 22 are electrically connected to the acquisition module, and the acquisition module is used to provide electrical energy.

[0085] As an optional embodiment, the freezing electrode plate 21 includes:

[0086] An outer heat insulation board 211; a channel for fluid to pass through is provided on the outer heat insulation board 211;

[0087] The inner metal plate 212 is fixedly connected to the outer heat insulation plate 211, and the structure of the inner metal plate 212 matches the structure of the outer heat insulation plate 211; the inner metal plate 212 is used to contact the sludge sample;

[0088] A refrigerant flow channel 213 is fixedly connected between an outer heat insulation plate 211 and an inner metal plate 212. The refrigerant enters through a refrigerant inlet 214 of the refrigerant flow channel 213 and is discharged through a refrigerant outlet 215 of the refrigerant flow channel 213.

[0089] The semi-cylindrical sealing protrusion and groove 216 are arranged between the outer insulation board 211 and the inner metal plate 212, and are used for sealing the edge of the gap between the outer insulation board 211 and the inner metal plate 212 after the outer insulation board 211 and the inner metal plate 212 are spliced.

[0090] As an optional embodiment, the freezing electrode plate 22 includes:

[0091] Outer insulation board 221;

[0092] The second inner metal plate 222 is fixedly connected to the second outer heat insulation plate 221. The structures of the second outer heat insulation plate 221 and the second inner metal plate 222 match each other. The second inner metal plate 222 is used to contact the sludge sample. The surface of the second inner metal plate 222 is coated with an anti-electro-corrosion coating 226.

[0093] The second refrigerant flow channel 223 is fixedly connected between the second outer heat insulation board 221 and the second inner metal plate 222. The refrigerant enters through the second refrigerant inlet 224 of the second refrigerant flow channel 223 and is discharged through the second refrigerant outlet 225 of the second refrigerant flow channel 223.

[0094] The semi-cylindrical sealing protrusion and groove 227 are arranged between the outer insulation board 221 and the inner metal plate 222, and are used to seal the edge of the gap between the outer insulation board 221 and the inner metal plate 222 after the outer insulation board 221 and the inner metal plate 222 are spliced.

[0095] The electroosmosis module includes a freezing electrode plate 1 21 , a freezing electrode plate 22 , an adjustable telescopic rod 23 , a temperature-controlled cold bath box 1 31 , a temperature-controlled cold bath box 2 32 , a constant temperature chamber 33 , a DC power supply 41 , and a wire 42 .

[0096] The freezing electrode plate 21 is composed of an outer heat insulation plate 211, an inner metal plate 212, a "snake-shaped" freezing liquid flow channel 213, a freezing liquid inlet 214, a freezing liquid outlet 215, a semi-cylindrical sealing protrusion and groove 216, and a fixing nut 217.

[0097] The freezing electrode plate 21 is designed as an "inverted E shape" to facilitate the discharge of moisture and heavy metal pollutants during the test; the outer insulation plate 211 is a copper plate with good electrical and thermal conductivity, which can realize both the freeze-thaw process and the electroosmosis process, and the inner metal plate 212 is a nylon plate with high thermal resistance, which can reduce the heat loss during the freezing process and improve the freezing efficiency; the freezing liquid flow channel 213 is a "snake-shaped" structure and is arranged between the inner and outer layers, which can make the temperature at both ends of the sample more uniform and improve the test accuracy; to prevent leakage of the freezing liquid, semi-cylindrical sealing protrusions and grooves 216 are also arranged on the upper part and both sides between the inner and outer layers; the outer insulation plate 211 and the inner metal plate 212 are connected to form a whole through four fixing nuts 217.

[0098] The freezing electrode plate 22 includes an outer insulation plate 221, an inner metal plate 222, a freezing liquid flow channel 223, a freezing liquid inlet 224, a freezing liquid outlet 225, an anti-electro-corrosion coating 226, a semi-cylindrical sealing protrusion and groove 227, and a fixing nut 228.

[0099] The differences between the second freezing electrode plate 22 and the first freezing electrode plate 21 are as follows:

[0100] The freezing electrode plate 22 is designed as a "rectangle" to maximize the freezing and conductive efficiency; the anti-electrocorrosion coating is painted around the inner layer, and the anti-electrocorrosion coating is selected as graphene, which can effectively slow down the corrosion of the inner metal plate during the electro-osmosis process and significantly improve the dehydration and decontamination efficiency in the electro-osmosis stage; a semi-cylindrical sealing protrusion and groove 227 are provided along the edge between the inner and outer layers to prevent leakage of the refrigerant.

[0101] The arrangement directions of the refrigerant flow channel 1 213 and the refrigerant flow channel 2 223 in the above two freezing electrode plates are different. The refrigerant flow channel 1 213 of the freezing electrode plate 1 21 is arranged vertically, and the refrigerant flow channel 2 223 of the right freezing electrode plate 2 22 is arranged horizontally.

[0102] As an optional implementation, the anti-filtration module includes:

[0103] A high-strength nylon plate outer frame 61 is filled with a sand cushion layer 62. The particle size of the sand cushion layer 62 increases along the fluid flow direction. This is similar to the design of the anti-filter layer of the earth-rock dam, which can filter the soil and drain water.

[0104] A plurality of PVC drainage flower pipes 63 are buried in the sand cushion layer 62. The plurality of PVC drainage flower pipes 63 are arranged in a matrix, which can further accelerate the drainage of the sludge sample.

[0105] The large-aperture geotextile 64 is fixed to the high-strength nylon plate outer frame 61 near the side of the silt sample box 11, which can prevent soil particles from entering the sand cushion layer to a certain extent, thereby avoiding blockage, and can also accelerate the entry of water and pollutants into the sand cushion layer, thereby accelerating drainage.

[0106] The small-aperture geotextile 65 is fixed to the side of the high-strength nylon plate outer frame 61 close to the water collection area 12, which can effectively prevent the particles in the sand cushion layer from being carried out by water migration during the drainage process.

[0107] As an optional embodiment, the freeze-thaw module includes:

[0108] Constant temperature room 33;

[0109] The movable platform 35 is slidably arranged at the bottom of the inner side of the constant temperature chamber 33 through a horizontal telescopic guide rail 36, and the model box module is placed in the movable platform 35. The horizontal telescopic guide rail 36 is located at one end outside the constant temperature chamber 33 and is detachably connected to the top of the vertical bracket 37 through a movable latch 38. The vertical bracket 37 is vertically arranged with the horizontal telescopic guide rail 36;

[0110] LED cold light lamp 34, fixed on the top of the inner side of constant temperature chamber 33;

[0111] The temperature-controlled cold bath box 31 is located outside the constant temperature chamber 33, and the inlet and outlet ends of the temperature-controlled cold bath box 31 are respectively connected to the freezing liquid outlet 215 and the freezing liquid inlet 214 through the freezing electrode plate liquid inlet and outlet bellows 311;

[0112] The second temperature-controlled cold bath box 32 is located outside the constant temperature chamber 33. The inlet and outlet ends of the second temperature-controlled cold bath box 32 are connected to the second freezing liquid outlet 225 and the second freezing liquid inlet 224 through the second freezing electrode plate liquid inlet and outlet bellows 321 respectively.

[0113] The freeze-thaw module includes a temperature-controlled cold bath box 31 and a temperature-controlled cold bath box 32. The temperature-controlled cold bath box 31 is connected to the freezing liquid inlet 214 and the freezing liquid outlet 215 of the freezing electrode plate 1 through the freezing electrode plate inlet and outlet liquid bellows 311. The temperature-controlled cold bath box 32 is connected to the freezing liquid inlet 224 and the freezing liquid outlet 225 of the freezing electrode plate 2 through the freezing electrode plate inlet and outlet liquid bellows 321. The temperature boundaries of the sludge sample at both ends of the sample can be accurately controlled during the freeze-thaw-electroosmosis process.

[0114] The liquid outlet of the second temperature-controlled cold bath box 32 is connected to the second freezing liquid inlet 224 on the side close to the bottom of the second freezing electrode plate 22, which can maximize the freezing efficiency of the test.

[0115] The constant temperature chamber 33 is arranged outside the model box module, the temperature-controlled cold bath box, the DC power supply, the electronic balance, the acquisition box and the acquisition computer are placed outside the constant temperature chamber 33, and the rest are placed inside the constant temperature chamber 33.

[0116] An LED cold light lamp 34 is installed on each side of the constant temperature chamber 33, and the direction of the light source is 45° to the surface of the sludge sample.

[0117] angle so as to obtain clear displacement and crack images; in addition, a movable platform 35 is provided in the constant temperature chamber 33, and the movable platform is located on the horizontal telescopic guide rail 36, which is convenient for pushing the model box into and out of the constant temperature chamber during the test. The horizontal telescopic guide rail and the vertical bracket 37 are connected by a movable pin 38, thereby realizing the installation and disassembly of the vertical bracket.

[0118] As an optional implementation, the acquisition module includes:

[0119] A DC power source 41, the positive electrode of which is electrically connected to the second inner metal plate 222 via a wire 42, and the negative electrode of which is electrically connected to the first inner metal plate 212 via another wire 42;

[0120] The front high-definition digital camera 47 and the top high-definition digital camera 48 are respectively located at the front side and the top of the sludge sample box 11, and the front high-definition digital camera 47 and the top high-definition digital camera 48 are both located in the constant temperature chamber 33;

[0121] A wide-mouth bottle 43, the liquid inlet end of which is connected to the drain hole 121 through a hose, and the wide-mouth bottle 43 is placed on an electronic balance 44;

[0122] One end of the acquisition box 45 is electrically connected to the electronic balance 44 , the front high-definition digital camera 47 , and the top high-definition digital camera 48 , and the other end of the acquisition box 45 is electrically connected to the acquisition computer 46 .

[0123] The positive and negative electrodes of the DC power supply 41 are respectively connected to the inner metal plate 222 of the freezing electrode plate 22 and the inner metal plate 1 212 of the freezing electrode plate 1 21 through the wire 42 to provide the required voltage at both ends of the sample during the freeze-thaw-electroosmosis process.

[0124] The data acquisition module includes a wide-mouth bottle 43, an electronic balance 44, a collection box 45, a collection computer 46, a front high-definition digital camera 47, and a top high-definition digital camera 48.

[0125] The wide-mouth bottle 43 is connected to the drainage hole 121 of the water collection area to collect the water and heavy metal pollutants discharged from the sludge sample. The electronic balance 44 is used for real-time monitoring of the drainage volume of the sludge sample. Two high-definition digital cameras are respectively arranged on the front side and the top of the sludge sample box, namely the front high-definition digital camera 47 and the top high-definition digital camera 48. The front high-definition digital camera is used to capture the consolidation process of the sludge sample under repeated freeze-thaw cycles, and the top high-definition digital camera is used to monitor the evolution of surface cracks of the sludge sample under freeze-thaw cycles; the electronic balance, the front high-definition digital camera, and the top high-definition digital camera are all connected to the collection computer 46 through the collection box 45, so as to display and record the above test results in real time.

[0126] A sludge dehydration and decontamination test method simulating freeze-thaw-electroosmosis, using the above-mentioned sludge dehydration and decontamination test device simulating freeze-thaw-electroosmosis, comprises the following steps:

[0127] S1. Prepare a sludge sample containing a pollution source, and fill the sludge sample into a model box module;

[0128] Determine the initial moisture content: Put the heavy metal-free sludge with a certain initial moisture content into a bucket and stir it evenly with a stirrer. Take out three sludge samples, each not less than 50g, place them in a 65° oven for drying, and then determine their initial moisture content.

[0129] Preparation of sludge samples: heavy metal ions are selected as pollution sources, and the reagents used to prepare heavy metal contaminated sludge are corresponding heavy metal compound solutions. The pollution concentration is set to X (heavy metal ion mass: dry mud mass), and the designed moisture content is W; based on the above initial moisture content, the mass of the required heavy metal compound and the mass of deionized water are calculated; the heavy metal compound is first dissolved in deionized water, and then fully stirred and mixed with the sludge sample in the bucket. After stirring, it is sealed with plastic wrap and left to stand for 24 hours to ensure that the sample is uniform; a layer of vaseline is applied along the side wall of the sludge sample box, and the sludge in the bucket is loaded into the sludge sample box to 3 / 4 of the height to obtain a sludge sample with a heavy metal pollution concentration of X and a moisture content of W; finally, the model box module is placed in the constant temperature chamber 33.

[0130] S2, assembling and setting the temperature gradient to be executed by the freeze-thaw module, performing a freeze-thaw cycle test, and acquiring test data and images through an acquisition module;

[0131] S3, when performing N freeze-thaw cycle tests under different freezing temperature gradients, the freeze-thaw cycle test is performed after changing the temperature gradient to be performed in step S2;

[0132] A high-definition digital camera is installed in front of and behind the sludge sample box 11. The height, angle and distance from the front high-definition digital camera 47 and the top high-definition digital camera 48 to the sludge sample box are adjusted so that the grid lines 111 in front of the sludge sample box can be clearly displayed at the center of the screen of the front high-definition digital camera 47, and the surface of the sludge sample in the sludge sample box 11 can be clearly displayed at the center of the top high-definition digital camera 48.

[0133] Temperature gradient setting: First, set the temperature of the constant temperature chamber 33 to a constant positive temperature T0; open the temperature-controlled cold bath box 2 32 and set it to the freezing temperature T2, and keep the temperature-controlled cold bath box 1 31 set to the positive temperature T1, that is: the left side is the warm end,

[0134] The right side is the cold end, so that the temperature of the refrigerant flow channel 1 213 and the temperature of the right refrigerant flow channel 2 223 form a stable temperature gradient grad(T) = (T1-T2) / L (L is the distance between the two freezing electrode plates).

[0135] One freeze-thaw cycle: the sample is frozen continuously for 12 hours under the temperature gradient formed in the above steps, and then the temperature of the two temperature-controlled cold baths is adjusted to positive temperature T3, so that the sample is thawed continuously for 12 hours at positive temperature T3, thus forming a freeze-thaw cycle; during the thawing process, the consolidation process and surface crack evolution law of the sludge sample are monitored in real time by a high-definition digital camera, and the total drainage of the sludge sample is monitored in real time by an electronic balance.

[0136] N freeze-thaw cycles: Repeat the above steps to complete N freeze-thaw cycle tests.

[0137] S4. After collating and analyzing the data, determine the optimal freezing temperature gradient and number of freeze-thaw cycles;

[0138] The optimal freezing temperature gradient and the number of freeze-thaw cycles are determined by the following steps:

[0139] According to the image results of N freeze-thaw cycle tests under different freezing temperature gradients, the optimal freezing temperature gradient and the number of freeze-thaw cycles can be determined, including the following steps:

[0140] Construct the first objective function: Based on the image data captured by the front high-definition digital camera, the image processing technology is used to analyze the changes in the settlement of the intersection points of n grid lines in the front of the sludge sample after N freeze-thaw cycles under different freezing temperature gradients, and the first objective optimization function is constructed with the settlement as the independent variable:

[0141]

[0142] T is the freezing temperature gradient;

[0143] N is the number of freeze-thaw cycles;

[0144] n is the number of grid line intersections on the surface of the sludge sample;

[0145] hi is the initial height value of the intersection of the i-th grid line;

[0146] is the height value of the intersection of the i-th grid line of the sludge sample after freezing and thawing;

[0147] Construct the second objective function: process the surface images of the sludge sample taken by the top high-definition digital camera after N freeze-thaw cycles at different freezing temperature gradients, calculate the area of ​​the cracks by counting the number of pixels, and construct the second objective optimization function with the crack area as the independent variable:

[0148] g(T,N)=1-r

[0149] T is the freezing temperature gradient;

[0150] N is the number of freeze-thaw cycles;

[0151] r is the crack ratio of the silt sample after freezing and thawing;

[0152] Construct a unified multi-objective function: Combine the first objective function and the second objective function to establish a unified multi-objective optimization function. When this function reaches a minimum value, the optimal freezing temperature gradient and freeze-thaw cycle number can be obtained:

[0153]

[0154] a is the weight coefficient of the first objective function, and b is the weight coefficient of the second objective function.

[0155] S5, based on the freeze-thaw test of the optimal freezing temperature gradient and the number of freeze-thaw cycles, the electroosmosis module is started to perform the drainage process, and the acquisition module acquires the test data;

[0156] The DC power supply was turned on, and the voltage value of the DC power supply was set according to the potential gradient of 1 V / cm. The electroosmosis time was 24 h. During the electroosmosis process, an electronic balance 44 was used to monitor the change of the drainage volume of the sludge sample in real time.

[0157] S6. Processing and analysis of test results.

[0158] After the test, the solution in the wide-mouth bottle 43 is taken, the content of heavy metals and the amount of water therein are determined, the total energy consumption of the freeze-thaw and electroosmosis stages is calculated, and the amount of water discharged and the amount of heavy metals removed under unit energy consumption are obtained; a certain mass of sludge samples are taken from different sections from left to right in the sludge sample box 11 for drying, the water content of the sludge samples is determined, and the dehydration efficiency of different sections from left to right in the sludge sample box 11 is calculated; the dried sludge samples are ground and sieved, and the occurrence forms of heavy metals in the sludge samples are determined according to the Tessier five-step extraction method, and then the concentrations of various forms of heavy metals in the sludge samples are determined by an atomic absorption spectrophotometer, and the residual concentrations of heavy metal ions and the removal efficiency of different sections from left to right in the sludge sample box are calculated.

[0159] The distance between the freezing electrode plate 1 21 and the freezing electrode plate 2 22 can be changed by three adjustable telescopic rods, and the influence of different temperature gradients and potential gradients on the dewatering and decontamination effect of sludge can be explored.

[0160] By flexibly controlling the test target temperature in the temperature-controlled cold bath box 1 31 and the temperature-controlled cold bath box 2 32, it is also possible to carry out sludge freeze-thaw dehydration and decontamination tests under various complex environmental boundary conditions such as two-way freezing and two-way melting.

[0161] During the freeze-thaw cycle of the simulated sludge sample, the temperature of the constant temperature chamber 33 remains constant and is always positive, and its target temperature is preferably 2-5°C.

[0162] A large number of cracks will appear in the sludge sample in the later stage of electroosmosis. By opening the temperature-controlled cold bath box 1 31 and the temperature-controlled cold bath box 2 32 to perform secondary freeze-thaw on the sample, the method of changing the freezing direction or freezing mode can heal some cracks on the surface of the sludge sample, which can improve the dehydration and decontamination efficiency in the electroosmosis stage.

[0163] Compared with the traditional technology, the present invention has the following effects:

[0164] 1. The freezing electrode plate in the present invention is divided into two layers, the inner layer is a copper plate with high thermal conductivity, and the outer layer is a nylon plate with high thermal resistance. A "snake-shaped" freezing liquid flow channel is arranged between the inner and outer layers, which can realize both the freeze-thaw process and the electroosmosis process.

[0165] 2. The freezing electrode plate in the present invention comprises two left and right pieces. The left freezing electrode plate is designed as an "inverted E shape", which is helpful for the discharge of moisture and heavy metal pollutants from the sample. The right freezing electrode plate is designed as a "rectangle", and its inner surface is painted with an anti-corrosion coating, which can significantly improve the freezing and conductive efficiency.

[0166] 3. The sample box in the present invention has an opening on the top, and is made of double-layer hollow transparent organic glass on the sides and the bottom, which can reduce heat loss in the test; in addition, through flexible control of the target temperature of the constant temperature chamber and the left and right temperature-controlled cold bath boxes, sludge dehydration and decontamination tests under various complex environmental boundaries such as one-way freezing, two-way freezing, and two-way melting can be carried out. The double-layer hollow design of the sample box combined with the internal and external combined temperature control method greatly improves the accuracy of the test.

[0167] 4. In the present invention, PVC drainage flower pipes are evenly arranged in the height and horizontal directions in the sand cushion layer. The drainage flower pipes are composed of a horizontal section and a tail inclined section, which can alleviate the clogging problem of the anti-filtration module during the test.

[0168] 5. The present invention couples intelligent means such as digital image tracking and real-time drainage monitoring, and uses a multi-objective optimization algorithm to propose a method for determining the "optimal number of freeze-thaw cycles" and the "optimal freezing temperature gradient".

[0169] 6. In the present invention, when a large number of cracks appear in the sludge sample in the later stage of the electroosmosis stage, a temperature-controlled cold bath can be opened to perform secondary freeze-thaw on the sample, and the method of changing the freezing direction or freezing mode is used to heal some cracks on the surface of the sludge sample. Further conducting a secondary electroosmosis test can significantly improve the dehydration and decontamination efficiency in the electroosmosis stage.

[0170] 7. The test device used in the present invention can carry out dehydration and pollution removal tests of sludge under the coupling effect of freeze-thaw-electroosmosis, realizing the intelligence and integration of deep dehydration and pollution removal of sludge. The device has low cost, simple operation method and high credibility of test results.

[0171] 8. The present invention adopts the freeze-thaw-electroosmosis coupling method, combines digital image processing technology with a multi-objective optimization algorithm, realizes the intelligence and integration of dehydration and pollution removal, and significantly improves the efficiency of sludge dehydration and pollution removal; in addition, the composite temperature control method of the constant temperature chamber combined with the temperature-controlled cold bath box can not only simulate a variety of complex temperature boundaries, but also improve the accuracy of the test and the reliability of the test results.

[0172] In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0173] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A sludge dewatering and decontamination test device simulating freeze-thaw-electroosmosis, characterized in that: include: A model box module, wherein the model box module is used to accommodate a sludge sample; An electroosmosis module is arranged in the model box module, and is used to apply an electric field to the sludge sample and to discharge water and heavy metal pollutants in the model box module during the electroosmosis stage; A freeze-thaw module, wherein the model box module and the electroosmosis module are both placed in the freeze-thaw module, and the freeze-thaw module is used to remove moisture from the sludge and heavy metal pollutants during the freeze-thaw stage and to adjust the ambient temperature inside the model box module during the electroosmosis stage; The acquisition module is used to acquire the temperature data inside the model box module, the electric field data applied by the electroosmosis module, the water sample data of the moisture and heavy metal pollutants, and the crack change information of the sludge sample.

2. A sludge dewatering and decontamination test device simulating freeze-thaw-electroosmosis according to claim 1, characterized in that: The model box module includes: Box; A sludge sample box (11) is fixedly connected to the box body, the sludge sample box (11) is used to contain sludge samples, and the sludge sample box (11) is provided with a window for observation; A water collection area (12) is formed by enclosing one side of the sludge sample box (11) and the inner wall of the box. The water collection area (12) is connected to the sludge sample box (11). The electroosmosis module is arranged in the sludge sample box (11). The water collection area (12) is used to temporarily store water and heavy metal pollutants discharged from the sludge. A drainage hole (121) is provided on one side of the bottom of the water collection area (12); The water inlet of the reverse filtration module is connected to the water outlet of the sludge sample box (11), and the water outlet of the reverse filtration module is connected to the water collection area (12). The reverse filtration module prevents the water outlet of the sludge sample box (11) from being blocked.

3. A sludge dewatering and decontamination test device simulating freeze-thaw-electroosmosis according to claim 2, characterized in that: The sides and bottom of the sludge sample box (11) are made of double-layer hollow transparent organic glass, and grid lines (111) are engraved on the front panel of the sludge sample box (11).

4. The sludge dewatering and decontamination test device simulating freeze-thaw-electroosmosis according to claim 2, characterized in that: The electroosmotic module comprises: A freezing electrode plate 1 (21) and a freezing electrode plate 2 (22) are installed in the sludge sample box (11), wherein the freezing electrode plate 1 (21) is located on a side close to the water collection area (12), and the freezing electrode plate 1 (21) is provided with a channel for fluid flow; the freezing electrode plate 1 (21) and the freezing electrode plate 2 (22) are electrically connected to the acquisition module, and the acquisition module is used to provide electrical energy.

5. The sludge dewatering and decontamination test device simulating freeze-thaw-electroosmosis according to claim 4, characterized in that: The freezing electrode plate 1 (21) comprises: An outer heat insulation board (211); the outer heat insulation board (211) is provided with a channel for fluid to pass through; An inner metal plate (212) is fixedly connected to the outer heat insulation plate (211), and the structure of the inner metal plate (212) matches the structure of the outer heat insulation plate (211); the inner metal plate (212) is used to contact the sludge sample; A refrigerant flow channel (213) is fixedly connected between the outer heat insulation plate (211) and the inner metal plate (212), and the refrigerant enters through a refrigerant inlet (214) of the refrigerant flow channel (213) and is discharged through a refrigerant outlet (215) of the refrigerant flow channel (213); A semi-cylindrical sealing protrusion and groove (216) is arranged between the outer insulation board (211) and the inner metal plate (212) and is used for sealing the edge of the gap between the outer insulation board (211) and the inner metal plate (212) after the outer insulation board (211) and the inner metal plate (212) are assembled.

6. The sludge dewatering and decontamination test device simulating freeze-thaw-electroosmosis according to claim 5, characterized in that: The second freezing electrode plate (22) comprises: Outer insulation board 2 (221); The second inner metal plate (222) is fixedly connected to the second outer heat insulation plate (221), the second outer heat insulation plate (221) and the second inner metal plate (222) are structurally matched, the second inner metal plate (222) is used to contact the sludge sample, and the surface of the second inner metal plate (222) is coated with an anti-electrocorrosion coating (226); A second refrigerant flow channel (223) is fixedly connected between the second outer heat insulation plate (221) and the second inner metal plate (222), and the refrigerant enters through a second refrigerant inlet (224) of the second refrigerant flow channel (223) and is discharged through a second refrigerant outlet (225) of the second refrigerant flow channel (223); A second semi-cylindrical sealing protrusion and groove (227) is arranged between the second outer heat insulation board (221) and the second inner metal plate (222) and is used for sealing the edge of the gap between the second outer heat insulation board (221) and the second inner metal plate (222) after the second outer heat insulation board (221) and the second inner metal plate (222) are assembled.

7. The sludge dewatering and decontamination test device simulating freeze-thaw-electroosmosis according to claim 2, characterized in that: The anti-filtration module comprises: A high-strength nylon plate outer frame (61), wherein the high-strength nylon plate outer frame (61) is filled with a sand cushion layer (62), and the particle size of the sand cushion layer (62) increases sequentially along the flow direction of the fluid; A plurality of PVC drainage flower pipes (63) are buried in the sand cushion layer (62), and the plurality of PVC drainage flower pipes (63) are arranged in a matrix; A large-aperture geotextile (64) is fixedly connected to a side of the high-strength nylon plate outer frame (61) close to the sludge sample box (11); A small-aperture geotextile (65) is fixedly connected to the high-strength nylon plate outer frame (61) on one side close to the water collection area (12).

8. The sludge dewatering and decontamination test device simulating freeze-thaw-electroosmosis according to claim 6, characterized in that: The freeze-thaw module comprises: Constant temperature room (33); A movable platform (35) is slidably arranged at the bottom of the inner side of the constant temperature chamber (33) via a horizontal telescopic guide rail (36), and the model box module is placed in the movable platform (35). One end of the horizontal telescopic guide rail (36) located outside the constant temperature chamber (33) is detachably connected to the top of a vertical bracket (37) via a movable latch (38), and the vertical bracket (37) is arranged vertically to the horizontal telescopic guide rail (36); An LED cold light lamp (34) is fixed on the top of the inner side of the constant temperature chamber (33); A temperature-controlled cold bath box (31) is located outside the constant temperature chamber (33), and the inlet and outlet ends of the temperature-controlled cold bath box (31) are respectively connected to the freezing liquid outlet (215) and the freezing liquid inlet (214) through a freezing electrode plate liquid inlet and outlet bellows (311); The second temperature-controlled cold bath box (32) is located outside the constant temperature chamber (33), and the inlet and outlet ends of the second temperature-controlled cold bath box (32) are respectively connected to the second freezing liquid outlet (225) and the second freezing liquid inlet (224) through the second freezing electrode plate liquid inlet and outlet bellows (321).

9. A sludge dehydration and decontamination test method simulating freeze-thaw-electroosmosis, using a sludge dehydration and decontamination test device simulating freeze-thaw-electroosmosis according to any one of claims 1 to 8, characterized in that: The steps include: Filling the sludge sample containing the pollution source into the model box module; Controlling the freeze-thaw module to adjust the temperature boundaries at both ends of the sludge sample in the model box module and the ambient temperature, carrying out sludge dehydration and decontamination tests with different freezing temperature gradients and different freezing-thaw cycle times, and using a multi-objective algorithm to determine the optimal freezing temperature gradient and freezing-thaw cycle times; After the freeze-thaw cycle test under the optimal freeze-thaw conditions determined above, controlling the electroosmosis module to perform an electroosmosis test to continue to discharge water and heavy metal pollutants; The acquisition module is used to acquire water sample data of water content and heavy metal pollutants in the freeze-thaw stage and the electroosmosis stage, and to calculate the dehydration efficiency of the sludge and the removal efficiency of the heavy metal ions.

10. A sludge dewatering and decontamination test method simulating freeze-thaw-electroosmosis according to claim 9, characterized in that: The step of determining the optimal freezing temperature gradient and the number of freeze-thaw cycles by the multi-objective algorithm comprises: According to the image data captured by the front high-definition digital camera in the acquisition module, the image processing technology is used to analyze the changes in the settlement of the front n grid line intersections of the sludge sample after N freeze-thaw cycles under different freezing temperature gradients, and the first objective optimization function is constructed with the settlement as the independent variable; The surface images of the sludge sample taken by the high-definition digital camera on the top of the acquisition module after N freeze-thaw cycles at different freezing temperature gradients are processed, the area of ​​the cracks is calculated by counting the number of pixels, and the second objective optimization function is constructed with the crack area as the independent variable; By combining the first objective function and the second objective function, a unified multi-objective optimization function can be established. When this function reaches a minimum value, the optimal freezing temperature gradient and number of freeze-thaw cycles can be obtained.

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