Physical model test device and method for underground coal seam mining and freeze-thaw cycle induced slip

Abstract

The invention relates to a physical model test device for landslide, in particular to a physical model test device for underground coal seam mining and freeze-thaw cycle induced slip, and belongs to the field of geological engineering. The experimental model comprises a rock mass and a coal seam, a kt plate is used for simulating the coal seam, and a small electric saw is operated to cut the kt plate so as to simulate coal seam mining; the freezing and thawing circulation system comprises a rainfall simulation system capable of adjusting rainfall and a temperature control system, the rock mass is saturated with water through rainfall, then freezing is formed after 6 h of low temperature, then 6 h of high temperature unfreezing is conducted, and the freezing and thawing circulation is completed; the monitoring sensing system comprises a grating displacement monitor, a stress sensor, a three-dimensional scanning device and a temperature sensor. According to the invention, the freeze-thaw cycle process can be simulated truly.

Description

Technical Field

[0001] The invention relates to a physical model test device for landslide, in particular to a physical model test device for landslide caused by underground coal seam mining and freeze-thaw cycle, belonging to the field of geological engineering. Background Art

[0002] my country's mountainous and hilly areas account for 65% of the country's land area, with complex geological conditions and a high frequency of geological disasters. In 2023, there were 3,668 geological disasters in China, including 925 landslides. Landslide geological disasters are the most serious in terms of casualties and property losses among all types of geological disasters because of their variety, difficulty in detection, wide distribution, and great harm.

[0003] The triggering factors of landslides are mainly: topography, geological structure, rock and soil structure, hydrogeological conditions, adverse geological effects, rainfall, human engineering activities, earthquakes, etc. Since the 20th century, more than 50% of large landslides have been closely related to human engineering activities. Among them, underground coal mining activities are frequent and the development level is high, which leads to a wide variety of geological disasters with serious hazards. Coal mining is prone to cause a variety of derivative geological disasters, such as ground fissures, mining collapse, landslides, etc. At the same time, the frost heave force during the freezing and thawing process causes the cracks caused by coal mining to expand downward, forming a front edge creeping section and a rear edge tensile cracking section. When the cracks deepen to a certain depth, the locking section is sheared off, and the potential energy of the slope rock mass is suddenly released, thus forming a high-speed landslide.

[0004] The occurrence of landslides is often not affected by a single factor, and the coupling of multiple factors needs to be considered. However, the current landslide physical model tests mainly consider unilateral factors, such as rainfall intensity, freeze-thaw cycles, etc., or the coupling of rainfall, strong earthquakes, temperature, etc., and have not considered the coupling of coal mining and freeze-thaw cycles. Summary of the invention

[0005] In view of the above problems, the present invention discloses a physical model test device and method for underground coal mining and freeze-thaw cycle-induced sliding. The experimental model of the present invention includes rock mass and coal seam, and the coal seam is simulated by a KT plate, and a small electric saw is used to cut the KT plate to simulate coal seam mining; the freeze-thaw cycle system includes a rainfall simulation system with adjustable rainfall and a temperature control system, which saturates the rock mass with water through rainfall, and then freezes after 6 hours of low temperature, and then thaws after 6 hours of high temperature to complete the freeze-thaw cycle; the monitoring sensor system includes a grating displacement monitoring, a stress sensor, a three-dimensional scanning device, and a temperature sensor. The present invention can simulate the freeze-thaw cycle process more realistically.

[0006] The technical solution of the present invention is: a physical model test device for underground coal seam mining and freezing-thawing cycle sliding, including an experimental model, the experimental model includes rock mass and coal seam, the rock mass includes mudstone, marl and siltstone; the rock layers of the experimental model are mudstone, coal seam, marl and siltstone from bottom to top, and stress sensors and displacement sensors are placed in each rock layer, characterized in that: the coal seam adopts a kt plate, when the coal seam is cut, coal pillars of different shapes are left in the coal room to support the roof, and the coal pillars can be divided into square coal pillars and rectangular coal pillars; the coal room size formula is as follows:

[0007] The ultimate span to ensure that the rock beam is not damaged due to the maximum tensile stress exceeding its strength limit:

[0008] The ultimate span that ensures that the rock beam will not be damaged due to the maximum shear stress exceeding its strength limit:

[0009] The smaller value of L1 and L2 is the maximum width of the coal room W o ;

[0010] Among them, q is the uniformly distributed load on the rock beam; h is the thickness of the top rock beam; σ is the allowable normal stress on the rock beam; τ is the allowable shear stress on the rock beam; W o is the width of the coal room;

[0011] The coal pillar dimensions are as follows:

[0012]

[0013] Among them, W o W is the width of the coal room; p is the width of the coal pillar; L p is the length of the coal pillar; K1 is the ratio of the length to the width of the coal pillar, that is, H is the thickness of the overburden above the coal seam; γ is the average bulk density of the rock; σ1 is the allowable compressive strength of the coal pillar; and K is the comprehensive safety factor.

[0014] According to the physical model test device for underground coal seam mining and freeze-thaw cycle sliding as described above, it is characterized in that the thickness range of the kt plate is 5mm to 30mm.

[0015] According to the physical model test device for underground coal seam mining and freeze-thaw cycle sliding as described above, it is characterized in that: the experimental model also includes a remote-controlled car, an electric saw and a camera, and the electric saw and the camera are arranged at the front end of the remote-controlled car.

[0016] According to the physical model test device for underground coal seam mining and freezing-thawing cycle-induced sliding, the feature is that the positions of reserved square coal pillars and rectangular coal pillars are drawn on the KT board and outlined with fluorescent powder.

[0017] According to the physical model test device for underground coal seam mining and freezing-thawing cycle-induced sliding as described above, the feature is that the length and width of the square coal pillar are 5 cm×5 cm, and the height of the coal pillar is 2.5 cm.

[0018] According to the physical model test device for underground coal seam mining and freezing-thawing cycle-induced sliding as described above, it is characterized in that the length and width of the rectangular coal pillar are 10 cm×5 cm, and the height of the coal pillar is 2.5 cm.

[0019] According to the physical model test device for underground coal mining and freeze-thaw cycle-induced slip as described above, it is characterized by: it also includes a box, a freeze-thaw cycle system, a monitoring sensor system and a computer module, wherein the freeze-thaw cycle system includes a temperature control system and a rainfall simulation system; the box size is 200 cm long, 70 cm wide and 120 cm high.

[0020] According to the physical model test device for underground coal mining and freeze-thaw cycle-induced slip as described above, it is characterized in that: the temperature control system adopts the Freon cycle to achieve refrigeration and heating, and the core device is the compressor; the refrigerant enters the compressor from the upper pipeline, is compressed by the compressor from a low-temperature and low-pressure state to a high-temperature and high-pressure state, and then is pressed out from the lower pipeline, enters the condenser to release heat and condense, changing from gas to liquid, the temperature is reduced, and the refrigerant liquid at room temperature and high pressure enters the throttling expansion valve from the pipeline, so that the refrigerant is throttled and reduced in pressure, becoming a low-temperature and low-pressure liquid, and then enters the evaporator to absorb heat and evaporate, changing from liquid to gas, and finally returns to the compressor to form a refrigeration cycle; the four-way valve reverses the flow direction of the refrigerant, allowing the high-temperature and high-pressure gas generated by the compressor to first enter the evaporator to release heat, and then the refrigerant flows into the throttling expansion valve to reduce pressure and vaporize, and then enters the condenser to absorb external heat, and finally returns to the compressor to complete the heating cycle.

[0021] According to the physical model test device for underground coal mining and freeze-thaw cycle-induced slip as described above, it is characterized in that: the rainfall simulation system includes a water tank, a water collecting tank and a rainfall nozzle; the water tank is arranged on the left side of the model box, wherein there is a rainwater pump; the rainfall is connected to the water pump in the water tank through a water pipe, and a valve is provided on the water pipe to adjust the rainfall; the rainfall nozzle is connected to the water tank through a water pump, and the rainfall nozzle is arranged on the upper part of the experimental model; the water collecting tank is arranged at the bottom of the model box at the lower part of the experimental model, collects excess rainfall after the rock mass is saturated, and a filter is provided at the connection with the model box, and the water tank is connected to the water collecting tank.

[0022] A physical model test method for underground coal seam mining and slip caused by freeze-thaw cycles is characterized by comprising the following steps:

[0023] Step 1: Lay out rock mass and coal seams, place monitoring sensors, install temperature control system and rainfall simulation system, and build a model test box;

[0024] Step 2: Control the remote control car to enter the lane and start the electric saw to cut the KT board;

[0025] Step 3: Simulate the summer and autumn seasons, start rainfall, saturate the rock mass with water, adjust the valve to control the rainfall, adjust the rainfall intensity, and monitor the rainfall;

[0026] Step 4: Simulate winter and start cooling down. The evaporator inside the box continuously absorbs heat, and the condenser outside the box continuously releases heat.

[0027] Step 5: Simulate spring, stop cooling, start the four-way valve to change the refrigerant flow direction, and start heating and thawing;

[0028] Step 6. Repeat steps 3, 4, and 5 until a landslide occurs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Overall diagram of the test device

[0030] Figure 2 The test device is trying

[0031] Figure 3 Top view of the test device

[0032] Figure 4 Rock mass diagram

[0033] Figure 5 Coal seam top view

[0034] Figure 6 Schematic diagram of the subsidence area

[0035] Figure 7 Remote control car schematic

[0036] Figure 8 Schematic diagram of a miniature electric saw

[0037] Fig. 9 Coal seam enlarged map

[0038] Explanation of the accompanying drawings: box 1, experimental model 2, rock mass 21, collapse 211, tension crack 212, coal seam 22, coal room 221, square coal pillar 222, rectangular coal pillar 223, remote-controlled car 224, electric saw 225, camera 226, compressor 41, condenser 42, throttling expansion valve 43, evaporator 44, four-way valve 45, water storage tank 51, water collecting tank 52, rainfall nozzle 53, stress sensor 61, three-dimensional scanning device 62, temperature sensor 63, displacement sensor 64, high-speed camera 65, rain gauge 66. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described in conjunction with the accompanying drawings.

[0040] like Figure 1 , Figure 2 As shown, the physical model test device for landslide caused by underground coal mining and freeze-thaw cycle of the present invention includes a box 1, an experimental model 2, a freeze-thaw cycle system, a monitoring sensor system and a computer module, wherein the freeze-thaw cycle system includes a temperature control system and a rainfall simulation system.

[0041] like Figure 1 , Figure 2 As shown, the experimental model 2 includes a rock mass 21 and a coal seam 22. The rock mass 21 includes mudstone, marlstone, and siltstone. The rock mass 21 is laid with lithology such as Figure 4 As shown, the rock layers of the experimental model 2 are mudstone, coal seam 22, marl, and siltstone from bottom to top. During the laying of the rock mass, stress sensors 61 and displacement sensors 64 are placed in each rock layer to monitor the stress changes of the top and bottom plates of the coal seam. In the present invention, the mudstone is below the coal seam 22, and the marl and siltstone are above the coal seam 22, so that the coal seam 22 can simulate different pressures applied from top to bottom, and the lithology of the rock mass 21 can be determined according to the actual situation, so that a more accurate simulation of the impact of actual underground coal seam mining activities on the rock mass 21 can be achieved, and help can be provided for disaster warnings such as landslides, ground fissures, and mining collapses.

[0042] In the present invention, a KT plate is used to simulate the coal seam 22. The KT plate is easy to cut and difficult to bend, and has a thickness range of 5 mm to 30 mm. The KT plate of appropriate thickness can be selected according to the coal seam thickness provided by the actual case. In this specification, the coal seam thickness is 3 cm, so six layers of 5 mm thick KT plates with good strength and stability are used. The thickness is thinner and is convenient for simulating cutting, so that the entire experimental model 2 equipment is relatively small and can be flexibly designed according to actual conditions.

[0043] like Figure 7 and Figure 8 As shown, the experimental model 2 of the present invention also includes a remote control car 224, an electric saw 225 and a camera 226. The electric saw 225 and the camera 226 are arranged at the front end of the remote control car 224. When laying the coal seam, the positions of the square coal pillars 222 and the rectangular coal pillars 223 can be drawn on the kt board, such as Figure 6 As shown, the remote control car 224 is outlined with fluorescent powder to provide direction guidance. The remote control car 224 is controlled to cut the kt board to simulate coal seam mining. The camera 226 transmits the picture of the car in the coal seam to the computer in real time for visualization. The electric saw 225 cuts the kt board as the car moves, leaving a square coal pillar 222 or a rectangular coal pillar 223.

[0044] In practice, the coal seam 22 can be divided into multiple coal rooms 221. When the coal seam is cut, coal pillars of different shapes, namely square coal pillars 222 and rectangular coal pillars 223, are left between the coal rooms 221 to support the roof. The length and width of the coal pillars are mostly (20-30m)×(20-30m), and the height is the same as the mining height. In this description, the length and width of the square coal pillar 222 is generally 5cm×5cm, the length and width of the rectangular coal pillar 223 is generally 10cm×5cm, and the height of the coal pillar is 2.5cm.

[0045] The optimum size of the coal room 221 is determined by the specific actual case, and the formula is as follows:

[0046] The ultimate span to ensure that the rock beam is not damaged due to the maximum tensile stress exceeding its strength limit:

[0047] The ultimate span that ensures that the rock beam will not be damaged due to the maximum shear stress exceeding its strength limit:

[0048] The smaller value of L1 and L2 is the maximum width W of the coal room 221 o .

[0049] Among them, q is the uniformly distributed load on the rock beam; h is the thickness of the top rock beam; σ is the allowable normal stress on the rock beam; τ is the allowable shear stress on the rock beam; W o The width of coal room 221.

[0050] The optimal size of the coal pillar is determined by the specific actual case, and the formula is as follows:

[0051]

[0052] like Fig. 9 As shown, where W o W is the width of the coal room; p is the width of the coal pillar; L p is the length of the coal pillar; K1 is the ratio of the length to the width of the coal pillar, that is, The square coal pillar K1 is 1; H is the thickness of the overburden above the coal seam; γ is the average bulk density of the rock; σ1 is the allowable compressive strength of the coal pillar; K is the comprehensive safety factor, which depends on the aspect ratio of the coal pillar, etc., and is generally 1.5 to 2.0.

[0053] The device of the present invention can simulate the actual mining situation more realistically, use KT plates to simulate coal seams for easy cutting, and determine the optimal mining dimensions of the coal room 221 and the coal pillars. It can minimize the number of reserved coal pillars without reducing the safety level, mine more coal and improve the mining rate.

[0054] When the stress intensity of the rock layers at the top and bottom plates of the goaf is not enough to resist the internal stress, cracks are generated, forming collapse 211 and uneven settlement, which eventually causes tension cracks 212. A three-dimensional scanning device 62 is provided on both sides of the rock mass 21 to monitor the crack morphology, and a high-speed camera 65 is provided on the outside of the box to record the position of the sliding body in real time.

[0055] like Figures 1 to 3 As shown, the freeze-thaw cycle system of the present invention includes a temperature control system and a rainfall simulation system. The temperature control system uses a Freon cycle to achieve refrigeration and heating, and the core device is a compressor 41. The refrigerant enters the compressor 41 from the upper pipeline, is compressed from a low-temperature and low-pressure state to a high-temperature and high-pressure state by the compressor 41, and then is pressed out from the lower pipeline, enters the condenser 42 to release heat and condense, and changes from gas to liquid, and the temperature is reduced. The refrigerant liquid at room temperature and high pressure enters the throttling expansion valve 43 from the pipeline, so that the refrigerant is throttled and depressurized, and becomes a low-temperature and low-pressure liquid, and then enters the evaporator 44 to absorb heat and evaporate, from liquid to gas, and finally returns to the compressor to form a refrigeration cycle. The four-way valve 45 reverses the flow of the refrigerant, allowing the high-temperature and high-pressure gas generated by the compressor 41 to first enter the evaporator 44 to release heat, and then the refrigerant flows into the throttling expansion valve 43 to reduce pressure and vaporize, and then enters the condenser 42 to absorb external heat, and finally returns to the compressor 41 to complete the heating cycle.

[0056] like Figures 1 to 3 As shown, the rainfall simulation system of the present invention includes a water storage tank 51, a water collection tank 52 and a rainfall nozzle 53. The water storage tank 51 is arranged on the left side of the model box, wherein there is a rainwater pump. The rainfall is connected to the water pump in the water storage tank through a water pipe, and a valve is arranged on the water pipe to adjust the rainfall. The rainfall nozzle 53 is connected to the water storage tank 51 through a water pump, and the rainfall nozzle 53 is arranged on the upper part of the experimental model 2. The water collection tank 52 is arranged at the bottom of the model box at the lower part of the experimental model 2 to collect the excess rainfall after the rock mass is saturated. A filter is arranged at the connection with the model box to prevent the soil from falling into the box. The water storage tank 51 is connected to the water collection tank 52, and a water pump is also arranged in the water collection tank 52 to return the collected rainwater to the water storage tank 51, so as to realize circulation and reduce waste.

[0057] like Figure 6As shown in the figure, during the coal seam mining process, the goaf within a certain range causes the upper rock and soil to lose support, thus causing ground collapse; after coal seam mining, cavities are formed inside the rock mass, which destroys its natural stress balance state and produces local stress concentration. When the goaf area becomes larger, the surrounding rock strength is not enough to resist the gravity of the overlying rock, and the tensile stress formed inside the top rock layer exceeds the tensile strength limit of the rock layer, downward bending and movement occur, and then the formation breaks to form ground fissures. As the mining range expands, the ground fissures will continue to extend to the surface. The frost heave force during the freeze-thaw process causes the cracks caused by coal mining to expand downward, forming a front edge creeping section and a rear edge tensile cracking section. When the cracks deepen to a certain depth, the locking section is sheared off, and the potential energy of the slope rock mass is suddenly released, forming a high-speed landslide.

[0058] The specific dimensions of the box 1 of the present invention can be 200 cm long, 70 cm wide, and 120 cm high, accommodating the experimental model 2, with a rainfall nozzle 53 on the top, a three-dimensional scanning device 62, a throttling expansion valve 43, an evaporator 44 and a temperature sensor 63 on the side wall, and a rain gauge 66 on the bottom.

[0059] During the implementation process, one day simulates a natural year, and each season corresponds to 6 hours. It rains a lot in summer and autumn. Rainfall is simulated in this process to saturate the rock mass with water. The temperature drops in winter to form ice, and the temperature rises in spring to thaw. During coal seam mining, 2 to 3 coal rooms 221 can be pushed forward at the same time, and 2 to 3 remote-controlled small cars can be placed in the mine at the same time. This cycle continues until a landslide occurs. The specific implementation steps are as follows:

[0060] Step 1: Lay the rock mass 21 and the coal seam 22, place relevant monitoring sensor devices, install the temperature control system and rainfall simulation system, and build the model test box.

[0061] Step 2: Control the remote control car to enter the tunnel and start the electric saw to cut the KT board.

[0062] Step 3: Simulate the summer and autumn seasons, start rainfall, saturate the rock mass with water, adjust the valve to control the rainfall, adjust the rainfall intensity, and set a flow meter 66 inside the model box to monitor the rainfall and connect it to the computer.

[0063] Step 4: Simulate winter and start cooling down. The evaporator 44 inside the box continuously absorbs heat, and the condenser 42 outside the box continuously releases heat to achieve a cooling effect.

[0064] The fifth step is to simulate spring, stop cooling, and start the four-way valve 45 to change the refrigerant flow direction and start heating and thawing.

[0065] Step 6. Repeat steps 3, 4, and 5 until a landslide occurs.

Claims

1. A physical model test device for underground coal mining and freezing-thawing cycle-induced sliding, comprising an experimental model, wherein the experimental model comprises a rock mass and a coal seam, wherein the rock mass comprises mudstone, marlstone and siltstone; the rock layers of the experimental model are mudstone, coal seam, marlstone and siltstone from bottom to top, and a stress sensor and a displacement sensor are placed in each rock layer, wherein the device is characterized in that: The coal seam adopts KT plate. When the coal seam is cut, coal pillars of different shapes are left in the coal room to support the roof. The coal pillars can be divided into square coal pillars and rectangular coal pillars. The formula for the size of the coal room is as follows: The ultimate span to ensure that the rock beam is not damaged due to the maximum tensile stress exceeding its strength limit: The ultimate span that ensures that the rock beam will not be damaged due to the maximum shear stress exceeding its strength limit: The smaller value of L1 and L2 is the maximum width of the coal room W o ; Among them, q is the uniformly distributed load on the rock beam; h is the thickness of the top rock beam; σ is the allowable normal stress on the rock beam; τ is the allowable shear stress on the rock beam; W o is the width of the coal room; The coal pillar dimensions are as follows: Among them, W o W is the width of the coal room; p is the width of the coal pillar; L p is the length of the coal pillar; K1 is the ratio of the length to the width of the coal pillar, that is, H is the thickness of the overburden above the coal seam; γ is the average bulk density of the rock; σ1 is the allowable compressive strength of the coal pillar; and K is the comprehensive safety factor.

2. The physical model test device for underground coal seam mining and freeze-thaw cycle sliding according to claim 1, characterized in that: The thickness range of kt plate is 5mm~30mm.

3. The physical model test device for underground coal seam mining and freeze-thaw cycle sliding according to claim 1, characterized in that: The experimental model also includes a remote-controlled car, an electric saw and a camera. The front end of the remote-controlled car is equipped with an electric saw and a camera.

4. The physical model test device for underground coal seam mining and freeze-thaw cycle sliding according to claim 1, characterized in that: Draw the reserved positions of square coal pillars and rectangular coal pillars on the KT board and outline them with fluorescent powder.

5. The physical model test device for underground coal seam mining and freeze-thaw cycle sliding according to claim 1, characterized in that: The length and width of the square coal pillar are 5cm×5cm, and the height of the coal pillar is 2.5cm.

6. The physical model test device for underground coal seam mining and freeze-thaw cycle sliding according to claim 1, characterized in that: The length and width of the rectangular coal pillar are 10cm×5cm, and the height of the coal pillar is 2.5cm.

7. The physical model test device for underground coal seam mining and freeze-thaw cycle sliding according to claim 1, characterized in that: It also includes a box, a freeze-thaw cycle system, a monitoring sensor system and a computer module, wherein the freeze-thaw cycle system includes a temperature control system and a rainfall simulation system; the box size is 200 cm long, 70 cm wide and 120 cm high.

8. The physical model test device for underground coal seam mining and freeze-thaw cycle sliding according to claim 7, characterized in that: The temperature control system uses Freon cycle to achieve cooling and heating, and the core device is the compressor; The refrigerant enters the compressor from the upper pipe and is compressed by the compressor from a low-temperature and low-pressure state to a high-temperature and high-pressure state. It is then pressed out from the lower pipe and enters the condenser to release heat and condense, changing from gas to liquid. The temperature drops, and the refrigerant liquid at room temperature and high pressure enters the throttling expansion valve from the pipe, causing the refrigerant to throttle and reduce pressure, becoming a low-temperature and low-pressure liquid. It then enters the evaporator to absorb heat and evaporate, changing from liquid to gas, and finally returns to the compressor, forming a refrigeration cycle. The four-way valve reverses the flow of the refrigerant, allowing the high-temperature and high-pressure gas generated by the compressor to first enter the evaporator to release heat, and then the refrigerant flows into the throttling expansion valve to reduce pressure and vaporize, then enters the condenser, absorbs external heat, and finally returns to the compressor to complete the heating cycle.

9. The physical model test device for underground coal seam mining and freeze-thaw cycle sliding according to claim 7, characterized in that: The rainfall simulation system includes a water storage tank, a water collecting tank and rainfall sprinklers. The water storage tank is located on the left side of the model box, which has a rainwater pump. The rainfall is connected to the water pump in the water storage tank through a water pipe. A valve is provided on the water pipe to adjust the rainfall. The rainfall sprinklers are connected to the water storage tank through a water pump, and the rainfall sprinklers are arranged on the upper part of the experimental model. The water collecting tank is located at the bottom of the model box at the lower part of the experimental model to collect excess rainfall after the rock mass is saturated. A filter is provided at the connection with the model box, and the water storage tank is connected to the water collecting tank.

10. A physical model test method for underground coal mining and slip caused by freeze-thaw cycles, characterized by: The following steps are involved: Step 1: Lay out rock mass and coal seams, place monitoring sensors, install temperature control system and rainfall simulation system, and build a model test box; Step 2: Control the remote control car to enter the lane and start the electric saw to cut the KT board; Step 3: Simulate the summer and autumn seasons, start rainfall, saturate the rock mass with water, adjust the valve to control the rainfall, adjust the rainfall intensity, and monitor the rainfall; Step 4: Simulate winter and start cooling down. The evaporator inside the box continuously absorbs heat, and the condenser outside the box continuously releases heat. Step 5: Simulate spring, stop cooling, start the four-way valve to change the refrigerant flow direction, and start heating and thawing; Step 6. Repeat steps 3, 4, and 5 until a landslide occurs.

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