Visualizing experiment method and device for fracture fluid flow pattern under controllable temperature gradient

Abstract

This invention discloses an experimental method and apparatus for visualizing the flow pattern of fractured fluids under a controllable temperature gradient, belonging to the field of geothermal resource experimental research technology. The apparatus includes a fluid temperature and injection system, a visualization chip, a temperature gradient control system, a clamping system, a monitoring system, and a data processing terminal. The temperature gradient control system connects the heat-generating element via T-shaped copper pillars and the Peltier cooling patch via I-shaped copper pillars, which are screwed into the grooves of the upper and lower temperature-conductivity clamps on the chip, allowing for flexible adjustment of the magnitude and direction of the temperature gradient. Matte black electrical tape is attached to the surface of the temperature-conductivity clamps in conjunction with infrared thermometry, and correction coefficients obtained by fitting a three-layer series steady-state heat conduction model with measured values ​​are used to accurately invert the true temperature field inside the chip. The monitoring system integrates a high-speed camera, fluorescence excitation, and a PIV particle tracking CCD to achieve real-time visual observation of the dynamic evolution of geothermal fracture fluid flow patterns and wall wettability.

Description

Technical Field

[0001] This invention relates to the field of geothermal resource experimental technology, specifically to an experimental method and apparatus for visualizing fracture fluid flow patterns under controllable temperature gradients. Background Technology

[0002] Geothermal energy, as a renewable energy source with abundant reserves, stable operation, and low carbon emissions, holds a crucial strategic position in my country's energy structure transformation and upgrading. The core scientific issues in geothermal extraction lie in the seepage and transport of cold / hot fluids within deep rock fracture networks, heat transfer, and solid-liquid interface interactions. Temperature gradients directly control fluid viscosity, interfacial tension, fracture wall wettability, and heat transfer efficiency, thus determining the geothermal system's heat extraction capacity and operational stability. Therefore, constructing an experimental platform capable of precisely controlling temperature gradients, simulating real fractured media, and enabling visualized observation is of significant value for revealing the geothermal fluid transport mechanism and optimizing injection and production processes.

[0003] Currently, relevant technologies have been explored both domestically and internationally for experimental research on fissure seepage heat transfer. For example, one existing visualization experimental device for fissure seepage and heat exchange in hot dry rock uses an experimental chamber and an integrated temperature control unit to observe fissure seepage heat transfer. However, it can only control the overall temperature and has a fixed heat source location, making it unable to flexibly adjust the magnitude, direction, and spatial distribution of the temperature gradient, thus failing to reproduce the dynamic temperature field of actual geothermal injection and production. Furthermore, the high thermal resistance between the clamping device and the heat-conducting structure easily leads to temperature field distortion, and the limited observation window and asynchronous acquisition of multiple physical quantities make it impossible to establish a quantitative correlation between the temperature gradient and fluid flow and wettability evolution. Another type of fissure rock seepage heat transfer device relies on an integrated heating mechanism for uniform heating, lacking the ability to construct a non-uniform temperature field and lacking microscopic visualization observation capabilities. It can only collect macroscopic data such as inlet and outlet water temperature and flow rate, which is insufficient to meet the needs of research on non-uniform geothermal temperature fields and microscale flow mechanisms. In addition, some visualization tracer experimental systems use transparent models and optical components to achieve flow observation, but they do not have independent temperature control and temperature gradient regulation structures, making it impossible to carry out high temperature difference geothermal environment experiments. They also lack low contact thermal resistance heat conduction components and infrared temperature measurement imaging functions, and have not established internal temperature calculation and correction models for the chip. They can only conduct qualitative observations and cannot quantitatively obtain the temperature field distribution, resulting in a large deviation from the actual geothermal reservoir conditions.

[0004] Existing technologies generally suffer from problems such as insufficient temperature gradient control capability, large contact thermal resistance leading to temperature field distortion, lack of microscopic visualization observation methods, asynchronous acquisition of multiple physical quantities, and inability to quantitatively invert internal temperature distribution. There is an urgent need to develop an experimental platform that can accurately construct a non-uniform stable temperature field, realize real-time observation of microscopic flow and wetting behavior, synchronously acquire multi-dimensional data, and quantitatively calculate the temperature field distribution. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes an experimental device for visualizing fracture fluid flow patterns under a controllable temperature gradient, comprising: Fluid temperature and injection system for preparing, storing, and delivering simulated fluids with preset temperatures and compositions; A visualization chip containing microfracture channels is used to simulate fracture channels in geothermal rock masses and provide a visual observation area for fluid flow and temperature distribution; A clamping system for fixing and adjusting the spatial position of the visualization chip; A temperature gradient control system is disposed above and / or below the visualization chip for vertically constructing and precisely controlling the temperature gradient in the microcrack channel chip. A monitoring system is installed on the observation optical path of the visualization chip to collect fluid flow images and surface temperature distribution data in the microcrack channel chip in real time. The data processing terminal is electrically connected to the monitoring system and is used to receive, process, and analyze the collected data.

[0006] Furthermore, the fluid temperature and injection system includes a sealed bottle, a micron bubble generator, a temperature control heater, an extraction pump, a flow sensor, valves, and connecting pipelines; The sealed bottle is used to store a mixture of liquid and fluorescent agent, and is equipped with a liquid injection tube, a gas and gas pressure balance tube, a temperature controller and a temperature sensor. The micron bubble generator is used to generate micro-nano bubbles. It is also equipped with liquid injection, gas and gas pressure balance pipes, temperature controller and temperature sensor, and its gas and liquid outlet pipes are connected to the extraction pump through pipelines. The temperature-controlled heater is connected to the temperature controller via wires to heat the fluid; The extraction pump is used to pump fluid into the subsequent pipeline, and the flow sensor is installed at its outlet. The valve is installed on the pipelines of the liquid injection, gas and gas pressure balance pipe and the gas and liquid outlet pipe, and is used to control the fluid on / off, flow rate and flow volume.

[0007] Furthermore, the temperature gradient control system includes a T-shaped copper column, a heat-generating element, an I-shaped copper column, a Peltier cooling pad, and a radiator; The visualization chip includes, from top to bottom, an upper temperature conductive clip, an upper matte black electrical tape, a micro-crack channel chip, a lower matte black electrical tape, and a lower temperature conductive clip. Both the upper and lower temperature conductor clips are provided with threaded grooves. The head end of the T-shaped copper column is screwed into the groove to form a threaded connection, and the tail end contacts the heat-generating element to form a heat conduction path. The head end of the I-shaped copper pillar is screwed into the groove to form a threaded connection, and the other end is attached to the cold side of the Peltier cooling patch to form a cold conduction path. The hot side of the Peltier cooling patch is attached to the heat sink.

[0008] Furthermore, one end of the heat-generating element is connected to a copper coil, and the copper coil is wrapped with a detachable heating element shell; An energized copper coil is installed inside the housing of a heating system. The energized copper coil and the copper coil are wirelessly coupled to achieve non-contact power transmission, thereby powering the heat-generating component.

[0009] Furthermore, the clamping system includes a base, a perforated bracket, a rotating disk, a helical gear, and jaws; The base is equipped with a track; Multiple perforated brackets are disposed on the track and can slide along the track to adjust their relative spacing; The perforated bracket has a row of square holes, and the claws are installed in the square holes to hold the azimuth angle of the visualization chip. The rotating disk is disposed below the perforated bracket, one side of which is provided with a rotating disk thread that engages with the threaded part of the perforated bracket, and the other side is provided with a ring of helical teeth; The helical gear meshes with the helical tooth, and drives the rotating disk to rotate through the rotation control groove, thereby synchronously adjusting the distance between each hole-containing bracket and the center to adapt to visualization chips of different sizes.

[0010] Furthermore, the monitoring system includes a high-speed camera, an infrared temperature monitor, a microscope, a fluorescence exciter, an external light source, and a PIV particle tracking CCD, which are supported and adjusted in spatial position by a robotic arm; The observation area of ​​the high-speed camera covers the entire micro-fracture channel chip, and is used to capture the flow pattern of fluid in the fracture. The infrared temperature monitoring instrument is used to monitor and collect surface temperature distribution images of the upper matte black electrical tape and the lower matte black electrical tape respectively; The microscope is nested within the high-speed camera or set independently in the observation optical path, and is used to adjust the optical magnification. The fluorescence exciter is used to excite the fluorescent agent in the simulated fluid; the external light source is used to provide illumination for the observation area; the PIV particle tracking CCD is used to track the movement trajectory of the micro- and nano-bubbles in real time to reflect the changes in the flow field inside the visualization chip.

[0011] Furthermore, the visualization chip also includes a gas / liquid inlet channel and a gas / liquid outlet channel; The gas and liquid inlet channel is connected to the liquid injection, gas and gas pressure balance pipe of the fluid temperature and injection system, and is used to inject the simulated fluid into the microcrack channel chip; the gas and liquid outlet channel is connected to the fluid separation and processing system, and is used to discharge the fluid after the experiment and perform recycling processing.

[0012] Furthermore, the data processing terminal pre-stores a three-layer series steady-state heat conduction model; The model calculates the total heat flow through the three-layer structure and the theoretical temperature distribution of each layer based on the thickness, thermal conductivity, and effective heat conduction area of ​​the thermally conductive clip, matte black electrical tape, and micro-crack channel chip, as well as the temperatures on the heat source side and the cold source side. The data processing terminal compares and fits the surface temperature of the matte black electrical tape measured by the infrared temperature monitor with the theoretical surface temperature of the matte black electrical tape calculated by the model to generate a temperature field correction coefficient K. The data processing terminal uses the correction coefficient K to calibrate the theoretical temperature distribution inside the microcrack channel chip, and then inversely calculates the actual temperature distribution inside the microcrack channel chip.

[0013] This invention also proposes an experimental method for a visualization experimental device for fracture fluid flow patterns under a controllable temperature gradient, comprising the following steps: S1. Place the micro-crack channel chip between the upper and lower thermal conductive clips that have been covered with matte black electrical tape, adjust the clamping system to clamp it in the center, screw the T-shaped copper pillar and the I-shaped copper pillar into the groove of the thermal conductive clip respectively, and spray the heat insulation coating on the part of the heat-conducting component exposed to air. S2. Connect the liquid injection and gas pressure balance pipe, valve, extraction pump, flow sensor and sealing bottle in sequence to form a fluid delivery circuit and complete the wiring of electrical components. S3. The high-speed camera, infrared temperature monitor, microscope, fluorescence exciter, external light source and PIV particle tracking CCD are adjusted to the observation position by the robotic arm, so that the optical path is precisely aligned with the chip observation area. S4. Start the temperature gradient control system to form a preset temperature gradient. Use a step-by-step temperature measurement method to first collect the surface temperature of the tape closest to the heat-generating component, then install the tape on the other side and measure the temperature to form a visual temperature gradient image. Through a three-layer series steady-state heat conduction model, use the measured tape surface temperature and the theoretical calculation value to fit the actual temperature and perform quantitative inversion on the internal temperature distribution of the chip. S5. Start the extraction pump, inject the liquid containing fluorescent agent into the chip after being processed by the micron bubble generator, and simultaneously turn on the fluorescence exciter. Track the micro and nano bubbles with PIV particle tracking CCD, capture the flow pattern with a high-speed camera, and monitor the fluid flow pattern and wettability dynamic evolution in real time. S6. After the experiment, turn off the power, release the clamping system, guide the outflowing fluid into the separation and processing system, clean the chip and pipeline, save the data and reset the device.

[0014] Furthermore, in step S4, when the heat-generating element is located below the micro-crack channel chip, the lower surface temperature image is first acquired using the infrared temperature monitor without the upper temperature-conducting clip and upper matte black electrical tape installed; then, the matte black electrical tape is installed, and the upper surface temperature image is acquired again; when the heat-generating element is located above the micro-crack channel chip, the order is reversed, prioritizing the monitoring of the surface temperature on the side closer to the heat-generating element, and then monitoring the surface temperature on the other side, in order to eliminate the influence of light path obstruction on temperature measurement.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: This invention addresses the technical challenge of distortion in geothermal temperature field simulation by proposing a systematic solution: First, it adopts a flexible and adjustable heat source / cold source layout and a two-way temperature control structure to precisely control the magnitude, direction and spatial distribution of the temperature gradient, and truly restore the in-situ temperature field between cold injection and heat recovery, deep and shallow strata, and fractures and bedrock, effectively improving the temperature field distortion problem of traditional equipment.

[0016] Secondly, it integrates a high-speed camera, an infrared thermometer, a fluorescence excitation system, and a PIV particle tracking CCD to achieve full-domain, real-time, and interference-free visualization of the flow morphology inside the fracture, microbubble migration, and wall wettability evolution, breaking through the bottlenecks of existing devices with narrow observation windows and large optical path interference.

[0017] Third, it simultaneously acquires multi-dimensional data such as surface temperature, flow rate, flow morphology, and wettability, and establishes a quantitative coupling relationship between temperature gradient, fluid flow law, and solid-liquid interface evolution, thus solving the shortcomings of existing technologies in that the acquisition of multiple parameters is not synchronized and cannot be analyzed in a unified manner.

[0018] Fourth, T-shaped and I-shaped copper pillars are used to connect the temperature-conducting clamps, combined with thermal insulation coating and Peltier cooling, which significantly reduces contact thermal resistance and environmental heat loss, improving temperature control accuracy and stability. Fifth, an adjustable clamping system is designed to flexibly adapt to various sizes of fracture chips and temperature control layouts, covering different fracture morphologies and injection / production parameters, serving the optimization and efficient and stable operation of enhanced geothermal systems. Attached Figure Description

[0019] Figure 1 A system architecture diagram for visualizing the experimental setup; Figure 2 Diagram of the monitoring system; Figure 3 This is a schematic diagram of the clamping system structure; Figure 4This is a schematic diagram of the temperature gradient control system structure; Figure 5 To visualize the chip structure diagram; Figure 6 This is a top view of the temperature conduction clip. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This embodiment employs the visualization experimental device for fracture fluid flow patterns under controllable temperature gradients described in this invention to conduct visualization simulation experiments on the migration and wettability evolution of fracture fluids in geothermal reservoirs. This accurately recreates the fluid flow and interfacial interaction characteristics under temperature gradients during geothermal extraction. Before the experiment, the visualization chip is assembled inside the clamping system. The microfracture channel chip is placed between the upper and lower temperature-conducting clamps. Matte black electrical tape is attached to the upper and lower surfaces of the chip, respectively. By rotating the helical gear of the clamping system, the rotating disk is rotated, adjusting the position of the jaws and the perforated support to ensure the chip is stably and centrally clamped, guaranteeing a tight fit between the chip and the temperature-conducting clamps, providing structural support for uniform temperature conduction and stable observation. The T-shaped and I-shaped copper pillars of the temperature gradient control system are screwed into the pre-set grooves of the temperature-conducting clamps, forming a reliable connection. Simultaneously, a heat-insulating coating is sprayed onto the copper pillars and the parts of the heat-generating components that come into contact with air, effectively reducing heat loss and improving the accuracy of temperature field control.

[0022] After assembling the chip and temperature control components, the liquid injection, gas and gas pressure balance pipes, gas-liquid outlet pipes, valves, extraction pumps, flow sensors, and sealed bottles are connected sequentially to form a complete fluid transport and circulation loop, ensuring continuous and stable fluid injection, transport, discharge, and recovery processes. Each electrical component is powered and transmits signals via wires. The temperature controller, temperature heater, display, and data processing terminal are connected to the system to achieve integrated control of temperature regulation, data acquisition, command transmission, and result display. The high-speed camera, infrared temperature monitor, microscope, fluorescence exciter, external light source, and PIV particle tracking CCD of the monitoring system are adjusted to suitable positions using a robotic arm to precisely align the light path with the observation area. The parameters of the light source and camera are adjusted to ensure clear and interference-free observation of fluid flow and temperature distribution.

[0023] Example 1 like Figure 1As shown, an experimental device for visualizing the flow pattern of fractured fluid under a controllable temperature gradient includes a display, wires, a temperature-controlled heater, a sealed bottle, a micron bubble generator, valves, an extraction pump, a flow sensor, a monitoring system, a visualization chip, a temperature gradient control system, a clamping system, and a fluid separation and processing system.

[0024] The sealed bottle and the microbubble generator together constitute the fluid supply and pretreatment unit. Both are equipped with liquid injection, gas and pressure balance pipes, a temperature controller, a gas-liquid outlet pipe, and a temperature sensor. The sealed bottle is installed in the fluid supply area to store the mixture of liquid and fluorescent agent; the microbubble generator is used to generate micro- and nanobubbles. The liquid injection, gas and pressure balance pipes are used to inject the relevant fluids and maintain stable internal pressure. The temperature controller is connected to a temperature-controlled heater via wires to heat the fluid. The gas-liquid outlet pipe is connected to a pump to deliver the fluid. The temperature sensor is located on the bottom wall of the container to detect the output temperature of the fluid.

[0025] like Figure 2 As shown, the monitoring system is positioned directly opposite the visualization chip and consists of a high-speed camera, an infrared temperature monitor, a microscope, a robotic arm, a fluorescence exciter, an external light source, and a PIV particle-tracking CCD. The high-speed camera captures the fluid flow state across the entire chip's fissures and transmits the image to a display in real time. The infrared temperature monitor monitors the surface temperature of the upper and lower matte black electrical tapes within the visualization chip to obtain the temperature distribution above and below the fissures. The microscope is nested within the observation optical path and used to adjust the magnification. The robotic arm supports and adjusts the illumination positions of the fluorescence exciter and the external light source. The fluorescence exciter excites the fluorescent agent in the fluid. The external light source provides illumination to the observation area. The PIV particle-tracking CCD tracks the movement of micro- and nano-bubbles in real time to reflect changes in the flow field inside the visualization chip.

[0026] like Figure 3As shown, the clamping system is installed at the center of the experimental platform and includes jaws, a base, a perforated bracket, a track, square holes, threads, a perforated bracket base, a rotating disk, rotating disk threads, helical teeth, helical gears, and a rotation control slot. The base supports the perforated bracket and the temperature gradient control system. A track is provided on the base to adjust the relative size of the area enclosed by the perforated bracket, thus accommodating visualization chips and temperature gradient control systems of different sizes. A row of square holes is formed on the perforated bracket for housing the jaws, which are used to fix the four azimuth angles of the visualization chip. The perforated bracket base has threads for movement adjustment in conjunction with the track and rotating disk threads. The rotating disk is located below the perforated bracket base. The side facing the perforated bracket base has rotating disk threads for adjusting the distance of the perforated bracket base from the center; the opposite side has a ring of helical teeth that mesh with the helical gears. By rotating the control slot and connecting an external device, the rotating disk can be rotated, thereby adjusting the spacing of the perforated brackets.

[0027] like Figure 4 As shown, the temperature gradient control system is arranged closely on the top and bottom sides of the visualization chip, including a T-shaped copper pillar, a heat-generating element, a copper coil, a heating element housing, a housing bottom clip, a heating system housing, a energized copper coil, an I-shaped copper pillar, a Peltier cooling patch, a thermal insulation coating, and a heat sink. The head of the T-shaped copper pillar is threaded into the groove of the thermal conductivity clip, and the tail contacts the heat-generating element, responsible for conducting the heat generated by the heat-generating element to the visualization chip. One end of the heat-generating element is connected to the copper coil, and the other end is connected to the T-shaped copper pillar; the copper coil powers the heat-generating element and is encased in a removable heating element housing. Different types of copper coils can be replaced via the housing bottom clip to provide different temperature ranges. An energized copper coil is located inside the heating system housing, and wireless inductive coupling between the coil and the heating system housing enables non-contact power transfer. The head of the I-shaped copper pillar is threaded into the groove of the thermal conductivity clip, and the other end is attached to the Peltier cooling patch for cooling the visualization chip. A heat sink is attached to the other side of the Peltier cooling patch for heat dissipation. All copper pillars and heat-generating components exposed to air are uniformly coated with an insulating coating to reduce the impact of ambient temperature and prevent burns to personnel.

[0028] like Figure 5 As shown, the visualization chip is fixed to the central observation position by a clamping system, including gas and liquid inlet channels, gas and liquid outlet channels, an upper temperature-conducting clip, an upper matte black electrical tape, a micro-fracture channel chip, a lower matte black electrical tape, a lower temperature-conducting clip, and grooves formed on the temperature-conducting clip. The micro-fracture channel chip is used to simulate underground dry hot rock fractures. The gas and liquid inlet channels are connected to the injection, gas, and gas pressure balance pipes for injecting gas-liquid mixtures into the chip; the gas and liquid outlet channels are connected to the gas and liquid outlet pipes for discharging the gas-liquid mixture.

[0029] like Figure 6As shown, upper and lower thermal conductivity clips are attached to the upper and lower surfaces of the chip, respectively. When the heat source is above the crack, the upper thermal conductivity clip conducts heat; when the heat or cold source is below the crack, the lower thermal conductivity clip conducts heat or cold. Upper and lower matte black electrical tapes are attached to the corresponding thermal conductivity clip surfaces, and used in conjunction with an infrared temperature monitor to monitor the temperature gradient between the upper and lower surfaces of the chip. Grooves are formed on the upper and lower thermal conductivity clips, with internal threads for connection to T-shaped and I-shaped copper pillars.

[0030] When using a monitoring system to collect the surface temperature of a microcrack channel chip, a specific temperature measurement sequence must be followed: If the heat-generating component is located below the chip, the lower surface temperature should be monitored first without the upper thermal conductive clip and matte black electrical tape; then, the matte black electrical tape should be installed, and the upper surface temperature of the chip should be monitored a second time. Similarly, in other layout conditions, the surface temperature of the chip closest to the heat-generating component should be monitored first, and then the matte black electrical tape on the other side should be installed for temperature measurement to obtain accurate temperature distribution data.

[0031] During the experiment, the temperature gradient control system establishes a stable temperature gradient above or below the visualization chip according to preset operating conditions. By adjusting the position of the heat source, the magnitude and distribution of the temperature gradient can be changed, thus closely resembling the actual in-situ temperature conditions of geothermal engineering. After the output value of the temperature gradient control system is determined, the monitoring system detects the surface temperature of the upper and lower matte black electrical tapes in real time, forming a visualized temperature gradient image. Simultaneously, it monitors the flow state and dynamic evolution of wettability of the fracture fluid under different temperature gradients. A fluorescence exciter triggers fluorescent substances in the fluid, and in conjunction with a PIV particle tracking CCD, it achieves real-time tracking of micro- and nano-bubbles. The motion state of the micro- and nano-bubbles intuitively reflects the changes in the flow field inside the visualization chip, while a high-speed camera simultaneously captures the global fracture fluid flow morphology of the chip, providing intuitive image evidence for flow pattern analysis.

[0032] The fluid delivery system processes the liquid and fluorescent agent mixture in the sealed bottle using a micron-sized bubble generator, then steadily injects it into the visualization chip through liquid injection, gas injection, and gas pressure balancing pipes. Valves and extraction pumps work together to control the fluid velocity and flow rate, while a flow sensor monitors the flow rate of the pumped fluid in real time, ensuring a stable and controllable experimental process. After flowing through the micro-slit channel chip, the fluid is discharged through gas and liquid outlet pipes and enters the fluid separation and treatment system for unified waste liquid treatment, ensuring environmentally friendly feedback operation of the experimental process. The clamping system maintains the relative position of the chip and temperature control components stable throughout the experiment. The chip height and orientation can be adjusted according to experimental needs, providing convenient conditions for the arrangement of the temperature gradient control system and the observation of the monitoring system.

[0033] Through the operation and experimentation of the device in this embodiment, the flow pattern characteristics and dynamic evolution of wettability of fracture fluids under different temperature gradients can be fully obtained. The experiment can achieve the experimental goals of controllable temperature gradient, clear observation, and synchronized data without relying on complex external equipment. It can provide reliable experimental basis and data support for the optimization of geothermal injection and production systems, the study of fracture seepage mechanisms, the improvement of heat recovery efficiency, and the prevention and control of fracture blockage. After the experiment, the power supply of each system is turned off in sequence, the clamping components are released, and the visualization chip, pipelines, and temperature conductivity clips are cleaned and tidied up. The device is then reset and the data is saved.

[0034] Example 2 A method for using an experimental setup for visualizing fracture fluid flow patterns under a controllable temperature gradient includes: The visualization chip is assembled into the clamping system: the micro-crack channel chip is placed between the upper temperature-conducting clip (with matte black electrical tape attached) and the lower temperature-conducting clip (with lower matte black electrical tape attached). A rotating helical gear drives a rotating disk and a perforated support to move, allowing the jaws to smoothly clamp the chip's four corners and center it securely, ensuring a tight fit between the chip and the upper and lower temperature-conducting clips. Subsequently, the T-shaped and I-shaped copper pillars of the temperature gradient control system are screwed into the grooves on the sides of the temperature-conducting clips, forming a reliable heat conduction path. Simultaneously, a thermal insulation coating is uniformly sprayed onto the copper pillars, heat-generating components, and areas in contact with air to reduce heat loss and improve temperature control accuracy.

[0035] The system sequentially connects the liquid injection pipe, gas and gas pressure balance pipe, gas-liquid outlet pipe, valve, extraction pump, flow sensor, and sealed bottle to form a complete fluid transport loop. Electrical wiring is completed between the temperature control heater, extraction pump, various sensors, monitoring system, and data processing terminal, achieving integrated power supply, command transmission, and data acquisition. A robotic arm adjusts the spatial positions of the monitoring system components—high-speed camera, infrared temperature monitor, microscope, fluorescence exciter, external light source, and PIV particle tracking CCD—ensuring the light path is aligned with the visualization chip's observation area. Real-time adjustments to the light source brightness, camera focus, and aperture are made using a display screen to ensure clear and interference-free imaging.

[0036] The temperature gradient control system is activated to establish a preset temperature gradient in the vertical direction of the visualized chip based on the experimental conditions. During temperature measurement, with the heat-generating component located below the chip, the surface temperature image of the matte black electrical tape is first acquired using an infrared temperature monitor without the upper temperature-conducting clip and matte black electrical tape installed, obtaining the temperature distribution of the lower surface near the heat source. Then, the matte black electrical tape is installed, and the temperature image of the upper surface of the chip is acquired again, forming a visualized temperature gradient image of the upper and lower surfaces. To obtain the true temperature distribution inside the microcrack channel chip, a three-layer series steady-state heat conduction model pre-stored in the data processing terminal is required. Based on the thickness, thermal conductivity, and effective heat conduction area of ​​the thermal conductivity clip, matte black electrical tape, and microcrack channel chip, combined with the temperatures on the heat source and cold source sides, the total heat flow through the three-layer structure and the theoretical temperature of the tape surface are first calculated. The actual temperature of the tape surface measured by the infrared temperature monitor is compared with the theoretical temperature to obtain the temperature field correction coefficient K. Then, the theoretical temperature distribution of each layer inside the chip is calibrated, and the internal temperature field of the chip, which cannot be directly measured, is quantitatively inverted, ensuring the authenticity of the temperature gradient feedback control and flow field observation temperature reference.

[0037] After the temperature field stabilizes, the extraction pump and valves are activated to inject the fluorescent agent mixture in the sealed bottle into a simulated fluid containing micro- and nano-bubbles via a microbubble generator. This simulated fluid is then injected into the micro-crack channel of the visualization chip at a set flow rate. Simultaneously, a fluorescence exciter is activated to excite the fluorescent material in the fluid. A PIV particle tracking CCD tracks the migration trajectory of the micro- and nano-bubbles in real time to reflect changes in the internal flow field, while a high-speed camera captures the global flow morphology within the crack. This enables real-time observation of the fluid flow pattern and dynamic evolution of the wall wettability under different temperature gradients. During the experiment, valves and flow sensors work together to control and monitor the fluid flow rate, ensuring stable and controllable injection conditions.

[0038] After the experiment, the fluid is discharged through the gas-liquid outlet pipe and enters the fluid separation and processing system for recycling. Turn off all power supplies, loosen the clamping system, remove the visualization chip, clean the chip, pipeline and temperature conduction clip, save the experimental images and temperature data, and reset the device.

[0039] The data processing terminal has a pre-stored three-layer series steady-state heat conduction calculation model. First, calculate the total heat flow Q using the following formula: In the formula: Q is the total heat flow, in W; T h Temperature on the heat source side, unit: K; T c Temperature on the cold source side, unit: K; The thickness of the thermal conductivity clip is in meters (m). Thermal conductivity of the thermally conductive clip, unit: W / (m K); A1 is the effective heat conduction area of ​​the thermally conductive clip, in m². The thickness of matte black electrical tape is expressed in meters (m). Thermal conductivity of matte black electrical tape, unit: W / (m) K); A2 represents the effective thermal conductivity area of ​​the matte black electrical tape, in m². 2 ; The thickness of the microcrack channel chip is expressed in meters (m). Thermal conductivity of the microcrack channel chip, unit: W / (m K); A3 is the effective thermal conductivity area of ​​the micro-slit channel chip, in m². 2 .

[0040] Based on the total heat flux Q, the theoretical temperature distribution of each layer is calculated respectively: The theoretical temperature distribution within the thermal conductivity clip is calculated using the following formula: ; In the formula: x is the distance (m) between the heat source and the inner edge of the thermal conductivity clip.

[0041] The theoretical temperature distribution inside matte black electrical tape is calculated using the following formula: ; In the formula: The temperature at the interface between the thermally conductive clip and the tape (K); The distance (m) is the distance from the inside of the tape to the interface of the clip.

[0042] The theoretical temperature distribution within the microcrack channel chip is calculated using the following formula: ; In the formula: Temperature at the tape-chip interface (K); Distance (m) between the chip interior and the tape interface. The theoretical surface temperature of matte black electrical tape is calculated using the following formula: ; The surface temperature (T) of matte black electrical tape was measured using an infrared temperature monitor. 2,实测 The temperature field correction coefficient K is obtained by comparing and fitting the measured values ​​with the theoretical calculation values, and is calculated according to the following formula: ; The theoretical temperature inside the microcrack channel chip was calibrated using a correction factor K to obtain the actual temperature distribution inside the chip, which was then calculated using the following formula: ; Through the above calculations and corrections, the influence of contact thermal resistance and environmental heat dissipation is eliminated, enabling precise quantitative construction of the temperature field of the three-layer composite structure and temperature gradient feedback control. This ensures the reliability of the temperature reference for infrared thermometry and internal flow field observation, and allows for the accurate derivation of the internal temperature field of the microcrack channel chip, which cannot be directly measured. The experimental results of installing the heating and cooling devices below the visualization chip are shown in Table 1.

[0043] Table 1 The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0044] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A device for visualizing fluid flow patterns in fractures under controlled temperature gradients, characterized in that, include: Fluid temperature and injection system for preparing, storing, and delivering simulated fluids with preset temperatures and compositions; A visualization chip containing a microfracture channel chip is used to simulate fissure channels in geothermal rock masses and provide a visual observation area for fluid flow and temperature distribution. The visualization chip includes, from top to bottom, an upper temperature-conducting clip, an upper matte black electrical tape, a microfracture channel chip, a lower matte black electrical tape, a lower temperature-conducting clip, and gas / liquid inlet and outlet channels. Both the upper and lower temperature-conducting clips have threaded grooves. The gas / liquid inlet channel is connected to the injection, gas, and pressure balance pipes of the fluid temperature and injection system, used to inject the simulated fluid into the microfracture channel chip. The gas and liquid discharge channels are connected to the fluid separation and processing system, which is used to discharge the fluid after the experiment and recycle it. A clamping system for fixing and adjusting the spatial position of the visualization chip; A temperature gradient control system is disposed above and / or below the visualization chip for vertically constructing and precisely controlling the temperature gradient in the microcrack channel chip. The temperature gradient control system includes a T-shaped copper pillar, a heat-generating element, an I-shaped copper pillar, a Peltier cooling pad, and a heat sink. The head end of the T-shaped copper pillar is screwed into the groove to form a threaded connection, and the tail end contacts the heat-generating element to form a heat conduction path. The head end of the I-shaped copper pillar is screwed into the groove to form a threaded connection, and the other end is attached to the cold side of the Peltier cooling pad to form a cold conduction path. The heat sink is attached to the hot side of the Peltier cooling pad. A monitoring system is installed on the observation optical path of the visualization chip to collect fluid flow images and surface temperature distribution data within the microcrack channel chip in real time. The data processing terminal is electrically connected to the monitoring system and is used to receive, process, and analyze the collected data.

2. The temperature-gradient-controlled, fracture-fluid-flow-pattern-visualizing experimental apparatus of claim 1, wherein, The fluid temperature and injection system includes a sealed bottle, a micron bubble generator, a temperature control heater, an extraction pump, a flow sensor, valves, and connecting pipelines; The sealed bottle is used to store a mixture of liquid and fluorescent agent, and is equipped with a liquid injection tube, a gas and gas pressure balance tube, a temperature controller and a temperature sensor. The micron bubble generator is used to generate micro-nano bubbles. It is also equipped with liquid injection, gas and gas pressure balance pipes, temperature controller and temperature sensor, and its gas and liquid outlet pipes are connected to the extraction pump through pipelines. The temperature-controlled heater is connected to the temperature controller via wires to heat the fluid; The extraction pump is used to pump fluid into the subsequent pipeline, and the flow sensor is installed at its outlet. The valve is installed on the pipelines of the liquid injection, gas and gas pressure balance pipe and the gas and liquid outlet pipe, and is used to control the fluid on / off, flow rate and flow volume.

3. The temperature-gradient-controlled, fracture-fluid-flow-pattern- visualizing experimental apparatus of claim 2, wherein, One end of the heat-generating element is connected to a copper coil, and the copper coil is wrapped with a detachable heating element shell. An energized copper coil is installed inside the housing of a heating system. The energized copper coil and the copper coil are wirelessly coupled to achieve non-contact power transmission, thereby powering the heat-generating component.

4. The temperature-gradient-controlled, fracture-fluid-flow-pattern- visualizing experimental apparatus of claim 3, wherein, The clamping system includes a base, a perforated bracket, a rotating disk, a helical gear, and chucks; The base is equipped with a track; Multiple perforated brackets are disposed on the track and can slide along the track to adjust their relative spacing; The perforated bracket has a row of square holes, and the claws are installed in the square holes to hold the azimuth angle of the visualization chip. The rotating disk is disposed below the perforated bracket, one side of which is provided with a rotating disk thread that engages with the threaded part of the perforated bracket, and the other side is provided with a ring of helical teeth; The helical gear meshes with the helical tooth, and drives the rotating disk to rotate through the rotation control groove, thereby synchronously adjusting the distance between each hole-containing bracket and the center to adapt to visualization chips of different sizes.

5. The experimental apparatus for visualizing fracture fluid flow patterns under controllable temperature gradients according to claim 4, characterized in that, The monitoring system includes a high-speed camera, an infrared temperature monitor, a microscope, a fluorescence exciter, an external light source, and a PIV particle tracking CCD. These components are supported and their spatial positions are adjusted by a robotic arm. The observation area of ​​the high-speed camera covers the entire micro-fracture channel chip, and is used to capture the flow pattern of fluid in the fracture. The infrared temperature monitoring instrument is used to monitor and collect surface temperature distribution images of the upper matte black electrical tape and the lower matte black electrical tape respectively; The microscope is nested within the high-speed camera or set independently in the observation optical path, and is used to adjust the optical magnification. The fluorescence exciter is used to excite the fluorescent agent in the simulated fluid; the external light source is used to provide illumination for the observation area; the PIV particle tracking CCD is used to track the movement trajectory of the micro- and nano-bubbles in real time to reflect the changes in the flow field inside the visualization chip.

6. The experimental apparatus for visualizing fracture fluid flow patterns under controllable temperature gradients according to claim 5, characterized in that, The data processing terminal has a three-layer series steady-state heat conduction model pre-stored. The three-layer series steady-state heat conduction model calculates the total heat flow through the three-layer structure and the theoretical temperature distribution of each layer based on the thickness, thermal conductivity, and effective heat conduction area of ​​the upper and lower temperature conductive clips, matte black electrical tape, and micro-crack channel chip, as well as the temperatures on the heat source side and the cold source side. The data processing terminal compares and fits the surface temperature of the matte black electrical tape measured by the infrared temperature monitor with the theoretical surface temperature of the matte black electrical tape calculated by the model to generate a temperature field correction coefficient K. The data processing terminal uses the correction coefficient K to calibrate the theoretical temperature distribution inside the microcrack channel chip, and then inversely calculates the actual temperature distribution inside the microcrack channel chip.

7. An experimental method using the visualization experimental apparatus for fracture fluid flow patterns under controllable temperature gradients as described in claim 6, characterized in that, Includes the following steps: S1. Place the micro-crack channel chip between the upper and lower thermal conductive clips that have been covered with matte black electrical tape, adjust the clamping system to clamp it in the center, screw the T-shaped copper pillar and the I-shaped copper pillar into the groove of the thermal conductive clip respectively, and spray the heat insulation coating on the part of the heat-conducting component exposed to air. S2. Connect the liquid injection and gas pressure balance pipe, valve, extraction pump, flow sensor and sealing bottle in sequence to form a fluid delivery circuit and complete the wiring of electrical components. S3. The high-speed camera, infrared temperature monitor, microscope, fluorescence exciter, external light source and PIV particle tracking CCD are adjusted to the observation position by the robotic arm, so that the optical path is precisely aligned with the chip observation area. S4. Start the temperature gradient control system to form a preset temperature gradient. Use a step-by-step temperature measurement method to first collect the surface temperature of the tape closest to the heat-generating component, then install the tape on the other side and measure the temperature to form a visual temperature gradient image. Through a three-layer series steady-state heat conduction model, use the measured tape surface temperature and the theoretical calculation value to fit the actual temperature and perform quantitative inversion on the internal temperature distribution of the chip. S5. Start the extraction pump, inject the liquid containing fluorescent agent into the chip after being processed by the micron bubble generator, and simultaneously turn on the fluorescence exciter. Track the micro and nano bubbles with PIV particle tracking CCD, capture the flow pattern with a high-speed camera, and monitor the fluid flow pattern and wettability dynamic evolution in real time. S6. After the experiment, turn off the power, release the clamping system, guide the outflowing fluid into the separation and processing system, clean the chip and pipeline, save the data and reset the device.

8. The experimental method according to claim 7, characterized in that, In step S4, when the heat-generating element is located below the micro-crack channel chip, the lower surface temperature image is first acquired using the infrared temperature monitor without the upper temperature-conducting clip and upper matte black electrical tape installed; then, the matte black electrical tape is installed, and the upper surface temperature image is acquired again; when the heat-generating element is located above the micro-crack channel chip, the order is reversed, prioritizing the monitoring of the surface temperature on the side closer to the heat-generating element, and then monitoring the surface temperature on the other side, in order to eliminate the influence of light path obstruction on temperature measurement.

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