Device and method for measuring dry heat flux density of debris bed based on heat balance inversion

Abstract

The invention discloses a device and a method for measuring dry heat flux density of a debris bed based on heat balance inversion, and belongs to the technical field of nuclear reactor thermal hydraulic experiments. The device comprises a large-size non-transparent silicon carbide heat-conducting cylinder body, and a heat-insulating heat-preserving layer and an induction heating coil which are coated outside the cylinder body, the water storage tank, the water pump and the flowmeter are connected with an experiment section inlet; the total condensation calorimetric heat exchanger, the flowmeter and the recovery water tank are connected to the downstream of the experiment section outlet; the data acquisition system is matched with the power supply and control system. The method comprises the following steps: pre-calibrating system heat loss; in the step heating process, a drying starting point is judged by monitoring an internal multi-point temperature sensor array; and intercepting heat balance data of the secondary side of the heat exchanger in a steady-state interval before drying, and carrying out inversion calculation on the effective drying power of the debris bed in combination with fluid sensible heat change, heat loss of a connecting pipeline and radial heat loss of a barrel. According to the invention, the wall channel effect and the induction heating efficiency estimation error are eliminated, and the accurate measurement of the dry heat flux density of the porous medium under the non-transparent and high-temperature working conditions is realized.

Description

A device and method for measuring the heat flux density of a dried fragment bed based on thermal equilibrium inversion Technical Field

[0001] This invention relates to the field of research on the cooling and heat transfer characteristics of the debris bed in the lower head of the pressure vessel after a severe nuclear reactor accident, specifically to a device and method for measuring the dry heat flux density of the debris bed based on thermal equilibrium inversion. Background Technology

[0002] In the event of a severe nuclear reactor accident, molten core material may migrate and accumulate again in the pressure vessel's lower head or reactor cavity, forming a porous, media-like debris bed with an internal heat source. Whether this debris bed can be effectively cooled by coolant directly determines whether the accident process is terminated and whether a large amount of radioactive material will leak. Dry heat flux (DHF) is a key thermohydraulic parameter for determining the cooling capacity limit of the debris bed; accurate measurement of this parameter is crucial for nuclear safety analysis and the development of accident management strategies.

[0003] To simulate the volumetric heating characteristics of decay heat within a debris bed, current experimental studies widely employ high-frequency electromagnetic induction heating technology. Compared to resistance wire heating, induction heating can directly generate eddy currents within metal particles, more realistically simulating the internal heat source conditions of nuclear fuel.

[0004] However, existing technologies for measuring the dry heat flux density (DHF) of debris beds suffer from several technical bottlenecks and limitations: 1. Limitations of experimental section materials and boundary conditions: To observe the bubble behavior and quenching front of two-phase flow, existing technologies typically use transparent quartz glass as the experimental section container. However, as an insulating material, quartz glass has fundamentally different thermal conductivity characteristics compared to the metal walls of a real reactor pressure vessel, making it impossible to simulate real thermal boundary conditions. Furthermore, due to the limited mechanical strength of glass, it is difficult to construct large-diameter (e.g., larger than 150 mm) experimental sections for such visualization experiments. This results in significant wall channeling effects within small-sized containers, where high-porosity wall regions form low-resistance channels, causing the measured DHF values ​​to deviate from the true values ​​of an infinitely large medium. Simultaneously, quartz glass is also unable to withstand the high-temperature and high-pressure environments under severe accident conditions.

[0005] 2. Insufficient accuracy in measuring effective heating power: In electromagnetic induction heating experiments, the displayed power (input power) of the induction power supply is not equal to the actual effective heat power absorbed by the particle bed. The difference is due to complex influences from coil copper losses, hysteresis losses, line losses, and inductive coupling efficiency. Existing measurement methods often lack online calibration, typically estimating heat flux density based solely on power supply readings or assuming a fixed heating efficiency. However, during the experiment, as the particle temperature increases, the resistivity and permeability of the material change, causing dynamic drift in the coupling efficiency. This leads to significant errors in heat flux density calculations, severely impacting the reliability of DHF data.

[0006] 3. Difficulty in Measuring Energy in Two-Phase Flow at the Outlet: When the fragmented bed boils, the outlet of the experimental section discharges a steam-water mixture with a certain degree of dryness. Because the dryness of the two-phase flow is difficult to measure accurately online, it is impossible to simply calculate the power absorbed by the fragmented bed using the enthalpy difference between the inlet and outlet of the working fluid. Existing technologies often overlook this problem or lack a dedicated post-metering module to close the energy balance equation.

[0007] 4. Lack of System Heat Loss Correction: In high-temperature experiments, radial heat dissipation from the experimental section cylinder to the environment, as well as heat dissipation along the connecting pipe between the experimental section outlet and the metering module, both result in effective energy loss. Existing technologies often focus on establishing theoretical models or numerical predictions, neglecting the aforementioned heat loss or lacking accurate correction algorithms in experimental measurements. This leads to lower measured DHF values ​​and affects the rigor of the data.

[0008] In summary, existing technologies lack an experimental apparatus and method that can eliminate wall effect interference under large-size, non-transparent, and high-temperature conditions, and accurately invert the effective heating power through rigorous thermal balance methods. Summary of the Invention

[0009] To overcome the problems in existing technologies, such as the difficulty in online calibration of effective induction heating power, distortion of thermal boundary conditions caused by quartz glass viewing windows, and inaccurate measurement of drying heat flux density in large-sized porous media, this invention provides a device and method for measuring the drying heat flux density of a debris bed based on thermal equilibrium inversion. This invention simulates real reactor conditions by constructing a large-sized, non-transparent thermally conductive experimental section and introducing a total condensation calorimetry module. It establishes a "black box" model using the principle of energy conservation and accurately inverts the effective drying power inside the porous media by measuring the thermal equilibrium parameters at the system boundary.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: a device for measuring the dry heat flux density of a fragmented bed based on thermal equilibrium inversion, comprising: an experimental section component: including a vertically arranged, non-transparent, high-strength, high-temperature resistant, and non-magnetic heat-conducting cylinder 3, the interior of which is filled with magnetically conductive metal particles to form a porous media fragmented bed; the outer wall of the heat-conducting cylinder 3 is tightly covered with a heat-insulating layer 5, and a high-frequency induction heating coil 4 is wound around the outside of the heat-insulating layer; a fluid circulation system: including a cooling water injection pipe connected to the bottom of the heat-conducting cylinder 3, a water tank 1, a water pump 2, and a valve 301 connected to the cooling water injection pipe, and a steam-water mixture discharge pipe connected to the top of the heat-conducting cylinder 3; a calorimeter module: a total condensing calorimeter heat exchanger 6 located downstream of the steam-water mixture discharge pipe; the primary side inlet of the total condensing calorimeter heat exchanger 6 is connected to the steam-water mixture discharge pipe, and the primary side outlet is connected to a recovery pipe and a recovery water tank 7; the secondary side of the total condensing calorimeter heat exchanger 6 is connected to... It is equipped with an independent cooling medium circuit; the total condensing calorimetric heat exchanger 6 has sufficient heat exchange area to ensure that the primary side fluid reaches a subcooled liquid state at the outlet; the precision measurement unit includes a multi-point temperature sensor array arranged inside the porous media fragment bed, a wall temperature monitoring multi-point temperature sensor array 110, a fifth temperature sensor 105 at the secondary side inlet of the total condensing calorimetric heat exchanger, a sixth temperature sensor 106 at the secondary side outlet, and a second flow meter 202 at the secondary side inlet; a third temperature sensor 103 at the primary side inlet and a fourth temperature sensor 104 at the primary side outlet; a first temperature sensor 101 at the bottom water inlet of the experimental section and a first flow meter 201 at the bottom water inlet of the experimental section, and a second temperature sensor 102 at the top outlet of the experimental section; experimental auxiliary equipment includes a data acquisition and processing system 8 for acquiring and processing signals from various sensors; and a power supply and control system 9 for ensuring stable operation and precise adjustment of the operating conditions throughout the experiment.

[0011] The heat-conducting cylinder 3 is made of silicon carbide ceramic, and the ratio of the inner diameter D of the heat-conducting cylinder 3 to the diameter d of the magnetic metal particles is greater than 40, so as to eliminate the wall channel effect and simulate a large-scale porous medium environment; the heat insulation layer 5 is made of high-temperature resistant fiber material, which is used to block the heat-conducting cylinder from radiating and convecting heat dissipation to the environment, and to construct a non-visible heat insulation boundary.

[0012] The multi-point temperature sensor array adopts a three-dimensional arrangement of "axial layering and radial partitioning": Axial arrangement: along the fluid flow direction, several temperature measuring layers are arranged at different heights inside the porous media fragment bed; Radial arrangement: on the cross-section of each temperature measuring layer, several temperature measuring points are arranged at different radial radii. The temperature measuring points include a center measuring point 109 located at the center of the porous media fragment bed, a radius measuring point 108 located at the midpoint of the line connecting the center of the porous media fragment bed and the wall of the heat-conducting cylinder, and an edge measuring point 107 located near the wall of the heat-conducting cylinder. This constructs a three-dimensional temperature monitoring grid to capture the starting position and non-uniformity of local drying within the large-size bed. A multi-point temperature sensor array 110 for wall temperature monitoring is arranged between the outer wall of the heat-conducting cylinder and the thermal insulation layer 5 to monitor the wall temperature of the heat-conducting cylinder in real time and calculate the radial heat loss power of the cylinder. .

[0013] The connecting pipe between the second temperature sensor 102 and the third temperature sensor 103 is defined as a heat loss correction pipe section, used to calculate the pipe heat loss power during the high-temperature fluid transport process. .

[0014] All pipes in the experimental system are covered with a thermal insulation layer to reduce heat loss and lower the error of experimental measurement data.

[0015] The method for measuring the drying heat flux density of a porous media fragment bed includes the following steps: Step S1, System heat loss calibration: Establish a pre-defined relationship between the wall temperature of the heat-conducting cylinder and the radial heat dissipation power, as well as the heat dissipation characteristics along the connecting pipes; Step S2, Step heating: Introduce a constant flow of cooling water into the porous media fragment bed and control the induction power supply to increase in a stepwise manner, maintaining this at each power step until the system reaches thermal equilibrium; Step S3, Drying determination and data acquisition: Monitor the multi-point temperature sensor array inside the porous media fragment bed in real time. When drying is determined, select a preset steady-state time window before the drying start time as the data calculation interval; Step S4, Power inversion: Based on the heat absorption power of the secondary side of the total condensation calorimeter heat exchanger within the calculation interval, combined with the fluid sensible heat change, the heat loss of the connecting pipes, and the radial heat loss of the heat-conducting cylinder, invert and calculate the critical drying power under this condition. This leads to the dry heat flux density (DHF).

[0016] The drying determination criterion mentioned in step S3 is as follows: when the temperature at any measuring point in the porous media fragment bed deviates from the saturation temperature and rises irreversibly and continuously, and the drying area expands, and this phenomenon lasts for 3 to 5 seconds, it is determined that drying has occurred; the preset steady-state time window is 3 to 5 minutes before the drying determination time; within this window, the fluctuation range of the secondary side outlet temperature of the total condensing calorimetric heat exchanger is less than the preset threshold.

[0017] The critical power for drying in step S4 The calculation formula is: in: The power absorbed on the secondary side of the total condensing calorimetric heat exchanger; The difference in sensible heat power between the fluid entering and exiting the system; This refers to the heat loss power of the connecting pipeline; The radial heat loss power of the heat-conducting cylinder; subsequently, the critical drying power... Divide by the effective cross-sectional area of ​​the fragment bed The dry heat flux density is obtained as follows: Among them, the effective cross-sectional area of ​​the fragment bed , The inner diameter of the heat-conducting cylinder; the heat loss of the connecting pipe. The calculation method is as follows: based on the temperature measured by the second temperature sensor at the top outlet of the experimental section. Temperature measured by the third temperature sensor at the primary inlet of the total condensing calorimetric heat exchanger Calculate the difference: in: This refers to the mass flow rate of the cooling water working fluid. This is the specific heat capacity of the cooling water compared to the working fluid; this correction is used to compensate for the effective energy lost by the high-temperature fluid after leaving the experimental section components but before entering the calorimeter module.

[0018] Radial heat loss of the heat-conducting cylinder The method for obtaining the thermal loss characteristics of the experimental section components is as follows: the thermal loss characteristics are obtained in advance; during the calculation in step S4, the measured temperature values ​​of the multi-point temperature sensor array for wall temperature monitoring are read, and the corresponding radial thermal loss power is determined using the thermal loss characteristics; the thermal loss characteristics are obtained through static thermal balance experimental calibration or heat transfer model calculation.

[0019] The system heat loss calibration described in step S1 includes: maintaining a static fluid or dry state in the experimental section component, adjusting the induction heating power to stabilize the wall temperature at different values, measuring the equilibrium heat dissipation power at each temperature point using the principle of energy conservation, and fitting the characteristic curve of the cylinder wall temperature versus radial heat dissipation power.

[0020] Compared with existing technologies, this invention has the following advantages: 1. The experimental device of this invention has high measurement accuracy, completely eliminating the estimation error of induction heating efficiency: Existing technologies mostly rely on the displayed power of the induction power supply or the estimated coupling efficiency to approximate the heating power, resulting in large errors and drift with temperature. This invention innovatively adopts the "post-calorimetric inversion" method. Regardless of whether the outlet of the experimental section is a single-phase fluid or a high-dryness steam-water mixture, all the energy carried by the fluid is ultimately captured by the all-condensing heat exchanger and converted into a precisely measurable single-phase temperature rise. By constructing a closed-loop energy equation that includes "heat exchanger heat absorption + sensible heat correction + pipeline heat loss + wall heat loss", accurate measurement of the effective drying power of the fragment bed is achieved, and the measurement uncertainty is significantly better than that of traditional methods.

[0021] 2. The experimental setup of this invention provides realistic boundary conditions, eliminating small-size wall effects and boundary distortion: Existing visualization experiments often use transparent quartz tubes, which suffer from adiabatic boundary distortion and size limitations. This invention uses a large-size (D / d>40), non-transparent silicon carbide (SiC) thermally conductive cylinder, which not only eliminates the wall channeling effect on a geometric scale, but also simulates the real thermal conductivity boundary and high-temperature tolerance environment of the pressure vessel metal wall under severe accidents in terms of physical properties. This makes the measured dry heat flux density (DHF) data closer to the actual physical laws of the nuclear reactor core.

[0022] 3. The experimental method of this invention features rigorous data processing and corrects for the heat loss along the pipes that is ignored in traditional methods: This invention is specifically designed for high-temperature experimental conditions and establishes a method that includes the heat loss along the connecting pipes. ) and radial heat loss of the cylinder ( The corrected model was developed. By introducing temperature drop monitoring of the "heat loss correction pipe section" and "in-situ wall heat loss calibration" technology, the energy loss during the process of fluid transfer from the experimental section outlet to the metering module was effectively compensated, avoiding the problem of low DHF calculation value due to neglecting heat dissipation, and ensuring the scientificity and rigor of the data.

[0023] 4. The experimental apparatus of this invention provides comprehensive monitoring, and the three-dimensional array effectively captures localized drying characteristics: Addressing the non-uniformity of heat transfer within large-sized porous media, this invention abandons the single-point monitoring mode and constructs a three-dimensional thermocouple array with axial layering and radial partitioning. This design can monitor the evolution of the temperature field within the bed from all angles, sensitively capturing even drying initiation in localized areas (such as the radius of the central high-temperature zone or the edge region), thereby improving the accuracy of drying determination and avoiding missed or false detections. Attached Figure Description

[0024] Figure 1 is a schematic diagram of the experimental system principle of the fragment bed dry heat flux density measurement device based on thermal balance inversion according to the present invention; Figure 2 is a schematic diagram of the experimental section component structure and sensor arrangement of the fragment bed dry heat flux density measurement device based on thermal balance inversion according to the present invention, showing the multi-point temperature sensor array inside the fragment bed and the multi-point temperature sensor array for wall temperature monitoring in three dimensions; Figure 3 is a flowchart of the fragment bed dry heat flux density measurement method based on thermal balance inversion according to the present invention; Figure 4 is a schematic diagram of the calibration principle of the friction loss coefficient of the connecting pipeline in the embodiment of the present invention. Detailed Implementation

[0025] To provide a clearer description of the present invention, the following detailed description is provided in conjunction with the accompanying drawings.

[0026] Example 1: A device for measuring the dry heat flux density of a fragment bed based on thermal equilibrium inversion.

[0027] The present invention provides a schematic diagram of a fragment bed dry heat flux density measurement device based on thermal equilibrium inversion, as shown in Figures 1 and 2. The device mainly consists of an experimental section component, a fluid circulation system, a calorimeter module, a precision measurement unit, and experimental auxiliary equipment.

[0028] 1. Experimental Section Components: The core of the apparatus is a vertically positioned heat-conducting cylinder 3. To simulate the true thermal conductivity boundary of a pressure vessel under severe accidents and eliminate wall channeling effects in small-scale experiments, the heat-conducting cylinder 3 is made of high-strength, high-temperature resistant, and non-magnetic silicon carbide (SiC) ceramic. The ratio of the cylinder's inner diameter (D) to the diameter (d) of the magnetically conductive metal particles filling it is greater than 40 (D / d>40) to eliminate wall channeling effects and simulate a large-scale porous media environment. A thermal insulation layer 5, made of high-temperature resistant fiber material, is tightly wrapped around the outer wall of the heat-conducting cylinder 3 to block radiation and convection heat loss from the cylinder to the environment, creating a non-visible thermal boundary. A high-frequency induction heating coil 4 is wound around the outside of the thermal insulation layer 5 for volumetric heating of the metal particles inside the cylinder.

[0029] 2. Fluid Circulation System: The fluid circulation loop can be either closed or open. Cooling water flows out from the water tank 1, is pressurized by the water pump 2, and then flows through the first flow meter 201 and valve 301 before being injected into the heat-conducting cylinder 3 from the bottom. To reduce heat loss, all connecting pipes in the system are externally covered with a thermal insulation layer. The steam-water mixture discharged from the top of the experimental section is transported to the subsequent calorimeter module through the discharge pipe.

[0030] 3. Calorimeter Module: A total condensing calorimeter heat exchanger 6 (e.g., a plate heat exchanger) is installed downstream of the experimental section discharge pipe. The primary side inlet of this total condensing calorimeter heat exchanger is connected to the experimental section discharge pipe, and the primary side outlet is connected to the recovery water tank 7. The total condensing calorimeter heat exchanger has sufficient heat exchange area to ensure that the high-temperature steam-water mixture can completely release its latent heat and be cooled to a subcooled liquid state when flowing through the primary side. The secondary side (cooling medium side) of the total condensing calorimeter heat exchanger is connected to an independent cooling medium circuit. The heat is removed by the temperature rise of the secondary side fluid, thus achieving energy metering.

[0031] 4. Precision Measurement Unit: This device is equipped with a comprehensive sensor system to support the "thermal balance inversion" algorithm: Three-dimensional temperature array: As shown in Figure 2, a three-dimensional arrangement of "axial layering and radial partitioning" is adopted inside the fragment bed. At different heights, edge measuring points 107 are located near the wall of the heat-conducting cylinder, radius measuring points 108 are located at the midpoint of the line connecting the center of the porous media fragment bed and the wall of the heat-conducting cylinder, and a center measuring point 109 is located at the center of the porous media fragment bed. This three-dimensional grid can accurately capture the starting position and non-uniformity of localized drying within a large-size porous media fragment bed.

[0032] Wall heat loss monitoring: A multi-point temperature sensor array 110 is arranged between the outer wall of the heat-conducting cylinder 3 and the thermal insulation layer 5 to monitor the wall temperature field in real time, which is for radial heat loss. The calculation provides the data.

[0033] Fluid and Energy Monitoring: The input end is equipped with a first temperature sensor 101 and a first flow meter 201 to monitor the state of the injected fluid. The pipeline heat loss correction section is defined as the area between the second temperature sensor 102 at the top outlet of the experimental section and the third temperature sensor 103 at the primary side inlet of the heat exchanger. The calorimetric end (total condensing calorimetric heat exchanger) has a second flow meter 202 and a fifth temperature sensor 105 at its secondary side inlet, and a sixth temperature sensor 106 at its secondary side outlet; the primary side outlet has a fourth temperature sensor 104 (used to monitor the sensible heat of the fluid flowing out of the system).

[0034] 5. Experimental Auxiliary Equipment: The power supply and control system 9 is used to provide high-frequency current to the induction coil and control the power. The data acquisition and processing system 8 is connected to all the above sensors, used to acquire signals and perform real-time calculations using a built-in core algorithm.

[0035] Example 2: A method for measuring the dry heat flux density of a fragment bed based on thermal equilibrium inversion.

[0036] As shown in Figure 3, the specific steps for measurement using the above device are as follows: Step S1: System loss calibration Before the formal experiment, the heat dissipation characteristics of the system are calibrated in situ: 1. Radial heat loss of the heat-conducting cylinder Calibration method: This invention uses the "static thermal balance method" to calibrate the radial heat dissipation characteristics of the heat-conducting cylinder in the experimental section in situ. This method is based on the principle that the input power equals the heat dissipation power under steady state. The specific steps are as follows: 1.1 Operating condition settings: Keep the experimental section full of cooling water but do not circulate it (i.e., the flow rate is zero), or keep the debris bed dry, close all inlet and outlet valves, and construct a closed static insulation system.

[0037] 1.2 Constant Temperature Heating: Adjust the output power of the induction heating power supply to slowly raise and stabilize the wall temperature of the experimental section (measured by the wall temperature monitoring sensor) at the first target temperature point. (e.g., 50℃).

[0038] 1.3 Equilibrium Determination: Maintain this state for at least 30 minutes. When the temperature fluctuation of the heat-conducting cylinder wall is less than ±0.5℃, the system is considered to have reached thermal equilibrium. At this point, the sustaining power input from the induction power supply is completely consumed by radial heat dissipation to the environment.

[0039] 1.4 Data Recording: Record the average wall temperature at this time. Balanced power with input .

[0040] 1.5 Curve Fitting: Change the target temperature (e.g., 70°C, 80°C, 90°C...), repeat the above steps, and obtain multiple sets of curves. , Data points. The characteristic curve or functional relationship between "heat-conducting cylinder wall temperature and radial heat dissipation power" is obtained by fitting using the least squares method. .

[0041] 2. Heat loss along the connecting pipeline Calibration method: This invention uses the "single-phase flow temperature drop method" to calibrate the heat dissipation of the pipeline from the outlet of the experimental section to the inlet of the total condensing calorimeter heat exchanger. The specific steps are as follows: 2.1 Operating condition settings: Turn on the circulating water pump to put the system in a single-phase water circulation state and set a constant mass flow rate. .

[0042] 2.2 Steady-state operation: Turn on induction heating to heat the fluid to a high temperature (e.g., 90°C~98°C, keeping the liquid from boiling).

[0043] 2.3 Temperature Difference Measurement: After the system stabilizes, the inlet temperature of the pipeline (i.e., the outlet temperature of the experimental section) is measured using a high-precision temperature sensor. ) and pipe outlet temperature (i.e., heat exchanger inlet temperature) ).

[0044] 2.4 Coefficient Determination: Calculating Temperature Drop According to the formula Calculate the heat dissipation power at different temperatures and establish a correction factor for the pipe heat dissipation power versus fluid temperature. .

[0045] Step S2: Step heating, turn on water pump 2, and set a constant cooling water mass flow rate. The power supply and control system 9 controls the induction heating power to increase in a stepwise manner, and maintains operation at each power level until the system reaches thermal equilibrium.

[0046] Step S3: Dryness determination and data interception. The internal multi-point temperature sensor array (i.e., sensors at measuring points 107, 108, and 109) is monitored in real time by the data acquisition and processing system 8.

[0047] Judgment criteria: When the temperature at any measuring point in the bed deviates from the saturation temperature and rises irreversibly and continuously, and this phenomenon lasts for 3 to 5 seconds, and the dry area is observed to expand, it is judged that dryness has occurred.

[0048] Data Acquisition: A steady-state time window of 3 to 5 minutes before the drying determination time was selected as the data calculation interval. Within this window, the fluctuation range of the secondary side outlet temperature (sensor 106) of the total condensation calorimetric heat exchanger should be less than a preset threshold (e.g., ±0.5℃) to ensure the stability of the calorimetric reference. Figure 4 shows a set of steady-state intervals under experimental conditions.

[0049] Step S4: Power Inversion and DHF Calculation. Based on the energy conservation principle of the "black box model," the critical power for drying out of the debris bed is calculated by inversion. .

[0050] 1. Calculation of power for each component: Secondary side absorption power of the total condensing calorimetric heat exchanger Based on secondary flow rate (Measured by the second flow meter 202) and the inlet and outlet temperature difference (sixth temperature sensor and fifth temperature sensor 106 and 105) are used for calculation: Fluid sensible heat power difference Calculated based on the enthalpy difference between the experimental section inlet (first temperature sensor 101) and the system outlet (fourth temperature sensor 104): (Note: If the outlet temperature of the total condensing calorimeter is lower than the inlet temperature, this item will be negative, indicating that the fluid has carried away some sensible heat.) Connecting pipe heat loss power The measured average temperature of the second temperature sensor 102 at the top outlet of the experimental section is read and directly obtained by substituting it into the heat loss characteristic relationship of the connecting pipeline obtained in step S1.

[0051] radial heat loss power of the cylinder The measured average temperature of the multi-point temperature sensor array 110 for wall temperature monitoring is read and directly obtained by substituting it into the radial heat loss characteristic relationship of the heat-conducting cylinder obtained in step S1.

[0052] 2. Critical drying power inversion: 3. Dry Heat Flux (DHF) Calculation: Calculate the effective cross-sectional area of ​​the debris bed based on the inner diameter D of the heat-conducting cylinder. .

[0053] .

Claims

1. A device for measuring the heat flux density of a dried-up fragment bed based on thermal equilibrium inversion, characterized in that, include: Experimental section components: including a vertically positioned, non-transparent, high-strength, high-temperature resistant, and non-magnetic heat-conducting cylinder (3), the interior of which is filled with magnetically conductive metal particles to form a porous media fragment bed; the outer wall of the heat-conducting cylinder (3) is tightly covered with a heat-insulating layer (5), and a high-frequency induction heating coil (4) is wound around the outside of the heat-insulating layer; fluid circulation system: including a cooling water injection pipe connected to the bottom of the heat-conducting cylinder (3), and a water storage tank (1) connected to the cooling water injection pipe.

1. Water pump (2), valve (301), and steam-water mixture discharge pipeline connected to the top of the heat-conducting cylinder (3); 2. Caloric metering module: a total condensing calorimetric heat exchanger (6) located downstream of the steam-water mixture discharge pipeline; the primary side inlet of the total condensing calorimetric heat exchanger (6) is connected to the steam-water mixture discharge pipeline, and the primary side outlet is connected to the recovery pipeline and the recovery water tank (7); the secondary side of the total condensing calorimetric heat exchanger (6) is connected to an independent cooling medium circuit; the total condensing calorimetric heat exchanger (6) It has sufficient heat exchange area to ensure that the primary side fluid reaches a subcooled liquid state at the outlet; Precision measurement unit: including a multi-point temperature sensor array arranged inside the porous media fragment bed, a wall temperature monitoring multi-point temperature sensor array (110), a fifth temperature sensor (105) set at the secondary side inlet of the total condensing calorimetric heat exchanger, a sixth temperature sensor (106) set at the secondary side outlet and a second flow meter (202) set at the secondary side inlet, a third temperature sensor (103) set at the primary side inlet of the total condensing calorimetric heat exchanger and a fourth temperature sensor (104) set at the primary side outlet; a first temperature sensor (101) at the bottom water inlet of the experimental section and a first flow meter (201) at the bottom water inlet of the experimental section, and a second temperature sensor (102) at the top outlet of the experimental section; Experimental auxiliary equipment: including a data acquisition and processing system (8): used to acquire and process the signals of each sensor; power supply and control system (9): used to ensure the stable operation of the entire experimental process and the precise adjustment of the working conditions.

2. The measuring device according to claim 1, characterized in that: The heat-conducting cylinder (3) is made of silicon carbide ceramic, and the ratio of the inner diameter D of the heat-conducting cylinder (3) to the diameter d of the magnetic metal particles is greater than 40, so as to eliminate the wall channel effect and simulate a large-scale porous medium environment; the heat insulation layer (5) is made of high-temperature resistant fiber material, which is used to block the heat-conducting cylinder from radiating and convecting heat dissipation to the environment and to construct a non-visual heat insulation boundary.

3. The measuring device according to claim 1, characterized in that: The multi-point temperature sensor array adopts a three-dimensional arrangement of "axial layering and radial partitioning": Axial arrangement: along the fluid flow direction, several temperature measuring layers are arranged at different heights inside the porous medium fragment bed; Radial arrangement: on the cross-section of each temperature measuring layer, several temperature measuring points are arranged at different radial radii. The temperature measuring points include a center measuring point (109) located at the center of the porous medium fragment bed, a radius measuring point (108) located at the midpoint of the line connecting the center of the porous medium fragment bed and the wall of the heat-conducting cylinder, and an edge measuring point (107) located near the wall of the heat-conducting cylinder. This constructs a three-dimensional temperature monitoring grid to capture the starting position and non-uniformity of local drying in the large-size bed. A multi-point temperature sensor array (110) for wall temperature monitoring is arranged between the outer wall of the heat-conducting cylinder and the heat insulation layer (5) to monitor the wall temperature of the heat-conducting cylinder in real time and calculate the radial heat loss power of the cylinder. 。 4. The measuring device according to claim 1, characterized in that: The connecting pipe between the second temperature sensor (102) and the third temperature sensor (103) is defined as a heat loss correction pipe section, used to calculate the pipe heat loss power during the high-temperature fluid transport process. 。 5. The measuring device according to claim 1, characterized in that: All pipes in the experimental system are covered with a thermal insulation layer to reduce heat loss and lower the error of experimental measurement data.

6. A method for measuring the drying heat flux density of a porous media fragment bed using the apparatus as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step S1, System Heat Loss Calibration: Establish the correspondence between the wall temperature of the heat-conducting cylinder and the radial heat dissipation power, as well as the heat dissipation characteristics along the connecting pipes; Step S2, Stepped Heating: Introduce a constant flow of cooling water into the porous media fragment bed, and control the induction power supply to increase in a stepped manner, maintaining it at each power step until the system reaches thermal equilibrium; Step S3, Drying Determination and Data Acquisition: Monitor the multi-point temperature sensor array inside the porous media fragment bed in real time. When drying is determined, select a preset steady-state time window before the drying start time as the data calculation interval; Step S4, Power Inversion: Based on the heat absorption power of the secondary side of the total condensation calorimeter heat exchanger within the calculation interval, combined with the fluid sensible heat change, the heat loss of the connecting pipes, and the radial heat loss of the heat-conducting cylinder, invert and calculate the critical drying power under this condition. This leads to the dry heat flux density (DHF).

7. The method according to claim 6, characterized in that, The drying determination criterion mentioned in step S3 is as follows: when the temperature at any measuring point in the porous media fragment bed deviates from the saturation temperature and rises irreversibly and continuously, and the drying area expands, and this phenomenon lasts for 3 to 5 seconds, it is determined that drying has occurred; the preset steady-state time window is 3 to 5 minutes before the drying determination time; within this window, the fluctuation range of the secondary side outlet temperature of the total condensing calorimetric heat exchanger is less than the preset threshold.

8. The method according to claim 6, characterized in that, The critical power for drying in step S4 The calculation formula is: in: The power absorbed on the secondary side of the total condensing calorimetric heat exchanger; The difference in sensible heat power between the fluid entering and exiting the system; This refers to the heat loss power of the connecting pipeline; The radial heat loss power of the heat-conducting cylinder; subsequently, the critical drying power... Divide by the effective cross-sectional area of ​​the fragment bed The dry heat flux density is obtained as follows: Among them, the effective cross-sectional area of ​​the fragment bed ， The inner diameter of the heat-conducting cylinder; the heat loss of the connecting pipe. The calculation method is as follows: based on the temperature measured by the second temperature sensor at the top outlet of the experimental section. Temperature measured by the third temperature sensor at the primary inlet of the total condensing calorimetric heat exchanger Calculate the difference: in: This refers to the mass flow rate of the cooling water working fluid. This is the specific heat capacity of the cooling water compared to the working fluid; this correction is used to compensate for the effective energy lost by the high-temperature fluid after leaving the experimental section components but before entering the calorimeter module.

9. The method according to claim 8, characterized in that, Radial heat loss of the heat-conducting cylinder The method for obtaining the thermal loss characteristics of the experimental section components is as follows: the thermal loss characteristics are obtained in advance; during the calculation in step S4, the measured temperature values ​​of the multi-point temperature sensor array for wall temperature monitoring are read, and the corresponding radial thermal loss power is determined using the thermal loss characteristics; the thermal loss characteristics are obtained through static thermal balance experimental calibration or heat transfer model calculation.

10. The method according to claim 6, characterized in that, The system heat loss calibration described in step S1 includes: maintaining a static fluid or dry state in the experimental section component, adjusting the induction heating power to stabilize the wall temperature at different values, measuring the equilibrium heat dissipation power at each temperature point using the principle of energy conservation, and fitting the characteristic curve of the cylinder wall temperature versus radial heat dissipation power.

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