Subcooled boiling state and dryout frequency detection device and method based on pressure measurement

Abstract

A kind of subcooled boiling state and steam bomb frequency detection device and method based on pressure measurement, comprising: pressure sensor, high-speed camera being arranged on experimental device, control module being connected with experimental device and computing module, wherein: computing module acquires the pressure signal output by pressure sensor, judges the boiling state in experimental device, control module outputs control instruction to adjust the inlet condition and heating power of experimental device, and high-speed camera is opposite the position of heating surface of experimental device to record the gas-liquid two-phase flow behavior and boiling flow pattern in flow channel.The boiling state in component can be indirectly judged by real-time measurement of pressure signal, to realize the real-time accurate monitoring of the boiling state of fluid in heat exchange equipment, and the characteristic frequency of possible large steam bomb in equipment can be obtained.

Description

Technical Field

[0001] This invention relates to a technology in the field of reactor control, specifically a device and method for detecting subcooled boiling state and bombardment frequency based on pressure measurement. Background Technology

[0002] Nucleus boiling heat transfer is widely used in heat exchange systems in chemical, energy, and refrigeration fields due to its excellent heat transfer performance. To identify the boiling state, direct observation is commonly used. While this method provides a direct view of the boiling state in the heated area, it requires a transparent window outside the heating zone, significantly increasing costs and posing safety hazards, making it difficult to implement in engineering practice. Alternatively, thermocouples can be placed on the heating surface to indirectly determine the boiling state and the occurrence of the critical heat flux density by measuring the heating wall temperature and heat flux density. However, this method requires multiple measurement points in the heating zone, resulting in high installation difficulty, high cost, and challenges in subsequent maintenance. Summary of the Invention

[0003] This invention addresses the shortcomings of existing technologies, which cannot simultaneously monitor the flow pattern of the gas-liquid two-phase system, the temperature of the heated surface, the heat flux density of the wall, and the frequency characteristics of the vapor bomb that occurs under fully developed boiling conditions. It proposes a device and method for detecting subcooled boiling state and vapor bomb frequency based on pressure measurement. By measuring the pressure signal in real time, the boiling state within the component can be indirectly determined, thereby achieving real-time and accurate monitoring of the boiling state of the fluid in the heat exchange equipment and obtaining the characteristic frequency of the large vapor bomb that may occur within the equipment.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a pressure-based device for detecting subcooled boiling state and vapor bomb frequency, comprising: a heating block mounted on an experimental device, a pressure sensor, a high-speed camera, a control module connected to the experimental device, and a calculation module, wherein: the control module outputs control commands to adjust the inlet conditions and heating power of the experimental device, the calculation module acquires the pressure signal output by the pressure sensor to determine the boiling state within the experimental device, and the high-speed camera records the gas-liquid two-phase flow behavior and boiling flow pattern within the flow channel.

[0006] The experimental setup consists of a transparent rectangular pipe with heating blocks mounted on its side, and a cooling medium inside the transparent rectangular pipe; a high-speed camera is positioned directly opposite the heated surface.

[0007] The heating block is specifically located on one side at a distance of 250cm from the pipe outlet, and is used to heat the working fluid and cause it to boil.

[0008] The pressure sensor is specifically located downstream of the heating block to record the fluid pressure signal at the outlet position.

[0009] At least one pressure sensor is provided, preferably located on the wall surface 5-10 cm away from the outlet of the heating surface of the experimental device, in order to ensure high accuracy and low delay in obtaining pressure fluctuation signals.

[0010] This invention relates to a method for detecting subcooled boiling state and vapor bomb frequency based on pressure measurement. By arranging pressure sensors on the outer wall of the experimental device of the heat exchange equipment, pressure fluctuation signals inside the heat exchange experimental device are collected in real time. The root mean square value of the pressure fluctuation signal is processed to obtain the root mean square value of the pressure amplitude under different heat flux density conditions, which can be used to determine the boiling state. The characteristic frequencies in the frequency domain distribution of the pressure signal obtained by performing a fast Fourier transform on the pressure fluctuation signal can characterize the vapor bomb frequency.

[0011] The frequency domain distribution of the pressure signal is obtained by performing a fast Fourier transform on the pressure signal.

[0012] The root mean square value of the pressure amplitude is obtained by solving for the root mean square value of the pressure signal:

[0013] The boiling state and vapor bomb determination refer to the following: when the root mean square pressure amplitude increases approximately linearly with heat flux density, the heating wall of the heat exchanger is in a single-phase convective heat exchange or isolated bubble boiling zone; when the root mean square pressure amplitude increases at an accelerated rate deviating from linearity with heat flux density, discrete small vapor clusters appear within the heat exchanger; when the slope of the root mean square pressure amplitude increase with heat flux density decreases significantly, a large vapor bomb appears within the heat exchanger, and the boiling state enters the fully developed boiling zone. A large vapor bomb refers to a periodically generated large vapor cluster covering the entire heating wall surface.

[0014] The linear growth mentioned above refers to the real-time rate of change of the root mean square value of the pressure amplitude and the heat flux density. The heat flux density remains essentially constant.

[0015] The accelerated growth mentioned above refers to the real-time rate of change of the root mean square value of the pressure amplitude and the heat flux density. After a certain heat flux density, it increases to more than 1.25 times the previous value.

[0016] The significant reduction refers to the real-time rate of change of the root mean square value of the pressure amplitude and the heat flux density. After a certain heat flux density, it drops to less than 0.75 times the previous value.

[0017] The heat exchange equipment includes: heat exchangers, evaporators, electric heating tubes, heating pipelines, cooling pipes, etc., and its cooling medium is a subcooled fluid.

[0018] The control module may include a temperature control system, a flow control system, a heating power adjustment system, etc., to ensure that the cooling medium at the inlet of the experimental device and the power of the heating block reach the predetermined state. Technical effect

[0019] This invention leverages the different pressure fluctuation characteristics corresponding to different heat flux densities within an experimental apparatus. It identifies the boiling state and vapor bomb frequency within a component in real-time, rapidly, and accurately by detecting the pressure signal. This invention directly characterizes the vapor bomb frequency occurring within the experimental apparatus under high heat flux density conditions through the frequency domain characteristics of the pressure signal, and the boiling state within the flow channel can be determined using the root mean square value of the pressure amplitude. The boiling state detection technology of this invention has wide applicability and can be used with different heating devices and operating conditions. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the present invention;

[0021] In the diagram: 1. Experimental apparatus; 2. Heating block; 3. Pressure sensor; 4. High-speed camera; 5. Calculation module; 6. Control module.

[0022] Figure 2 The root mean square P of the pressure amplitude in Example 1 RMS Schematic diagram showing the change in heat flux density;

[0023] Figure 3 This is a schematic diagram showing the change of the frequency domain distribution of the pressure signal with heat flux density in Example 1;

[0024] Figure 4 This is a schematic diagram comparing the characteristic frequency of the pressure signal with the measured frequency of the gas bomb in Example 1. Detailed Implementation

[0025] like Figure 1 As shown in this embodiment, a pressure-based subcooled boiling state and vapor bomb frequency detection system includes: a heating block 2 and a pressure sensor 3 mounted on an experimental device 1; a control module 6 and a calculation module 5 connected to the experimental device 1; wherein: the calculation module 5 acquires the pressure signal output by the pressure sensor 3 to determine the boiling state within the experimental device; and the control module 6 adjusts the heating power of the heating block 2. Simultaneously, a high-speed camera 4 records the gas-liquid two-phase flow behavior within the flow channel.

[0026] The pressure sensor 3 can withstand a maximum ultimate pressure impact of 1.5 MPa, which is sufficient to handle the peak pressure in this embodiment.

[0027] The pressure sensor 3 is fixed to the wall of the experimental device, with the detection surface flush with the wall, so that it can directly contact the working fluid without interfering with the flow of the working fluid.

[0028] The pressure sensor is further equipped with a thermocouple within a 25cm range to detect temperature fluctuations of the working fluid near the measuring point.

[0029] The high-speed camera 4 is used to observe the flow pattern of the boiling gas-liquid two-phase flow in the flow channel, and record the flow pattern video after the boiling steady state is reached.

[0030] During boiling heat transfer, under low heat flux density conditions, the heat transfer on the heating wall inside the heat exchanger is in a single-phase convective heat transfer zone or an isolated bubble boiling zone. At this time, the internal pressure of the component is mainly the dynamic pressure generated by the fluid flow, and the root mean square value of the pressure amplitude is P. RMS The pressure is relatively small and increases linearly with heat flux density; as heat flux density increases, wall activation and nucleation intensify, and bubbles coalesce to form small vapor clusters, which mix with the subcooled mainstream and then condense. During this process, the pressure fluctuation within the working fluid intensifies, and the root mean square value of the pressure amplitude P... RMS As heat flux density deviates from linearity, it increases at an accelerated rate. When the heat flux density increases to a certain level, vapor bubbles coalesce to form periodic large vapor bombs. After entering the unheated zone, these vapor bombs undergo intense condensation, leading to liquid phase reflux and generating strong pressure fluctuations, resulting in a root mean square pressure amplitude P. RMS A sudden increase. Subsequently, the root mean square value of the pressure amplitude P RMS The rate of increase slows down as heat flux density increases.

[0031] Through specific practical experiments, under the condition of atmospheric pressure at the outlet, with an inlet mass flow rate of 100-400 kg / m³, 2 Operating the above device under conditions of 1-20K subcooling and a 15° pipe inclination angle, key data can be obtained, including wall heat flux density, outlet pressure, and video recordings of the gas-liquid two-phase flow pattern. A transparent rectangular tube (60mm*30mm) with upward flow within an inclined tube and single-sided heating was used as the experimental setup, with deionized water as the cooling medium. The total length of the heating zone was 110mm. Multiple thermocouples were placed on the outer wall at distances of 10mm, 40mm, and 70mm from the outlet of the heating zone to collect the temperature of the heating block and calculate the heating wall temperature and heat flux density. A pressure sensor was placed on the unheated wall at a distance of 300mm from the heating outlet to measure the pressure, with a sampling frequency of 10kHz. The heating block was powered by a DC power supply, and the heat flux density was adjusted by controlling the voltage across the heater. The thermocouple and pressure sensor measurements were displayed in real time using a LabVIEW program in the calculation module. Temperature and pressure data were recorded after the thermocouple temperature measurements stabilized, with a data recording time of 1 minute. Meanwhile, a high-speed camera was used to record the vapor-liquid two-phase flow at a frequency of 1 kHz for a duration of at least 2 seconds.

[0032] like Figure 2 As shown, this is the root mean square value of the pressure amplitude, P. RMS As heat flux density changes, it can be seen that under low heat flux density conditions, the root mean square pressure amplitude P... RMSThe heat flux density increases approximately linearly, at which point the wall surface is in a single-phase convective heat transfer zone or an isolated bubble boiling zone. As the heat flux density increases, the root mean square pressure amplitude P... RMS The increase accelerates as the heat flux density deviates from linearity, while simultaneously forming coalesced small vapor clusters on the heated wall surface. When the heat flux density increases to a certain value, the root mean square pressure amplitude P... RMS A sudden increase occurs, forming periodic large vapor bombs on the heated wall surface. Subsequently, the root mean square pressure amplitude P... RMS It shows a slow increasing trend with the increase of heat flux density.

[0033] like Figure 3 The figure shows the frequency domain distribution of the pressure signal as a function of heat flux density. It can be seen that under low heat flux density conditions, the pressure frequency domain distribution is uniform. When the heat flux density increases to a certain value, a significant peak (characteristic frequency) appears in the frequency domain graph, at which point periodic large gas bombs occur within the experimental setup.

[0034] like Figure 4 As shown, the characteristic frequency of the pressure signal is compared with the measured vapor bomb frequency, and the error between the two is within ±6%. This indicates that the characteristic frequency of the pressure signal can accurately characterize the vapor bomb frequency. Therefore, by analyzing the pressure signal collected by the pressure sensor, accurate detection of boiling state zones and vapor bomb frequency can be achieved.

[0035] Compared with existing technologies that indirectly obtain the frequency of the gas bomb in the flow channel through pressure fluctuation characteristics without the need for additional observation windows in the structure to measure the gas bomb frequency, the present invention can quickly obtain the gas bomb frequency while preserving the integrity of the original structure as much as possible, thus greatly improving efficiency.

[0036] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for detecting subcooled boiling state and vapor bombardment frequency based on pressure measurement, characterized in that, The detection device includes: a heating block, a pressure sensor, a high-speed camera, a control module connected to the experimental device, and a calculation module, wherein: the control module outputs control commands to adjust the inlet conditions and heating power of the experimental device; the calculation module collects the pressure signal output by the pressure sensor to determine the boiling state in the experimental device; and the high-speed camera is positioned directly opposite the heating surface of the experimental device to record the gas-liquid two-phase flow behavior and boiling flow pattern in the flow channel. The experimental setup consists of a transparent rectangular pipe with heating blocks mounted on its side, and a cooling medium is installed inside the transparent rectangular pipe; a high-speed camera is positioned directly opposite the heated surface. The method refers to: arranging pressure sensors on the outer wall of the experimental device of the heat exchange equipment to collect pressure fluctuation signals in the heat exchange experimental device in real time; processing the root mean square value of the pressure fluctuation signal to obtain the root mean square value of the pressure amplitude under different heat flux density conditions, which can be used to determine the boiling state; and performing a fast Fourier transform on the pressure fluctuation signal to obtain the characteristic frequency in the frequency domain distribution of the pressure signal, which can characterize the vapor bomb frequency. The root mean square value of the pressure amplitude is obtained by solving the root mean square value of the pressure signal: ; The boiling state and vapor bomb judgment refer to the following: when the root mean square pressure amplitude increases approximately linearly with heat flux density, the heating wall of the heat exchange equipment is in a single-phase convective heat exchange or isolated bubble boiling zone; when the root mean square pressure amplitude increases at an accelerated rate with heat flux density, discrete small vapor clusters appear in the heat exchange equipment; when the slope of the root mean square pressure amplitude increasing with heat flux density decreases significantly, large vapor bombs appear in the heat exchange equipment, and the boiling state enters the fully developed boiling zone. A large vapor bomb refers to a large vapor cluster that is periodically generated and covers the entire heating wall surface.

2. The method according to claim 1, characterized in that, The heating block is specifically located on one side at a distance of 250cm from the pipe outlet, and is used to heat the working fluid and cause it to boil.

3. The method according to claim 1, characterized in that, The pressure sensor is specifically installed on the wall surface 5-10cm downstream of the heating block, at the outlet position of the experimental device, to ensure high accuracy and low delay in obtaining pressure fluctuation signals.

4. The method according to claim 1, characterized in that, The linear growth mentioned above refers to the real-time rate of change of the root mean square value of the pressure amplitude and the heat flux density. The heat flux density remains essentially constant. The accelerated growth mentioned above refers to the real-time rate of change of the root mean square value of the pressure amplitude and the heat flux density. After reaching a certain heat flux density, it increases to more than 1.25 times the previous value; The significant reduction refers to the real-time rate of change of the root mean square value of the pressure amplitude and the heat flux density. After a certain heat flux density, it drops to less than 0.75 times the previous value.

5. A device for detecting subcooled boiling state and vapor bombardment frequency based on pressure measurement, characterized in that, Implement the method described in any one of claims 1-4.

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