CN117169259A - Perspective imaging method for carbon deposition inside metal structure by using salt solution as contrast agent - Google Patents
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Abstract
The invention provides a perspective imaging method for carbon deposition in a metal structure by using a salt solution as a contrast agent, which is characterized in that the salt solution contrast agent is injected into a metal channel structure, the salt solution fills a gap between the metal channel structure and the carbon deposition, and an X-ray CT micro-focus plane scanning technology is adopted to obtain an X-ray gray level image of a carbon deposition contour. The invention solves the difficult problem of direct visual nondestructive detection of carbon deposition and blockage of the millimeter-sized heat exchange channel of the engine, and overcomes the defects of complex operation of pre-adjusting the surface tension of liquid metal, influence of liquid metal oxide on imaging and difficulty in subsequent thorough removal of solid oxide.
Description
Technical Field
The invention provides a perspective imaging method for carbon deposition in a metal structure by using a salt solution as a contrast agent, and belongs to the technical field of carbon deposition detection.
Background
Advanced aerospace engine regenerative cooling and thermal management systems typically include a large number of millimeter diameter heat exchange channels disposed within the metallic structure of the heated component. Hydrocarbon fuels such as kerosene serve as cooling media in the heat exchange channels, and cooling and thermal management of the engine are achieved through physical and chemical reaction endotherms. For engines that require long-term operation and re-use, hydrocarbon fuels undergo thermal oxidation and thermal cracking chemical reactions in high temperature environments, leading to coke generation and accumulation, and possible blockage of the passages leading to overheating damage of critical components. The carbon deposition detection in the heat exchange channel of the engine is carried out, and the method has important significance for the evaluation and maintenance of the engine, the optimization and research and development of the engine structure. However, no mature method for carrying out nondestructive detection on carbon deposition in the metal structure of the engine is still available at present.
Basel Ismail et al (Ismail B, ewing D, chang J S, et al development of a non-destructive neutron radiography technique to measure the three-dimensional soot deposition profiles in diesel engine exhaust systems [ J ]. Journal of Aerosol Science,2004,35 (10): 1275-1288.) used real-time neutron radiography (RTNR, real-time neutron radiography) to achieve non-destructive measurement of three-dimensional soot thickness of diesel exhaust components. The principle is that neutron rays are significantly attenuated when passing through light hydrogen compounds, but not when passing through metals. Experiments using RTNR equipment of a mawster nuclear reactor to generate neutron beams, test objects (an aluminum tube 105.3 mm in length and 9.6 mm in diameter) containing diesel soot layers were placed on a computer-controlled 360 ° turntable which was added to the facility in the path of the thermal neutron beam. The intensity of the neutron beam passing through the test object at each angle is converted into photons by DNIS (digital neutron imaging system ), the optical signal is enhanced by a silicon photon amplifier, the photon image is captured by a low-light camera, and the image is analyzed. Although RTNR technology can display carbon deposition profile, adopting carbon deposition detection requires nuclear reactor to generate thermal neutron beam, neutron radiography technology is not mature, and test safety cannot be guaranteed; detecting the radiation of the tested piece presents a great challenge for the reusability of the aeroengine; meanwhile, neutron radiography technology is too complex, detection cost is extremely high, and implementation difficulty is extremely high.
Giyoung Park et al (Park G, ryu H, kwon M, et al A Study on Soot and Ash Accumulation Characteristics of Diesel Particulate Filter Substrate Using Nondestructive Computed Radiography X-ray Imaging Technique [ J ]. Applied Sciences,2021,11 (20): 9483.) tested soot (soot) in diesel particulate filters of diesel engines based on computer X-ray imaging techniques. X-ray imaging is based on the fact that the absorption levels of X-rays by different materials are different, and the outgoing X-rays of different intensities exhibit different signal distributions on the signal receiver, so that objects inside the structure are imaged. Since the density and composition of the different materials cause the absorption level of the X-rays to be different, the different substances can be distinguished by the property of differential absorption, which is the physical basis of the objects inside the X-ray fluoroscopy and photography structures. However, since general stainless steel metals have a strong absorption level for X-rays, industrial nondestructive inspection X-rays are generally maintained at a high energy intensity and have extremely strong penetrability. The coke layer and the empty area occupied by air have extremely low absorptivity to high-energy X-rays, so that the X-rays have no obvious difference in X-ray intensity signal distribution of the carbon layer area and the air area obtained on the receiver when the X-rays penetrate through the stainless steel metal structure with coke accumulation. Therefore, conventional computer-aided X-ray imaging techniques cannot intuitively discern whether coke has accumulated inside the metal structure. Even if the researchers in document 2 perform pixel enhancement processing on the obtained image by a program algorithm, only a very blurred soot profile can be obtained.
The patent 2023102958832 discloses a nondestructive testing method for carbon deposition in an engine heat exchange channel, which is characterized in that normal-temperature liquid metal (gallium indium tin alloy) is injected into a millimeter-sized channel of a stainless steel experimental workpiece, the density of an air area of the channel is changed, and an auxiliary X-ray digital scanning technology is used for successfully realizing nondestructive visual testing of carbon particles deposited in the channel. The method is based on common X-ray computer digital imaging, and the density of the void area of the internal channel of the stainless steel metal structure is changed by adding liquid metal contrast agent, so that the original void area is improved for X-rayThe absorption level of the line is further increased, the distribution difference of the X-ray intensity signals of the carbon deposition area and the void area is further increased, and the obtained image is processed through a detail enhancement program algorithm to obtain an X-ray gray image with the outline of the carbon particles. The obtained carbon deposition X-ray gray level image has a very clear carbon particle morphology outline, can rapidly judge the carbon accumulation condition in the channel, and reduces the maintenance and repair cost of an engine system. However, the high surface tension of liquid metal (10 times the surface tension of water) limits its wetting ability on the surface of carbon particles, possibly resulting in distortion of the profile image. According to the technology, the sodium hydroxide electrolyte is filled in advance to reduce the surface tension of liquid metal, and the operation process is complex. In addition, the liquid metal increases in potential after contact with graphite, resulting in the formation of an oxide layer (beta-Ga 2 O 3 ) The patent technology adopts inert gas to purge the channel in advance to inhibit metal oxidation, has complicated operation process and limited effect, and is difficult to clean the solid oxide residue.
Disclosure of Invention
Aiming at the three prior arts, the neutron radiography technology is complex and has low maturity, the nuclear reactor is high in cost, and the radiation carried by the detected object is difficult to process and the repeated use is difficult; the high-energy X-ray has strong penetrability to a carbon deposition layer, and the imaging of the carbon deposition profile is unclear; the surface tension of the liquid metal contrast agent is too high, so that the infiltration capacity of the carbon particle surface is limited, and the alkaline electrolyte has limited capacity of reducing the surface tension of the liquid metal; solid oxide is easy to generate, imaging is affected, coke accumulation is misjudged, the operation of purging the channel in advance by inert gas is complex, the effect is limited, and oxide residues are difficult to thoroughly remove.
Based on the X-ray radiography technology, the invention creatively proposes to utilize a water-soluble salt solution contrast agent (metatungstate solution or NaI solution) to realize clear imaging of carbon deposition contours of a millimeter-level heat exchange channel of an engine in the plane scanning of an auxiliary X-ray microfocus CT system. The method makes up for the excessive X-ray penetrability of the computer X-ray imaging technology and unclear imaging of carbon deposit; the complex operation of preconditioning the surface tension of the liquid metal contrast agent is easy to generate solid oxide, and the imaging and the repeated use of the heat exchange channel are affected; the neutron radiation technology is unsafe, expensive and the measured piece is difficult to reuse.
The specific technical scheme is as follows:
a perspective imaging method for carbon deposition in a metal structure by using a salt solution as a contrast agent is based on a computer X-ray contrast technology and can be used for nondestructive perspective detection of carbon deposition of a heat exchange channel of an engine. To highlight the accumulation of coke in the heat exchange channels, water-soluble salt solution contrast agents, such as sodium iodide (NaI) solution, metatungstate solution (e.g., ammonium Metatungstate (AMT) solution or Sodium Metatungstate (SMT) solution) are injected into the heat exchange channels. Because sodium metatungstate can prepare a salt solution with higher density at room temperature, in addition, the absorption level of sodium metatungstate to X rays is higher, the density of the solution can be conveniently adjusted in the application range, and the solution has the characteristics of no toxicity, small surface tension, uniformity, transparency, easy removal and difficult decomposition at high temperature (within 90 ℃), the solute of the salt solution can be preferably sodium metatungstate.
The surface tension of the water-soluble salt solution is obviously smaller than that of liquid metal, the liquid can easily enter a millimeter-sized cooling tube due to the fluidity and wettability of the liquid, and the salt solution contrast agent can fully fill gaps between carbon deposition and a metal structure under the condition of not damaging the carbon deposition structure by combining an X-ray CT micro-focus plane scanning technology, so that a finer carbon deposition profile X-ray gray image is obtained.
The method comprises the following specific steps:
step one: preparing a water-soluble salt solution contrast agent for carbon deposit contour contrast in a heat exchange channel, weighing a proper amount of water-soluble salt solute, and preparing a solution by deionized water; at room temperature, after the solute is completely dissolved, the solution is clear and transparent;
step two: injecting a sufficient amount of water-soluble salt solution contrast agent from a low-level end inlet of the heat exchange channel; when the water-soluble salt solution contrast agent slowly fills the heat exchange channel and overflows from the outlet, the water-soluble salt solution contrast agent is considered to completely fill the residual space except carbon deposition in the channel; sealing the injection port and the outlet;
step three: carrying out industrial X-ray CT micro-focus plane scanning on an engine heat exchange channel which is filled with a water-soluble salt solution contrast agent and is well sealed, transmitting signals received by an X-ray signal detector to a computer end, and processing an image by utilizing a detail enhancement algorithm to obtain an imaging result schematic diagram 2; the brighter part of the channel is accumulated coke C, and the shaded part is water-soluble salt solution contrast agent L; clearly observing the carbon deposition profile in the pipeline from the brightness degree of each material in different parts;
step four: opening the inlet and the outlet, blowing out the water-soluble salt solution contrast agent in the channel, and then cleaning the channel pipeline by deionized water and absolute ethyl alcohol in sequence to completely discharge the water-soluble salt solution contrast agent in the channel.
The invention solves the difficult problem of direct visual nondestructive detection of carbon deposition and blockage of the millimeter-sized heat exchange channel of the engine, and overcomes the defects of complex operation of pre-adjusting the surface tension of liquid metal, influence of liquid metal oxide on imaging and difficulty in subsequent thorough removal of solid oxide. The salt solution contrast agent which is nontoxic, harmless, homogeneous and transparent has small surface tension, easily controllable density and high X-ray absorption level, and can obtain the carbon deposition profile and channel blockage condition inside the metal millimeter-sized channel by combining the micro-focus CT planar scanning technology. The technical scheme of the invention greatly improves the accuracy and the detection efficiency of the carbon deposition detection of the cooling pipeline and reduces the maintenance cost of the aerospace engine.
Drawings
FIG. 1 is a schematic representation of a carbon deposition X-ray imaging in an embodiment regenerator channel;
FIG. 2 is a schematic representation of the results of partial imaging of carbon deposition in the regenerator channels of an example;
FIG. 3 is a diagram of an experimental work piece according to an embodiment;
FIG. 4 is a graphical representation of example fuel and saline contrast agents;
FIG. 5 is an X-ray gray scale image of a sample of the contrast agent experiment of different saline solutions of example 1;
FIG. 6 is an X-ray gray scale image of a sample of the SMT solution contrast agent test of example 2 at different densities.
Detailed Description
The following examples are presented to illustrate the process, with experimental salt solutes NaI, AMT and SMT all having a purity of 99.99%. The method is further described below with reference to the accompanying drawings:
step one: preparing a salt solution contrast agent for carbon deposit profile radiography in a heat exchange channel, weighing a proper amount of salt solute, and preparing a solution by deionized water. And (3) at room temperature, after the solute is completely dissolved, the solution is clear and transparent, and the preparation of the water-soluble salt solution contrast agent is completed. The solution density can be measured by a densitometer, the solution density is reduced by dilution with deionized water, and the solvent can be evaporated or the solute can be added by increasing the density.
Step two: a sufficient amount of water soluble salt solution contrast agent is injected from the low end inlet of the heat exchange channel. When the solution slowly fills the heat exchange channels and a small amount of solution overflows from the outlet, the water-soluble salt solution contrast agent is considered to be completely filled in the residual space except carbon deposition in the channels. At this time, both the inlet and the outlet are sealed.
Step three: as shown in fig. 1, an engine heat exchange channel filled with a water-soluble salt solution contrast agent and well sealed is subjected to industrial X-ray CT micro-focus plane scanning, signals are received by an X-ray signal detector and transmitted to a computer end, and an image is processed by a detail enhancement algorithm to obtain an imaging result schematic diagram shown in fig. 2. As shown in fig. 2, the brighter part of the channel should be accumulated coke C, and the shaded part should be water-soluble salt solution contrast agent L, at which time the metallic wall surface S has a similar brightness to the coke C. The carbon deposition profile in the pipeline can be clearly observed from the brightness of each material in different parts.
Step four: opening the inlet and the outlet, blowing out the water-soluble salt solution contrast agent in the channel, and then cleaning the channel pipeline by deionized water and absolute ethyl alcohol in sequence to completely discharge the water-soluble liquid in the channel. To ensure complete drainage of the water-soluble salt solution contrast agent, the heat exchange channel can be subjected to microfocus CT planar scanning again to observe whether the water-soluble salt solution contrast agent remains in the tube.
Example 1
Aiming at a millimeter-sized heat exchange channel sample of an engine with a straight structure, the method provided by the invention is used for detecting the carbon particle deposition condition in the sample, and the process is as follows:
(1) Using a flat metal member with a specification of 70 x 40mm long and 8mm wide and thick, 5 millimeter-scale heat exchange channels with a depth of phi 4 x 35mm are machined on one side. In addition, each channel has a standard M5 thread of 5mm depth for bolt sealing, as shown in FIG. 3;
(2) First, each channel is pre-loaded with an equal amount of carbon particles, approximately 1/3-1/2 of the channel volume, and then numbered 1-5, respectively.
(3) Salt solution contrast agent, a near saturated solution of NaI, AMT, SMT was prepared separately, see fig. 4. The detailed preparation process comprises the following steps: and respectively weighing about 13g, 16g and 24g of NaI, AMT, SMT reagent into 3 beakers, adding about 10ml of deionized water into each beaker, fully stirring, standing for 3-5min until the solute is completely dissolved, and if no crystal is separated out, completing the preparation of 3 nearly saturated solutions. At this time, the densities of the 3 solutions were 1.74g/cm, respectively 3 (NaI solution), 2.03g/cm 3 (AMT solution), 2.78g/cm 3 (SMT solution).
(4) No liquid (containing only air) was added to channel 1 as a blank experiment; the common circulating medium Chinese RP-3 fuel in the heat exchange channel is added in the channel 2 to serve as an environment control experiment; adding NaI solution into the channel 3; adding an AMT solution into the channel 4; an SMT solution was added to channel 5. Lanes 3-5 served as parallel control experiments. Performing bolt sealing treatment on the 5 channels to obtain an engine millimeter-scale heat exchange channel sample;
(5) The sample of the millimeter-sized heat exchange channel of the engine is subjected to digital planar scanning imaging by using an industrial X-ray CT micro-focus imaging system, and an example photo of the gray level image of the carbon particles in the sample of the millimeter-sized heat exchange channel shown in figure 5 can be obtained. As shown in fig. 5, carbon particles C in air a or chinese RP-3 fuel F placed in channels 1 and 2 cannot be clearly imaged under X-rays; the addition of the NaI solution to the channel 3 can image the carbon particles C in the internal channel of the metal structure, but the outline of the carbon particles C is quite fuzzy; channels 4 and 5 used AMT solution, SMT solution, respectively, clearly seen the carbon particle C position and profile. The two channels differ in that the SMT contrast agent zone is developed darker than the AMT contrast agent zone, which will make the imaging of carbon particles C in the SMT contrast agent clearer, so that SMT solution is preferred as saline contrast agent.
Example 2
The SMT can prepare a salt solution with higher density at room temperature, and the high absorption level of the SMT solution to X rays enables the imaging of carbon particles C in the SMT contrast agent to be clearer, and in addition, the density of the SMT solution can be conveniently adjusted in the application range. The purpose of example 2 was to explore the range of densities in which SMT salt solutions were able to image carbon particles.
(1) Also, using a flat metal member as shown in FIG. 3, an equal amount of carbon particles was previously placed in each channel, accounting for about 1/3 to 1/2 of the volume of the channel, and then numbered 1-5, respectively.
(2) The detailed preparation process of the SMT salt solution contrast agent comprises the following steps: 40ml deionized water was added to a 100ml beaker, followed by adding excess SMT, stirring well, and standing for 10min. Wait for undissolved solute to settle to the bottom of the beaker, and the supernatant is completely clear and transparent. Sucking out the supernatant with a syringe, sub-packaging into 4 small beakers, and diluting with water. The density of the SMT solution in the 4 beakers was controlled to be 1.25g/cm, respectively 3 、1.51g/cm 3 、1.76g/cm 3 、2.02g/cm 3 。
(4) Pure water was added in channel 1 as a blank experiment; channels 2-5 were each filled with 4 density SMT saline solutions in order of density from low to high as a parallel control experiment. Performing bolt sealing treatment on the 5 channels to obtain an engine millimeter-scale heat exchange channel sample;
(5) The sample of the millimeter-sized heat exchange channel of the engine is subjected to digital planar scanning imaging by using an industrial X-ray CT micro-focus imaging system, and an example photo of the gray scale image of the carbon particles in the sample of the millimeter-sized heat exchange channel shown in figure 6 can be obtained. As shown in fig. 6, the carbon particles C placed in the pure water W of the channel 1 cannot be clearly imaged under X-rays; 1.25g/cm in channel 2 3 Fails to image carbon particles C; 1.51g/cm in channel 3 3 Can make carbon by SMT solutionParticle C is imaged but shows that the profile of carbon particle C is quite blurred; the SMT solution densities in channels 4 and 5 were 1.76 and 2.02g/cm, respectively 3 The carbon particle C position and profile can be clearly seen. The experimental results clearly show that the profile of carbon particles C is progressively clearer as the density of the SMT solution increases. However, since crystals are easily precipitated in the saturated salt solution, the SMT solution is preferably formulated to have a density of 1.76 to 2.78g/cm 3 Between them.
Claims (4)
1. A perspective imaging method for carbon deposition in a metal structure by using a salt solution as a contrast agent is characterized in that the salt solution contrast agent is injected into a metal heat exchange channel structure, the salt solution fills a gap between the metal channel structure and the carbon deposition, and an X-ray CT micro-focus plane scanning technology is adopted to obtain an X-ray gray scale image of a carbon deposition contour.
2. The method of claim 1, wherein the water-soluble salt solution contrast agent comprises at least one of the following: sodium iodide NaI solution, metatungstate solution.
3. The method for perspective imaging of carbon deposition inside a metal structure using a salt solution as a contrast agent according to claim 2, wherein the metatungstate solution is an ammonium metatungstate AMT solution or a sodium metatungstate SMT solution.
4. The method for perspective imaging of carbon deposition inside a metal structure using a salt solution as a contrast agent according to claim 1, comprising the specific steps of:
step one: preparing a water-soluble salt solution contrast agent for carbon deposit contour contrast in a heat exchange channel, weighing a proper amount of water-soluble salt solute, and preparing a solution by deionized water; at room temperature, after the solute is completely dissolved, the solution is clear and transparent;
step two: injecting a sufficient amount of water-soluble salt solution contrast agent from a low-level end inlet of the heat exchange channel; when the water-soluble salt solution contrast agent slowly fills the heat exchange channel and overflows from the outlet, the water-soluble salt solution contrast agent is considered to completely fill the residual space except carbon deposition in the channel; sealing the injection port and the outlet;
step three: carrying out industrial X-ray CT micro-focus plane scanning on an engine heat exchange channel which is filled with a water-soluble salt solution contrast agent and is well sealed, transmitting signals received by an X-ray signal detector to a computer end, and processing an image by utilizing a detail enhancement algorithm to obtain an imaging result schematic diagram; the brighter part of the channel is accumulated coke C, and the shaded part is water-soluble salt solution contrast agent L; clearly observing the carbon deposition profile in the channel from the brightness of each material in different parts;
step four: opening the inlet and the outlet, blowing out the water-soluble salt solution contrast agent in the channel, and then cleaning the channel pipeline by deionized water and absolute ethyl alcohol in sequence to completely discharge the water-soluble salt solution contrast agent in the channel.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202311160620.7A CN117169259B (en) | 2023-09-11 | 2023-09-11 | Perspective imaging method for carbon deposition inside metal structure by using salt solution as contrast agent |
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| CN202311160620.7A CN117169259B (en) | 2023-09-11 | 2023-09-11 | Perspective imaging method for carbon deposition inside metal structure by using salt solution as contrast agent |
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| CN117169259A true CN117169259A (en) | 2023-12-05 |
| CN117169259B CN117169259B (en) | 2024-04-09 |
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| US20130010918A1 (en) * | 2011-06-23 | 2013-01-10 | Schlumberger Technology Corporation | Method for determining spatial distribution and concentration of a component in a pore volume of a porous material |
| CN103308532A (en) * | 2012-11-12 | 2013-09-18 | 西安航空动力股份有限公司 | Method for detecting redundant non-metal in inner chamber of hollow blade |
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