Hole Blockage Research Articles

Investigation of the cooling hole blockage induced by different thermal spray TBC deposition processes

High-temperature turbine airfoils and combustion chamber walls in jet engines require sufficient cooling via cooling holes and thermal barrier coating systems (TBCs) to protect them from hot combustion gases. As the demand for greater efficiency and higher firing temperatures in jet engines increases, there is a corresponding need for more advanced film cooling methods, such as the use of more complex hole geometries. The use of Additive Layer Manufacturing (ALM) techniques allows the production of such intricate cooling holes, enhancing the flow of cooling air onto component surfaces. Conventional TBC deposition techniques, for example Atmospheric Plasma Spraying (APS) or Electron Beam Physical Vapor Deposition (EB-PVD), often lead to partial or complete blockage of cooling holes. This study compares the blockage of TBCs deposited on conventionally-sheet alloys with standard cooling holes and ALM alloys with more complex cooling holes using APS as a baseline process. Additionally, alternative plasma spray deposition technologies such as Suspension Plasma Spraying (SPS) and Plasma Spray-Physical Vapor Deposition (PS-PVD) were explored. The aim was to determine the effectiveness of these processes in preventing blockage compared to the traditional APS process. The experimental results showed that the formation of the coating, whether originating from splats or from the vapor phase, the feedstock particle size, and the cooling hole geometry can all affect the blockage. It was demonstrated that PS-PVD, with its vapor-induced deposition, is highly effective in minimizing blockage, regardless of the cooling hole geometry.

Vortex Cleaning Device for Rice Harvester: Design and Bench Test

To solve the problem of increased grain impurity rate and grain loss rate caused by clogging of sieve holes during the cleaning process of ratooning rice, a spiral step cleaning device was designed, which disturbed the flow field at the sieve holes through vortex in the slot and disrupted the force balance of the blockages at the sieve holes. The device mainly includes a cleaning separation core and a cleaning separation core shell. Firstly, the main parameters of the cleaning separation core were determined, and the critical shear airflow velocity was obtained through theoretical analysis. Through energy loss analysis, the fan wind speed was determined to be 11.5 m/s. Secondly, the CFD-DEM coupling method was used to analyze the flow patterns inside the slot and the movement patterns of blockages on the sieve surface, confirming the effectiveness of vortex guided blockage removal. Finally, a prototype was designed and built for testing, and the results showed that when the wind speed of the fan was 11.5 m/s, the grain impurity rate was 1.35%, the grain loss rate was 2.13%, and the average sieve blockage rate was ≤0.1%. All indicators were better than traditional cleaning devices and could meet the cleaning requirements. During the continuous operation of the spiral step cleaning device, performance indicators such as sieve hole blockage rate remained basically unchanged.

Preparation of modified wood-based metal nanoparticles synthesized in situ and efficient removal of organic pollutants from wastewater

Wood has excellent properties such as biodegradability, high reactivity and rich channel skeleton structure. However, the defects such as hole blockage and limited specific surface area limit the application of wood-based materials in wastewater treatment. Therefore, in this research, wood substrates (DTWS) were treated using a deep eutectic solvent method, which was able to remove both lignin and hemicellulose from wood. Wood-based carriers with high specific surface area and high chemical activity were formed. The DTWS-Ag material was formed by growing Ag nanoparticles (NPs) in wood channels by hydrothermal method. The results showed that with the increase of lignin and hemicellulose removal, the degradation performance of DTWS-Ag material showed a volcanic trend due to the interaction between Ag and the inner wall of the pipe. The pore size and the amount of Ag NPs are very important to the degradation rate of dye molecules. DTWS-4-Ag composite material makes wood pore diameter and Ag NPs production reach a high balance, so that it has the highest degree of reduction. DTWS-4-Ag showed high catalytic degradation efficiency and stability for methylene blue degradation, with the degradation efficiency up to 98.3 %. This low-cost, renewable wood-based filter has high dye degradation efficiency and can be widely used in practical wastewater treatment.

Sol-gel prepared amorphous Ta2O5 thin film for application in high LIDT antireflection coating and UV photodetection

In this report, a sol–gel method has been developed using tantalum ethoxide to produce homogenous thin films of amorphous Ta2O5 for application in optical coating for high power laser as well as photodetection in the UV range. Morphology, stoichiometry, optical properties, short range atomic structure and valence band have been investigated at various annealing temperature up to 500 °C. A large valence band onset of 3.5 ± 0.20 eV has been measured for the film annealed at 500 °C, ensuring hole blockage through the film and electron selective transport. Extended X-ray absorption fine structure (EXAFS) study has revealed the Ta–O bond distance to be 1.85 Å for as-deposited film, which increased with annealing and approached the crystallographic value. The sol-gel prepared Ta2O5 film has been used as antireflection (AR) coating on silicon and fused silica (FS) substrates. 99.4% transmission with a LIDT of 20 J/cm2 @6 ns at 1064 nm is obtained for Ta2O5/SiO2 AR coatings on FS. Using these sol-gel films, Ta2O5/Si vertical heterojunction photodetectors have been fabricated, which exhibited a responsivity of 560 mA/W, external quantum efficiency of 213%, and specific detectivity ∼1 × 1012 Jones at −1 V bias voltage and 325 nm illumination wavelength.

Effects of Hole Blockage on Endwall Film Cooling and Vane Phantom Cooling Performances of a Transonic Turbine Vane

Abstract Although the thermal-barrier coating (TBC) can protect the gas turbine components from the hot mainstream gas, it is not uncommon that the TBC partially blocks the film cooling holes during the spraying process. The film cooling hole blockage will alter the coolant flow behaviors and lead to a significant variation in film cooling performance. In this paper, a physical model of blockage holes including two key parameters of blockage ratios (B) and blockage angles (α), was proposed to analyze the effects of hole blockage on endwall film cooling performance, phantom cooling performance of vane pressure side surface (PS), and overall cooling performance. Based on a proposed double-coolant-temperature prediction method, the endwall film cooling effectiveness, phantom cooling effectiveness of the vane PS and area-averaged cooling effectiveness of an actual vane passage were numerically calculated and analyzed, for the common holes and blockage holes (three different blockage ratios of B and three different blockage angles of α) at the similarly realistic operating conditions of a gas turbine. Results indicated the hole blockage is pernicious to endwall film cooling performance, leading to a significant decrement of endwall film cooling effectiveness (up to 30% at B = 0.4), where the decrement magnitudes increase with increasing the blockage ratios (B). Compared to the blockage ratios (B), the effects of blockage angle (α) on endwall film cooling effectiveness are secondary and slight (less than 10% in η). Nonetheless, the hole blockage is beneficial to phantom cooling performance of the vane PS, leading to an obvious enhancement (more than 40%) in area-averaged phantom cooling effectiveness with increasing blockage ratios (B), due to the increase of the local blowing ratio (BReff). The area-averaged cooling effectiveness including endwall film cooling and phantom cooling on PS, decreases with the increase of blockage angle (α), and the benefits of hole blockage in overall cooling performance are negative at α = 20 deg. This suggests that the overlarge blockage ratios and short blockage lengths (correspond to the blockage position near film cooling holes exit or large blockage angle of α), should be utmost avoided during the spraying process of the TBC, otherwise, the film cooling scheme designs, based on the geometry of the pristine holes, may be inefficient.

Investigation of cooling hole blockage in the plasma spraying of thermal barrier coatings on super-alloy

ABSTRACT Ceramic materials will get deposited inside pre-drilled cooling holes and partially or completely block during thermal barrier coating (TBC). In this study, the hole blockage produced by atmosphere plasma spraying (APS) was investigated using industrial computed tomography. The results show that the geometric features of the blockage owing to APS coating are significantly affected by the inclination angle of the pre-drilled holes. The coating deposition in the vertical holes is rotationally symmetric and mainly concentrates at the entrance. For the inclined holes, the deposition on the trailing edge is much more than that on the leading edge. The deposition height and length on the trailing edge increase with the inclination angle; however, they are little disturbed by the hole size. Therefore, the blockage ratio decreases with the increase of the hole size. In addition, greater TBC thickness causes larger deposition height and length and subsequently results in a larger blockage ratio.

Dynamic evolution of keyhole during multi-pulse drilling with a millisecond laser on 304 stainless steel

The efficiency of millisecond laser drilling is high due to the molten material ejection, and is applied in many industries like aerospace, automobile and electronics. However, there may be some defects such as hole blockage, low machining accuracy and low repeatability, especially for the process of multi-pulse drilling. The melt flow remaining inside keyhole due to inefficient ejection, is responsible for the formation of those defects. Hence, it is necessary to investigate the dynamic behavior of melt flow during multi-pulse drilling. In this paper, the dynamic evolution of keyhole is investigated combining in-situ observation and numerical simulation methods. According to the ejection efficiency, the multi-pulse drilling process can be divided into three periods, namely rapid drilling period, linear drilling period, and moderate drilling period. The melt flow behaves differently in each period. In rapid drilling period, a conical keyhole is formed in the end. The melt flow behavior is affected dominantly by the recoil pressure when the laser is on and by the surface tension when the laser is off. In linear drilling period, the blocked keyhole occurs occasionally. The melt flow behavior is affected by gravity and recoil pressure when the laser is on and by the surface tension and recoil pressure when the laser is off. In moderate drilling period, the keyhole profile is wavy. The melt flow behavior is affected by surface tension and recoil pressure dominantly during the whole period. The melt flow transition and its influence factors are investigated in this paper, which is helpful for understanding the physical processes during the multi-pulse laser irradiation process.

Automatic Classification System of Drainage Hole Blockage Based on Convolution Neural Network Transfer Learning

The blockage or failure of the drainage holes will endanger the stability of the slopes and traffic safety of a highway tunnel. This paper studies an algorithm for the automatic classification of drainage hole blockage degree based on convolutional neural network transfer learning to explore the intelligent detection method of drainage hole blockage. The model transfer method is adopted to input drainage hole image samples to retrain the pretrained network to classify new images. Experiments are performed on the collected samples of drainage hole images, and the accuracy of different network models is compared, ResNet‐18 being the best. The ResNet‐18 performance is compared using different transfer strategies and parameters. The results show that when the SGDM gradient optimisation algorithm is used and the learning rate is 0.0001, the identification effect of these samples is the best. The validation accuracy can reach 91.7%, test accuracy is 90.0%, and the effective classification of drainage hole blockage to different degrees is realised under the transfer learning strategy of ResNet‐18 model 1–34 frozen layers. Furthermore, with an expansion of the samples in the future, the identification accuracy will be further improved. The automatic classification system of the blockage degree of drainage hole greatly reduces the cost of manual detection, plays a guiding role in the maintenance of drainage pipes, and effectively improves the safety of highway tunnels and slopes.

Numerical Investigations of Film Cooling and Particle Impact on the Blade Leading Edge

As a vital power propulsion device, gas turbines have been widely applied in aircraft. However, fly ash is easily ingested by turbine engines, causing blade abrasion or even film hole blockage. In this study, a three-dimensional turbine cascade model is conducted to analyze particle trajectories at the blade leading edge, under a film-cooled protection. A deposition mechanism, based on the particle sticking model and the particle detachment model, was numerically investigated in this research. Additionally, the invasion efficiency of the AGTB-B1 turbine blade cascade was investigated for the first time. The results indicate that the majority of the impact region is located at the leading edge and on the pressure side. In addition, small particles (1 μm and 5 μm) hardly impact the blade’s surface, and most of the impacted particles are captured by the blade. With particle size increasing, the impact efficiency increases rapidly, and this value exceeds 400% when the particle size is 50 μm. Invasion efficiencies of small particles (1 μm and 5 μm) are almost zero, and the invasion efficiency approaches 12% when the particle size is 50 μm.

Analysis of High Slope Seepage Influence Based on Multi-scale Measurement Data

In order to study the influence of seepage on high slope stability, the impact of drainage hole blockage on slope stability is analyzed by in-situ test technology, near-field photogrammetry and indoor test and numerical simulation.According to the groundwater monitoring of the water meter and pore pressure meter, when the drainage hole blockage exceeds 80%, the pore water pressure increases by about 13m, by 25kPa; is monitored by the steel gauge and anchor gauge. When the drainage hole blockage exceeds 80%, the shear force of the slope anti-sliding pile increases by 20%, about 30kN; analyzes the slope deformation by the near-view photography technique, when the drainage hole blockage exceeds 80%, and the slope deformation of 44mm, exceeds the slope deformation warning value of 30mm,.After theoretical calculation and numerical simulation analysis, the groundwater level and support structure under different blockage conditions. Numerical simulation results show that when the drainage hole is less than 60%, the supporting structure and slope deformation grow linearly, while when the blockage degree exceeds 80%, the support structure increases sharply, and according to the finite element strength, when the blockage degree exceeds 60%, the slope stability coefficient decreases sharply and the risk of instability.

Cause Analysis and Prevention of Hole Collapse by Water Injection and Dust Removal in Qi Panjing Coal Mine

To solve the “special coal seam” with complex coal seam structure, fault phenomenon, and many gangue layers and complex gangue lithology in Qi Panjing coal mine, the problems such as hole collapse and blockage of coal seam water injection dust removal drilling are caused. From the aspects of drilling layout, drilling technology, and gangue material consolidation, a complete set of key technologies for prevention and control of water injection and dust removal in “special coal seam,” have been formed. Seven boreholes have been drilled in I020902 return air roadway of Qi Panjing coal mine, and field comparative test has been carried out. The results show that: after adopting the complete set of key technologies of drilling prevention and control, the drilling depth is 85-100 m, the average depth is 98 m, and the drilling depth of coal seam water injection can reach 170-185 m; the footage per cycle is greatly improved, with the minimum increase of 30.86%, the maximum increase of 46.38%, and the average increase of 36.77%, to save drilling time and bring good economic benefits, and there is no collapse in the borehole hole, to ensure the safety of production. It has a good reference, and practical guiding significance for other coal mining faces, especially for “special coal seam” working face.

Angle of attack measurement using low-cost 3D printed five hole probe for UAV applications

This paper presents a low-cost 3D printed Five Hole Probe (FHP) for Angle of Attack (AOA) measurement and a solution to predict the missing pressure data due to hole blockage using machine learning. The five Hole Probe is designed and fabricated taking reference to the open-source probe called “the oxford probe”. It is intended to use this probe in Mini Unmanned Aerial Vehicles for AOA measurement because the UAVs are primarily designed to carry out unconventional missions like flying at low speed and low altitude, which makes the AOA measurement as one of the absolute requirement. The main challenges involved in mini flyers are their size and weight constraints. Due to these constraints, the probe should have lightweight but highly accurate. Keeping this in mind, suitable design modifications and material selection are made on the Oxford probe and it is manufactured by 3D printing. Then the 3D printed probe is tested in the wind tunnel. In parallel, a CFD analysis of the FHP is carried out in the ANSYS WORKBENCH environment and the results are presented. The CFD results are compared with windtunnel measurements of AOA, and the results are analyzed. Calibration of FHP is carried out, and a lookup table is generated using the pressure coefficients CPα and CPβ corresponding to respective AOA and AOS. For validation, the probe is kept at known AOA and AOS, and the pressure coefficients were calculated. It has been found that the accuracy of measurement is increased by using the mean of ten pressure samples for calculating the pressure coefficients, instead of every pressure sample. And due to the small diameter, the ports may get blocked from dust particles. The machine learning algorithm (SVR – Support Vector Regression) has been trained and tested to tackle the problem of hole blockage. Various regression models were tested to predict the missing Pressure. The Quadratic SVR regression model is selected based on RMSE value. The selected regression model is validated by blocking one of the ports of FHP.

Measurements of detailed heat transfer characteristics on a high-pressure turbine vane endwall with coolant injection

Detailed heat transfer characteristics over high-pressure turbine endwall surfaces with coolant injection were experimentally studied in this paper. Heat transfer experiments were conducted in a properly scaled-up endwall model for an engine-representative oncoming flow profile with a high freestream turbulence intensity of 9.8% at an exit Reynolds number of 0.76 × 106 and an exit Mach number of 0.37. Cooling for the endwall was accomplished by upstream purge flow from a slot and film coolant from three axial rows of discrete film-cooling holes within the vane passage on the endwall. An engine-like coolant-to-mainstream density ratio of 1.70 was achieved by using cooled foreign gas. High-resolution measurements of the endwall heat transfer coefficients were conducted by using a steady, high-resolution infrared thermography technique based on the superposition principle for purge flow blowing ratios of 0.1–0.45 and film coolant injection blowing ratios of 1.4–3.6, respectively. In particular, the effects of the cooling geometries without blowing were considered to simulate hole blockage due to deposition. Results showed that local heat transfer coefficients near the film-cooling hole exits were significantly enhanced due to strong interactions between film coolant injection and mainstream flows, but those downstream of the slot were inhibited, somewhat, by purge flow, resulting from the suppression of purge flow on horseshoe vortex at the vane leading edge. The inhibiting effects of purge flow on the endwall heat transfer are more prominent when purge flow and the film coolant are injected simultaneously. For the discrete holes, higher coolant injection rates generate increased heat transfer levels. Because ingestion and re-injection of mainstream flows through the slot or the film-cooling holes without blowing, the presence of both cooling geometries causes heat transfer enhancement, and the enhancement by the film-cooling holes is higher than that by the slot. The detailed heat transfer measurements in this paper can provide useful thermal boundaries for an optimized endwall film-cooling design that will be investigated in a follow-up study.

Feasibility Study of Microneedle Fabrication from a thin Nitinol Wire Using a CW Single-Mode Fiber Laser

Abstract In this paper, feasibility studies are presented on microneedle fabrication by using a multiple-pulse laser microhole drilling technique to drill an axial hole into a thin nitinol wire of 150 μm in diameter. Nitinol is chosen for its biocompatibility and excellent super-elasticity to eliminate breakage risk. One potential use of this microneedle is for drawing a small amount of blood for glucose monitoring. The critical factor for drilling microholes into a thin nitinol wire axially is the restoration of the semi-infinite material condition, which is the key to prevent the thin wire from being melt away by the laser due to excessive heat transfer in the radial direction. The results show that holes, up to 607 μmin depth, can be drilled into a thin nitinol wire of 150 μm in diameter using 18 repetitions of a 3-pulse group with 13 μs pluses. However, hole quality is poor. The challenges for improving hole qualities, such as centering, hole blockage, through holes, and process parameters, are discussed.

Numerical simulation of melt hydrodynamics induced hole blockage in Quasi-CW fiber laser micro-drilling of TiAl6V4

Laser drilling in the melt expulsion regime often inherits defects such as melt debris around the hole vicinity, recast layer deposition, melt shadow, taper, barreling and melt flow induced hole blockage. Thus, it is imperative to study and scrutinize the mechanism responsible for defects in laser drilling. In this paper, a two-dimensional free surface numerical model of quasi-CW drilling is presented which describes complex time-varying melt flow patterns considering the effects of recoil pressure, surface tension, Marangoni shear stress which are all dependent on surface temperature. It has been found out that in case of laser heating during initial pulses, recoil pressure is the dominating factor resulting in the expulsion of melt near hole entrance. However, during solidification surface tension induced backflow of melt creates a shadow at hole entrance. In the later stages, the drag force induced by surface tension constraints the recoil pressure, limiting the penetration depth due to which significant amount of melt remains inside the drilled hole, leading to melt re-closure induced hole blockage. The predicted hole depth dimensions and defects such as recast layer, melt shadowing, and hole blockage agrees reasonably well with experimental micrographs and literature data.

Application and Development of an Environmentally Friendly Blast Hole Plug for Underground Coal Mines

Drilling and blasting technology is one of the main methods for pressure relief in deep mining. The traditional method for blasting hole blockage with clay stemming has many problems, which include a large volume of transportation, excess loading time, and high labor intensity. An environmentally friendly blast hole plug was designed and developed. This method is cheap, closely blocks the hole, is quickly loaded, and is convenient for transportation. The impact test on the plug was carried out using an improved split Hopkinson pressure bar test system, and the industrial test was carried out in underground tunnel of coal mine. The tests results showed that, compared with clay stemming, the new method proposed in this paper could prolong the action time of the detonation gas, prevent premature detonation gas emissions, reduce the unit consumption of explosives, improve the utilization ratio, reduce the labor intensity of workers, and improve the effect of rock blasting with low cost of rock breaking.

Effect of spherical blockage configurations on film cooling

With increasing inlet temperature of gas turbines, turbine blades need to be effectively protected by using cooling technologies. However, the deposition from the fuel impurities and dust particles in the air is often found inside film holes, which results in partial hole blockage. In this paper, the deposition geometry is simplified as a rectangular channel, and the effect of three blockage ratios is investigated by using the computational fluid dynamics. In addition, water droplets are also released from the coolant inlet to provide a comparison of the results with and without mist injection. It is found that the lateral film cooling effectiveness is reduced with increasing blockage ratio. For all the cases with the blowing ratio 0.6, 1% mist injection provides an improvement of the cooling performance by approximately 10%.

Effect of Hole Blockage Configurations on Film Cooling in Gas Turbine Components

Usually, turbine blades operate under a harsh environmental condition. The inlet temperature of gas turbines increases with an improvement of the engine efficiency. Some cooling schemes are adopted to prevent the blades from thermal erosion of the hot mainstream. Film cooling technology is used widely and effectively in the blade cooling. In this paper, a comparison of hole blockage configurations was conducted by computational fluid dynamics. The results show that the film cooling effectiveness for a tetrahedral blockage case is higher than for other cases with various hemispherical blockages.

Selective removal Pb(ii) ions form wastewater using Pb(ii) ion-imprinted polymers with bi-component polymer brushes

Ion imprinted polymers (IIPs) are very difficult to apply in actual wastewater containing solid particles and floccules due to the imprinting hole blockage of losing adsorption performance.

Inorganic Matter Behavior during Coal Gasification: Effect of Operating Conditions and Particle Trajectory on Ash Deposition and Slag Formation

Ash particle deposition and uncontrolled slag flow, which can lead to tap hole blockage, are some of the main issues during coal gasification. In this work, a special collector probe was used to collect ash deposition and analyze slag formation and blockage probability in terms of operating conditions and particle trajectories. Increasing the temperature led to the increase in the total deposition for all of the experiments. However, when the temperature was increased, the weight of produced slag flow increased, but it was observed that increasing the temperature could not guarantee the safe operation by preventing deposition blockage. Using two Canadian coal types proved that the ash composition of coal has a significant effect on the amount and thickness of deposition on the wall. For fuel with low ash viscosity, increasing the temperature increased slag flow and blockage never happened. However, for fuel with high bulk ash viscosity, when the temperature was increased, the blockage probability did not decrease. The reason might be related to the different effects of the temperature on particle stickiness and slag viscosity at a specific range of the temperature. Computer-controlled scanning electron microscopy (CCSEM) analysis showed that excluded iron-bearing minerals of the first coal and included calcium-bearing minerals of the second coal had a substantial effect on the deposition tendency of these fuels. Increasing the velocity of the particles by gas flow rate mostly resulted in reduction of deposition. Fuel with a higher particle size range at a low temperature and high gas flow has the lowest deposition tendency. To evaluate the effect of particle trajectory/aerodynamics, two different types of feeding configurations were used and the results showed that the feeder type has a significant effect on the deposition pattern and growth at different locations. One feeder by injecting the particles in a narrow area led to high inorganic accumulation near the feeding spot, resulting in severe depositions with a thickness of several centimeters. The other feeder caused more uniform deposition by producing a wider sticky surface with a lower deposition thickness on the wall of the furnace.