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1
Chen, Shen Li y Shun Tai Chung. "Charge Programming and Erasing Characteristics of the Submicron Stacked-Gate Flash Cells". Advanced Materials Research 634-638 (enero de 2013): 2446–49. http://dx.doi.org/10.4028/www.scientific.net/amr.634-638.2446.
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A non-Maxwellian hot-carrier generation current model for simulation of charge injection and erasing in the 0.35um flash EEPROM device is presented in this paper. Unlike the conventional model, which is based on the local electric fields in the device, and it accounts for non-local effects resulting from the large variations in electric field in a submicron flash EEPROM. Good agreements between the measured and calculated results in the charge writing and the Fower-Nordheim erasing operations.
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Jin, Yuxuan y Zefeng Chen. "High gain hot-carrier WSe2 phototransistor with gate-tunable responsivity". Advances in Engineering Technology Research 7, n.º 1 (26 de julio de 2023): 21. http://dx.doi.org/10.56028/aetr.7.1.21.2023.
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Hot-carrier injection at semiconductor/metal interface shows great potentials in infrared photodetection. However, the photoresponsivity of hot-carrier photodetector with diode mode is still limited in the scale of 1 mA/W due to the low injection efficiency of hot carriers and the lack of gain. Here, we demonstrate a high gain hot-carrier WSe2 phototransistor with gate-tunable responsivity. In this device, plasmonic resonances is used to enhance the light absorption of gold nanodisk, which provide hot holes. The hot holes are trapped into WSe2 and recycled in WSe2 channel in lateral direction, which introduce high gain for photodetection. Experiment shows that the photoresponsivity of the device can be over 0.23 A/W with a gain of 270 at the wavelength of 1310 nm. More interestingly, the responsivity of the device can be tuned by gate, which can be used to encode synaptic weights of the sensor pixel.
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Sun, Lei, Liyang Pan, Huiqing Pang, Ying Zeng, Zhaojian Zhang, John Chen y Jun Zhu. "Characteristics of Band-to-Band Tunneling Hot Hole Injection for Erasing Operation in Charge-Trapping Memory". Japanese Journal of Applied Physics 45, n.º 4B (25 de abril de 2006): 3179–84. http://dx.doi.org/10.1143/jjap.45.3179.
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Manzini, S. y A. Gallerano. "Avalanche injection of hot holes in the gate oxide of LDMOS transistors". Solid-State Electronics 44, n.º 7 (julio de 2000): 1325–30. http://dx.doi.org/10.1016/s0038-1101(99)00317-2.
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Jeong, Yoon Seong y Jun Su Park. "Effect of Inlet Compound Angle of Backward Injection Film Cooling Hole". Energies 13, n.º 4 (13 de febrero de 2020): 808. http://dx.doi.org/10.3390/en13040808.
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Backward injection film cooling holes were studied to improve film cooling effectiveness using simple cylindrical holes, and this principle was applied to an actual gas turbine. Although film cooling effectiveness was improved using a backward injection film cooling hole, the backward flow of combustion gas from the backward injection cooling hole was one of the major reasons for cracks in the hot components. To prevent cracks and backward flow in the backward injection film cooling hole, this study changed the inlet compound angle of the backward injection film cooling hole. Numerical analysis using CFX v. 17.0 was performed to calculate the flow characteristics and film cooling effectiveness of backward injection film cooling. Aa a result, the effect of the inlet compound angle of the backward injection film cooling hole was confirmed to prevent the backward flow, which increased upon increasing the inlet compound angle. This study shows that the backward flow and cracks in the backward injection film cooling hole can be prevented simply by changing the inlet compound angle.
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Williamson, J. G., H. van Houten, C. W. J. Beenakker, M. E. I. Broekaart, L. I. A. Spendeler, B. J. van Wees y C. T. Foxon. "Injection of ballistic hot electrons and cool holes in a two-dimensional electron gas". Surface Science 229, n.º 1-3 (abril de 1990): 303–6. http://dx.doi.org/10.1016/0039-6028(90)90894-e.
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Liu, Jian, Mengyao Xu y Wenxiong Xi. "Effects of Gas Thermophysical Properties on the Full-Range Endwall Film Cooling of a Turbine Vane". Aerospace 10, n.º 7 (28 de junio de 2023): 592. http://dx.doi.org/10.3390/aerospace10070592.
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To protect turbine endwall from heat damage of hot exhaust gas, film cooling is the most significant method. The complex vortex structures on the endwall, such as the development of horseshoe vortices and transverse flow, affects cooling coverage on the endwall. In this study, the effects of gas thermophysical properties on full-range endwall film cooling of a turbine vane are investigated. Three kinds of gas thermophysical properties models are considered, i.e., the constant property gas model, ideal gas model, and real gas model, with six full-range endwall film cooling holes patterns based on different distribution principles. From the results, when gas thermophysical properties are considered, the coolant coverage in the pressure side (PS)-vane junction region is improved in Pattern B, Pattern D, Pattern E, and Pattern F, which are respectively designed based on the passage middle gap, limiting streamlines, heat transfer coefficients (HTCs), and four-holes pattern. Endwall η distribution is mainly determined by relative ratio of ejecting velocity and density of the hot gas and the coolant. For the cooling holes on the endwall with an injection angle of 30°, the density ratio is more dominant in determining the coolant coverage. At the injection angle of 45°, i.e., the slot region, the ejecting velocity is more dominant in determining the coolant coverage. When the ejecting velocity Is large enough from the slot, the coolant coverage on the downstream endwall region is also improved.
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Lin, Y. L. y T. I. P. Shih. "Film Cooling of a Cylindrical Leading Edge With Injection Through Rows of Compound-Angle Holes". Journal of Heat Transfer 123, n.º 4 (9 de enero de 2001): 645–54. http://dx.doi.org/10.1115/1.1370513.
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Computations, based on the k-ω shear-stress transport (SST) turbulence model in which all conservation equations were integrated to the wall, were performed to investigate the three-dimensional flow and heat transfer about a semi-cylindrical leading edge with a flat afterbody that is cooled by film-cooling jets, injected from a plenum through three staggered rows of compound-angle holes with one row along the stagnation line and two rows along ±25 deg. Results are presented for the surface adiabatic effectiveness, normalized temperature distribution, velocity vector field, and surface pressure. These results show the interactions between the mainstream hot gas and the cooling jets, and how those interactions affect surface adiabatic effectiveness. Results also show how “hot spots” can form about the stagnation zone because of the flow induced by the cooling jets. The computed results were compared with experimental data generated under a blind test. This comparison shows the results generated to be reasonable and physically meaningful. With the SST model, the normal spreading was under predicted from 20 to 50 percent. The lateral spreading was over predicted above the surface, but under predicted on the surface. The laterally averaged surface effectiveness was well predicted.
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Gustafsson, K. M. Bernhard y T. Gunnar Johansson. "An Experimental Study of Surface Temperature Distribution on Effusion-Cooled Plates". Journal of Engineering for Gas Turbines and Power 123, n.º 2 (23 de enero de 2001): 308–16. http://dx.doi.org/10.1115/1.1364496.
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A parametric study of temperature distribution on effusion-cooled plates under conditions typical for combustion chambers was performed using infrared thermography. In this investigation, the effects of different temperature ratios, velocity ratios of the two air streams, the injection hole spacing, inclination angle of the injection holes, and the thermal heat conductivity of the plates were studied. For a given amount of cooling air, the cooling efficiency was found to increase markedly with a reduction in hole spacing, i.e., when the number of holes was increased. Reducing the injection angle results in more attached jets, especially for small amounts of cooling air, and marginally lowers the wall temperature. A high thermal conductivity of the plate was found to decrease its surface temperature in front of the first row of holes but not the mean temperature in downstream positions. The most important operational parameters were the temperature ratio and the velocity ratio of the hot and cold air streams. An almost linear relation was found between the temperature ratio and the surface temperature when the jet velocity was large compared to the crossflow velocity. For plates with sparse hole spacing, a change in the velocity ratio had a small effect on the surface temperature, whereas the effect was large for dense hole spacings and the same amount of cooling air.
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Kafaei, Amir, Fahime Salmani, Esmail Lakzian, Włodzimierz Wróblewski, Mikhail S. Vlaskin y Qinghua Deng. "The best angle of hot steam injection holes in the 3D steam turbine blade cascade". International Journal of Thermal Sciences 173 (marzo de 2022): 107387. http://dx.doi.org/10.1016/j.ijthermalsci.2021.107387.
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Burd, S. W., R. W. Kaszeta y T. W. Simon. "Measurements in Film Cooling Flows: Hole L/D and Turbulence Intensity Effects". Journal of Turbomachinery 120, n.º 4 (1 de octubre de 1998): 791–98. http://dx.doi.org/10.1115/1.2841791.
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Hot-wire anemometry measurements of simulated film cooling are presented to document the influence of the free-stream turbulence intensity and film cooling hole length-to-diameter ratio on mean velocity and on turbulence intensity. Measurements are taken in the zone where the coolant and free-stream flows mix. Flow from one row of film cooling holes with a streamwise injection of 35 deg and no lateral injection and with a coolant-to-free-stream flow velocity ratio of 1.0 is investigated under free-stream turbulence levels of 0.5 and 12 percent. The coolant-to-free-stream density ratio is unity. Two length-to-diameter ratios for the film cooling holes, 2.3 and 7.0, are tested. The Measurements document that under low free-stream turbulence conditions pronounced differences exist in the flowfield between L/D= 7.0 and 2.3. The difference between L/D cases are less prominent at high free-stream turbulence intensities. Generally, Short-L/D injection results in “jetting” of the coolant farther into the free-stream flow and enhanced mixing. Other changes in the flowfield attributable to a rise in free-stream turbulence intensity to engine-representative conditions are documented.
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Ningaraju, Vivek, Shao Ming Yang, Gene Sheu, Mohammad Amanullah, Erry Dwi Kurniawan y Subramanyaj. "Improvement of On-Resistance Degradation Induced by Hot Carrier Injection in SOI-LDMOS". Applied Mechanics and Materials 764-765 (mayo de 2015): 521–25. http://dx.doi.org/10.4028/www.scientific.net/amm.764-765.521.
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This paper presents how to improve specific o n-state resistance (Ron) induced by the HCI of a SOI LDMOS device. In manufacturing of UHV device, trade-off between on state resistance and breakdown voltage is always present. But with our process design we are able to improve Ron degradation without compromising the-breakdown voltage. In our design the peak electric field is under gate near source side, due to low electric field near drain helps to increase the current flow much better hence it helps to improve Ron and Vth. If the peak field is located near drain side, the hot holes is easy to penetrate to field oxide and avoid current flow then it causes increase in the Ron.Our simulation results shows 0.27% and 0.95% Ron and Vth increases respectively even at 1e5 second stress time .The Ron degradation phenomenon was analyzed with the 2-D simulation of electric field and impact ionization generation.
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Heiles, Carl. "Clustered Supernovae vs. The Gaseous Disk and Halo: A Rematch". International Astronomical Union Colloquium 120 (1989): 484–93. http://dx.doi.org/10.1017/s0252921100024295.
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ABSTRACT.Recent developments, both observational and theoretical, require a reevaluation of the effects of clustered supernovae on the two-dimensional porosity parameter Q2D and the rates of mass injection into the halo Ṁ of both cold and hot gas. Clustered supernovae produce two types of bubble. Most clusters produce breakthrough bubbles, which do no more than break through the dense gas disk. But large clusters produce enough energy to make blowout bubbles, which blow gas up into the halo. We calculate area filling factors and mass injection rates into the halo for different types of galaxy. We relate our calculations to two observables, the area covered by H I ‘holes’ and the area covered by giant H II regions. We also reiterate the difficulty of producing the very largest supershells by clusered supernovae.
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York, William D. y James H. Leylek. "Leading-Edge Film-Cooling Physics—Part III: Diffused Hole Effectiveness". Journal of Turbomachinery 125, n.º 2 (1 de abril de 2003): 252–59. http://dx.doi.org/10.1115/1.1559899.
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A proven computational methodology was applied to investigate film cooling from diffused holes on the simulated leading edge of a turbine airfoil. The short film-hole diffuser section was conical in shape with a shallow half-angle, and was joined to a plenum by a cylindrical metering section. The diffusion resulted in a film-hole breakout area of 2.5 times that of a cylindrical hole. In the present paper, predictions of adiabatic effectiveness for the cases with diffused holes are compared to results for standard cylindrical holes, and performance is analyzed in the context of extensive flowfield data. The leading edge surface was elliptic in shape to accurately model a turbine airfoil. The geometry consisted of one row of holes centered on the stagnation line, and two additional rows located 3.5 hole (metering section) diameters downstream on either side of the stagnation line. Film holes in the downstream rows were centered laterally between holes in the stagnation row. All holes were angled at 20 deg with the leading edge surface, and were turned 90 deg with respect to the streamwise direction (radial injection). The average blowing ratio was varied from 1.0 to 2.5, and the coolant-to-mainstream density ratio was equal to 1.8. The steady Reynolds-averaged Navier-Stokes equations were solved with a pressure-correction algorithm on an unstructured, multi-block grid containing 4.6 million finite-volumes. A realizable k-ε turbulence model was employed to close the equations. Convergence and grid-independence was verified using strict criteria. Based on the laterally averaged effectiveness over the leading edge, the diffused holes showed a marked advantage over standard holes through the range of blowing ratios. However, ingestion of hot crossflow and thermal diffusion into the second row of film holes was observed to cause significant, and potentially detrimental, heating of the film-hole walls.
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Haas, W., W. Rodi y B. Scho¨nung. "The Influence of Density Difference Between Hot and Coolant Gas on Film Cooling by a Row of Holes: Predictions and Experiments". Journal of Turbomachinery 114, n.º 4 (1 de octubre de 1992): 747–55. http://dx.doi.org/10.1115/1.2928028.
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The two-dimensional boundary-layer procedure of Scho¨nung and Rodi [1] for calculating film cooling by a row of holes was extended to account for density differences between hot gas and injected coolant gas. The extensions concern the injection model for leaping over the immediate blowing region in the boundary-layer calculation and also the dispersion model for taking into account three-dimensional effects. The extended model is tested for a density ratio of ρj/ρe ≈ 2 for both flat-plate situations and film cooling on a model turbine blade. The predicted laterally averaged film cooling effectiveness is compared with measurements for these cases. Results for the flat-plate experiments were taken from the literature, while experiments for a model turbine blade are also described in this paper. For a fixed injection angle of 32 deg, the film cooling effectiveness was measured for various spacings and velocity ratios Uj/Ue. The density ratio ρj/ρe ≈ 2 was achieved by adding Freon to the injection gas. The results are compared with those reported in [2] for negligible density difference. At the same blowing rate M = Uj/Ue, the film cooling effectiveness was found to increase with the density ratio ρj/ρe. In general, the influence of the density difference is well predicted by the model.
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Heckman, Timothy M. y Philip N. Best. "A Global Inventory of Feedback". Galaxies 11, n.º 1 (24 de enero de 2023): 21. http://dx.doi.org/10.3390/galaxies11010021.
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Feedback from both supermassive black holes and massive stars plays a fundamental role in the evolution of galaxies and the inter-galactic medium. In this paper, we use available data to estimate the total amount of kinetic energy and momentum created per co-moving volume element over the history of the universe from three sources: massive stars and supernovae, radiation pressure and winds driven by supermassive black holes, and radio jets driven by supermassive black holes. Kinetic energy and momentum injection from jets peaks at z ≈ 1, while the other two sources peak at z ≈ 2. Massive stars are the dominant global source of momentum injection. For supermassive black holes, we find that the amount of kinetic energy from jets is about an order-of-magnitude larger than that from winds. We also find that the amount of kinetic energy created by massive stars is about 2.5 εstar times that carried by jets (where εstar is the fraction of injected energy not lost to radiative cooling). We discuss the implications of these results for the evolution of galaxies and IGM. Because the ratio of the black hole mass to galaxy mass is a steeply increasing function of mass, we show that the relative importance of black hole feedback to stellar feedback likewise increases with mass. We show that there is a trend in the present-day universe which, in the simplest picture, is consistent with galaxies that have been dominated by black hole feedback being generally quenched, while galaxies that have been dominated by stellar feedback are star-forming. We also note that the amount of kinetic energy carried by jets and winds appears to be sufficient to explain the properties of hot gas in massive halos (>1013 Mʘ).
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Kuehn, T., Y. Wu y B. Liu. "Particle Contamination Below a Robot Arm in a Cleanroom". Journal of the IEST 36, n.º 5 (1 de septiembre de 1993): 43–51. http://dx.doi.org/10.17764/jiet.2.36.5.dx782n4433225717.
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Experimental velocity and particle concentration data have been obtained near a circular cylinder robot arm in a chamber that simulates a vertical unidirectional flow Class 10 cleanroom. The airflow field around the robot arm has been characterized using a hot wire anemometer. Both mean velocities and turbulence spectral data were obtained. Sodium chloride particles were injected through small holes below the arm to simulate particles generated by moving joints. Results indicate that the turbulent wake near the arm causes an unsymmetrical widespread dispersion of the particles from a single point source on the arm. Particles disperse much stronger along the cylinder axis than normal to the cylinder near the injection point.
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Kim, Y. W. y D. E. Metzger. "Heat Transfer and Effectiveness on Film Cooled Turbine Blade Tip Models". Journal of Turbomachinery 117, n.º 1 (1 de enero de 1995): 12–21. http://dx.doi.org/10.1115/1.2835630.
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In unshrouded axial turbine stages, a small but generally unavoidable clearance between the blade tips and the stationary outer seal allows a clearance gap leakage flow to be driven across the blade tip by the pressure-to-suction side pressure difference. In modern high-temperature machines, the turbine blade tips are often a region prone to early failure because of the presence of hot gases in the gap and the resultant added convection heating that must be counteracted by active blade cooling. The blade tip region, particularly near the trailing edge, is often very difficult to cool adequately with blade internal coolant flow, and film cooling injection directly onto the blade tip region can be used in an attempt to reduce the heat transfer rates directly from the hot clearance flow to the blade tip. An experimental program has been designed and conducted to model and measure the effects of film coolant injection on convection heat transfer to turbine blade tips. The modeling approach follows earlier work that found the leakage flow to be mainly a pressure-driven flow related strongly to the airfoil pressure loading distribution and only weakly, if at all, to the relative motion between blade tip and shroud. In the present work the clearance gap and blade tip region is thus modeled in stationary form with primary flow supplied to a narrow channel simulating the clearance gap above a plane blade tip. Secondary film flow is supplied to the tip surface through a line array of discrete normal injection holes near the upstream or pressure side. Both heat transfer and effectiveness are determined locally over the test surface downstream of injection through the use of thin liquid crystal coatings and a computer vision system over an extensive test matrix of clearance heights, clearance flow Reynolds numbers, and film flow rates. The results of the study indicate that film injection near the pressure-side corner on plane turbine blade tips can provide significant protection from convection heat transfer to the tip from the hot clearance gap leakage flow.
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Imram, Ahmed A., Humam K. Jalghef y Falah F. Hatem. "The Effect of Using Ramps with Trench Cylindrical Holes on Film Cooling Effectiveness". Wasit Journal of Engineering Sciences 3, n.º 2 (1 de octubre de 2015): 15–27. http://dx.doi.org/10.31185/ejuow.vol3.iss2.37.
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The effect of introducing ramp with a cylindrical slot hole on the film cooling effectiveness has been investigated experimentally and numerically. The film cooling effectiveness measurements are obtained experimentally. A test study was performed at a single mainstream with Reynolds number 76600 at three different coolant to mainstream blowing ratios 1.5, 2, and 3. Numerical simulation is introduced to primarily estimate the best ramp configurations and to predict the behavior of the transport phenomena in the region linked closely to the interaction between the coolant air injection and the hot air mainstram flow. The results showed that using ramps with trench cylindrical holes would enhanced the overall film cooling effectiveness by 83.33% compared with baseline model at blowing ratio of 1.5, also the best overall flim cooling effectevness was obtained at blowing ratio of 2 while it is reduced at blowing ratio of 3.
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Siddiqui, Muhammad Ehtisham, Ammar A. Melaibari y Fahad Sarfraz Butt. "Experimental Investigation of Temperature Distribution in a Laminar Boundary Layer over a Heated Flat Plate with Localized Transverse Cold Air Injections". Energies 16, n.º 17 (25 de agosto de 2023): 6171. http://dx.doi.org/10.3390/en16176171.
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This study presents an experimental investigation focused on the interaction between a transverse injection of cold air (blowing) and the boundary layer over a heated flat plate. The flat plate was equipped with a cylindrical coil heater positioned at its center along the flow direction. The constant heat flux was maintained using a variable resistance potentiometer. The flat plate with the heater was mounted inside a subsonic wind tunnel to sustain a constant laminar air flow. The primary objective of this research was to examine the effects of cold air injections through localized holes in the flat plate near the trailing edge on the thermal boundary layer thickness δt(x,Rex,Pr). The thermal boundary layer thickness was measured using K-type thermocouples and PT-100 RTD sensors, which are made to move precise, small distances using a specially constructed traversing mechanism. Cold air was injected using purposefully fabricated metal capillary tubes force-fitted into holes through the hot flat plate. The metal tubes were thermally insulated using class-F insulation, which is used in electric motor windings. The presented work focused on a fixed free-stream velocity and a fixed cold-injection velocity less than the free-stream velocity but for two-variable heat fluxes. The results show that the thermal boundary layer thickness generally increased due to the secondary cold flow.
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McGovern, K. T. y J. H. Leylek. "A Detailed Analysis of Film Cooling Physics: Part II—Compound-Angle Injection With Cylindrical Holes". Journal of Turbomachinery 122, n.º 1 (1 de febrero de 1997): 113–21. http://dx.doi.org/10.1115/1.555434.
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Detailed analyses of computational simulations with comparisons to experimental data were performed to identify and explain the dominant flow mechanisms responsible for film cooling performance with compound angle injection, Φ, of 45, 60, and 90 deg. A novel vorticity and momentum based approach was implemented to document how the symmetric, counterrotating vortex structure typically found in the crossflow region in streamwise injection cases, becomes asymmetric with increasing Φ. This asymmetry eventually leads to a large, single vortex system at Φ=90 deg and fundamentally alters the interaction of the coolant jet and hot crossflow. The vortex structure dominates the film cooling performance in compound angle injection cases by enhancing the mixing of the coolant and crossflow in the near wall region, and also by enhancing the lateral spreading of the coolant. The simulations consist of fully elliptic and fully coupled solutions for field results in the supply plenum, film hole, and crossflow regions and includes surface results for adiabatic effectiveness η and heat transfer coefficient h. Realistic geometries with length-to-diameter ratio of 4.0 and pitch-to-diameter ratio of 3.0 allowed for accurate capturing of the strong three-way coupling of flow in this multiregion flowfield. The cooling configurations implemented in this study exactly matched experimental work used for validation purposes and were represented by high-quality computational grid meshes using a multiblock, unstructured grid topology. Blowing ratios of 1.25 and 1.88, and density ratio of 1.6 were used to simulate realistic operating conditions and to match the experiments used for validation. Predicted results for η and h show good agreement with experimental data. [S0889-504X(00)01301-5]
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Liu, Kunzi, Li Chen, Tian Luo, Zihui Zhao, Ping Ouyang, Jiaxin Zhang, Qiushuang Chen et al. "Implementation of electron restriction layer in n-AlGaN toward balanced carrier distribution in deep ultraviolet light-emitting-diodes". Applied Physics Letters 121, n.º 24 (12 de diciembre de 2022): 241105. http://dx.doi.org/10.1063/5.0131013.
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The distribution of electrons and holes inside the multiple-quantum wells is highly non-uniform for AlGaN-based deep ultraviolet light-emitting diodes (DUV-LEDs) due to both insufficient hole injection and excessive electron leakage. A key factor to improve the quantum efficiency of DUV-LED is to reduce the proportion of hot electrons in n-AlGaN through carrier deceleration. In this work, we propose a structure design by introducing an additional Al0.55Ga0.45N/Al0.42Ga0.58N superlattice electron restriction layer between the active region and n-AlGaN for electron deceleration. The superlattice structure not only reduces the mobility of the electrons, which helps to balance the distribution of carriers in the active region, thus, promoting radiative recombination, but also facilitates the lateral transport of the electrons, thus, reducing the current crowding effect through band engineering. Low temperature electroluminescence analysis reveals that the improvement of quantum efficiency is due to both enhanced carrier injection efficiency and radiation recombination efficiency in the active region.
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Li, Xianchang y Ting Wang. "Simulation of Film Cooling Enhancement With Mist Injection". Journal of Heat Transfer 128, n.º 6 (9 de diciembre de 2005): 509–19. http://dx.doi.org/10.1115/1.2171695.
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Cooling of gas turbine hot-section components, such as combustor liners, combustor transition pieces, and turbine vanes (nozzles) and blades (buckets), is a critical task for improving the life and reliability of them. Conventional cooling techniques using air-film cooling, impingement jet cooling, and turbulators have significantly contributed to cooling enhancements in the past. However, the increased net benefits that can be continuously harnessed by using these conventional cooling techniques seem to be incremental and are about to approach their limit. Therefore, new cooling techniques are essential for surpassing these current limits. This paper investigates the potential of film-cooling enhancement by injecting mist into the coolant. The computational results show that a small amount of injection (2% of the coolant flow rate) can enhance the adiabatic cooling effectiveness about 30–50%. The cooling enhancement takes place more strongly in the downstream region, where the single-phase film cooling becomes less powerful. Three different holes are used in this study including a two-dimensional (2D) slot, a round hole, and a fan-shaped diffusion hole. A comprehensive study is performed on the effect of flue gas temperature, blowing angle, blowing ratio, mist injection rate, and droplet size on the cooling effectiveness with 2D cases. Analysis on droplet history (trajectory and size) is undertaken to interpret the mechanism of droplet dynamics.
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Khosru, Quazi Deen Mohd, Naoki Yasuda, Akinori Maruyama, Kenji Taniguchi y Chihiro Hamaguchi. "Spatial Distribution of Trapped Holes in the Oxide of Metal Oxide Semiconductor Field-Effect Transistors after Uniform Hot-Hole Injection". Japanese Journal of Applied Physics 30, Part 1, No. 12B (30 de diciembre de 1991): 3652–56. http://dx.doi.org/10.1143/jjap.30.3652.
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Ligrani, P. M., C. S. Subramanian, D. W. Craig y P. Kaisuwan. "Effects of Vortices With Different Circulations on Heat Transfer and Injectant Downstream of a Row of Film-Cooling Holes in a Turbulent Boundary Layer". Journal of Heat Transfer 113, n.º 1 (1 de febrero de 1991): 79–90. http://dx.doi.org/10.1115/1.2910555.
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Results are presented that illustrate the effects of single embedded longitudinal vortices on heat transfer and injectant downstream of a row of film-cooling holes in a turbulent boundary layer. Attention is focused on the changes resulting as circulation magnitudes of the vortices are varied from 0.0 to 0.15 m2/s. Mean temperature results are presented that show how injectant is distorted and redistributed by vortices, along with heat transfer measurements and mean velocity surveys. Injection hole diameter is 0.952 cm to give a ratio of vortex core diameter to hole diameter of about 1.5–1.6. The free-stream velocity is maintained at 10 m/s, and the blowing ratio is approximately 0.5. Film-cooling holes are oriented 30 deg with respect to the test surface. Stanton numbers are measured on a constant heat flux surface with a nondimensional temperature parameter of about 1.5. Two different situations are studied: one where the middle injection hole is beneath the vortex downwash, and one where the middle injection hole is beneath the vortex upwash. For both cases, vortex centers pass within 2.9–3.4 vortex core diameters of the centerline of the middle injection hole. To quantify the influences of the vortices on the injectant, two new parameters are introduced. S is defined as the ratio of vortex circulation to injection hole diameter times mean injection velocity. S1 is similarly defined except vortex core diameter replaces injection hole diameter. The perturbation to film injectant and local heat transfer is determined by the magnitudes of S and S1. When S is greater than 1–1.5 or when S1 is greater than 0.7–1.0, injectant is swept into the vortex upwash and above the vortex core by secondary flows, and Stanton number data show evidence of injectant beneath the vortex core and downwash near the wall for x/d only up to about 17.5. For larger x/d, local hot spots are present, and the vortices cause local Stanton numbers to be augmented by as much as 25 percent in the film-cooled boundary layers. When S and S1 are less than these values, some injectant remains near the wall beneath the vortex core and downwash where it continues to provide some thermal protection. In some cases, the protection provided by film cooling is augmented because of vortex secondary flows, which cause extra injectant to accumulate near upwash regions.
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Ahmed, Guelailia, Khorsi Azzeddine, Slimane Sid Ahmed, Blala Hamza y Slimane Abdelkader. "Effects of Crescent Shaped Block Width and Length on Flow Field and Film Cooling Performance". Trends in Sciences 20, n.º 7 (17 de marzo de 2023): 5339. http://dx.doi.org/10.48048/tis.2023.5339.
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Turbine blades and rocket nozzles can be efficiently protected from combustion chamber exhaust hot gases by film cooling technic. A crescent-shaped block placed downstream of the injection hole can significantly improve cooling effectiveness. The main objective of this research work is to investigate the influence of the crescent-shaped block length and width on film cooling effectiveness. ANSYS CFX was used to conduct analysis of a flat plate configuration with cylindrical holes. Nine configurations of the crescent shaped blocks were considered. For each case, the effect of blowing ratios (0.5 and 1) was investigated. The turbulence model shear stress transport (SST) is used for approximating turbulence. Good agreement was obtained by comparing the analysis results with the experimental data. The result indicated that block width variation has a considerable impact on film cooling performance. However, slight effect of block length on cooling effectiveness was obtained. Comparing all analyzed configurations, the best cooling effectiveness was reached for the model 9 (W = 3d, B = 1.5d). HIGHLIGHTS Rocket nozzles can be efficiently protected from combustion chamber exhaust hot gases by film cooling technic One of the latest techniques to optimize the overall performance of film cooling is adding an obstacle configuration downstream the coolant perforation Film cooling performance is considerably enhanced by placing a crescent shaped block downstream the injection hole The maximum enhancement in overall film cooling effectiveness using the optimal configuration (model 6: W = 2d, B = 1.5d) is about 252 % achieved at a blowing ratio of M = 1 GRAPHICAL ABSTRACT
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Ganguli, Sagar, Ziwen Zhao, Onur Parlak, Yocefu Hattori, Jacinto Sa y Alina Sekretareva. "Nano-Impact Single-Entity Electrochemistry Enables Plasmon-Enhanced Electrocatalysis". ECS Meeting Abstracts MA2023-02, n.º 54 (22 de diciembre de 2023): 2623. http://dx.doi.org/10.1149/ma2023-02542623mtgabs.
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Plasmon-enhanced electrocatalysis (PEEC), based on a combination of localised surface plasmon resonance excitation and electrochemical bias applied to plasmonic material, can result in improved electrical-to-chemical energy conversion compared to conventional electrocatalysis.1 Here, we demonstrate the advantages of nano-impact single-entity electrochemistry (SEE) over conventional ensemble electrochemical measurements for investigating the intrinsic activity of plasmonic catalysts towards PEEC at the single-particle level using glucose electrooxidation on gold nanoparticles (AuNPs) as a model reaction. First, we performed conventional ensemble measurements using AuNPs coated highly oriented pyrolytic graphite (HOPG) electrodes and AuNPs coated ITO electrodes. Identical photocurrents (Figures A-B,F) were observed at wavelengths where the AuNPs plasmons are active (532 nm) and inactive (650 nm) in an electrolyte consisting of 100 mM NaOH and 30 mM glucose. Controlled experiments demonstrated that in ensemble measurements with working electrodes, where the plasmonic AuNPs are in direct contact with the conductive support, the underlying support material, such as HOPG, is the primary photo-absorber and responsible for the photocurrent. Near-identical photo-absorption of HOPG across the visible region causes consistent temperature increase at different wavelengths. This increased temperature at the electrode-electrolyte interface enhances the charge transfer kinetics and this gets reflected in the identical photocurrent at different wavelengths.2 In ensemble measurements, plasmonic effects have minimal impact on photocurrents. We suggest that this is due to continuous equilibration of the Fermi level (EF) of the AuNPs with the EF of the working electrode, leading to fast neutralisation of hot carriers by the measuring circuit (Figure G). Therefore, the hot carriers generated in plasmonic materials can not participate in catalysing chemical reactions. In SEE, a catalytically inactive carbon ultramicroelectrode (C-UME) is used as the working electrode and AuNPs diffused (~5 pM) in the electrolyte act as the catalyst. When the AuNPs collide with biased C-UME or are at close distances that enable charge tunnelling, electrocatalysis occurs on the AuNPs. This leads to formation of current spikes in the chronoamperograms. Contrary to ensemble measurements, different rate enhancements were detected at different wavelengths, with the charge/spike being higher under 532 nm illumination (1.230±0.058 fC) compared to dark (0.870±0.034 fC) and 650 nm illumination (0.920±0.036 fC) in an electrolyte consisting 10 mM NaOH and 30 mM glucose (Figures C-E,F). This wavelength dependence of photocurrent is in accordance with the absorption properties of AuNPs and therefore confirms that plasmonic effects are contributing to the photocurrents. We suggest that this is due to decoupling of the EF of the dispersed AuNPs and the C-UME. Within the charge transfer distance from the electrode or even at collision, EF level equilibration does not necessarily occur in SEE when the colliding particle does not stick to the electrode.3 The first possibility for current enhancement arises from the injection of hot carriers. When the AuNPs are not in direct contact with the electrode to enable rapid EF equilibration but at a distance sufficient for charge transfer, the hot electrons will be transferred to the C-UME due to the large difference in the energies of the electrode and hot electrons (Figure G). At the same time, the hot holes inside the AuNPs can not be neutralised by electron transfer from the electrode at the same rate as hot electrons are removed to the external circuit as the energies of the holes are either higher than that of the electrons at the electrode or only slightly lower depending on the exact value of EF of the AuNPs and the energy distribution of the hot holes.4 These remaining hot holes participate in charge transfer with glucose molecules. As the hot carrier generation in AuNPs is a wavelength-dependent phenomenon, the participation of hot charge carriers in the catalytic reaction is possible only under 532 nm but not under 650 nm irradiation.5 The second possibility is the facilitation of the catalytic reaction by thermal contribution due to the recombination of charge carriers. As the diffused AuNPs are exposed to laser irradiation, the hot carriers will recombine leading to lattice heating. When a 532 nm laser-irradiated AuNP comes into contact with the working electrode, thereby becoming active for the catalytic reaction, its temperature is already higher compared to the AuNPs in the dark or 650 nm illumination. The interfacial charge transfer will become faster on the heated AuNP leading to enhanced charge/nano-impact. References Chem. Soc. Rev. 2021, 50, 12070-12097 ACS Catal. 2022, 12, 4110–4118 J. Phys. Chem. Lett. 2017, 8, 3564–3575 ACS Nano 2019, 13, 3629–3637 Angew. Chem., Int. Ed. 2023, e202302394, DOI: 10.1002/anie.202302394 Figure 1
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Rydholm, H. A. "An Experimental Investigation of the Velocity and Temperature Fields of Cold Jets Injected Into a Hot Crossflow". Journal of Turbomachinery 120, n.º 2 (1 de abril de 1998): 320–26. http://dx.doi.org/10.1115/1.2841409.
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It is shown here by dimensional analysis that the near-wall flow field of an effusion-cooled combustor can be scaled if the Reynolds, Mach, and Prandtl numbers and the temperature and velocity ratios are kept constant. It is also demonstrated that a practical model experiment can be designed, which fulfills all the scaling laws. A test rig meeting these requirements has been designed, built and tested. The experimental conditions have been chosen to correspond to the conditions usually met in a real effusion-cooled combustion chamber. One geometric configuration has been investigated. This consists of one transverse row of holes drilled with a 30 deg angle to the wall through which the cooling air enters a cross-flowing mainstream. The mean values of all three velocity components and the three normal fluctuating Reynolds stresses as well as the mean temperature have been measured in a large number of points surrounding the central injection hole. Experiments were carried out for jet-to-mainstream density ratios of 1.2 and 1.8. The results indicate that realistic density ratios are necessary to provide data directly applicable to effusion-cooling design.
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Murakami, Fumikazu, Kazunori Serita, Iwao Kawayama, Hironaru Murakami, Kingshuk Bandopadhyay, Andrzej Materna, Augustine M. Urbas, Dorota A. Pawlak y Masayoshi Tonouchi. "Probing photocarrier dynamics in a Bi2Te3–Te eutectic p–n junction with a laser terahertz emission microscope". APL Materials 11, n.º 3 (1 de marzo de 2023): 031102. http://dx.doi.org/10.1063/5.0137862.
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Bismuth telluride (Bi2Te3)-based heterostructures have attracted considerable attention owing to their interesting anisotropic properties and expected higher thermoelectric performance. Therefore, exploring the nature of the carrier dynamics in these heterostructures has been an important subject in the design and optimization of advanced materials. In the present study, hot carrier injection and its subsequent spatiotemporal behavior in a multilayered crystalline Bi2Te3–Tellurium (Te) eutectic composite were studied using a laser terahertz (THz) emission microscopy (LTEM). The THz emission electric fields at the Bi2Te3–Te interface were polarized perpendicular to the interface. The polarities of these waveforms reveal the direction of the electric field between the Bi2Te3 and Te regions, indicating the carrier types of these components and the p–n junction formed at the interface. In addition, in the Te region, a strong THz emission with an electric field polarized parallel to the interface was observed. This unique THz emission can be qualitatively explained through hot photocarrier anisotropic transport by considering the effective mass of electrons and holes. LTEM clarified the local carrier dynamics in the microstructures and revealed the potential distribution and anisotropic transport properties. These findings contribute to the exploration of eutectic heterostructures as new functional materials and provide new avenues for cutting-edge thermoelectric and photovoltaic devices.
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Li, Shao Hua, Hong Wei Qu, Mei Li Wang y Ting Ting Guo. "An Experimental Investigation of Flow Characteristics Downstream of Discrete Film Cooling Holes on Turbine Blade Leading Edge". Advanced Materials Research 383-390 (noviembre de 2011): 5553–60. http://dx.doi.org/10.4028/www.scientific.net/amr.383-390.5553.
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The gas turbine blade was studied on the condition that the mainstream velocity was 10m/s and the Renolds number based on the chord length of the blade was 160000.The Hot-film anemometer was used to measure the two-dimension speed distribution along the downstream of the film cooling holes on the suction side and the pressure side. The conclusions are as follows: When the blowing ratio of the suction side and the pressure side increasing, the the mainstream and the jet injection mixing center raising. Entrainment flow occurs at the position where the blade surface with great curvature gradient, simultaneously the mixing flow has a wicked adhere to the wall. The velocity gradient of the u direction that on the suction side increase obviously, also the level of the wall adherence is better than the pressure side. With the x/d increasing, the velocity u that on the pressure side gradually become irregularly, also the secondary flow emerged near the wall region where the curvature is great. The blowing ratio on the suction side has a little influence on velocity v than that on the pressure side.
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Coward, R. N., N. M. Clark y S. J. Pinnock. "The Tartan Field, Block 15/16, UK North Sea". Geological Society, London, Memoirs 14, n.º 1 (1991): 377–84. http://dx.doi.org/10.1144/gsl.mem.1991.014.01.47.
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AbstractTartan Field lies 118 miles northeast of Aberdeen in UK Block 15/16 on the southern flank of the Witch Ground Graben. The Field consists of two major southerly-dipping rotated fault blocks, the 'Upthrown Block' to the south and the 'Downthrown Block' to the north. The primary reservoir comprises Oxfordian-Kimmeridgian shallow marine sandstone of the Piper Formation deposited during a regional marine transgression. The secondary reservoir consists of Volgian turbidites (the 'Hot Lenses') within the Kimmeridge Clay Formation. The accumulations have been sourced from maturation of the Kimmeridge Clay Formation below approximately 10000 ft in adjacent basins. The Piper Formation exhibits markedly different petrophysical properties within each block. A relatively homogeneous intergranular porosity system is present throughout the oil zone of the 'Upthrown Block'. Porosities are lower and more variable in the 'Downthrown Block' as a result of cementation and the presence of an intense compaction fabric. The trapping mechanism is a combination of structural and stratigraphic elements. The Field was discovered in December 1974 by the 15/16-1 well which penetrated 263 ft of Piper Formation sandstone full to base with oil. A further ten straight holes and three sidetracked holes delineated the structure. Tartan Field came onstream in January 1981 and is currently producing 30000 BOPD through eight platform producers, assisted by six subsea water injection wells. Ultimate recoverable reserves are currently estimated at 116 MMBBL of crude oil.
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Yoon, Gilsang, Donghoon Kim, Iksoo Park, Bo Jin y Jeong-Soo Lee. "Fabrication and Characterization of Nanonet-Channel LTPS TFTs Using a Nanosphere-Assisted Patterning Technique". Micromachines 12, n.º 7 (24 de junio de 2021): 741. http://dx.doi.org/10.3390/mi12070741.
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We present the fabrication and electrical characteristics of nanonet-channel (NET) low-temperature polysilicon channel (LTPS) thin-film transistors (TFTs) using a nanosphere-assisted patterning (NAP) technique. The NAP technique is introduced to form a nanonet-channel instead of the electron beam lithography (EBL) or conventional photolithography method. The size and space of the holes in the nanonet structure are well controlled by oxygen plasma treatment and a metal lift-off process. The nanonet-channel TFTs show improved electrical characteristics in terms of the ION/IOFF, threshold voltage, and subthreshold swing compared with conventional planar devices. The nanonet-channel devices also show a high immunity to hot-carrier injection and a lower variation of electrical characteristics. The standard deviation of VTH (σVTH) is reduced by 33% for a nanonet-channel device with a gate length of 3 μm, which is mainly attributed to the reduction of the grain boundary traps and enhanced gate controllability. These results suggest that the cost-effective NAP technique is promising for manufacturing high-performance nanonet-channel LTPS TFTs with lower electrical variations.
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Alig, C., A. Prieto, M. Blaña, M. Frischman, C. Metzl, A. Burkert, O. Zier y A. Streblyanska. "The Accretion Mode in Sub-Eddington Supermassive Black Holes: Getting into the Central Parsecs of Andromeda". Astrophysical Journal 953, n.º 1 (1 de agosto de 2023): 109. http://dx.doi.org/10.3847/1538-4357/ace2c3.
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Abstract The inner kiloparsec regions surrounding sub-Eddington (luminosity less than 10−3 in Eddington units, L Edd) supermassive black holes (BHs) often show a characteristic network of dust filaments that terminate in a nuclear spiral in the central parsecs. Here we study the role and fate of these filaments in one of the least accreting BHs known, M31 (10−7 L Edd) using hydrodynamical simulations. The evolution of a streamer of gas particles moving under the barred potential of M31 is followed from kiloparsec distance to the central parsecs. After an exploratory study of initial conditions, a compelling fit to the observed dust/ionized gas morphologies and line-of-sight velocities in the inner hundreds of parsecs is produced. After several million years of streamer evolution, during which friction, thermal dissipation, and self-collisions have taken place, the gas settles into a disk tens of parsecs wide. This is fed by numerous filaments that arise from an outer circumnuclear ring and spiral toward the center. The final configuration is tightly constrained by a critical input mass in the streamer of several 103 M ☉ (at an injection rate of 10−4 M ⊙ yr − 1 ); values above or below this lead to filament fragmentation or dispersion respectively, which are not observed. The creation of a hot gas atmosphere in the region of ∼106 K is key to the development of a nuclear spiral during the simulation. The final inflow rate at 1 pc from the center is ∼1.7 × 10−7 M ☉ yr−1, consistent with the quiescent state of the M31 BH.
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Dutta, Sandip, Inderjot Kaur y Prashant Singh. "Review of Film Cooling in Gas Turbines with an Emphasis on Additive Manufacturing-Based Design Evolutions". Energies 15, n.º 19 (23 de septiembre de 2022): 6968. http://dx.doi.org/10.3390/en15196968.
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Film-cooling technology is used in high-temperature components of gas turbines to extend their service lives. Hot-gas path components are susceptible to damage or failure in the absence of film cooling. Much of the optimization research efforts have been focused on film hole shapes, heat/mass transfer measurement techniques, and film cooling performance under various mainstream and coolant side operating conditions. Due to recent rapid advancements in the areas of measurement techniques (e.g., pressure-sensitive paints and fast high-resolution imaging) and metal additive manufacturing (AM), film cooling technology has undergone significant changes and shows potential new development. In this review, a historical perspective is discussed covering over five decades of innovation: the geometrical effects from injection angle and hole shapes; flow effects from density ratio, momentum-flux ratio, blowing ratio, advective capacity ratio, and freestream conditions; and more items related to AM. The impact of AM on film hole design strategies, the challenges posed by state-of-the-art AM technology, and pathways for future research are discussed. A comparative analysis of AM assisted film hole fabrication and conventionally manufactured film holes is elaborated.
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Joy, J., PC Wang y SCM Yu. "Effect of geometric modification on flow behaviour and performance of reverse flow combustor". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, n.º 4 (25 de enero de 2018): 1457–71. http://dx.doi.org/10.1177/0954410017752717.
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Numerical investigation had been performed on the reverse flow combustor of a mini gas turbine engine so as to investigate the performance characteristics of the combustor by means of geometry modifications. In order to enhance the thrust performance of the reverse flow combustor, the baseline combustor (Model A) was previously modified by increasing its chamber volume by 15%, the fuel-air ratio (FAR) by 40% and by raising the injection point density to two (Model B). However, the thrust optimization of the baseline combustor resulted in high combustor exit temperature that could potentially damage the combustor liners. To rectify the adversity of high exit temperature, the combustor cooling effects were achieved by subsequently adding additional passage holes at the dilution zone of the Model B combustor so as to direct the incoming cold flow from the compressor exit towards the outgoing hot flow in the reverse flow combustor (Model C). The commercial software ANSYS Fluent 17.0 was adopted in this study and to solve the turbulence model, Reynolds Averaged Navier–Stokes methodology was adopted by employing standard k-ɛ turbulence model with standard wall function. A probability density function model was generated to introduce the combustion species and a discrete phase Model was employed to specify the kerosene fuel-based injector properties. The numerical results of Model A combustor were validated against the previous experimental results using grid convergence test. The numerical results were observed to be in good agreement with the experimental results. However, ineffective mixing was found to be a setback for the baseline combustor (Model A) indicating the need for combustor performance improvement. The comparative results of the revised combustor model (Model C) showed that better cooling effects at the combustor exit could be achieved by adding supplementary passage holes at the downstream of the combustor outer liner, respectively. The addition of dilution holes also resolved the issue of high pressure loss that was observed in Model A combustor with no significant change in the specific fuel consumption. The present paper confirms that the performance of the reverse flow combustor model could be affected by slight geometric modification. The performance characteristics of the combustor models are presented in terms of thrust, thrust-to-weight ratio, specific fuel consumption, pressure loss and pattern factor.
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Geng, Xinjian, Mohamed Abdellah, Robert Bericat Vadell, Matilda Folkenant, Tomas Edvinsson y Jacinto Sá. "Direct Plasmonic Solar Cell Efficiency Dependence on Spiro-OMeTAD Li-TFSI Content". Nanomaterials 11, n.º 12 (8 de diciembre de 2021): 3329. http://dx.doi.org/10.3390/nano11123329.
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The proliferation of the internet of things (IoT) and other low-power devices demands the development of energy harvesting solutions to alleviate IoT hardware dependence on single-use batteries, making their deployment more sustainable. The propagation of energy harvesting solutions is strongly associated with technical performance, cost and aesthetics, with the latter often being the driver of adoption. The general abundance of light in the vicinity of IoT devices under their main operation window enables the use of indoor and outdoor photovoltaics as energy harvesters. From those, highly transparent solar cells allow an increased possibility to place a sustainable power source close to the sensors without significant visual appearance. Herein, we report the effect of hole transport layer Li-TFSI dopant content on semi-transparent, direct plasmonic solar cells (DPSC) with a transparency of more than 80% in the 450–800 nm region. The findings revealed that the amount of oxidized spiro-OMeTAD (spiro+TFSI−) significantly modulates the transparency, effective conductance and conditions of device performance, with an optimal performance reached at around 33% relative concentration of Li-TFSI concerning spiro-OMeTAD. The Li-TFSI content did not affect the immediate charge extraction, as revealed by an analysis of electron–phonon lifetime. Hot electrons and holes were injected into the respective layers within 150 fs, suggesting simultaneous injection, as supported by the absence of hysteresis in the I–V curves. The spiro-OMeTAD layer reduces the Au nanoparticles’ reflection/backscattering, which improves the overall cell transparency. The results show that the system can be made highly transparent by precise tuning of the doping level of the spiro-OMeTAD layer with retained plasmonics, large optical cross-sections and the ultrathin nature of the devices.
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Ekkad, Srinath V., Shichuan Ou y Richard B. Rivir. "A Transient Infrared Thermography Method for Simultaneous Film Cooling Effectiveness and Heat Transfer Coefficient Measurements From a Single Test". Journal of Turbomachinery 126, n.º 4 (1 de octubre de 2004): 597–603. http://dx.doi.org/10.1115/1.1791283.
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In film cooling situations, there is a need to determine both local adiabatic wall temperature and heat transfer coefficient to fully assess the local heat flux into the surface. Typical film cooling situations are termed three temperature problems where the complex interaction between the jets and mainstream dictates the surface temperature. The coolant temperature is much cooler than the mainstream resulting in a mixed temperature in the film region downstream of injection. An infrared thermography technique using a transient surface temperature acquisition is described which determines both the heat transfer coefficient and film effectiveness (nondimensional adiabatic wall temperature) from a single test. Hot mainstream and cooler air injected through discrete holes are imposed suddenly on an ambient temperature surface and the wall temperature response is captured using infrared thermography. The wall temperature and the known mainstream and coolant temperatures are used to determine the two unknowns (the heat transfer coefficient and film effectiveness) at every point on the test surface. The advantage of this technique over existing techniques is the ability to obtain the information using a single transient test. Transient liquid crystal techniques have been one of the standard techniques for determining h and η for turbine film cooling for several years. Liquid crystal techniques do not account for nonuniform initial model temperatures while the transient IR technique measures the entire initial model distribution. The transient liquid crystal technique is very sensitive to the angle of illumination and view while the IR technique is not. The IR technique is more robust in being able to take measurements over a wider temperature range which improves the accuracy of h and η. The IR requires less intensive calibration than liquid crystal techniques. Results are presented for film cooling downstream of a single hole on a turbine blade leading edge model.
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Zinger, Elad, Annalisa Pillepich, Dylan Nelson, Rainer Weinberger, Rüdiger Pakmor, Volker Springel, Lars Hernquist, Federico Marinacci y Mark Vogelsberger. "Ejective and preventative: the IllustrisTNG black hole feedback and its effects on the thermodynamics of the gas within and around galaxies". Monthly Notices of the Royal Astronomical Society 499, n.º 1 (31 de agosto de 2020): 768–92. http://dx.doi.org/10.1093/mnras/staa2607.
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ABSTRACT Supermassive black holes (SMBHs) that reside at the centres of galaxies can inject vast amounts of energy into the surrounding gas and are thought to be a viable mechanism to quench star formation in massive galaxies. Here, we study the $10^{9-12.5}\, \mathrm{M_\odot }$ stellar mass central galaxy population of the IllustrisTNG simulation, specifically the TNG100 and TNG300 volumes at z = 0, and show how the three components – SMBH, galaxy, and circumgalactic medium (CGM) – are interconnected in their evolution. We find that gas entropy is a sensitive diagnostic of feedback injection. In particular, we demonstrate how the onset of the low-accretion black hole (BH) feedback mode, realized in the IllustrisTNG model as a kinetic, BH-driven wind, leads not only to star formation quenching at stellar masses $\gtrsim 10^{10.5}\, \mathrm{M_\odot }$ but also to a change in thermodynamic properties of the (non-star-forming) gas, both within the galaxy and beyond. The IllustrisTNG kinetic feedback from SMBHs increases the average gas entropy, within the galaxy and in the CGM, lengthening typical gas cooling times from $10\!-\!100\, \mathrm{Myr}$ to $1\!-\!10\, \mathrm{Gyr}$, effectively ceasing ongoing star formation and inhibiting radiative cooling and future gas accretion. In practice, the same active galactic nucleus (AGN) feedback channel is simultaneously ‘ejective’ and ‘preventative’ and leaves an imprint on the temperature, density, entropy, and cooling times also in the outer reaches of the gas halo, up to distances of several hundred kiloparsecs. In the IllustrisTNG model, a long-lasting quenching state can occur for a heterogeneous CGM, whereby the hot and dilute CGM gas of quiescent galaxies contains regions of low-entropy gas with short cooling times.
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Misawa, Hiroaki, Tomoya Oshikiri, Xu Shi y Yoshiki Suganami. "(Invited) Enhanced Water Splitting at Visible Wavelength Region Using Modal Strong Coupled Photoanode and Photocathode". ECS Meeting Abstracts MA2022-02, n.º 48 (9 de octubre de 2022): 1818. http://dx.doi.org/10.1149/ma2022-02481818mtgabs.
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Plasmon-induced hot electron transfer at the metal/semiconductor interface has attracted considerable attention as a novel mechanism to promote artificial photosynthesis under visible and near-infrared irradiation.[1-4] However, a single layer of gold nanoparticles (Au-NPs) cannot efficiently harvest light. Recently, we reported that the modal strong coupling between a Fabry–Pérot (F-P) nanocavity mode and a localized surface plasmon resonance (LSPR) facilitates water splitting reactions.[5] We used a Au-NPs/TiO2/Au-film (ATA) structure as a photoanode. The TiO2/Au-film component of this photoanode acts as F-P nanocavity. The light absorption of the ATA was promoted by the optical hybrid modes based on the strong coupling formation across a broad range of wavelengths, followed by a hot electron transfer to TiO2. We observed an 11-fold increase in the incident photon-to-current conversion efficiency (IPCE) with respect to a photoanode structure without Au-film. Importantly, the internal quantum efficiency (IQE) was enhanced 1.5 times under a strong coupling over that under uncoupled conditions. We speculated that the coupling strength of the modal strong coupling affects the hot electron transfer efficiency. To increase the coupling strength, we developed a photoanode consisting of Au-Ag alloy nanoparticles /TiO2/Au-film (AATA).[6] It was expected that the splitting energy of the modal strong coupling system increase with increasing LSPR oscillator strength by mixing Ag in the nanoparticle. The AATA structure formed under modal strong coupling with a large splitting energy of 520 meV, which can be categorized into the ultrastrong coupling regime. The AATA photoanode showed a 4.0% maximum IPCE obtained at 580 nm, and the IQE was 4.1%. Additionally, the highly efficient hot-electron injection on AATA was directly observed by transient absorption measurements. Furthermore, hybrid mode-induced water oxidation using AATA structures was performed with a Faraday efficiency of more than 70% for O2 evolution. We have applied the concept of photoanodes with modal strong coupling to photocathodes as well. As a semiconductor for constructing F-P nanocavity, we employed p-type nickel oxide (NiO) which is capable of transferring holes generated in Au-NPs and fabricated a photocathode consisting of Au-NP/NiO/Pt-film (ANP).[7] The ANP structure can absorb visible light over a wide wavelength range from 500 nm to 850 nm due to a hybrid mode based on the modal strong coupling. The IPCE based on H2evolution through water/proton reduction by hot electrons reached 0.2% at 650 nm and 0.04% at 800 nm, which was significantly larger than that of Au-NPs on NiO without Pt-film. Y. Nishijima, K. Ueno, Y. Kotake, K. Murakoshi, H. Inoue, H. Misawa, J. Phys. Chem. Lett. 2012, 3, 1248-1252. Y. Zhong, K. Ueno, Y. Mori, X. Shi, T. Oshikiri, K. Murakoshi, H. Inoue, H. Misawa, Angew. Chem. Int. Ed. 2014, 53, 10350-10354. T. Oshikiri, K. Ueno, H. Misawa, Angew. Chem. Int. Ed. 2016, 55, 3942-3946. M. Okazaki, Y. Suganami, N. Hirayama, H. Nakata, T. Oshikiri, T. Yokoi, H. Misawa, K. Maeda, ACS Appl. Energy Mater. 2020, 3, 5142–5146. X. Shi, K. Ueno, T. Oshikiri, Q. Sun, K. Sasaki, H. Misawa, Nat. Nanotechnol. 2018, 13, 953-958. Y. Suganami, T. Oshikiri, X. Shi, H. Misawa, Angew. Chem. Int. Ed. 2021, 60, 18438-18442. T. Oshikiri, H. Jo, X. Shi, and H. Misawa, Chem. Eur. J. 2022, published online, DOI: 10.1002/chem.202200288
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Kiani, Fatemeh, Alan R. Bowman, Milad Sabzehparvar, Can O. Karaman, Ravishankar Sundararaman y Giulia Tagliabue. "Transport and Interfacial Injection of d-Band Hot Holes Control Plasmonic Chemistry". ACS Energy Letters, 19 de septiembre de 2023, 4242–50. http://dx.doi.org/10.1021/acsenergylett.3c01505.
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Malé, Quentin, Olivier Vermorel, Frédéric Ravet y Thierry Poinsot. "Jet ignition prediction in a zero-dimensional pre-chamber engine model". International Journal of Engine Research, 6 de mayo de 2021, 146808742110150. http://dx.doi.org/10.1177/14680874211015002.
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This paper presents a multi-chamber, multi-zone engine model to predict the ignition of a lean main chamber by a pre-chamber. The two chambers are connected by small cylindrical holes: the flame is ignited in the pre-chamber, hot gases propagate through the holes and ignite the main chamber through Turbulent Jet Ignition (TJI). The model original features are: (i) separate balance equations for the pre- and main chambers, (ii) a specific model for temperature and composition evolution in the holes and (iii) a DNS-based model to predict the ignition of the main chamber fresh gases by the burnt gases turbulent jets exiting the holes. Chemical reactions during TJI are the result of two competing mixing processes: (1) the hot jet gases mix with the fresh main chamber to produce heated zones and (2) at the same time, these hot gases cool down. (1) increases combustion and leads to ignition while (2) decreases it and can prevent ignition. The overall outcome (ignition or failure) is too complex to be modelled simply and the present model relies on recent DNSs of TJI which provided a method to predict the occurrence of ignition. Incorporating this DNS information into the engine model allows to predicts whether ignition will occur or not, an information which is not accessible otherwise using simple models. The resulting approach is tested on multiple cases to predict ignition limits for very lean cases, effects of H2 injection into the pre-chamber and optimum size for the holes connecting the two chambers as a function of equivalence ratio.
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Heneka, Christian, Achmed Schulz, Hans-Jörg Bauer, Andreas Heselhaus y Michael E. Crawford. "Film Cooling Performance of Sharp Edged Diffuser Holes With Lateral Inclination". Journal of Turbomachinery 134, n.º 4 (21 de julio de 2011). http://dx.doi.org/10.1115/1.4003726.
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An experimental study on film cooling performance of laterally inclined diffuser shaped cooling holes is presented. The measurements have been conducted on a flat plate with coolant ejected from a plenum. The film cooling effectiveness downstream of a row of four laidback fanshaped holes with sharp edged diffusers has been determined by means of infrared (IR) thermography. A variety of geometric parameters has been tested, including the inclination angle, the compound angle, the area ratio, and the pitch to diameter ratio. All tests have been performed over a wide range of engine typical blowing ratios (M=0.5–3.0). The hot gas Reynolds number and the coolant to hot gas density ratio have been kept constant close to engine realistic conditions. The results, presented in terms of contour plots of related adiabatic film cooling effectiveness as well as laterally averaged related values, clearly show the influences of the cooling hole geometry. Increasing the area ratio and the compound angle, in general, leads to higher values of the effectiveness, whereas steeper injection causes a reduction of the effectiveness.
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Makri, Kassandra, Russel Lockett y Mahesh Jeshani. "Dynamics of post-injection fuel flow in mini-sac diesel injectors part 1: Admission of external gases and implications for deposit formation". International Journal of Engine Research, 26 de diciembre de 2019, 146808741989542. http://dx.doi.org/10.1177/1468087419895425.
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Samples of unadditised, middle distillate diesel fuel were injected through real-size optically accessible mini-sac diesel injectors into ambient air at common rail pressures of 250 and 350 bar, respectively. High-resolution images of white light scattered from the internal mini-sac and nozzle flow were captured on a high-speed monochrome video camera. Following the end of each injection, the momentum-driven evacuation of fuel liquid from the mini-sac and nozzle holes resulted in the formation of a vapour cloud and bubbles in the mini-sac, and vapour capsules in the nozzle holes. This permitted external gas to gain entrance to the nozzle holes. The diesel fuel in the mini-sac was observed to rotate with large initial vorticity, which decayed until the fuel became stationary. The diesel fuel remaining in the nozzle holes was observed to move inwards towards the mini-sac or outwards towards the nozzle exit in concert with the rotational flow in the mini-sac. The mini-sac bubbles’ internal pressure differences revealed that the bubbles must have contained previously dissolved oxygen and nitrogen. Under diesel engine operating conditions, this multi-phase mixture would be highly reactive and could initiate local pyrolysis and/or oxidation reactions. Finally, the dynamical behaviour of the diesel fuel in the nozzle holes would support the admission of external hot combustion gases into the nozzle holes, establishing the conditions for oxidation/pyrolysis reactions with surrounding liquid fuel films.
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Andreini, Antonio, Riccardo Da Soghe, Bruno Facchini, Lorenzo Mazzei, Salvatore Colantuoni y Fabio Turrini. "Local Source Based CFD Modeling of Effusion Cooling Holes: Validation and Application to an Actual Combustor Test Case". Journal of Engineering for Gas Turbines and Power 136, n.º 1 (25 de octubre de 2013). http://dx.doi.org/10.1115/1.4025316.
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State-of-the-art liner cooling technology for modern combustion chambers is represented by effusion cooling (or full-coverage film cooling). Effusion is a very efficient cooling strategy typically based on the use of several inclined small diameter cylindrical holes, where liner temperature is controlled by the combined protective effect of coolant film and heat removal through forced convection inside each hole. A CFD-based thermal analysis of such components implies a significant computational cost if the cooling holes are included in the simulations; therefore many efforts have been made to develop lower order approaches aiming at reducing the number of mesh elements. The simplest approach models the set of holes as a uniform coolant injection, but it does not allow an accurate assessment of the interaction between hot gas and coolant. Therefore higher order models have been developed, such as those based on localized mass sources in the region of hole discharge. The model presented in this paper replaces the effusion hole with a mass sink on the cold side of the plate, a mass source on the hot side, whereas convective cooling within the perforation is accounted for with a heat sink. The innovative aspect of the work is represented by the automatic calculation of the mass flow through each hole, obtained by a run time estimation of isentropic mass flow with probe points, while the discharge coefficients are calculated at run time through an in-house developed correlation. In the same manner, the heat sink is calculated from a Nusselt number correlation available in literature for short length holes. The methodology has been applied to experimental test cases of effusion cooling plates and compared to numerical results obtained through a CFD analysis including the cooling holes, showing a good agreement. A comparison between numerical results and experimental data was performed on an actual combustor as well, in order to prove the feasibility of the procedure.
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Yang, Junjie, Jin Wei, Yanlin Wu, Jingjing Yu, Jiawei Cui, Xuelin Yang, Xiaosen Liu et al. "Enhanced robustness against hot-electron-induced degradation in active-passivation p-GaN gate HEMT". Applied Physics Letters 124, n.º 10 (4 de marzo de 2024). http://dx.doi.org/10.1063/5.0186902.
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The hot-electron-related reliability is an important issue for GaN power devices under harsh operation condition or environment. These high-energy electrons can scatter toward the device surface or buffer layer, introducing newly generated traps/defects and resulting in the degradation of dynamic ON-resistance (RON). This work investigates the dynamic characteristics in active-passivation p-GaN gate HEMTs (AP-HEMTs) after hot-electron stress (HES). Unlike the dielectric passivation whose dynamic RON performance is often reported to severely worsen as hot-electron-induced defects/traps accumulate, the active passivation is found to have a superior robustness against hot-electron stress. In this study, after an HES of 30 min with VD = 200 V and IS = 10 mA/mm, the dynamic RON/static RON of a conventional HEMT increases dramatically from 3.63 to 9.35 for VDS-OFF = 650 V, whereas that of AP-HEMT only shows a slight increase from 1.51 to 1.85. Two mechanisms have been experimentally proved for the improved hot-electron robustness in AP-HEMT. (i) The mobile holes in active passivation layer can effectively screen the preexisting and/or newly generated surface defects/traps from affecting the 2DEG channel. (ii) The recovery of buffer trapping is accelerated by hole injection from gate and active passivation.
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Bakueva, Ludmila, Sergei Musikhin, Edward H. Sargent y Alexander Shik. "Experimental Studies and Physical Model of Efficient, Tunable Injection Using Tunnel-Transparent Dielectric Contacts on Polymer Light-Emitting Devices". MRS Proceedings 734 (2002). http://dx.doi.org/10.1557/proc-734-b7.2.
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ABSTRACTMost conducting polymers used for light-emitting devices have a small electron affinity, creating a high barrier for electron injection resulting in low injection efficiency. To improve injection characteristics, we fabricated and investigated multi-layer contacts with a tunneltransparent dielectric layer of nanometer thickness. Polymer layers were prepared by spin coating, and dielectric and metallic contact layers subsequently grown by vacuum deposition. Samples with such multi-layer cathodes demonstrated a current-voltage characteristic with negative differential resistance. At larger applied voltage, electroluminescence was observed with an efficiency larger than for a simple cathode of the same metal. We have developed a model to describe double injection through multi-layer contacts which explains these salient observed features. The increase in injection efficiency is caused by the voltage drop at the dielectric layer, shifting the metal Fermi level relative to the polymer molecular orbitals responsible for carrier transport. The negative differential resistance is explained by the strong dependence of dielectric tunnel transparency on voltage, a dependence which is qualitatively different for electrons and holes. Further flexibility in the functional characteristics of the injecting contacts is achieved through the use of an additional thin metallic layer playing the role of a base electrode, similar to hot-electron transistors with metallic base.
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Shen, Dawen, Miao Cheng, Guangyao Rong, Zhaohua Sheng, Yunzhen Zhang y Jianping Wang. "Effects of film cooling injection inclination angle on cooling performance in rotating detonation combustors". Physics of Fluids 36, n.º 2 (1 de febrero de 2024). http://dx.doi.org/10.1063/5.0188972.
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Film cooling is a promising thermal management solution for rotating detonation combustors (RDCs) maturing toward long-duration engineering implementation. Aimed at elucidating the interaction between air coolant and rotating detonation waves (RDWs) and assessing the cooling performance, three-dimensional numerical simulations are conducted on an RDC utilizing four different film cooling injection inclination angles and compared to a case without coolant injection. Increasing injection angles from 30° to 90° results in a broader detachment region and deeper penetration, negatively influencing the cooling performance. A time-averaged method is adopted to evaluate the overall cooling performance, including axial temperature profiles, film protection coverage, RDC film effectiveness, and pattern factor. The results show that the cylindrical cooling hole with a 30° injection angle outperforms others due to enhanced wall attachment of the coolant and reduced interaction with the mainstream hot gas. Consequently, a low injection angle within the manufacturing limits is recommended for practical applications. Furthermore, this study uncovers several phenomena unique to RDCs when introducing film cooling, absent in conventional gas turbines, such as temperature discrepancy between the inner and outer walls, elevated upstream temperature caused by coolant injection, and non-uniform cooling effectiveness between the two sides of the cooling holes. Finally, the interplay between film cooling and RDW is illustrated through temperature and pressure gradient contours.
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Kafaei, Amir, Esmail Lakzian, Goodarz Ahmadi y Sławomir Dykas. "An investigation of finding the best arrangement of hot steam injection holes in the 3D steam turbine blade cascade". Journal of Thermal Analysis and Calorimetry, 21 de febrero de 2022. http://dx.doi.org/10.1007/s10973-022-11242-6.
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Andrei, Luca, Antonio Andreini, Cosimo Bianchini, Bruno Facchini, Lorenzo Mazzei y Fabio Turrini. "Investigation on the Effect of a Realistic Flow Field on the Adiabatic Effectiveness of an Effusion-Cooled Combustor". Journal of Engineering for Gas Turbines and Power 137, n.º 5 (1 de mayo de 2015). http://dx.doi.org/10.1115/1.4028676.
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Effusion cooling represents the state of the art of liner cooling technology for modern combustors. This technique consists of an array of closely spaced discrete film cooling holes and contributes to lower the metal temperature by the combined protective effect of coolant film and heat removal through forced convection inside each hole. Despite many efforts reported in literature to characterize the cooling performance of these devices, detailed analyses of the mixing process between coolant and hot gas are difficult to perform, especially when superposition and density ratio effects as well as the interaction with complex gas side flow field become significant. Furthermore, recent investigations on the acoustic properties of these perforations pointed out the challenge to maintain optimal cooling performance also with orthogonal holes, which showed higher sound absorption. The objective of this paper is to investigate the impact of a realistic flow field on the adiabatic effectiveness performance of effusion cooling liners to verify the findings available in literature, which are mostly based on effusion flat plates with aligned cross flow, in case of swirled hot gas flow. The geometry consists of a tubular combustion chamber, equipped with a double swirler injection system and characterized by 22 rows of cooling holes on the liner. The liner cooling system employs slot cooling as well: its interactions with the cold gas injected through the effusion plate are investigated too. Taking advantage of the rotational periodicity of the effusion geometry and assuming axisymmetric conditions at the combustor inlet, steady state RANS calculations have been performed with the commercial code Ansys® CFX simulating a single circumferential pitch. Obtained results show how the effusion perforation angle deeply affects the flow-field around the corner of the combustor, in particular, with a strong reduction of slot effectiveness in case of 90 deg angle value.
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Ogawa, Hideyuki, Kazuma Mori, Tomoki Ishikawa, Yoshimitsu Kobashi y Gen Shibata. "Improvement of diesel combustion with suppression of mutual fuel spray flame interactions with staggered nozzle hole arrangement and a spatially divided combustion chamber". International Journal of Engine Research, 18 de agosto de 2023. http://dx.doi.org/10.1177/14680874231191563.
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A combination of a fuel injector with staggered nozzle hole arrangement with a combustion chamber divided into upper and lower layers by placing a lip at the middle of the side wall is proposed to improve diesel combustion with suppression of interactions among fuel spray flames. The fuel injector has twelve alternately arranged spray holes ( ϕ0.09 mm), staggered at two injection angles, 79° and 55° from the central axis of the injector. Two ordinary injectors with eight ( ϕ0.113 mm) and twelve ( ϕ0.092 mm) holes with an injection angle of 78° from the central axis with a conventional re-entrant combustion chamber were also examined as references. The experimental results showed that the improvements in thermal efficiencies and the reduction in smoke emissions can be established over a wide IMEP range with the proposed combination of the staggered nozzle hole injector and the divided combustion chamber. The exhaust loss is reduced with the combination of the injector and the combustion chamber while the cooling loss increases slightly. The rate of heat release from the combination of the injector and the combustion chamber has a more active main combustion and smaller afterburning than conventional systems. The three-dimensional CFD simulations showed that the combination of the injector and the combustion chamber can efficiently suppress the interactions among fuel spray flames at the combustion chamber wall after the impingement of fuel spray flames and also suitably distribute the fuel mixture, resulting in reductions in the afterburning and the smoke emissions. The slight increase in cooling loss with the proposed combination may be due to the increase in contact area of hot burned gas on the cylinder head; further improvements in thermal efficiency can be expected with optimization of the design factors related to the fuel injection and the combustion chamber configuration.