To see the other types of publications on this topic, follow the link: Low blade temperatures.
Journal articles on the topic 'Low blade temperatures'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Low blade temperatures.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Cheng, Wenjie, Boqin Gu, and Chunlei Shao. "A numerical study on the steady flow in molten salt pump under various conditions for improved hydraulic performance." International Journal of Numerical Methods for Heat & Fluid Flow 27, no. 8 (August 7, 2017): 1870–86. http://dx.doi.org/10.1108/hff-06-2016-0238.
Full textAbstract:
Purpose This paper aims to figure out the steady flow status in the molten salt pump under various temperatures and blade number conditions, and give good insight on the structure and temperature-dependent efficiencies of all pump cases. Finally, the main objective of present work is to get best working condition and blade numbers for optimized hydraulic performance. Design/methodology/approach The steady flow in the molten salt pump was studied numerically based on the three-dimensional Reynolds-Averaged Navier–Stokes equations and the standard k-ε turbulence model. Under different temperature conditions, the internal flow fields in the pumps with different blade number were systematically simulated. Besides, a quantitative backflow analysis method was proposed for further investigation. Findings With the molten salt fluid temperature, sharply increasing from 160°C to 480°C, the static pressure decreases gently in all pump cases, and seven-blades pump has the least backflow under low flow rate condition. The efficiencies of all pump cases increase slowly at low temperature (about 160 to 320°C), but there is almost no variation at high temperature, and obviously seven-blades pump has the best efficiency and head in all pump cases over the wide range of temperatures. The seven-blades pump has the best performance in all selected pump cases. Originality/value The steady flow in molten salt pumps was systematically studied under various temperature and blade number conditions for the first time. A quantitative backflow analysis method was proposed first for further investigation on the local flow status in the molten salt pump. A definition about the low velocity region in molten salt pumps was built up to account for whether the studied pump gains most energy. This method can help us to know how to improve the efficiencies of molten salt pumps.
2
Bachelez, Andreas, and Steven A. Martinez. "Heat Generation by Two Different Saw Blades Used for Tibial Plateau Leveling Osteotomies." Journal of the American Animal Hospital Association 48, no. 2 (March 1, 2012): 83–88. http://dx.doi.org/10.5326/jaaha-ms-5698.
Full textAbstract:
During tibial plateau leveling osteotomy (TPLO) the saw blade produces frictional heat. The purpose of this study was to evaluate and compare heat generated by two TPLO blade designs (Slocum Enterprises [SE] and New Generation Devices [NDG]), with or without irrigation, on cadaveric canine tibias. Thirty-six paired tibias were used to continuously measure bone temperatures during osteotomy through both cortices (i.e., the cis and trans cortices). Each pair was assigned to either an irrigation or nonirrigation group during osteotomy, and each tibia within a pair was osteotomized using a different saw blade design. Saw blade temperatures were recorded and temperatures were compared for all combinations of blade type, cortex, and irrigation. In the cis cortex group, the SE blade generated more bone heat than the NGD blade (P=0.0258). Significant differences in temperature generation between saw blade types were seen only when the osteotomy site was not irrigated (P=0.0156). For all variables measured, bone and saw blade temperature generation was lower with irrigation (P<0.05). None of the osteotomies performed with either saw blade produced a critical duration of damaging temperature ranges in this study. Although saw blade design and irrigation influence heat generation during the TPLO, the potential for bone thermal damage during TPLO is low. The use of the NGD blade with irrigation is recommended.
3
Arakere, N. K. "High-Temperature Fatigue Properties of Single Crystal Superalloys in Air and Hydrogen." Journal of Engineering for Gas Turbines and Power 126, no. 3 (July 1, 2004): 590–603. http://dx.doi.org/10.1115/1.1501075.
Full textAbstract:
Hot section components in high-performance aircraft and rocket engines are increasingly being made of single crystal nickel superalloys such as PWA1480, PWA1484, CMSX-4, and Rene N-4 as these materials provide superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over their polycrystalline counterparts. Fatigue failures in PWA1480 single crystal nickel-base superalloy turbine blades used in the space shuttle main engine fuel turbopump are discussed. During testing many turbine blades experienced stage II noncrystallographic fatigue cracks with multiple origins at the core leading edge radius and extending down the airfoil span along the core surface. The longer cracks transitioned from stage II fatigue to crystallographic stage I fatigue propagation, on octahedral planes. An investigation of crack depths on the population of blades as a function of secondary crystallographic orientation (β) revealed that for β=45+/−15 deg tip cracks arrested after some growth or did not initiate at all. Finite element analysis of stress response at the blade tip, as a function of primary and secondary crystal orientation, revealed that there are preferential β orientations for which crack growth is minimized at the blade tip. To assess blade fatigue life and durability extensive testing of uniaxial single crystal specimens with different orientations has been tested over a wide temperature range in air and hydrogen. A detailed analysis of the experimentally determined low cycle fatigue properties for PWA1480 and SC 7-14-6 single crystal materials as a function of specimen crystallographic orientation is presented at high temperature (75°F–1800°F) in high-pressure hydrogen and air. Fatigue failure parameters are investigated for low cycle fatigue data of single crystal material based on the shear stress amplitudes on the 24 octahedral and 6 cube slip systems for FCC single crystals. The max shear stress amplitude [Δτmax] on the slip planes reduces the scatter in the low cycle fatigue data and is found to be a good fatigue damage parameter, especially at elevated temperatures. The parameter Δτmax did not characterize the room temperature low cycle fatigue data in high-pressure hydrogen well because of the noncrystallographic eutectic failure mechanism activated by hydrogen at room temperature. Fatigue life equations are developed for various temperature ranges and environmental conditions based on power-law curve fits of the failure parameter with low cycle fatigue test data. These curve fits can be used for assessing blade fatigue life.
4
Guijarro, Rubén, Alberto Tapetado, David Sánchez Montero, and Carmen Vázquez. "Cleaving of PMMA Microstructured Polymer Optical Fibers with 3- and 4-Ring Hexagonal Cladding Structures." Polymers 13, no. 9 (April 22, 2021): 1366. http://dx.doi.org/10.3390/polym13091366.
Full textAbstract:
The cleaving of a novel microstructured polymer optical fiber (mPOF) to obtain an acceptable connectorized fiber end-face is studied. The effect of the blade temperature and the speed of the cutting blade on the end-face is qualitatively assessed. Recently manufactured mPOFs with air-structured 3- and 4-ring hexagonal-like hole cladding structures with outer fiber diameters of around 250 μm are employed. Good quality end-faces can be obtained by cleaving mPOF fibers at room temperature for blade temperatures within the range 60–80 °C and at a low blade speed at 0.5 mm/s. The importance of the blade surface quality is also addressed, being a critical condition for obtaining satisfactory mPOF end-faces after cleaving. From our experiments, up to four fiber cuts with the same razor blade and blade surface can be carried out with acceptable and similar fiber end-face results.
5
Wang, Xiaopeng, Wenchen Xu, Peng Xu, Haitao Zhou, Fantao Kong, and Yuyong Chen. "High Nb–TiAl Intermetallic Blades Fabricated by Isothermal Die Forging Process at Low Temperature." Metals 10, no. 6 (June 6, 2020): 757. http://dx.doi.org/10.3390/met10060757.
Full textAbstract:
In this study, the isothermal die forging process of high Nb–TiAl (Ti-44Al-8Nb-0.2W-0.2B-Y, at.%) alloy blades was simulated using the ABAQUS V6.11 software and the blades were fabricated successfully. The influence of a low forging temperature (lower than 1000 °C) and strain rate on the distributions of effective strain and stress were analyzed. The results indicate that the effective strain exhibits negative temperature sensitivity and positive strain rate sensitivity. The stress exponent (n = 3.02) and the apparent activation energy (Q = 293.381 kJ/mol) of the present alloy suggests that this as-forged high Nb–TiAl alloy exhibits good deformability at low temperatures. With the reduction in strain rate and the increase in forging temperature, the effective stress decreases. Finally, high-quality high Nb–TiAl alloy blades were fabricated using an isothermal die forging technology at a rate of 0.01 mm/s and temperature of 950 °C, chosen on the basis of the simulations results. Scanning electron microscopy (SEM) and electron back scatter diffraction (EBSD) results indicated that the center of the TiAl alloy blade possessed a duplex microstructure, consisting of remnant lamellar colonies and recrystallized γ/B2 grains. The refined α2 laths showed a typical forging flow line feature in the edge position, whereas the γ laths had broken down and recrystallized.
6
Cosack, T., L. Pawlowski, S. Schneiderbanger, and S. Sturlese. "Thermal Barrier Coatings on Turbine Blades by Plasma Spraying With Improved Cooling." Journal of Engineering for Gas Turbines and Power 116, no. 1 (January 1, 1994): 272–76. http://dx.doi.org/10.1115/1.2906805.
Full textAbstract:
Turbine blades were coated with a thermal barrier coating system consisting of an MCrAlY bond coat about 100 μm thick deposited by Low-Pressure Plasma Spraying (LPPS) and a 300 μm thick ZrO2-7 wt. % Y2O3 top coat. The latter was manufactured by both Atmosphere and Temperature Controlled Spraying (ATCS) and Air Plasma Spraying (APS) using internal air cooling through the cooling holes of the turbine blades. Coated blades were submitted to thermal cycling tests in a burner rig with hot gas temperature of 1485°C. In the case of ATCS coated blades the number of cycles until the first spallation at the leading edge of the blade was between 350 and 2400. The number of cycles of the thermal barrier coatings sprayed with internal cooling was between 1200 and 1800. Furnace cycling tests were also carried out with ATCS coated blades at temperatures of 1100 and 1200°C. The results of thermal cycle tests and the investigations of the microstructure are discussed.
7
Weber, H. E. "Wave Engine Aerothermodynamic Design." Journal of Engineering for Gas Turbines and Power 114, no. 4 (October 1, 1992): 790–96. http://dx.doi.org/10.1115/1.2906658.
Full textAbstract:
A method for aerothermodynamic preliminary design of a wave engine is presented. The engine has a centrifugal precompressor for the wave rotor, which feeds high and low-pressure turbines. Three specific wave engine designs are presented. Wave rotor blades are naturally cooled by the ingested air; thus combustion temperatures can be as high as 1900 K. Engine pressure ratios of over 25 are obtained in compact designs. It is shown that placing no nozzles at the end of the rotor blade passages yields the highest cycle efficiencies, which can be over 50 percent. Rotor blades are straight and easily milled, cast, or fabricated.
8
Wilson, M., R. Pilbrow, and J. M. Owen. "Flow and Heat Transfer in a Preswirl Rotor–Stator System." Journal of Turbomachinery 119, no. 2 (April 1, 1997): 364–73. http://dx.doi.org/10.1115/1.2841120.
Full textAbstract:
Conditions in the internal-air system of a high-pressure turbine stage are modeled using a rig comprising an outer preswirl chamber separated by a seal from an inner rotor-stator system. Preswirl nozzles in the stator supply the “blade-cooling” air, which leaves the system via holes in the rotor, and disk-cooling air enters at the center of the system and leaves through clearances in the peripheral seals. The experimental rig is instrumented with thermocouples, fluxmeters, pitot tubes, and pressure taps, enabling temperatures, heat fluxes, velocities, and pressures to be measured at a number of radial locations. For rotational Reynolds numbers of Reφ ≃ 1.2 × 106, the swirl ratio and the ratios of disk-cooling and blade-cooling flow rates are chosen to be representative of those found inside gas turbines. Measured radial distributions of velocity, temperature, and Nusselt number are compared with computations obtained from an axisymmetric elliptic solver, featuring a low-Reynolds-number k–ε turbulence model. For the inner rotor-stator system, the computed core temperatures and velocities are in good agreement with measured values, but the Nusselt numbers are underpredicted. For the outer preswirl chamber, it was possible to make comparisons between the measured and computed values for cooling-air temperatures but not for the Nusselt numbers. As expected, the temperature of the blade-cooling air decreases as the inlet swirl ratio increases, but the computed air temperatures are significantly lower than the measured ones. Overall, the results give valuable insight into some of the heat transfer characteristics of this complex system.
9
Ion, Ion, Anibal Portinha, Jorge Martins, Vasco Teixeira, and Joaquim Carneiro. "Analysis of the energetic/environmental performances of gas turbine plant: Effect of thermal barrier coatings and mass of cooling air." Thermal Science 13, no. 1 (2009): 147–64. http://dx.doi.org/10.2298/tsci0901147i.
Full textAbstract:
Zirconia stabilized with 8 wt.% Y2O3 is the most common material to be applied in thermal barrier coatings owing to its excellent properties: low thermal conductivity, high toughness and thermal expansion coefficient as ceramic material. Calculation has been made to evaluate the gains of thermal barrier coatings applied on gas turbine blades. The study considers a top ceramic coating Zirconia stabilized with 8 wt.% Y2O3 on a NiCoCrAlY bond coat and Inconel 738LC as substrate. For different thickness and different cooling air flow rates, a thermodynamic analysis has been performed and pollutants emissions (CO, NOx) have been estimated to analyze the effect of rising the gas inlet temperature. The effect of thickness and thermal conductivity of top coating and the mass flow rate of cooling air have been analyzed. The model for heat transfer analysis gives the temperature reduction through the wall blade for the considered conditions and the results presented in this contribution are restricted to a two considered limits: (1) maximum allowable temperature for top layer (1200?C) and (2) for blade material (1000?C). The model can be used to analyze other materials that support higher temperatures helping in the development of new materials for thermal barrier coatings.
10
Ford, D. A., K. P. L. Fullagar, H. K. Bhangu, M. C. Thomas, P. S. Burkholder, P. S. Korinko, K. Harris, and J. B. Wahl. "Improved Performance Rhenium Containing Single Crystal Alloy Turbine Blades Utilizing PPM Levels of the Highly Reactive Elements Lanthanum and Yttrium." Journal of Engineering for Gas Turbines and Power 121, no. 1 (January 1, 1999): 138–43. http://dx.doi.org/10.1115/1.2816301.
Full textAbstract:
Turbine inlet temperatures have now approached 1650°C (3000°F) at maximum power for the latest large commercial turbofan engines, resulting in high fuel efficiency and thrust levels approaching or exceeding 445 kN (100,000 lbs.). High reliability and durability must be intrinsically designed into these turbine engines to meet operating economic targets and ETOPS certification requirements. This level of performance has been brought about by a combination of advances in air cooling for turbine blades and vanes, computerized design technology for stresses and airflow, and the development and application of rhenium (Re) containing, high γ’ volume fraction nickel-base single crystal superalloys, with advanced coatings, including prime-reliant ceramic thermal barrier coatings (TBCs). Re additions to cast airfoil superalloys not only improve creep and thermomechanical fatigue strength but also environmental properties, including coating performance. Re slows down diffusion in these alloys at high operating temperatures [1]. At high gas temperatures, several issues are critical to turbine engine performance retention, blade life, and integrity. These are tip oxidation in particular for shroudless blades, internal oxidation for lightly cooled turbine blades, and TBC adherence to both the airfoil and tip seal liner. It is now known that sulfur (S) at levels, <10 ppm but >0.2 ppm in these alloys reduces the adherence of α alumina protective scales on these materials or their coatings by weakening the Van der Waal’s bond between the scale and the alloy substrate. A team approach has been used to develop an improvement to CMSX-41 alloy which contains 3 percent Re, by reducing S and phosphorus (P) levels in the alloy to <2 ppm, combined with residual additions of lanthanum (La) + yttrium (Y) in the range 10-30 ppm. Results from cyclic, burner rig dynamic oxidation testing at 1093°C (2000°F) show thirteen times the number of cycles to initial alumina scale spallation for CMSX-4 [La + Y] compared to standard CMSX-4. A key factor for application acceptance is of course manufacturing cost. The development of improved low reactivity prime coats for the blade shell molds along with a viable, tight dimensional control yttrium oxide core body are discussed. The target is to attain grain yields of single crystal CMSX-4 (ULS) (La + Y) turbine blades and casting cleanliness approaching standard CMSX-4. The low residual levels of La + Y along with a sophisticated homogenisation/solutioning heat treatment procedure result in full solutioning with essentially no residual γ/γ’ eutectic phase, Ni (La, Y) low melting point eutectics, and associated incipient melting pores. Thus, full CMSX-4 mechanical properties are attained. The La assists with ppm chemistry control of the Y throughout the single crystal turbine blade castings through the formation of a continuous lanthanum oxide film between the molten and solidifying alloy and the ceramic core and prime coat of the shell mold. Y and La tie up the <2 ppm but >0.2 ppm residual S in the alloy as very stable Y and La sulfides and oxysulfides, thus preventing diffusion of the S atoms to the alumina scale layer under high temperature, cyclic oxidising conditions. La also forms a stable phosphide. CMSX-4 (ULS) (La + Y) HP shroudless turbine blades will commence engine testing in May 1998.
11
Masci and Sciubba. "A Gas Turbine Cooled-Stage Expansion Model for the Simulation of Blade Cooling Effects on Cycle Performance." International Journal of Turbomachinery, Propulsion and Power 4, no. 4 (November 8, 2019): 36. http://dx.doi.org/10.3390/ijtpp4040036.
Full textAbstract:
Modern gas turbine firing temperatures (1500–2000 K) are well beyond the maximum allowable blade material temperatures. Continuous safe operation is made possible by cooling the HP turbine first stages, nozzle vanes and rotor blades, with a portion of the compressor discharge air, a practice that induces a penalty on the thermal efficiency cycle. Therefore, a current issue is to investigate the real advantage, technical and economical, of raising maximum temperatures much further beyond current values. In this paper, process simulations of a gas turbine are performed to assess HP turbine first-stage cooling effects on cycle performance. A new simplified and properly streamlined model is proposed for the non-adiabatic expansion of the hot gas mixed with the cooling air within the blade passage, which allows for a comparison of several cycle configurations at different turbine inlet temperatures (TIT) and total turbine expansion ratio (PR) with a realistically acceptable degree of approximation. The calculations suggest that, at a given PR, the TIT can be increased in order to reach a higher cycle efficiency up to a limit imposed by the required amount and temperature of the cooling air. Beyond this limit, no significant gains in thermal efficiency are obtained by adopting higher PR and/or increasing the TIT, so that it is convenient in terms of cycle performance to design at a lower rather than higher PR. The small penalty on cycle efficiency is compensated by the lower plant cost. The results of our model agree with those of some previous and much more complex and computationally expensive studies, so that the novelty of this paper lies in the original method adopted on which the proposed model is based, and in the fast, accurate, and low resource intensity of the corresponding numerical procedure, all advantages that can be crucial for industry needs. The presented analysis is purely thermodynamic and it includes no investigation on the effects of the different configurations on plant costs. Therefore, performing a thermo-economic analysis of the air-cooled gas turbine power plant is the next logical step.
12
Nikparto, Ali, and Meinhard T. Schobeiri. "Combined numerical and experimental investigations of heat transfer of a highly loaded low-pressure turbine blade under periodic inlet flow condition." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 232, no. 7 (February 14, 2018): 769–84. http://dx.doi.org/10.1177/0957650918758158.
Full textAbstract:
This paper experimentally and numerically investigates heat transfer characteristics of a low-pressure turbine blade under steady/unsteady flow conditions. Generally, the low-pressure turbine blades are not exposed to excessive temperatures that require detailed heat transfer predictions. In aircraft engines, they operate at low Re-numbers causing the inception of large separation bubbles on their suction surface. As documented in previous papers, the results of detailed aerodynamic simulations have shown significant discrepancies with experiments. It was the objective of the current investigation to determine the discrepancies between the experimental and numerical heat transfer results. It is shown that small errors in aero-calculation results in large deviations of heat transfer results. The characteristics of the blades mentioned above, make low-pressure turbine blades suitable candidates for evaluating the predictive capability of any numerical method. Documenting the scope of these discrepancies defines the framework of the current paper. The periodic flow inside the gas turbine engine was simulated using the cascade facility at the Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. In this study, the wakes that originate from stator blades were simulated by moving rods. The instrumented blade was covered with a liquid crystal sheet and it was used to measure heat transfer coefficient. Reynolds-averaged Navier–Stokes equations were used for numerical investigation purposes. Measurements and simulations were conducted at three different Reynolds numbers (110,000, 150,000, and 250,000). Furthermore, for unsteady flow condition, reduced frequencies of the incoming wakes were varied. The current paper includes a comprehensive heat transfer assessment of the predictive capability of Reynolds-averaged Navier–Stokes based tools. The effect of the separation bubbles on heat transfer is thoroughly discussed in this paper. Comparisons of the experimental and numerical results detail the differences and identify the sources of error that leads to in accurate calculations in terms of predicting heat transfer calculation results.
13
Cueto-Rodriguez, Maria M., Erika O. Avila-Davila, Victor M. Lopez-Hirata, Maribel L. Saucedo-Muñoz, Luis M. Palacios-Pineda, Luis G. Trapaga-Martinez, and Juan M. Alvarado-Orozco. "Numerical and Experimental Analyses of the Effect of Heat Treatments on the Phase Stability of Inconel 792." Advances in Materials Science and Engineering 2018 (December 9, 2018): 1–16. http://dx.doi.org/10.1155/2018/4535732.
Full textAbstract:
A study about the precipitation and phase stability was carried out in an IN-792 superalloy used as a blade in a gas turbine. Microstructure analysis was conducted experimentally on three different cross sections of the blade designated as high temperature (HT), medium temperature (MT), and low temperature (LT). To identify the HT, MT, and LT sections, a numerical thermal analysis was performed using ANSYS software. To obtain the distribution gradient of temperature in the blade, the real conditions of operation in steady state of the gas turbine were considered. A numerical study about the occurrence of phases in the IN-792 superalloy was carried out with Thermo-Calc and TC-PRISMA software. The analysis of the as-cast IN-792 superalloy with Scheil-Gulliver equations permitted to explain the phase formation during the solidification process. The calculated time-temperature-precipitation (TTP) diagram explains consistently the precipitation process observed after two different heat treatment conditions applied experimentally and numerically to regenerate the original microstructure of the IN-792 superalloy. The experimental results were consistent with the calculated isoplethic and TTP diagrams. In terms of accuracy, the further development of the Thermo-Calc databases for thermodynamic calculations in superalloys is evident. It was possible to calculate precipitation temperatures and the local evolution of precipitated particles for two different heat treatment conditions.
14
Nyaupane, Parashu R., Yasnahir Perez-Delgado, David Camejo, Lesley M. Wright, and Carlos E. Manzanares. "Cavity Ring-Down Absorption of O2 in Air as a Temperature Sensor for an Open and a Cryogenic Optical Cavity." Applied Spectroscopy 71, no. 5 (June 30, 2016): 847–55. http://dx.doi.org/10.1177/0003702816657567.
Full textAbstract:
The A-band of oxygen has been measured at low resolution at temperatures between 90 K and 373 K using the phase shift cavity ring down (PS-CRD) technique. For temperatures between 90 K and 295 K, the PS-CRD technique presented here involves an optical cavity attached to a cryostat. The static cell and mirrors of the optical cavity are all inside a vacuum chamber at the same temperature of the cryostat. The temperature of the cell can be changed between 77 K and 295 K. For temperatures above 295 K, a hollow glass cylindrical tube without windows has been inserted inside an optical cavity to measure the temperature of air flowing through the tube. The cavity consists of two highly reflective mirrors which are mounted parallel to each other and separated by a distance of 93 cm. In this experiment, air is passed through a heated tube. The temperature of the air flowing through the tube is determined by measuring the intensity of the oxygen absorption as a function of the wavenumber. The A-band of oxygen is measured between 298 K and 373 K, with several air flow rates. To obtain the temperature, the energy of the lower rotational state for seven selected rotational transitions is linearly fitted to a logarithmic function that contains the relative intensity of the rotational transition, the initial and final rotational quantum numbers, and the energy of the transition. Accuracy of the temperature measurement is determined by comparing the calculated temperature from the spectra with the temperature obtained from a calibrated thermocouple inserted at the center of the tube. This flowing air temperature sensor will be used to measure the temperatures of cooling air at the input (cold air) and output (hot air) after cooling the blades of a laboratory gas turbine. The results could contribute to improvements in turbine blade cooling design.
15
Gent, A. N., S.-M. Lai, C. Nah, and Chi Wang. "Viscoelastic Effects in Cutting and Tearing Rubber." Rubber Chemistry and Technology 67, no. 4 (September 1, 1994): 610–18. http://dx.doi.org/10.5254/1.3538696.
Full textAbstract:
Abstract Measurements of cutting resistance have been made for a crosslinked styrene—butadiene copolymer over a wide range of cutting speeds and temperatures. A characteristic fracture energy was determined using the procedure of Lake and Yeoh. A lower limit, about 150 J/m2, was obtained at low cutting speeds. This value is significantly higher than the threshold tear strength, about 30 J/m2, due to roughness of the blade tip. The tear resistance increased dramatically as the test temperature was lowered, by a factor of over 1000X, whereas the cutting resistance remained largely unchanged over a considerable temperature range. Much of the enhanced tear resistance at low temperatures is therefore attributed to increasing roughness of the tear tip, the intrinsic strength remaining approximately constant. As the tear strength followed a WLF temperature dependence closely, roughening of the tear tip is associated with viscoelastic effects. Higher cutting resistance was shown by a sulfur vulcanizate, but carbon black had no additional effect. Variations in tensile strength with rate of elongation and temperature are discussed in terms of tearing from an initial edge flaw.
16
Lu, Jing, Yan Hui Wang, Jian Bing Zang, and Shu Xian Shan. "Effect of Si and Ti Coating on Interface Bonding between Diamond and Fe-Based Metal Bond." Key Engineering Materials 359-360 (November 2007): 15–18. http://dx.doi.org/10.4028/www.scientific.net/kem.359-360.15.
Full textAbstract:
Fe-based metal bond has been widely used in fabricating diamond tools recently since the production cost could be greatly reduced for the low price of iron. However, graphitizing elements such as Fe, Co and Ni in the matrix catalyze the transformation of diamond to graphite during high temperature sintering process, which significantly decreases the tool’s efficiency and lifetime. In this paper, Si and Ti coating were coated on diamond grits by quasi atomic layer deposition (QALD) and vacuum slow vapor deposition (VSVD) separately not only to protect diamond from erosion but also to promote the adhesion between diamond grits and the bond. Three-point bending experiment was taken to measure the bending strength of Fe-Cu-Sn-Ni based metal bond diamond blade. In comparison with uncoated diamond blade, the bending strength of coated diamond blade improves dramatically. The theoretic calculation shows that the interface bonding strength between diamond and the metal bond increases by 181.68MPa owing to the Si coating. The effect of Si and Ti coating on interface bonding between diamond and the bond under different sintering temperatures was also illuminated.
17
Chang, Sung, and Ki-Yong Oh. "Contribution of High Mechanical Fatigue to Gas Turbine Blade Lifetime during Steady-State Operation." Coatings 9, no. 4 (March 31, 2019): 229. http://dx.doi.org/10.3390/coatings9040229.
Full textAbstract:
In this study, the contribution of high thermomechanical fatigue to the gas turbine lifetime during a steady-state operation is evaluated for the first time. An evolution of the roughness on the surface between the thermal barrier coating and bond coating is addressed to elucidate the correlation between operating conditions and the degradation of a gas turbine. Specifically, three factors affecting coating failure are characterized, namely isothermal operation, low-cycle fatigue, and high thermomechanical fatigue, using laboratory experiments and actual service-exposed blades in a power plant. The results indicate that, although isothermal heat exposure during a steady-state operation contributes to creep, it does not contribute to failure caused by coating fatigue. Low-cycle fatigue during a transient operation cannot fully describe the evolution of the roughness between the thermal barrier coating and the bond coating of the gas turbine. High thermomechanical fatigue during a steady-state operation plays a critical role in coating failure because the temperature of hot gas pass components fluctuates up to 140 °C at high operating temperatures. Hence, high thermomechanical fatigue must be accounted for to accurately predict the remaining useful lifetime of a gas turbine because the current method of predicting the remaining useful lifetime only accounts for creep during a steady-state operation and for low-cycle fatigue during a transient operation.
18
Gascó, Antonio, Andrea Nardini, and Sebastiano Salleo. "Resistance to water flow through leaves of Coffea arabica is dominated by extra-vascular tissues." Functional Plant Biology 31, no. 12 (2004): 1161. http://dx.doi.org/10.1071/fp04032.
Full textAbstract:
The leaf hydraulic conductance (Kleaf) of Coffea arabica L. was measured for shoots exposed to non-lethal temperature stress or to a freeze–thaw cycle, and compared with Kleaf of non-stressed samples (controls). Exposure to temperatures below 6°C for 1 h caused measurable damage to the functional integrity of cell membranes as shown by increased membrane leakiness to electrolytes. A 1 : 1 relationship was found to exist between relative electrolyte leakage and relative Kleaf suggesting that membrane damage caused Kleaf to increase. Low temperatures did not cause membrane disruption as shown by the comparison of chilled samples with frozen–thawed ones. In frozen leaves, membranes were extensively disrupted and both electrolyte leakiness and Kleaf increased 5-fold. Low temperatures did not induce alterations of the hydraulic properties of the leaf vascular system, as revealed by measurements of Kleaf after up to 500 cuttings of minor veins were made in the leaf blade of control and chilled leaves. Calculations showed that 62–75% of leaf hydraulic resistance resided in the extra-vascular water pathway. Results are discussed within the frame work of our current understanding of leaf hydraulic architecture as well as in terms of plant adaptation to extremes in temperature.
19
Krishnamoorthy, V., B. R. Pai, and S. P. Sukhatme. "Influence of Upstream Flow Conditions on the Heat Transfer to Nozzle Guide Vanes." Journal of Turbomachinery 110, no. 3 (July 1, 1988): 412–16. http://dx.doi.org/10.1115/1.3262212.
Full textAbstract:
The influence of a combustor located just upstream of a nozzle guide vane cascade on the heat flux distribution to the nozzle guide vane was experimentally investigated. The surface temperature distribution around the convectively cooled vane of the cascade was obtained by locating the cascade, firstly in a low-turbulence uniform hot gas stream, secondly in a high-turbulence, uniform hot gas stream, and thirdly in a high-turbulence, nonuniform hot gas stream present just downstream of the combustor exit. The results indicate that the increased blade surface temperatures observed for the cascade placed just downstream of the combustor can be accounted for by the prevailing turbulence level measured at cascade inlet in cold-flow conditions and the average gas temperature at the cascade inlet.
20
FANG, Y. W., L. W. YANG, S. H. ZHAO, Y. WANG, and X. S. GAN. "RESEARCH ON DYNAMIC RESPONSES AND RESIDUAL STRESSES FIELDS INDUCED BY LSP IN DD6 ALLOY BLADE." Latin American Applied Research - An international journal 45, no. 4 (October 30, 2015): 233–37. http://dx.doi.org/10.52292/j.laar.2015.411.
Full textAbstract:
The aim of this article was to address the dynamic responses properties and the residual stresses fields induced by laser shock processing (LSP) in a DD6 alloy blade. The dynamic characteristics with [001] and [111] orientations were investigated under different rotor speeds and temperatures by finite element method (FEM) simulation and vibration experiment. As a result, the corresponding static frequencies were analyzed for different temperature, rotor speed and orientation. The residual stresses fields induced by LSP were addressed for [001] orientation at 9800C based on simulation and LSP experiment. Results shown the proposed model was effective. The analyses indicate that the trends of different orders static frequencies were same along [001] and [111], and the orientation had stronger effect on high order static frequencies than it had on low order ones. The best compressive residual stress was achieved to be about 600 MPa when the power density was 4.5 GPa.
21
Chang, Kay W., Grace A. Carlson, and Huang Eric. "Evaluation of the PEAK PlasmaBlade for ENT Surgery." Otolaryngology–Head and Neck Surgery 139, no. 2_suppl (August 2008): P104—P105. http://dx.doi.org/10.1016/j.otohns.2008.05.534.
Full textAbstract:
Problem Traditional electrosurgical instruments are known to have an associated zone of thermal injury to the residual tissue. The compromised tissue left behind in the body may compromise wound healing and also may cause post operative pain. The PEAK PlasmaBlade is a new tissue dissection tool that uses pulsed radiofrequency energy to generate a highly focused plasma field at the tip of the device. This creates an effective cutting edge with simultaneous hemostasis while the blade remains near body temperature. A comparative study of tissue cutting and hemostasis was conducted to evaluate the characteristics of this technology. Methods Porcine mucosal and lymphoid tissue was subjected to a series of surgical incisions using the PlasmaBlade, a scalpel, a traditional electrosurgery (bovie) blade style tip, and a Coblation EVac 70 wand. Both low and high settings were evaluated for PlasmaBlade, bovie, and Coblation. Blood loss following the cut was evaluated. Histology samples were harvested immediately after and evaluated for collateral tissue damage at the incision site. Thermal imaging of all the devices in an active cutting mode was also conducted. Results Histological evaluation of the tissue samples showed that the PlasmaBlade cuts produced minimal collateral damage compared to cuts made with the other electrosurgical instruments, which demonstrated greater thermal damage. Bleeding control (hemostasis) was equivalent for the Plasma-Blade versus bovie and Coblation. Thermal imaging showed the PlasmaBlade operating in a range of 40 to 100 C which was similar to the Coblation operating temperatures. Traditional electrosurgery produced temperatures well in excess of 200 C. Conclusion The PEAK PlasmaBlade is a promising new instrument which provides atraumatic, scalpel–like, cutting and bovie-like hemostasis, resulting in minimal bleeding and tissue injury. Significance There is great potential for this becoming an important tool for common ENT procedures such as tonsillectomy and adenoidectomy, specifically in reducing the pain and morbidity of recovery.
22
Ding, Xian Fei, Xue Da Chen, Qing Li, Cheng Bo Xiao, Wei Peng Ren, and Qiang Feng. "Effect of Salt-Deposit Hot Corrosion on Creep Rupture Behaviors of DZ466 Superalloy." Materials Science Forum 850 (March 2016): 56–65. http://dx.doi.org/10.4028/www.scientific.net/msf.850.56.
Full textAbstract:
Since gas turbine blades in engines suffer centrifugal stress and gas corrosion during service, a good creep resistance in hot corrosion environment is one of the important considerations to evaluate service performance of the blade materials. In this work, the creep rupture behaviors of the directionally solidified superalloy DZ466 with and without salt deposition at 760°C/765MPa, 850°C/500MPa and 950°C/220MPa are preliminarily investigated based on the creep properties measurement and microstructure observations. The effects of hot corrosion on the creep properties and fracture mode are examined. The results show that the creep-rupture life in salt-deposit environment is lower than that in air-exposure environment at different temperatures. The creep-rupture life reduction caused by hot corrosion is increased with increase of the creep temperature. The fracture mode is exhibited by transgranular fracture in all crepted specimens. The propagation directions of all the secondary cracks are almost perpendicular to the crept specimen surface or the stress axis. The surface cracks are mainly produced in air-exposure environment at low temperature or in salt-deposited environment at high temperature. Induced by the stress concentration, the internal cracks are initiated surrounding the carbides in both air-exposure and salt-deposit environments. The creep-rupture life is dependent on the crack initiation at low temperature but on the crack propagation at high temperature. The reduction of the active load bearing area in transversal direction is the main reason why the creep-rupture life is decreased at 950°C.
23
Wang, Rongqiao, and Jingxu Nie. "A New Experimental Method to Study Combined Fatigue of Actual Turbine Disk Mortise Teeth at Elevated Temperatures." Journal of Engineering for Gas Turbines and Power 119, no. 4 (October 1, 1997): 969–72. http://dx.doi.org/10.1115/1.2817084.
Full textAbstract:
This paper presents a new experimental system to study the L-HCCF of an actual turbine disk mortise teeth at elevated temperature, using an actual disk as experimental component. This system ingeniously achieves combined loading (simulating low cycle radial centrifugal force and high cycle crosswise vibration of blade), high-frequency induction local heating (550°C constant temperature), control of high cycle vibrating frequency and amplitude, and crack real-time detection. The experimental result is identical with the practical flight failure. This method can be easily popularized to study the L-HCCF of many components.
24
Yaoita, Shinji, Takehiko Watanabe, and Tomohiro Sasaki. "Brazing of Cemented Carbides at Lower Temperatures." Advanced Materials Research 409 (November 2011): 865–70. http://dx.doi.org/10.4028/www.scientific.net/amr.409.865.
Full textAbstract:
Cemented carbides have been widely used for cutting tools because of their high hardness and abrasion resistance. Since the cemented carbides are so expensive, it is desirable to reuse a tool shank made of cemented carbides. For the reason, so far, a new blade of a tool has been brazed to used shanks. However, when cemented carbides are heated for brazing, heating inevitably causes the deterioration in the mechanical properties. This study was carried out to braze the cemented carbides at lower temperatures for reducing the deterioration of the shank. First of all, authors developed a new Ag-based brazing filler metal with a low melting point of about 605°C, and investigated the effects of the new Ag filler metal on the properties of a brazed joint. Moreover, Co element or Ni element was added into the Ag filler metal to make the bending strength of a brazed joint improved. The addition of Co element increased the bending strength of a joint and the strength was equivalent to that of a joint brazed at 750°C using a conventional Ag filler metal, but the addition of Ni element decreased the bending strength of a brazed joint.
25
Tran, Tu Anh, Varughese Mathew, Wen Shi Koh, K. Y. Yow, and Y. K. Au. "Dicing Development for low-k Copper Wafers using Nickel-Palladium-Gold Bond Pads for Automotive Application." International Symposium on Microelectronics 2013, no. 1 (January 1, 2013): 000657–62. http://dx.doi.org/10.4071/isom-2013-wp24.
Full textAbstract:
New automotive requirements expect plastic packages to survive higher operating temperatures with extended thermal duration. Mission profiles for under-the-hood and transmission application historically specified minimal duration at maximum junction temperature, such as 50 total hours at 150C, while keeping most of the total operating duration at lower temperatures. Further module integration and more stringent environmental requirements push modules and thus plastic packages closer to the heat source. As such, new mission profiles include more than 3500 total hours at 150°C. To satisfy new automotive requirements, plastic packages must meet AEC Grade 0 or higher. One key limitation of the conventional plastic package is the use of gold bond wire on aluminum bond pad. Au-Al intermetallic degradation due to intermetallic transformation in high temperature storage condition remains the main reliability concern. More reliable intermetallic systems have been proposed that change the wire material and/or the bond pad metallization. An alternative wire material to gold, copper, has many benefits including low cost, high electrical and thermal conductivities and excellent reliability with aluminum pad metallization. Pad re-metallization using nickel/palladium, nickel/gold or nickel/palladium/gold over aluminum bond pad or copper bond pad offers a noble and reliable metal interconnect. This study focused on the development of dicing process for low-K-copper wafers having aluminum pad re-metallized with electroless nickel / electroless palladium / immersion gold Over Pad Metallization (OPM). Development wafers were pizza mask wafers on which multiple die designs and scribe grid production control (SGPC) modules were designed. SGPC modules are designed with aluminum probe pads that are used to monitor wafer-level process control. All aluminum features on the wafer were plated with nickel/palladium/gold OPM. With the hardness of nickel and palladium being more than 10 to 15 times the hardness of aluminum, OPM-plated SGPC's were much more difficult to dice than conventional SGPC's with aluminum pads. Cracking on silicon sidewall with crack propagating towards the die was found to cause back-end-of-line (BEOL) delamination and device failure. Extensive mechanical dicing studies were conducted to modulate the failures and resolve the dicing challenge. Specifically, dicing was observed to be not centered on SPGC pads on the pizza mask. Off-centered dicing produced drastic change in Ni loading at the center of the blade and on the edges of the blade. Packages underwent extensive reliability stress conditions. The associated process improvements described in this paper supported a successful integration of a 55nm die technology in Low Profile Quad Flat Package with Exposed Pad (LQFP-EP) meeting and exceeding AEC grade 0 requirements.
26
Karabay, Hasan, Robert Pilbrow, Michael Wilson, and J. Michael Owen. "Performance of Pre-Swirl Rotating-Disc Systems." Journal of Engineering for Gas Turbines and Power 122, no. 3 (January 3, 2000): 442–50. http://dx.doi.org/10.1115/1.1285838.
Full textAbstract:
This paper summarizes and extends recent theoretical, computational, and experimental research into the fluid mechanics, thermodynamics, and heat transfer characteristics of the so-called cover-plate pre-swirl system. Experiments were carried out in a purpose-built rotating-disc rig, and the Reynolds-averaged Navier-Stokes equations were solved using two-dimensional (axisymmetric) and three-dimensional computational codes, both of which incorporated low-Reynolds-number k-ε turbulence models. The free-vortex flow, which occurs inside the rotating cavity between the disc and cover-plate, is controlled principally by the pre-swirl ratio, βp: this is the ratio of the tangential velocity of the air leaving the nozzles to that of the rotating disc. Computed values of the tangential velocity are in good agreement with measurements, and computed distributions of pressure are in close agreement with those predicted by a one-dimensional theoretical model. It is shown theoretically and computationally that there is a critical pre-swirl ratio, βp,crit, for which the frictional moment on the rotating discs is zero, and there is an optimal pre-swirl ratio, βp,opt, where the average Nusselt number is a minimum. Computations show that, for βp<βp,opt, the temperature of the blade-cooling air decreases as βp increases; for βp>βp,opt, whether the temperature of the cooling air increases or decreases as βp increases depends on the flow conditions and on the temperature difference between the disc and the air. Owing to the three-dimensional flow and heat transfer near the blade-cooling holes, and to unquantifiable uncertainties in the experimental measurements, there were significant differences between the computed and measured temperatures of the blade-cooling air. In the main, the three-dimensional computations produced smaller differences than the two-dimensional computations. [S0742-4795(00)01902-5]
27
Dunn, M. G. "Heat-Flux Measurements for the Rotor of a Full-Stage Turbine: Part I—Time-Averaged Results." Journal of Turbomachinery 108, no. 1 (July 1, 1986): 90–97. http://dx.doi.org/10.1115/1.3262029.
Full textAbstract:
This paper describes time-averaged heat-flux distributions obtained for the blade of a Garrett TFE 731-2 hp full-stage rotating turbine. Blade measurements were obtained both with and without injection. The injected gas was supplied from a separate reservoir and was directed into the turbine gas path via nozzle guide vane (NGV) pressure surface slots located at approximately 63 percent of the wetted distance. Blade heat-flux measurements were performed for two different injection gas temperatures, Tc/T0 = 0.53 and Tc/T0 = 0.82. A shock tube is used as a short-duration source of heated air to which the turbine is subjected and thin-film gages are used to obtain the heat-flux measurements. Results are presented along the blade in the flow direction at 10, 50, and 90 percent span for both the pressure and suction surfaces. A sufficient number of measurements were obtained to also present span-wise distributions. At approximately the 50 percent span location, two contoured inserts containing closely spaced gages were installed in the blade so that the leading-edge region distribution could be resolved in detail. The blade results are compared with predictions obtained using a flat-plate technique and with predictions obtained using a version of STAN 5. The results suggest that: (1) The suction surface laminar flat-plate prediction is in reasonable agreement with the data from the stagnation point up to approximately 10 percent of the wetted distance. Beyond 10 percent, the laminar prediction falls far below the data and the turbulent flat-plate prediction falls above the data by about 60 percent. The laminar portion of the STAN 5 prediction as configured for the present calculation does not provide good comparison with the data. However, the turbulent flat-plate boundary-layer portion of STAN 5 does provide reasonably good comparison with the data. On the pressure surface, the turbulent flat-plate prediction is in good agreement with the data, but the laminar flat-plate and the STAN 5 predictions fall far low. (2) The influence of upstream NGV injection is to significantly increase the local blade heat flux in the immediate vicinity of the leading edge; i.e., up to 20 percent wetted distance on the suction surface and up to 10 percent on the pressure surface. (3) The effect on local heat flux of increasing the coolant-gas temperature was generally less than 10 percent.
28
Bons, Jeffrey P., Rolf Sondergaard, and Richard B. Rivir. "The Fluid Dynamics of LPT Blade Separation Control Using Pulsed Jets." Journal of Turbomachinery 124, no. 1 (February 1, 2001): 77–85. http://dx.doi.org/10.1115/1.1425392.
Full textAbstract:
The effects of pulsed vortex generator jets on a naturally separating low-pressure turbine boundary layer have been investigated experimentally. Blade Reynolds numbers in the linear turbine cascade match those for high-altitude aircraft engines and industrial turbine engines with elevated turbine inlet temperatures. The vortex generator jets (30 deg pitch and 90 deg skew angle) are pulsed over a wide range of frequency at constant amplitude and selected duty cycles. The resulting wake loss coefficient versus pulsing frequency data add to previously presented work by the authors documenting the loss dependency on amplitude and duty cycle. As in the previous studies, vortex generator jets are shown to be highly effective in controlling laminar boundary layer separation. This is found to be true at dimensionless forcing frequencies F+ well below unity and with low (10 percent) duty cycles. This unexpected low-frequency effectiveness is due to the relatively long relaxation time of the boundary layer as it resumes its separated state. Extensive phase-locked velocity measurements taken in the blade wake at an F+ of 0.01 with 50 percent duty cycle (a condition at which the flow is essentially quasi-steady) document the ejection of bound vorticity associated with a low-momentum fluid packet at the beginning of each jet pulse. Once this initial fluid event has swept down the suction surface of the blade, a reduced wake signature indicates the presence of an attached boundary layer until just after the jet termination. The boundary layer subsequently relaxes back to its naturally separated state. This relaxation occurs on a timescale which is five to six times longer than the original attachment due to the starting vortex. Phase-locked boundary layer measurements taken at various stations along the blade chord illustrate this slow relaxation phenomenon. This behavior suggests that some economy of jet flow may be possible by optimizing the pulse duty cycle and frequency for a particular application. At higher pulsing frequencies, for which the flow is fully dynamic, the boundary layer is dominated by periodic shedding and separation bubble migration, never recovering its fully separated (uncontrolled) state.
29
Heck, K. A., J. S. Smith, and R. Smith. "INCONEL® Alloy 783: An Oxidation-Resistant, Low Expansion Superalloy for Gas Turbine Applications." Journal of Engineering for Gas Turbines and Power 120, no. 2 (April 1, 1998): 363–69. http://dx.doi.org/10.1115/1.2818131.
Full textAbstract:
INCONEL® alloy 783 is an oxidation-resistant low coefficient of thermal expansion (low CTE) superalloy developed for gas turbine applications. Turbine efficiency can be increased through the use of low-CTE shrouds and case components that maintain tight blade tip clearances at different turbine operating temperatures. To achieve low CTE, alloys based on Ni–Fe–Co compositions require Cr content be maintained at low levels. Added Cr lowers the Curie temperature and thereby increases thermal expansion rate over a wider temperature range. The necessary lack of Cr minimizes resistance to both general oxidation and stress-accelerated grain boundary oxygen enhanced cracking (SAGBO). Increased amounts of Al in alloys strengthened by γ′ alone also promotes SAGBO. Alloy 783 is the culmination in the development of an alloy system with very high aluminum content that, in addition to forming γ′, causes β aluminide phase precipitation in the austenitic matrix. It was discovered that this type of structure can be processed to resist both SAGBO and general oxidation, while providing low thermal expansion and useful mechanical properties up to 700°C. The high Al content also reduces density to 5 percent below that of superalloys such as INCONEL alloy 718. Key aspects of the alloy development are presented, including the assessment of SAGBO resistance by evaluating elevated temperature crack growth in air. The alloy, now commercially available, has been successfully fabricated and welded into gas turbine engine components.
30
Bons, Jeffrey P., Rolf Sondergaard, and Richard B. Rivir. "Turbine Separation Control Using Pulsed Vortex Generator Jets." Journal of Turbomachinery 123, no. 2 (February 1, 2000): 198–206. http://dx.doi.org/10.1115/1.1350410.
Full textAbstract:
The application of pulsed vortex generator jets to control separation on the suction surface of a low-pressure turbine blade is reported. Blade Reynolds numbers in the experimental, linear turbine cascade match those for high-altitude aircraft engines and aft stages of industrial turbine engines with elevated turbine inlet temperatures. The vortex generator jets have a 30 deg pitch and a 90 deg skew to the free-stream direction. Jet flow oscillations up to 100 Hz are produced using a high-frequency solenoid feed valve. Results are compared to steady blowing at jet blowing ratios less than 4 and at two chordwise positions upstream of the nominal separation zone. Results show that pulsed vortex generator jets produce a bulk flow effect comparable to that of steady jets with an order of magnitude less massflow. Boundary layer traverses and blade static pressure distributions show that separation is almost completely eliminated with the application of unsteady blowing. Reductions of over 50 percent in the wake loss profile of the controlled blade were measured. Experimental evidence suggests that the mechanism for unsteady control lies in the starting and ending transitions of the pulsing cycle rather than the injected jet stream itself. Boundary layer spectra support this conclusion and highlight significant differences between the steady and unsteady control techniques. The pulsed vortex generator jets are effective at both chordwise injection locations tested (45 and 63 percent axial chord) covering a substantial portion of the blade suction surface. This insensitivity to injection location bodes well for practical application of pulsed VGJ control where the separation location may not be accurately known a priori.
31
Luu, Anh Tuan, Dat Vinh Vuong, and Anh Phan Nhat Nguyen. "SYNTHESIS OF COPPER NANOPARTICLES WITH VARIOUS SIZES TOWARDS IMPROVING THE ELECTRICAL CONDUCTIVITY OF COPPER FILMS AT LOW SINTERING TEMPERATURE." Vietnam Journal of Science and Technology 57, no. 3A (October 28, 2019): 48. http://dx.doi.org/10.15625/2525-2518/57/3a/14073.
Full textAbstract:
The use of copper nanoparticles (CuNPs) in conductive inks has attracted much attention to printed circuit board manufacturers due to its high electrical conductivity and low cost. The synthesis of CuNPs by surfactant-assisted chemical reduction method was studied aiming to identify the content of PVP-surfactant corresponding to the size of copper particles. The crystallite size and phase of CuNPs were determined by X-ray diffraction (XRD) analysis while transmission and scanning electron microscopy (TEM and SEM) were used to characterize the size of copper particles. The results showed that the crystallite and particle size of CuNPs decrease with increasing the PVP-surfactant concentration. The crystallite size values measured by TEM and XRD methods have a slight variation. The copper films were fabricated by the doctor-blade technique on PI and Al2O3 substrates. The effect of sintering temperature on conductive properties of the copper film after sintering was investigated. The copper film was sintered at low temperatures below 300oC. The electrical conductivity of copper films was measured by using the four-point probe method. The electrical resistivity of copper films archives stable at the low sintering temperature above 200°C about 0.22 mΩ.cm and 0.63 mΩ.cm for that of Al2O3 and PI substrates respectively.
32
CALLE, ALEXANDRA, ANNA C. S. PORTO-FETT, BRADLEY A. SHOYER, JOHN B. LUCHANSKY, and HARSHAVARDHAN THIPPAREDDI. "Microbiological Safety of Commercial Prime Rib Preparation Methods: Thermal Inactivation of Salmonella in Mechanically Tenderized Rib Eye†." Journal of Food Protection 78, no. 12 (December 1, 2015): 2126–35. http://dx.doi.org/10.4315/0362-028x.jfp-15-154.
Full textAbstract:
Boneless beef rib eye roasts were surface inoculated on the fat side with ca. 5.7 log CFU/g of a five-strain cocktail of Salmonella for subsequent searing, cooking, and warm holding using preparation methods practiced by restaurants surveyed in a medium-size Midwestern city. A portion of the inoculated roasts was then passed once through a mechanical blade tenderizer. For both intact and nonintact roasts, searing for 15 min at 260°C resulted in reductions in Salmonella populations of ca. 0.3 to 1.3 log CFU/g. For intact (nontenderized) rib eye roasts, cooking to internal temperatures of 37.8 or 48.9°C resulted in additional reductions of ca. 3.4 log CFU/g. For tenderized (nonintact) rib eye roasts, cooking to internal temperatures of 37.8 or 48.9°C resulted in additional reductions of ca. 3.1 or 3.4 log CFU/g, respectively. Pathogen populations remained relatively unchanged for intact roasts cooked to 37.8 or 48.9°C and for nonintact roasts cooked to 48.9°C when held at 60.0°C for up to 8 h. In contrast, pathogen populations increased ca. 2.0 log CFU/g in nonintact rib eye cooked to 37.8°C when held at 60.0°C for 8 h. Thus, cooking at low temperatures and extended holding at relatively low temperatures as evaluated herein may pose a food safety risk to consumers in terms of inadequate lethality and/or subsequent outgrowth of Salmonella, especially if nonintact rib eye is used in the preparation of prime rib, if on occasion appreciable populations of Salmonella are present in or on the meat, and/or if the meat is not cooked adequately throughout.
33
LUCHANSKY, JOHN B., ANNA C. S. PORTO-FETT, BRADLEY SHOYER, RANDALL K. PHEBUS, HARSHAVARDHAN THIPPAREDDI, and JEFFREY E. CALL. "Thermal Inactivation of Escherichia coli O157:H7 in Blade-Tenderized Beef Steaks Cooked on a Commercial Open-Flame Gas Grill†‡." Journal of Food Protection 72, no. 7 (July 1, 2009): 1404–11. http://dx.doi.org/10.4315/0362-028x-72.7.1404.
Full textAbstract:
Beef subprimals were inoculated on the lean side with ca. 4.0 log CFU/g of a cocktail of rifampin-resistant (Rifr) Escherichia coli O157:H7 strains and then passed once through a mechanical blade tenderizer with the lean side facing upward. Inoculated subprimals that were not tenderized served as controls. Two core samples were removed from each of three tenderized subprimals and cut into six consecutive segments starting from the inoculated side. A total of six cores were also obtained from control subprimals, but only segment 1 (topmost) was sampled. Levels of E. coli O157:H7 recovered from segment 1 were 3.81 log CFU/g for the control subprimals and 3.36 log CFU/g for tenderized subprimals. The percentage of cells recovered in segment 2 was ca. 25-fold lower than levels recovered from segment 1, but E. coli O157:H7 was recovered from all six segments of the cores obtained from tenderized subprimals. In phase II, lean-side–inoculated (ca. 4.0 log CFU/g), single-pass tenderized subprimals were cut into steaks of various thicknesses (1.91 cm [0.75 in.], 2.54 cm [1.0 in.], and 3.18 cm [1.25 in.]) that were subsequently cooked on a commercial open-flame gas grill to internal temperatures of 48.8°C (120°F), 54.4°C (130°F), and 60°C (140°F). In general, regardless of temperature or thickness, we observed about a 2.6- to 4.2-log CFU/g reduction in pathogen levels following cooking. These data validate that cooking on a commercial gas grill is effective at eliminating relatively low levels of the pathogen that may be distributed throughout a blade-tenderized steak.
34
Giel, Paul W., Robert J. Boyle, and Ronald S. Bunker. "Measurements and Predictions of Heat Transfer on Rotor Blades in a Transonic Turbine Cascade." Journal of Turbomachinery 126, no. 1 (January 1, 2004): 110–21. http://dx.doi.org/10.1115/1.1643383.
Full textAbstract:
Detailed heat transfer measurements and predictions are given for a power generation turbine rotor with 127 deg of nominal turning and an axial chord of 130 mm. Data were obtained for a set of four exit Reynolds numbers comprised of the facility maximum point of 2.50×106, as well as conditions which represent 50%, 25%, and 15% of this maximum condition. Three ideal exit pressure ratios were examined including the design point of 1.443, as well as conditions which represent −25% and +20% of the design value. Three inlet flow angles were examined including the design point and ±5deg off-design angles. Measurements were made in a linear cascade with highly three-dimensional blade passage flows that resulted from the high flow turning and thick inlet boundary layers. Inlet turbulence was generated with a blown square bar grid. The purpose of the work is the extension of three-dimensional predictive modeling capability for airfoil external heat transfer to engine specific conditions including blade shape, Reynolds numbers, and Mach numbers. Data were obtained by a steady-state technique using a thin-foil heater wrapped around a low thermal conductivity blade. Surface temperatures were measured using calibrated liquid crystals. The results show the effects of strong secondary vortical flows, laminar-to-turbulent transition, and also show good detail in the stagnation region.
35
Xue, Y. P., Jia Rong Li, Jin Qian Zhao, and J. C. Xiong. "The Precipitation Behavior of γ′ Phase in Single Crystal Ni-Based DD6 Superalloy for Turbine Blade." Materials Science Forum 898 (June 2017): 534–44. http://dx.doi.org/10.4028/www.scientific.net/msf.898.534.
Full textAbstract:
The precipitation behavior of γ′ precipitates in typical section dimensions of DD6 single crystal superalloy turbine blade was investigated experimentally during directional solidification process. The phase transformation temperatures in the single crystal Ni-based DD6 superalloy from DSC analysis and JmatPro simulation were basically in consistent with the isothermal solidification experiments. The solidification route of DD6 single crystal superalloy could be described as follows: L1 → γ + L2; L2 → (γ + γ′)eutectic + MC; γ → γ′/γ. With increasing continuous cooling rates, the primary γ′ precipitates tended to be refined, and the size distributions of the primary γ′ precipitates at every temperature measuring position followed the normal distribution. In comparison to the interdendritic regions, nearly a 60% reduction in the average sizes of the primary γ′ precipitates was measured in the dendritic core regions. The result of the primary γ′ size difference was strongly affected by the multi-component segregations between the interdendritic and dendritic regions, where the γ′ forming elements of Al and Ta segregated towards the interdendritic regions. Furthermore, the secondary γ′ precipitation was found to occur within a relatively wide corridor of γ matrix for low cooling rates (12.6, 23.3 and 29.7 °C/min) during the directional solidification process. The occurrence of the secondary γ′ precipitation resulted from the complex interaction of multiple thermodynamic and kinetic factors in the γ′ nucleation and the diffusion rate of γ′ forming elements.
36
Nguyen, HT, CP Joshi, N. Klueva, J. Weng, KL Hendershot, and A. Blum. "The Heat-Shock Response and Expression of Heat-Shock Proteins in Wheat Under Diurnal Heat Stress and Field Conditions." Functional Plant Biology 21, no. 6 (1994): 857. http://dx.doi.org/10.1071/pp9940857.
Full textAbstract:
The occurrence of heat-shock proteins (HSPs) in response to high temperature stress is a universal phenomenon in higher plants and has been well documented. However, in agriculturally important species, less is known about the expression of HSPs under natural environments. A review of the heat-shock response in wheat (Triticum aestivum L.) is presented and recent results on the expression of wheat HSPs under diurnal stress and field conditions are reported. In the field experiment, flag leaf blade temperatures were obtained and leaf blades collected for northern blot analysis using HSP 16.9 cDNA as a probe. Temperatures of leaf blades ranged from 32 to 35�C under the tested field conditions at New Deal near Lubbock, Texas. Messenger RNAs encoding a major class of low molecular weight HSPs, HSP 16.9, were detected in all wheat genotypes examined. The results suggested that HSPs are synthesised in response to heat stress under agricultural production, and furthermore, that HSPs are produced in wheats differing in geographic background. In the controlled growth chamber experiment, HSP expression in two wheat cultivars, Mustang (heat tolerant) and Sturdy (heat susceptible) were analysed to determine if wheat genotypes differing in heat tolerance differ in in vitro HSP synthesis (translatable HSP mRNAs) under a chronic, diurnal heat-stress regime. Leaf tissues were collected from seedlings over a time-course and poly (A)+RNAs were isolated for in vitro translation and 2-D gel electrophoresis. The protein profiles shown in the 2-D gel analysis revealed that there were not only quantitative differences of individual HSPs between these two wheat lines, but also some unique HSPs which were only found in the heat tolerant line. This data provides evidence of a correlation between HSP synthesis and heat tolerance in wheat under a simulated field environment and suggests that further genetic analysis of HSPs in a segregating population is worthy of investigation. In conclusion, the results of this study provide an impetus for the investigation of the roles of HSP genes in heat tolerance in wheat.
37
Rentsch, Rüdiger, Olaf Grohmann, Alwin Schulz, and Volker Uhlenwinkel. "Application of a Composite Hot Shearing Tool Manufactured by Co-Spray Forming." Materials Science Forum 825-826 (July 2015): 771–78. http://dx.doi.org/10.4028/www.scientific.net/msf.825-826.771.
Full textAbstract:
In modern manufacture, like in automotive industry, high quality products and high output rates as well as low costs are achieved by highly efficient processes. Optimized tool design represents a key factor for such processes, leading to long tool life and hence to low tooling costs. Early in the industrial manufacturing chain of roller bearings for example, hot bars are sheared into billets, which are subsequently transported automatically to the first forming stage of a press. The shear blades should have a high wear resistance at high temperatures. In this study the first bi-metal composite shear blade made by spray-forming has been developed and tested in industrial environment. The composite tool has been deposited in a co-spray forming process to directly combine a hard-facing alloy layer with a hot working steel body in order to take advantage of the high microstructural homogeneity and the low segregation generated in spray forming. After machining, heat treating and quality inspection of the new material composite, the hot working tool was used in manufacture to prove its wear resistance and durability. The results show that the interface properties of the composite are of high quality and the material has a lower vulnerability to cracks after use in production than the conventional tool, respectively material. Only the porous zone near the interface leads to fissures which are partially going deep into the tool. Hence the parameters of the co-spray forming process need to be improved.
38
Nickel, H., D. Clemens, W. J. Quadakkers, and L. Singheiser. "Development of NiCrAlY Alloys for Corrosion-Resistant Coatings and Thermal Barrier Coatings of Gas Turbine Components." Journal of Pressure Vessel Technology 121, no. 4 (November 1, 1999): 384–87. http://dx.doi.org/10.1115/1.2883719.
Full textAbstract:
The demand for improved efficiency and power output of energy conversion systems has lead to an increase of gas inlet temperatures in modern land-based gas turbines. The resulting increase of component surface temperature leads to an enhanced oxidation attack of the blade coating, which, in stationary gas turbines, is usually of the MCrAlY (with M = Co and/or Ni) type. Considerable efforts have been made in the improvement of the high temperature properties of MCrAlY coatings by additions of minor alloying elements. In the present paper, the effect of systematic composition variations, especially yttrium, silicon, and titanium additions, on the protective properties of MCrAlY coatings are presented. The coatings were applied to a steel substrate by low-pressure plasma spraying. Then, free-standing MCrAlY-bodies were machined from the coating. Isothermal and cyclic oxidation tests were carried out in the temperature range 950°C–1100°C. The effect of systematic variation of titanium and silicon contents on oxidation and micro structural stability was studied by characterization of the coating and the corrosion products using light and electron optical microscopy and by secondary neutrals mass spectrometry (SNMS).
39
Eriksson, Robert, Johan Moverare, Zhe Chen, and Kjell Simonsson. "THE EFFECT OF NOTCHES ON THE FATIGUE LIFE OF A NICKEL-BASE GAS TURBINE DISK MATERIAL." Acta Polytechnica CTU Proceedings 20 (December 31, 2018): 34–42. http://dx.doi.org/10.14311/app.2018.20.0034.
Full textAbstract:
Gas turbine disks carry significant load under high temperatures and may be subject to fatigue failure. Disks contain several notches in the form of the fir tree blade attachments. Low cycle fatigue tests were performed on blunt notch compact tension specimens made from alloy 718. The results indicated that notch support needed to be incorporated not to cause an overly conservative life prediction. The notch support diminished as the plastic strain range decreased, indicating that notch support is only present in the low cycle fatigue regime. A critical distance approach was applied to account for the notch support. An equation relating the critical distance to the notch root stress was derived. The chosen life model was formulated in terms of a variation on the Smith–Watson–Topper (SWT) parameter. The modified SWT parameter taken at the critical distance was used in a life model calibrated for smooth specimens to successfully predict the fatigue life of notched specimens.
40
Preve´y, Paul S., Ravi A. Ravindranath, Michael Shepard, and Timothy Gabb. "Case Studies of Fatigue Life Improvement Using Low Plasticity Burnishing in Gas Turbine Engine Applications." Journal of Engineering for Gas Turbines and Power 128, no. 4 (September 18, 2006): 865–72. http://dx.doi.org/10.1115/1.1807414.
Full textAbstract:
Surface enhancement technologies such as shot peening, laser shock peening, and low plasticity burnishing (LPB) can provide substantial fatigue life improvement. However, to be effective, the compressive residual stresses that increase fatigue strength must be retained in service. For successful integration into turbine design, the process must be affordable and compatible with the manufacturing environment. LPB provides thermally stable compression of comparable magnitude and even greater depth than other methods, and can be performed in conventional machine shop environments on CNC machine tools. LPB provides a means to extend the fatigue lives of both new and legacy aircraft engines and ground-based turbines. Improving fatigue performance by introducing deep stable layers of compressive residual stress avoids the generally cost prohibitive alternative of modifying either material or design. The x-ray diffraction based background studies of thermal and mechanical stability of surface enhancement techniques are briefly reviewed, demonstrating the importance of minimizing cold work. The LPB process, tooling, and control systems are described. An overview of current research programs conducted for engine OEMs and the military to apply LPB to a variety of engine and aging aircraft components are presented. Fatigue performance and residual stress data developed to date for several case studies are presented including the following. (1) The effect of LPB on the fatigue performance of the nickel based super alloy IN718, showing the fatigue benefit of thermal stability at engine temperatures. (2) An order of magnitude improvement in damage tolerance of LPB processed Ti-6-4 fan blade leading edges. (3) Elimination of the fretting fatigue debit for Ti-6-4 with prior LPB. (4) Corrosion fatigue mitigation with LPB in Carpenter 450 steel. (5) Damage tolerance improvement in 17-4 PH steel. Where appropriate, the performance of LPB is compared to conventional shot peening after exposure to engine operating temperatures.
41
Rosisca, Juliandra Rodrigues, Carolina Maria Gaspar de Oliveira, Altamara Viviane de Souza Sartori, Renata Stolf-Moreira, Marcelo Augusto de Aguiar e. Silva, and Heverly Morais. "Condutividade elétrica como indicador de danos por temperaturas baixas em folhas de feijão." Semina: Ciências Agrárias 40, no. 3 (May 21, 2019): 1011. http://dx.doi.org/10.5433/1679-0359.2019v40n3p1011.
Full textAbstract:
The electrical conductivity test indirectly evaluates cell membrane disorganization by quantifying the electrolytes released into the water after tissue imbibing. The objective of this work was to evaluate methodological variations in the electrical conductivity test, for it to serve as an indicator of low temperature-induced damages and estimate the cold tolerance of bean plants. Cultivar IPR Uirapuru plants were subjected to minimum temperatures of 4 °C, 2 °C, 0 °C, -1 °C, -2 °C, -3 °C, and -4 °C for 1 h in a growth chamber under controlled conditions. After the treatment period, the response of plants to cold stress was evaluated by determination of the total protein content, and catalase (CAT) and ascorbate peroxidase (APX) enzymatic activities, and evaluation of photosystem II (Fm/Fv) efficiency and leaf anatomy. These results were compared with those obtained in the electrical conductivity test, which was performed in plants under cold stress as well as under a non-stress environment, with 2, 4, 6, and 8 leaf discs immersed in 30 mL of distilled water for 24 h in BOD, at temperatures of 25 °C, 30 °C, and 35°C. Analysis of variance was performed using a completely randomized design, and for electrical conductivity, a number of discs × cold stress temperature combinations were used for each soak temperature. The averages were compared using the Turkey's test at 5% and 10% probability. Pearson correlation coefficient (r) between the conductivity averages and other cold stress evaluation data was also performed. The results showed a marked reduction in the ratio (Fv/Fm) only in the treatments at -3 °C and -4°C, which indicated tissue death. At temperatures below 0°C, there was a collapse of the leaf blade tissues, and it was not possible to differentiate the palisade parenchyma from the spongy parenchyma in the treatments at -2°C, -3°C, and -4°C. There was an increase in the protein content since the temperature -3°C. The enzyme activity of CAT decrease at -4°C whereas that of APX increased. In the electrical conductivity test, there was a significant interaction between soak temperature and the number of discs, and an increase in conductivity of the solution with a decrease in temperature was verified in several treatments, among which, the combination that best correlated with the other tests was 25°C with six leaf discs. It was concluded that the electrical conductivity test presents results similar to those obtained from other physiological, biochemical, and anatomical tests, and therefore, it can be used to evaluate the damage caused by low temperatures in bean plants.
42
Zhang, Li Ping, Jing Xie, Tai Wang, and Qing Xiong. "Study of Physicochemical Properties of Chinese Small Cabbage(Brassica chinensis L.) Stored at Four Temperatures." Advanced Materials Research 690-693 (May 2013): 1275–81. http://dx.doi.org/10.4028/www.scientific.net/amr.690-693.1275.
Full textAbstract:
Chinese small cabbage (Brassica rapa L.Chinensis Group.), is one of Shanghai special vegetables, whose storage qualities were rarely studied by domestic researchers yet. Hence for, physical and chemical indexes of Chinese small cabbage ( harvested in Lingang new city, Shanghai) stored at temperature 2 °C, 6 °C, 10 °C, 15°Cwere determined in this study. It was shown that as temperature lower, the degradation rate of reduced ascorbic acid and chlorophyll were smaller, respiratory rate and weight loss rate rate were lower. Taking into account the quality of Chinese small cabbage in the whole experiment process stored at a single temperature concerned, degradation rate of nutrients , such as, reduced ascorbic acid and chlorophyll were more and more smaller. Due to environmental stress effect, total phenolic content was increased at first days, and then decreased as antioxidant capacity reducing. On the other hand, respiratory rate increased along with blade decay which was caused by injury breathing and moisture loss leading enhancement of hydrolase activity. Changes of chrome parameters like L*, a*, b*,BI, h*and E had positive correlation with physiological quality. Overall, low temperature inhibits the physiological activities of the Chinese small cabbage and prolongs the shelf life, but chilling injury should be paid attention to.
43
Yan, Xiaojun, Xiaoyu Qin, and Dawei Huang. "High-Temperature Combined Fatigue Tests on Full-Scale Turbine Blades." Journal of Multiscale Modelling 10, no. 03 (September 2019): 1842003. http://dx.doi.org/10.1142/s1756973718420039.
Full textAbstract:
Compared with standard specimens, fatigue tests on full-scale turbine blades can take factors such as geometry and manufacturing process into consideration of life assessment. However, for combined fatigue tests of full-scale turbine blades, there exist two challenges. The first one is that it is difficult to apply combined loads of centrifugal force (low cycle fatigue, LCF) and vibration force (high cycle fatigue, HCF) properly because of the interaction between these loads. The second one is that it is hard to determine the range of HCF load/stress which the blade experiences at service conditions. To address these two challenges, firstly, a set of two-path fixture is designed to apply combined loads on the test blade, which can transfer LCF and HCF load separately by different paths. And secondly, two methods, i.e. the inverse method and the contrast method are proposed to estimate the HCF stress level for turbine blades at service conditions. The inverse method infers the HCF stress level by comparing blade failure data between field (in service) and bench tests conditions, while the contrast method obtains HCF stress level by comparing blade failure data between new and used blades under bench tests conditions. Detailed procedures of high temperature combined fatigue tests on full-scale blade are presented, and experimental life data is also included and analyzed.
44
Krishnaswamy, Karthik, and Srikanth Salyan. "Effect of Discrete Ribs on Heat Transfer and Friction Inside Narrow Rectangular Cross Section Cooling Passage of Gas Turbine Blade." International Journal of Engineering and Advanced Technology 10, no. 6 (August 30, 2021): 192–209. http://dx.doi.org/10.35940/ijeat.f3074.0810621.
Full textAbstract:
The performance of a gas turbine during the service life can be enhanced by cooling the turbine blades efficiently. The objective of this study is to achieve high thermohydraulic performance (THP) inside a cooling passage of a turbine blade having aspect ratio (AR) 1:5 by using discrete W and V-shaped ribs. Hydraulic diameter (Dh) of the cooling passage is 50 mm. Ribs are positioned facing downstream with angle-of-attack (α) of 30° and 45° for discrete W-ribs and discerte V-ribs respectively. The rib profiles with rib height to hydraulic diameter ratio (e/Dh) or blockage ratio 0.06 and pitch (P) 36 mm are tested for Reynolds number (Re) range 30000-75000. Analysis reveals that, area averaged Nusselt numbers of the rib profiles are comparable, with maximum difference of 6% at Re 30000, which is within the limits of uncertainty. Variation of local heat transfer coefficients along the stream exhibited a saw tooth profile, with discrete W-ribs exhibiting higher variations. Along spanwise direction, discrete V-ribs showed larger variations. Maximum variation in local heat transfer coefficients is estimated to be 25%. For experimented Re range, friction loss for discrete W-ribs is higher than discrete-V ribs. Rib profiles exhibited superior heat transfer capabilities. The best Nu/Nuo achieved for discrete Vribs is 3.4 and discrete W-ribs is 3.6. In view of superior heat transfer capabilities, ribs can be deployed in cooling passages near the leading edge, where the temperatures are very high. The best THPo achieved is 3.2 for discrete V-ribs and 3 for discrete W-ribs at Re 30000. The ribs can also enhance the power-toweight ratio as they can produce high thermohydraulic performances for low blockage ratios.
45
dos Santos Horbach, Cristina, Elizaldo Domingues dos Santos, Liércio André Isoldi, and Luiz Alberto Oliveira Rocha. "Constructal Design of Y-Shaped Conductive Pathways for Cooling a Heat-Generating Body." Defect and Diffusion Forum 348 (January 2014): 245–60. http://dx.doi.org/10.4028/www.scientific.net/ddf.348.245.
Full textAbstract:
This paper applies constructal design to obtain numerically the configuration that facilitates the access of the heat that flows through Y-shaped pathways of a high-conductivity material embedded within a square-shaped heat-generating medium of low-conductivity to cooling this finite-size volume. The objective is to minimize the maximal excess of temperature of the whole system, i.e., the hot spots, independent of where they are located. The total volume and the volume of the material of high thermal conductivity are fixed. Results show that there is no universal optimal geometry for the Y-shaped pathways for every value of high conductivity investigated here. For small values of high thermal conductivity material the best shape presented a well defined format of Y. However, for larger values of high thermal conductivity the best geometry tends to a V-shaped (i.e., the length of stem is suppressed and the bifurcated branches penetrates deeply the heat-generating body towards the superior corners). A comparison between the Y-shaped pathway configuration with a simpler I-shaped blade and with X-shaped configuration was also performed. For constant values of area fraction occupied with a high-conductivity material and the ratio between the high thermal conductivity material and low conductivity of the heat-generating body (φ = 0.1 and = 100) the Y-shaped pathways performed 46% and 13% better when compared to I-shaped and X-shaped pathway configuration, respectively. The best thermal performance is obtained when the highest temperatures (hot spots) are better distributed in the temperature field, i.e., according to the constructal principle of optimal distribution of imperfections.
46
Muthersbaugh, Michael S., W. Mark Ford, Karen E. Powers, and Alexander Silvis. "Activity Patterns of Bats During the Fall and Spring Along Ridgelines in the Central Appalachians." Journal of Fish and Wildlife Management 10, no. 1 (March 1, 2019): 180–95. http://dx.doi.org/10.3996/082018-jfwm-072.
Full textAbstract:
Abstract Many central Appalachian ridges offer high wind potential, making them attractive to future wind-energy development. Understanding seasonal and hourly activity patterns of migratory bat species may help to reduce fatalities at wind-energy facilities and provide guidance for the development of best management practices for bats. To examine hourly migratory bat activity patterns in the fall and spring in Virginia in an exploratory fashion with a suite of general temporal, environmental, and weather variables, we acoustically monitored bat activity on five ridgelines and side slopes from early September through mid-November 2015 and 2016 and from early March through late April 2016 and 2017. On ridges, bat activity decreased through the autumn sample period, but was more variable through the spring sample period. In autumn, migratory bat activity had largely ceased by mid-November. Activity patterns were species specific in both autumn and spring sample periods. Generally, migratory bat activity was negatively associated with hourly wind speeds but positively associated with ambient temperatures. These data provide further evidence that operational mitigation strategies at wind-energy facilities could help protect migratory bat species in the Appalachians; substantially slowing or locking wind turbine blade spin during periods of low wind speeds, often below where electricity is generated, and warm ambient temperatures may minimize mortality during periods of high bat activity.
47
Brailko, Valentina, Natalya Ivanova, Irina Zhdanova, and Olga Mitrofanova. "Morphological and anatomical features of narrow-leaved lavender plants with prolonged conservation under in vitro genebank." BIO Web of Conferences 24 (2020): 00015. http://dx.doi.org/10.1051/bioconf/20202400015.
Full textAbstract:
Optimization of plants long-term conservation under in vitro conditions and identification of their structural and functional features during preservation is the basis for the creation of a genebank of cultured and wild plant species in vitro. The aim of our work was to study morphological and anatomical features of plants in lavender cultivar ‘Sineva’ after two years of in vitro storage at low positive temperatures. The plant material was evaluated after 24 months of conservation. A significant decrease in the linear parameters of leaves in the preserved plants was noted. Leaf shape altered from narrowly linear to oblong. With prolonged storage, the thickness of the leaf blade slightly increased. The integumentary tissues were thinner, compared with the plants cultured under standard in vitro conditions, the cuticle was not clear. The number of stomata decreased. The number of small vascular bundles decreased. The obtained data demonstrate viability of in vitro preserved explants, despite significant differences in structure, preservation of chlorophyll-containing tissues, a decrease in transpiration, and an increase of trichomes number. The stability of the vegetative organs functioning was revealed.
48
Nickel, Hubertus, Willem J. Quadakkers, and Lorenz Singheiser. "Determination of Corrosion Layers and Protective Coatings on Steels and Alloys Used in Simulated Service Environment of Modern Power Plants." Journal of Pressure Vessel Technology 128, no. 1 (October 6, 2005): 130–39. http://dx.doi.org/10.1115/1.2137769.
Full textAbstract:
The development of modern power generation systems with higher thermal efficiency requires the use of constructional materials of higher strength and improved resistance to the aggressive service atmospheres. In this paper, the following examples are discussed. (i) The oxidation behavior of 9% Cr steels in simulated combustion gases: The effects of O2 and H2O content on the oxidation behavior of 9% Cr steels in the temperature range 600-800°C showed that in dry oxygen a protective scale was formed with an oxidation rate controlled by diffusion. In contrast, that in the presence of water vapor, after an incubation period, the scale became nonprotective as a result of a change in the oxidation mechanism. (ii) The development of NiCrAlY alloys for corrosion-resistant coatings and thermal barrier coatings of gas turbine components: The increase of component surface temperature in modern gas turbines leads to an enhanced oxidation attack of the blade coating. Considerable efforts have been made in the improvement of the temperature properties of MCrAlY coatings by the additions of minor elements, such as yttrium, silicon, and titanium. The experimental results show the positive, but different influence of the oxidation behavior of the MCrAlY coatings by the addition of these minor elements. (iii) The development of lightweight intermetallics of TiAl-basis: TiAl-based intermetallics are promising materials for future turbine components because of the combination of high-temperature strength and low density. These alloys, however, possess poor oxidation resistance at temperatures above 700°C. The experimental results showed that the oxidation behavior of TiAl-based intermetallics can be strongly improved by minor additions of 1-2at.% silver. (iv) The oxide-dispersion-strengthened (ODS) alloys provide excellent creep resistance up to much higher temperatures than can be achieved with conventional wrought or cast alloys in combination with suitable high-temperature oxidation/corrosion resistance. The growth mechanisms of protective chromia and alumina scales were examined by a two-stage oxidation method with O18 tracer. The distribution of the oxygen isotopes in the oxide scale was determined by secondary ion-mass spectroscopy and SNMS. The results show the positive influence of a Y2O3 dispersion on the oxidation resistance of the ODS alloys and its effect on growth mechanisms.
49
Gatto, I., A. Saccà, A. Carbone, R. Pedicini, and E. Passalacqua. "MEAs for Polymer Electrolyte Fuel Cell (PEFC) Working at Medium Temperature." Journal of Fuel Cell Science and Technology 3, no. 3 (February 8, 2006): 361–65. http://dx.doi.org/10.1115/1.2217959.
Full textAbstract:
Recently, the CNR-ITAE activity has been addressed to the components development (electrodes and membranes) able to work in medium temperature PEFCs (80-130°C). One of the main problems to work at these temperatures is the proton conductivity loss due to a not full hydration of the membrane. For this reason a study on the modification of perfluorosulphonic membranes (like Nafion) was carried out by introducing different percentages of inorganic oxides (like SiO2, ZrO2) in the polymer matrix. These compounds have the function to improve the properties of the materials at high temperature due to their characteristics of softly proton conductor and/or hygroscopicity. The membranes were prepared by the Doctor-Blade casting technique that permits a good check of the thickness and a good reproducibility. A commercial ZrO2 was used to prepare the membranes varying the inorganic amount between 3 and 20wt%. The most promising results were obtained at 120°C with a Nafion-recast membrane loaded with a 10wt%ZrO2; a power density value of about 330mW∕cm2 at 0.6V was reached. On the other side, an optimization of the electrode structure was carried out, by introducing the inorganic oxide in the catalyst layer in order to improve the performance in the range of considered temperature. By using a spray technique, thin film electrodes with a Pt loading of 0.5mg∕cm2 in the catalyst layer, low PTFE content in the diffusion layer and a 30% Pt/Vulcan (E-Tek, Inc.) as an electro catalyst were prepared. Different amounts of ZrO2 were introduced in the catalytic layer of the electrodes to increase the working temperature and help the water management of the fuel cell. These electrodes assembled to the modified membrane have shown a better performance at higher cell temperature than standard MEA with a power density of about 330mWcm−2 at 130°C.
50
Li, Peng, Zhonghe Han, Xiaoqiang Jia, Zhongkai Mei, and Xu Han. "Analysis of the Effects of Blade Installation Angle and Blade Number on Radial-Inflow Turbine Stator Flow Performance." Energies 11, no. 9 (August 28, 2018): 2258. http://dx.doi.org/10.3390/en11092258.
Full textAbstract:
Organic Rankine cycle (ORC) is a reliable technology to recover low-grade heat sources. The radial-inflow turbine is a critical component, which has a significant influence on the overall efficiency of ORC system. This study investigates the effects of the blade installation angle and blade number on the flow performance of radial-inflow turbine stator. R245fa and toluene were selected as the working fluids in the low and high temperature range, respectively. Two-dimensional stator blades model for the two working fluids were established, and numerical simulation was conducted through Computational Fluid Dynamics (CFD) software. The results show that for low temperature working fluid R245fa, when the installation angle is 32° and blade number is 22, the distribution of static pressure along the stator blade has no obvious pressure fluctuation, and the flow loss is least. Meanwhile, the stator blade obtained the optimal performance. For high temperature working fluid toluene, when the installation angle is 28° and blade number is 32, the average outlet temperature is the lowest, while the average outlet velocity is the largest. The flow state is well and smooth, and the remarkable flow separation and shock wave are not present. Moreover, the stator blade for R245fa has a larger chord length, cascade inlet diameter, and cascade outside diameter but a lower blade number compared to toluene.