► Effect of gas turbine blade tip shape on the tip leakage flow and total pressure loss. ► 11 tip shapes including plane, squealer, dimpled, and newly proposed grooved tips. ► Proposed grooved tips ...showed comparable loss reduction performance with conventional double squealer tip.
Leakage flow through the turbine blade tip clearance causes a strong leakage vortex near the suction side of the blade. The leakage vortex induces aerodynamics losses and a high heat transfer coefficient on the suction side of the near blade tip region. In this study, the effects of blade tip shape on the secondary flow and total pressure loss in a turbine cascade have been investigated experimentally. A total of 11 tip shapes including plane, single or double squealer, dimpled, chamfered, and grooved tips were tested. Tip clearances of 1.5% and 2.3% of the blade span were tested. The Reynolds number, based on the blade chord and cascade exit velocity, was 2.48×105. The secondary flow and total pressure were measured by a five-hole probe at one-chord downstream from the blade trailing edge. The total pressure loss coefficient increased as the tip clearance increased, and the effect of tip shape on secondary flow and total pressure loss was significant. Among the tested tip shapes, the double squealer tip and the grooved along pressure side tip performed best and both tips showed smaller total pressure loss coefficients than that of the plane tip.
•Hybrid nanofluid flow over the porous longitudinal moving fin is addressed.•Darcy's model is implemented for the flow behavior.•Thermal radiation and natural convection effects are ...considered.•Differential system is non-dimensionalized and numerically solved via RKF.
The numerical investigation of nanoparticles embedded water based hybrid nanoliquid flow over porous longitudinal fin moving with constant velocity is carried out together with thermal radiation and natural convection condition. Darcy's model is implemented for the flow behaviour. The two types of boundary conditions are considered at the tip i.e., insulated tip fin and fin with known convective condition.
The modelled ordinary differential equation is non-dimensionalized and tackled mathematically by applying RKF (Runge Kutta Fehlberg) technique.
The parametric evaluation is carried out through graphs and interpreted physically. From obtained outcomes, it is noticed that, fin with known convective coefficient at the tip shows greater heat transfer rate than fin with insulated tip.
Mechanical scanning probe lithography using AFM tips has been applied to the fabrication of nanostructures on material surfaces. Particularly, the dynamic lithography under the AFM tapping mode is ...promising in fabricating the surface nanostructures at the width of around 20 nm. However, tip blunting and gradual atom-by-atom wear occurred during the process although the tip tapping motion has largely reduced the tip-surface interaction force and time. This study aims to investigate the blunting rate and mechanism of such AFM tips. It was found that the maximum contact stress was in the range of 0.7 to 1.0 GPa when a silicon AFM tip (initial tip radius under 20 nm) was tapped on a PMMA thin-film surface. And the contact stress was mainly attributed to the tip radius, which was the key factor to limit machinability and machining efficiency of the dynamic lithography. Furthermore, the mechanism of the tip blunting was through its plastic deformation and tip wear. A stress analysis indicated that it was the large stress gradient that contributed to the high density of wrinkles in the tips, and that ninety percent of the blunting of a tip were caused by the plastic deformation, leading to a significant increase of the tip radius.
•Explored the variation of silicon AFM tip radius caused by blunting and wear during dynamic lithography.•Identified the tip blunting mechanisms by systematic microscopy analysis.•Discovered high density wrinkles of Si tip caused by dynamic lithography.
•The application of atomic force microscopy to atom probe tips is pioneered.•Apex and shank region of 3 different atom probe tips were successfully measured.•AFM reveals the tip shape asymmetry due ...to laser tip interaction effects.•Tip shape variations are resolved in a system with low and high field materials.•This method represents an efficient and affordable routine to extract the tip shape.
For the very first time, atomic force microscopy is used to determine quantitatively the 3-dimensional shape of an atom probe tip, which is key towards improved accuracy and understanding of artefacts in atom probe tomography. We have successfully measured by atomic force microscopy the apex and shank region of 3 different atom probe tips, of which two show (severe) deviations from a hemisphere due to either non-uniform laser light absorption or the presence of two different materials. Clearly, our method which overcomes the challenge of aligning two very sharp tips on top of each other, offers new pathways to study physical mechanisms in (laser-assisted) atom probe. It represents an important step towards improved reconstruction algorithms as the image formation in atom probe tomography is based on the intricate link between the tip shape (down to the atomic level), the electric field distribution and the ions’ flight path towards the detector. Further on, present reconstruction algorithms solely account for a hemispherical tip shape, which does not hold true for most applications and results in complex artefacts. Therefore our method is an attractive novel approach to assess the 3D tip shape.
Transonic turbine blade Over-Tip Leakage (OTL) flow has significant effects on turbine efficiency and blade thermal load. At present, most of the numerical studies on OTL flow are based on ...Reynolds-Averaged Navier-Stokes (RANS) method. However, it is difficult to characterize the physical mechanisms of transonic OTL flow accurately due to the inherent shortcomings of RANS method, especially for the unsteady characteristics. To understand the underlying loss mechanisms and aerothermal characteristics of the transonic OTL flow with tip gap variations, the present study applies a Very Large Eddy Simulation (VLES) method based on Wilcox k–ω model to study a transonic cascade OTL flow. The feasibility and accuracy of the VLES turbulence model in OTL flow simulations are confirmed by numerical assessments comparison with the experimental results. The detailed flow structure and its effect on the losses of tip leakage flow are studied for different cases with varying tip gap heights. It is observed that the flow structures including separation vortex and shock waves in the gap become more complex with increasing the tip gap. The mass flow rate, pressure loss, entropy generation, and aerothermal performance for different tip gap heights are further discussed.
Although clean drinking water is a basic human need, freshwater scarcity has been identified as a major global problem of the 21st century. Nature has long served as a source of inspiration for human ...beings to develop new technology. The cactus in the desert possesses a multifunctional integrated fog collection system originating from the cooperation of a Laplace pressure gradient and the wettability difference. In this contribution, inspired by the cactus, an artificial fog collector on a large scale is first fabricated through integrating cactus spine‐like hydrophobic conical micro‐tip arrays with the hydrophilic cotton matrix. The novel cactus‐inspired fog collector can spontaneously and continuously collect, transport, and preserve fog water, demonstrating high fog collection efficiency and promising applications in the regions with drinking water scarcity. Furthermore, the present approach is simple, time‐saving and cost‐effective, which provides a potential device and new idea to solve the global water crisis.
Inspired by the fog‐harvesting behavior of the cactus, a novel fog collector in large scale is first fabricated through integrating cactus spine‐like hydrophobic conical micro‐tip arrays with a hydrophilic cotton matrix, which can spontaneously and continuously collect, transport, and preserve fog water.
A novel single-sensor method for monitoring rotating blade vibration is proposed and utilized to identify vibration parameters under the non-stationary condition. By analyzing the pulse-signal ...waveform, the blade tip displacement and vibration velocity are extracted. Then, the motion equation under the non-stationary condition is further developed to provide a theoretical basis. Finally, the optimization technology is applied to extract vibration parameters. Compared with multiple-sensor methods, the proposed method has lower installation difficulty, less equipment cost, fewer sensors, and no strict sensor layout requirement. Numerical simulations and experiments are conducted to validate the effectiveness and robustness of the proposed method. The relative error in the natural frequency does not exceed 0.1%. Additionally, errors in other parameters are less than 8% in the experiment.
•A novel single-sensor method is proposed to identify the vibration parameters of the blade under non-stationary condition.•A novel measurement approach is proposed, which is based on the blade tip vibration velocity (BTVV).•Dynamic characteristic of the non-stationary vibration is investigated by the theoretical analysis. And the formula expression of BTVV under non-stationary condition is first derived.•Simulations and the experiment are performed to validate the proposed method.
Patients with end-stage renal disease need vascular access to ensure sufficient blood flow during hemodialysis (HD). Patients who are poor candidates for arteriovenous access creation require ...long-term catheter placement. Problems such as dialysate recirculation, thrombosis, catheter-related infections, and malfunction can occur with HD catheters. Different tip designs (step, split, and symmetrical) have been developed to ameliorate the catheter-related problems. The aim of the study was to compare the efficacy and safety of split-tip, step-tip, and symmetrical-tip HD catheters.
The PubMed, Embase, Cochrane Library, and Scopus databases and the ClinicalTrials.gov registry were searched for studies published before November 2017. Studies comparing the clinical and rheologic outcomes of step-, split-, or symmetrical-tip catheters in patients undergoing HD were included in this meta-analysis. We conducted meta-analyses using random-effects models. The primary outcomes were catheter survival time and incidence of functioning catheters. The secondary outcomes were delivered blood flow rate, blood recirculation rate, and incidence of catheter-related complications.
Seven randomized controlled trials and one retrospective study with a total of 988 patients were included. No significant differences were observed in the delivered blood flow rate (weighted mean difference, −5.37 mL/min; 95% confidence interval CI, −23.75 to 13.02), incidence of catheter-related infections (risk ratio RR, 1.18; 95% CI, 0.63-2.22), or incidence of catheter-related thrombosis (RR, 1.29; 95% CI, 0.64-2.59) between step-tip catheters and advanced (both split-tip and symmetrical-tip) catheters. Moreover, a meta-analysis of the incidence of functioning catheters at 1 month, 6 months, and 12 months revealed that the outcome of step-tip catheter use was better than that of split-tip catheter use, but with a significant difference only at 6 months (RR, 1.22; 95% CI, 1.02-1.46).
None of the catheter types exhibited unique features that can enhance their suitability for application. Hence, catheters can be selected by also considering different factors, including costs, ease of procedures, expertise of the clinician, and education and preference of the patient.
An efficient sample preparation based on pipette tip microextraction that can be used for the analysis of retinol in human serum has been developed. Altogether, nine commercial pipette tips were ...compared based on recovery, sample volume, use of organic solvent, handling difficulty, duration of the preparation process, price, and greenness of the method. Retinol acetate was used as the internal standard. The extraction efficiency for both compounds was evaluated to optimize and select the best pipette tip for sample preparation, which was the WAX-S XTR pipette tip containing an ion exchanger and salt. This tip combined solid phase extraction and salting-out assisted liquid‒liquid extraction. Satisfying recoveries of 100 and 80% for retinol and retinol acetate, respectively, and good repeatability were demonstrated. The action of this pipette tip was based on the clean-up workflow in which the interferences were retained on the sorbent. The presence of residual interferences in the extracted samples did not affect the HPLC separation of compounds of interest. The simplicity of the clean-up workflow reduced the time of the sample preparation compared to the bind-wash-elute counterpart workflow. The advantages of our technique are its environmental friendliness and cost effectiveness. The selected pipette tip with an excellent microextraction efficiency enables sample preparation in both clinical research and practice.
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•Novel sample preparation technique for retinol analysis has been developed.•Pipette tips were used for microextraction of retinol and retinol acetate from human serum.•Various tips were compared in extraction efficiency and other critical aspects in sample preparation.•The WAX-S XTR tip had the best applicability in clinical research.
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