Instantaneous, quantitative measurements of molecular mixing in the axisymmetric jet near field

1999 ◽  
Vol 11 (2) ◽  
pp. 403-416 ◽  
Author(s):  
G. F. King ◽  
J. C. Dutton ◽  
R. P. Lucht
Keyword(s):  
Near Field ◽  
Molecular Mixing ◽  
Axisymmetric Jet ◽  
Quantitative Measurements

scholarly journals Giant heat transfer in the crossover regime between conduction and radiation

2017 ◽  
Vol 8 (1) ◽  
Author(s):  
Konstantin Kloppstech ◽  
Nils Könne ◽  
Svend-Age Biehs ◽  
Alejandro W. Rodriguez ◽  
Ludwig Worbes ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Near Field ◽  
Black Body ◽  
Black Body Radiation ◽  
Quantitative Measurements ◽  
Atomic Spacing ◽  
Large Heat ◽  
Vacuum Gaps ◽  
Near Field Scanning

Abstract Heat is transferred by radiation between two well-separated bodies at temperatures of finite difference in vacuum. At large distances the heat transfer can be described by black body radiation, at shorter distances evanescent modes start to contribute, and at separations comparable to inter-atomic spacing the transition to heat conduction should take place. We report on quantitative measurements of the near-field mediated heat flux between a gold coated near-field scanning thermal microscope tip and a planar gold sample at nanometre distances of 0.2–7 nm. We find an extraordinary large heat flux which is more than five orders of magnitude larger than black body radiation and four orders of magnitude larger than the values predicted by conventional theory of fluctuational electrodynamics. Different theories of phonon tunnelling are not able to describe the observations in a satisfactory way. The findings demand modified or even new models of heat transfer across vacuum gaps at nanometre distances.

Near-Field Characteristics of a Jet With a Coil-Insert Injector

2006 ◽  
Author(s):  
Hamid R. Rahai ◽  
Ayaz Alware ◽  
Daniel Carpio ◽  
Eyass Khansa
Keyword(s):  
Near Field ◽  
Axial Flow ◽  
Volume Flow ◽  
Turbulent Velocity ◽  
Time Resolved ◽  
Axisymmetric Jet ◽  
Inside Diameter ◽  
Shaped Tube ◽  
Coil Diameter ◽  
Radial Injection

Simultaneous time resolved measurements of two components of turbulent velocity and their cross moments are made at the exit and downstream of an axisymmetric jet with a coil-insert injector. The coil-insert injector is a coil shaped tube with ratios of coil diameter, pitch spacing and length to the jet inside diameter of 0.1, 1.0, and 1.5 respectively. The coil had three round holes of 0.2 mm diameter at the middle of each pitch for radial injection. The volume flow ratios of the radial blowing to the axial flow were 0.075, 0.10, 0.125, and 0.15. Results indicate that the radial blowing enhances asymmetry and increased generation of turbulence intensities at the jet outlet. However, increased entrainment and mixing between the injected flow and the axial flow reduces the asymmetry downstream, resulting in relatively constant intensities in the region with high axial momentum.

A Near-Field Microwave Probe for Quantitative Characterization of Dielectric Thin Films

2004 ◽  
Vol 838 ◽  
Author(s):  
Vladimir V. Talanov ◽  
Robert L. Moreland ◽  
André Scherz ◽  
Bin Ming ◽  
Andrew R. Schwartz
Keyword(s):  
Dielectric Constant ◽  
Semiconductor Industry ◽  
Near Field ◽  
Spot Size ◽  
Dielectric Films ◽  
Quantitative Measurements ◽  
Sample Separation ◽  
Film Dielectric ◽  
Microwave Probe ◽  
Thin Dielectric Films

ABSTRACTWe have developed a novel scanning near-field microwave probe capable of precise quantitative measurements of dielectric constant of thin dielectric films. The technique is noncontact and has a few-micron sampling spot-size. For dielectric films with k<7 and thickness down to 200 nm the probe provides precision and accuracy better than 1% and 5%, respectively. The probe is based on a balanced parallel-plate microwave transmission line operating at 4 GHz. Unlike the apertureless STM- or AFM-based schemes that have been previously employed, our “apertured” approach allows for truly quantitative measurements on a few-micron length scale with result that is insensitive to the material property outside this probing volume.We will present quantitative measurements on a variety of so-called low-k dielectric films, which are of great interest to the semiconductor industry as replacements for SiO2 in interconnect wiring. When the probe is placed in close proximity to the film under test its fringe capacitance is governed by the sample permittivity, the tip geometry, and the tip-sample separation. We measure this capacitance with a resolution down to 30 zF using a microwave resonator. Extraction of the film dielectric constant is based on an original approach providing for removal of the substrate contribution. Bulk Si and a set of variable thickness thermal oxide films are employed to calibrate the probe. There is no need to know the absolute value of the tip-sample separation for either measurement or calibration procedures; this separation must only be kept nominally the same for both measurements, which is achieved by a virtually material independent shear-force distance control.

scholarly journals Microwave Microscopy and Its Applications

2020 ◽  
Vol 50 (1) ◽  
pp. 105-130 ◽  
Author(s):  
Zhaodong Chu ◽  
Lu Zheng ◽  
Keji Lai
Keyword(s):  
Domain Walls ◽  
Materials Science ◽  
Near Field ◽  
Data Interpretation ◽  
General Purpose ◽  
Topological Order ◽  
Microwave Frequencies ◽  
Microwave Microscopy ◽  
Quantitative Measurements ◽  
Materials Research

Understanding the nanoscale electrodynamic properties of a material at microwave frequencies is of great interest for materials science, condensed matter physics, device engineering, and biology. With specialized probes, sensitive detection electronics, and improved scanning platforms, microwave microscopy has become an important tool for cutting-edge materials research in the past decade. In this article, we review the basic components and data interpretation of microwave imaging and its broad range of applications. In addition to the general-purpose mapping of permittivity and conductivity, microwave microscopy is now exploited to perform quantitative measurements on semiconductor devices, photosensitive materials, ferroelectric domains and domain walls, and acoustic-wave systems. Implementation of the technique in low-temperature and high-magnetic-field chambers has also led to major discoveries in quantum materials with strong correlation and topological order. We conclude the review with an outlook of the ultimate resolution, operation frequency, and future industrial and academic applications of near-field microwave microscopy.

Velocity and Pressure Measurements of a Mach 0.85 Axisymmetric Jet

2007 ◽  
Author(s):  
Richa Mann ◽  
Lawrence S. Ukeiley ◽  
John M. Seiner
Keyword(s):  
Velocity Field ◽  
Radial Velocity ◽  
Nozzle Exit ◽  
Near Field ◽  
Streamwise Velocity ◽  
Pressure Measurements ◽  
Pressure Transducers ◽  
Axisymmetric Jet ◽  
Two Jets ◽  
Heated Jet

The turbulent properties of a heated and unheated Mach 0.85 axisymmetric jet have been studied. The velocity field of the jet at static temperature ratios of 0.87 and 2.34, was measured in the streamwise radial plane using Particle Image Velocimetry. The velocity measurements were acquired between streamwise locations of 3D and 8D downstream from the nozzle exit. Proper Orthogonal Decomposition (POD) was applied to the velocity field using snapshot POD. The POD analysis showed that the eigenvalues of the heated jet had higher fraction of energy. The POD eigenfunctions or modes of the streamwise velocity of both jets were similar, while the POD modes of the radial velocity of both jets were very different. The POD modes of radial velocity of the unheated jet were symmetrical about the jet centerline, and the modes of the heated jet seemed to merge at the centerline. The near field pressure measurements were acquired just outside the shearlayer. A linear array of five pressure transducers was placed at 7° to the nozzle lipline, so that it would be parallel to the shear layer. The transducers in the array were spaced one diameter apart. Pressure measurements were acquired at streamwise locations between 4.25D and 10.25D from the nozzle exit. Based on the slope of the pressure spectra, the propagating events in the two jets were identified. The POD was also applied to the pressure data, and the POD modes of the two jets were compared. The peak in the amplitude of the POD mode of the heated jet was at a higher frequency. With increasing mode numbers, the peak in the POD mode of both jets shifted to a downstream location.

Experimental investigation of the fluctuating static pressure in a subsonic axisymmetric jet

2021 ◽  
pp. 1475472X2110048
Author(s):  
Songqi Li ◽  
Lawrence S Ukeiley
Keyword(s):  
Static Pressure ◽  
Near Field ◽  
Scaling Law ◽  
Pressure Fluctuations ◽  
Power Spectra ◽  
Hydrodynamic Pressure ◽  
Turbulent Velocity ◽  
Fluctuating Pressure ◽  
Jet Mixing ◽  
Axisymmetric Jet

Measuring the fluctuating static pressure within a jet has the potential to depict in-flow sources of the jet noise. In this work, the fluctuating static pressure of a subsonic axisymmetric jet was experimentally investigated using a 1/8” microphone with an aerodynamically shaped nose cone. The power spectra of the fluctuating pressure are found to follow the -7/3 scaling law at the jet centerline with the decay rate varying as the probe approaches the acoustic near field. Profiles of skewness and kurtosis reveal strong intermittency inside the jet shear layer. By applying a continuous wavelet transform (CWT), time-localized footprints of the acoustic sources were detected from the pressure fluctuations. To decompose the fluctuating pressure into the hydrodynamic component and its acoustic counterpart, two techniques based on the CWT are adopted. In the first method the hydrodynamic pressure is isolated by maximizing the correlation with the synchronously measured turbulent velocity, while the second method originates from the Gaussian nature of the acoustic pressure where the separation threshold is determined empirically. Similar results are obtained from both separation techniques, and each pressure component dominates a certain frequency band compared to the global spectrum. Furthermore, cross-spectra between the fluctuating pressure and the turbulent velocity were calculated, and spectral peaks appearing around Strouhal number of 0.4 are indicative of the footprint of the convecting coherent structures inside the jet mixing layer.

Sign in / Sign up

Export Citation Format

Share Document