The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "Arguably, one of the most important yet least understood problems in the field of classical mechanics is turbulence. Although the governing equations have been known since 1845, no theory of turbulence has emerged that can be applied universally to predict turbulent flow behavior, despite a century of study. Sir
"In order to understand the difficulty with turbulence, it is necessary to briefly lay out the relevant equations. The equations describing the motion of a fluid of constant density and small temperature fluctuations are:
".differential. u i .differential. x i = 0 .differential. u i .differential. t + u j .differential. u i .differential. x j = - 1 .rho. .differential. p .differential. x i + v .differential. 2 u i .differential. x j 2 .differential. .theta. .differential. t + u j .differential. .theta. .differential. x j = .kappa. .differential. 2 .theta. .differential. x j 2 ( 1 ) ##EQU00001##
"where u.sub.i is the instantaneous local velocity in the x.sub.i direction, .rho. is density, .theta. is instantaneous local temperature, p is instantaneous local pressure, v is kinematic viscosity, and .kappa. is thermal diffusivity. If the Reynolds number of the flow is large enough that the flow fluctuates randomly or unpredictably in time, it then is considered turbulent.
"This system of second order partial differential equations is not amenable to easy solution. Modeling, most often based on hypotheses and ad hoc assumptions, is always required to computationally solve these equations, and analytical solutions are limited to very restricted cases.
"Solving the equations directly using numerical procedures requires that all the relevant length and time scales are resolved in the numerical simulation. Unfortunately, the spatial numerical resolution required in a particular direction is approximately proportional to the ratio of the length of the energy-containing eddies, l, to the Kolmogorov length scale, .eta., where l/.eta..apprxeq.Re3/4=(ul/v).sup.3/4, and u is an rms velocity scale, and for all three spatial dimensions, the resolution goes as .about.(R.sup.3/4).sup.3. It can also be shown that the temporal resolution goes as R.sup.3/4. Therefore, the required number of grid points necessary to resolve turbulent flows within a space-time continuum goes as Re.sup.3. Because of this strong dependence on the Reynolds number, only lower Reynolds number flows can be considered for direct numerical simulation with present computational capabilities.
"Consequently one is typically left with no choice but to work with the time-averaged Navier-Stokes equations, which requires finding and testing turbulence models that properly and accurately represent the averaged pressure-strain rate term, the pressure-velocity terms, the turbulent heat flux, and the Reynolds stress.
"Unfortunately, no experimental method at present exists for the simultaneous determination of the turbulent fluctuation terms u'.sub.iu'.sub.j, the Reynolds stress term, u'.sub.ip', the pressure-velocity term, u'.sub.ip', the pressure-strain-rate, and .theta.'u'.sub.j, the turbulent heat flux term. The experimental study and measurement of these terms would allow new models to be developed that are based on experimentally-determined physics.
"In general, digital particle image velocimetry ('DPIV') is a method for measuring time-dependent velocity fields in a fluid using image acquisition techniques. The flow field is seeded with small reflective particles, and the flow field is illuminated with a bright light, typically a bright laser light sheet. Images of the seed particles' reflections are captured with an imaging system. Through known image processing techniques, the velocity field of the fluid may be accurately inferred from the motion of the particles. Conventional DPIV provides velocimetry in the flow field. For thermometry and barometry we propose to use particles that are configured to respond to both temperature and pressure, such that the time-varying and spatially-varying velocity, pressure and temperature in a flow field may be experimentally determined.
"Pressure-sensitive paint ('PSP') is known in the art, typically made of an oxygen-sensitive fluorescent or phosphorescent molecule that is incorporated into an oxygen-permeable polymer binder and dissolved in a volatile solvent to form a paint that can be easily applied to surfaces. Exposing the luminescent molecule, or luminophore, to light of an appropriate wavelength places the luminophore in an excited state. The luminophore will release its energy over time, primarily by either emitting photons of a known wavelength, or by transferring energy to diatomic oxygen molecules (known as luminescence quenching). A higher concentration of oxygen surrounding the luminophore results in higher energy transfer to oxygen, rather than emission of photons. Therefore, the light emission from the luminophore may be used to measure the local concentration of oxygen. Because the oxygen concentration of air is proportional to pressure, quantitatively measuring changes in the luminophore intensity yields a measure of the pressure.
"PSP has allowed for the non-intrusive global measurement of pressure on aerodynamic surfaces. Fast-responding PSP has been used in unsteady aerodynamic applications, such as airflow over rotor blades. Conventional PSPs contain oxygen-sensitive molecules that are held within an oxygen permeable polymer binder. When illuminated with absorbing wavelengths, the excited molecules release part of their energy as photons. However, surrounding oxygen molecules can absorb some of the emitted photons.
"For example, in a typical system a surface may be painted with a PSP. The oxygen-sensitive molecules in the PSP are substantially in a ground state until they are excited by absorbing a photon from an excitation illumination source. The excited electrons return to the ground state by radiative processes ('luminescence') and by non-radiative processes. The radiative processes include fluorescence (e.g., luminescence by direct transition from an excited state to the ground state) and phosphorescence (e.g., luminescence after intersystem crossing to a triplet system from an excited state to the ground state).
"A significant non-radiative process is luminescence quenching by oxygen, wherein surrounding oxygen molecules absorb some of the emitted photons. Luminescent quenching is proportional to the local concentration of oxygen. Hence, the luminescence observed is inversely proportional to the oxygen concentration within the surrounding atmosphere. The concentration of oxygen in the air is proportional to pressure, and therefore PSPs can be used to accurately measure pressure. In a typical implementation, one or more light sources having the appropriate wavelengths illuminate the PSP-painted surface, thereby exciting luminophores in the PSP. Charge-coupled device (CCD) cameras are used to measure the light emissions from the PSP-painted surfaces. This methodology has been successfully used in wind-tunnel applications and is now commercially available.
"The present inventors with others at the
"A state-of-the-art imaging-based measurement method and media are proposed that provide detailed short-response time, simultaneous measurements of time-evolving velocity and pressure and/or temperature fields. The measurement system is based on digital particle image velocimetry using tracer particles that enable pressure and temperature measurements. The disclosed microbeads have very short response times, making them suitable for monitoring unsteady and rapidly evolving flow fields."
As a supplement to the background information on this patent application, NewsRx correspondents also obtained the inventors' summary information for this patent application: "This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
"A microbead for measuring temperature and/or pressure with short response times includes a preformed microbead substrate that is loaded with a plurality of luminophores. A first luminophore and a second luminophore are applied to the exposed surface of the microbead substrate. The second luminophore is pressure-sensitive or temperature-sensitive. The first and second luminophores absorb light at a predetermined wavelength, and luminesce at different wavelengths.
"In an embodiment, the first luminophore is a non-pressure-sensitive reference luminophore, and the second luminophore is pressure-sensitive. For example in some embodiments the pressure-sensitive luminophore is platinum octaethylporphine, platinum meso-tetra(pentafluorophenyl)porphine, and bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl))iridium III.
"In some embodiments, the pressure-sensitive luminophore is an organometallic complex. For example, in some embodiments the pressure-sensitive luminophore is selected from platinum octaethylporphine, platinum meso-tetra(pentafluorophenyl)porphine, platinum tetra(pentafluorophenyl)porpholactone, platinum tetrabenztetraphenylporphine, palladium meso-tetra(pentafluorophenyl)porphine, ruthenium tris(4,7-diphenyl-1,10-phenanthroline)Cl2, osmium tris(bathophenanthroline)Cl2, bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl))iridium, and iridium tris(2-(beilzo[b]thiopliene-2-yl)pyridine).
"In some embodiments the pressure-sensitive luminophore is an organic complex. For example, in some embodiments the pressure-sensitive luminophore is selected from coproporphyrin I tetramethyl ester, pyrene, acridine orange, and pyrenebutyric acid.
"In an embodiment the first luminophore is a temperature-insensitive luminophore and the second luminophore is a temperature-sensitive luminophore.
"In an embodiment the first luminophore is a non-pressure-sensitive reference luminophore, and the second luminophore is a pressure-sensitive luminophore, and a third luminophore is applied to the microbead substrate that is a temperature-sensitive luminophore. For example, in some embodiments the temperature-sensitive luminophore is selected from europium thenoyltrifluoroacetonate, rhodamine base B, Eu(tta)3DEADIT, coumarin 485, and 4-pyrazolinylnaphthalic anhydride. In some embodiments the pressure-insensitive luminophore is one of meso-tetra(pentafluorophenyl)porphine, magnesium meso-tetra(pentafluoro-phenyl) porphine, coumarin 500, aluminum phthalocyanine tetrasulfonate, silicon octaethylporphine, fluorescein, rhodamine 6G, and sulforhodamine 101.
"In some embodiments the microbead substrate is a silica particle. In some embodiments the microbead substrate is one of a silicon dioxide particle, a titanium dioxide particle, an aluminum oxide particle, a calcium carbonate particle, a zinc oxide particle, a zirconium dioxide particle, and a hollow glass sphere. In some embodiments the microbead substrate is microporous or mesoporous.
"A method of making microbeads includes (i) fabricating or obtaining microbead substrates having a characteristic dimension less than two millimeters, (ii) preparing a fluid mixture that includes a plurality of luminophores that absorb energy at a predetermined wavelength, wherein the emission characteristics of at least one of the luminophores is sensitive to pressure or temperature, (iii) immersing the microbead substrates in the mixture, (iv) removing the microbead substrates from the mixture such that a portion of the luminophores in the mixture are retained on the microbead substrates, and rinsing the luminophore-retaining microbead substrates.
"In an embodiment the plurality of luminophores include at least one temperature-sensitive luminophore and at least one pressure-sensitive luminophore.
"In some embodiments the microbead substrates are immersed for an extended period of time greater than about an hour. In some embodiments the fluid mixture is stirred while the microbeads are immersed therein.
"In some embodiments the microbead substrates are silicon dioxide particles, titanium dioxide particles, aluminum oxide particles, calcium carbonate particles, zinc oxide particles, zirconium dioxide particles, or hollow glass spheres.
"In some embodiments, the pressure-sensitive luminophores may include one or more of platinum octaethylporphine, platinum meso-tetra(pentafluorophenyl)porphine, platinum tetra(pentafluorophenyl)porpholactone, platinum tetrabenztetraphenylporphine, palladium meso-tetra(pentafluorophenyl)porphine, coproporphyrin I tetramethyl ester, pyrene, acridine orange, ruthenium tris(4,7-diphenyl-1,10-phenanthroline)Cl2, osmium tris(bathophenanthroline)Cl2, pyrenebutyric acid, bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium, and iridium tris(2-(beilzo[b]thiopliene-2-yl)pyridine).
"In some embodiments the temperature-sensitive luminophore is one or more of europium thenoyltrifluoroacetonate, rhodamine base B, Eu(tta)3DEADIT, coumarin 485, and 4-pyrazolinylnaphthalic anhydride.
DESCRIPTION OF THE DRAWINGS
"The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
"FIG. 1 illustrates emission spectra detected for four different microbead configurations excited with a 365 nm LED, and showing peaks at the emission wavelengths of the loaded dyes (dye B, dye E, and dye H); and
"FIG. 2 shows plots of the pressure response time for pressure-sensitive microbeads fabricated in accordance with the two-step process disclosed herein, and compared to the response time for microbeads formed by prior art one-step methods, wherein the microbeads are excited with light from a continuous 405 nm laser."
For additional information on this patent application, see: Dabiri, Dana; Khalil, Gamal-Eddin. Simultaneous Global Thermometry, Barometry, and Velocimetry Systems and Methods. Filed
Keywords for this news article include: Iridium, Chemicals, Chemistry, Chalcogens, Zinc Oxide, Silicon Dioxide, Titanium Dioxide, Transition Elements,
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