Tomohide Niimi

Application of pressure-sensitive paints to low-pressure range

The pressure-sensitive paint (PSP) technique has potential as a powerful diagnostic tool for measurements in the high Knudsen number regime because it is based on luminescence of molecules. Three types of PSP [two composed of organic dye and polymer (luminophore/binder), platinum octaethylporphyrin (PtOEP)/silicone polymer (GP197) and platinumtetrakis (pentafluorophenyl) porphyrin (PtTFPP)/poly[1-(trimethylsilyl)-propyne] [poly(TMSP)], and the other ruthenium II tris (4,7-diphenyl-1, 10-phenanthrolin chloride (Bath-Ru) adsorbed on anodized aluminum] are applied to the rarefied gas flow mainly lower than 150 Pa (about 1 torr) to examine fundamental properties, such as pressure/temperature sensitivity, time response of luminescence, and so on

Experimental detection of rotational non-Boltzmann distribution in supersonic free molecular nitrogen flows

In the present study, we measure the rotational population in supersonic nitrogen-free jets using a resonantly enhanced multiphoton ionization (REMPI) method [Chem. Phys. Lett. 115, 492 (1985)], which is not influenced by secondary electrons, unlike the electron beam method. Nitrogen ions are detected as a REMPI signal and its spectra, depending on the wavelength of an irradiated laser beam, are analyzed to measure rotational temperature through the Boltzmann plot. Nitrogen gas expands into a vacuum chamber from a sonic nozzle with a D=0.50mm diameter, setting P0∙D (where P0 is the source pressure), depending inversely on the nozzle Knudsen number, at 15Torrmm or lower. For P0∙D=15Torrmm, the rotational temperature distribution along the centerline of the jet, measured by using only the linear portion of the Boltzmann plot lying at smaller rotational quantum numbers, coincides with Marrone’s data [Phys. Fluids 10, 521 (1967)] measured by electron beam fluorescence, and the rotational relaxation rate ZR ca...

Pressure Sensitive Paint Suitable to High Knudsen Number Regime

Pressure sensitive paint (PSP) techniques have the capability to be applied to high Knudsen number flows, such as low density gas flows, micro-flows, and so on. In this study, to inspect the feasibility of PSP for measurement of pressure on a solid surface in high Knudsen number flows, the fundamental properties of PSPs are examined, especially in the range of pressure below 130 Pa (about 1 Torr). As a result, it is clarified that the PSP using poly(TMSP) as a binder and using PdOEP or PdTFPP as a luminophore has very high sensitivity to oxygen pressure under low pressure conditions below 130 Pa. Pressure sensitivity to nitrogen monoxide is also examined for the above PSPs, and it is clarified that PdTFPP bound by poly(TMSP) has very high sensitivity while PdOEP has very low sensitivity to nitrogen monoxide. The combination of the PdTFPP-based PSP and NO-LIF technique enables composite measurement of flow field structures and surface pressure in the high-Kn regime.

Molecular number flux detection using oxygen sensitive luminophore

Experimental analyses of thermofluid phenomena with a high Knudsen number, related to low-density gas flows or nanotechnologies, need the measurement techniques based on atoms or molecules, such as emission and absorption of photons. Because the principle of the pressure sensitive paint (PSP) technique is based on oxygen quenching of luminescence, the technique has the capability to be applied to high Knudsen number flows such as microflows and low-density gas flows. In this study, to inspect the feasibility of PSP for measurement of pressure on a solid surface in high Knudsen number flows, fundamental properties of three types of PSP [palladium tetrakis (pentafluorophenyl) porphyrin, palladium octaethylporphyrin (PdOEP), and platinum tetrakis (pentafluorophenyl) porphyrin bound by poly[1–(trimethylsilyl)-1–propyne] (poly(TMSP))] are examined especially in the range of pressure below 130 Pa (about 1 Torr). As an application of PSP to high Knudsen number flows, we measure the pressure distribution on a jet...

Application of PSP to Low Density Gas Flows

Recently optical pressure measurement systems using pressure sensitive paints (PSP) have actively developed to measure continuous pressure distributions on solid surfaces. However, the pressure range has been almost limited above 130 Pa (about 1 Torr) and there is no application to lower pressure range because the pressure sensitivity seems to be not so high in that range. In this study, we have applied three types of PSP [two types are composed by organic dye and polymer (luminophore/binder); PtOEP/GP197 and PtTFPP/poly(TMSP), and another one is Bath-Ru adsorbed on anodized aluminum] to the rarefied gas flow mainly lower than 130 Pa and examine those fundamental properties such as pressure sensitivity, leading to selection of the most suitable PSP among them for the low-pressure range. Since PtTFPP/poly(TMSP) has the highest sensitivity, it is applied successfully to the measurement of the two-dimensional pressure distribution on the surface interacting with a low density supersonic free jet.

Experimental Analyses of Flow Field Structures around Clustered Linear Aerospike Nozzles

An aerospike nozzle has been expected as a candidate for an engine of a reusable space shuttle to respond to growing demand for rocket‐launching and its cost reduction. In this study, the flow field structures in any cross sections around clustered linear aerospike nozzles are visualized and analyzed, using laser induced fluorescence (LIF) of NO seeded in the carrier gas N2. Since flow field structures are affected mainly by pressure ratio (Ps/Pa, Ps: the source pressure in a reservoir, Pa: the ambient pressure in the vacuum chamber), the clustered linear aerospike nozzle is set inside a vacuum chamber to carry out the experiments in the wide range of pressure ratios from 75 to 200. Flow fields are visualized in several cross‐sections, demonstrating the complicated three‐dimensional flow field structures. Pressure sensitive paint (PSP) of PtTFPP bound by poly‐IBM‐co‐TFEM is also applied to measurement of the complicated pressure distribution on the spike surface, and to verification of contribution of a t...

Organic Electroluminescent Sensor for Pressure Measurement

We have proposed a novel concept of a pressure sensor called electroluminescent pressure sensor (ELPS) based on oxygen quenching of electroluminescence. The sensor was fabricated as an organic light-emitting device (OLED) with phosphorescent dyes whose phosphorescence can be quenched by oxygen molecules, and with a polymer electrode which permeates oxygen molecules. The sensor was a single-layer OLED with Platinum (II) octaethylporphine (PtOEP) doped into poly(vinylcarbazole) (PVK) as an oxygen sensitive emissive layer and poly(3,4-ethylenedioxythiophene) mixed with poly(styrenesulfonate) (PEDOT:PSS) as an oxygen permeating polymer anode. The pressure sensitivity of the fabricated ELPS sample was equivalent to that of the sensor excited by an illumination light source. Moreover, the pressure sensitivity of the sensor is equivalent to that of conventional pressure-sensitive paint (PSP), which is an optical pressure sensor based on photoluminescence.

Electric Conductive Pattern Element Fabricated Using Commercial Inkjet Printer for Paper-Based Analytical Devices

Herein, we proposed the addition of an inkjet-printed conductive pattern to paper-based analytical devices (PADs) in order to expand their applications. An electric conductive pattern was easily, quickly, and inexpensively fabricated using a commercial inkjet printer. The addition of a printed electric element will enhance the applications of PADs without the loss of properties such as cost efficiency, disposability, and portability. In this study, we applied an inkjet-printed heater to a piece of paper and investigated its characteristics. The use of the heater as a valve, concentrator, and heat source for chemical reactions on PADs was investigated. Previously, these functions were difficult to realize with PADs. The inkjet-printed heater was used as a valve and concentrator through evaporation of the working fluid and solvent, and was also found to be useful for providing heat for chemical reactions. Thus, the combination of printed electric circuits and PADs has many potential applications.

Polymer-Particle Pressure-Sensitive Paint with High Photostability

We propose a novel fast-responding and paintable pressure-sensitive paint (PSP) based on polymer particles, i.e. polymer-particle (pp-)PSP. As a fast-responding PSP, polymer-ceramic (PC-)PSP is widely studied. Since PC-PSP generally consists of titanium (IV) oxide (TiO2) particles, a large reduction in the luminescent intensity will occur due to the photocatalytic action of TiO2. We propose the usage of polymer particles instead of TiO2 particles to prevent the reduction in the luminescent intensity. Here, we fabricate pp-PSP based on the polystyrene particle with a diameter of 1 μm, and investigate the pressure- and temperature-sensitives, the response time, and the photostability. The performances of pp-PSP are compared with those of PC-PSP, indicating the high photostability with the other characteristics comparable to PC-PSP.

Molecular Dynamics Study on Rare Gas‐Graphite (0001) Surface Scattering

We have investigated the scattering of a hyperthermal rare gas atom from a graphite (0001) surface using molecular dynamics simulations. To clarify the mass effect of incident gas atoms on gas‐surface scattering, angular flux and energy ratio distributions were obtained and compared at an incidence energy of 1.5 eV, an incidence angle of 35° and a surface temperatures of 300 K. From molecular dynamics simulations, scattering angular flux and energy ratio distributions show quite similar tendencies and the mass ratio is found to be constant independent of gas species, except He. They are well modeled by the Hard‐Cube model. On the contrary, He shows different scattering behavior which can be modeled by the Washboard model. Since He is small in mass and size, the scattering at hyperthermal incidence energies is strongly affected by the static and dynamic surface corrugation.