Micro-scale Analysis of High Knudsen Number Flows

To describe the degree of rarefaction，Knudsen number(Kn)is defined by the ratio of the mean free path(λ)divided by the characteristic dimension(L)of the flow。Provided that the Kn exceeds 0.01，we cannot approximate the flow as a continuum one，but have to perceive the flow as an atomic or molecular one。We call these flows with large Kn“High Knudsen number flows，”which correspond not only to low density gas flows with largeλ，but also to gas flows in micro-or nano-systems with small L.In the case of largeλ，there appear the strong non-equilibrium phenomena because of few intermolecular collisions。For extremely small L，on the other hand，the flow field is strongly influenced by interaction of molecules with a solid boundary rather than intermolecular collisions.Experimental analyses of thermo-fluid phenomena related to the high Knudsen number flows need the optical measurement techniques based on atoms or molecules，such as their emission and absorption of photons.Howe……More ver，the experimental techniques are behind in development compared with the molecular simulation techniques.In this study，I introduce a resonantly enhanced multiphoton ionization(REMPI)method and a pressure sensitive molecular film(PSMF)。We established the 2R+2N_2-REMPI technique，in which nitrogen molecules are ionized by two steps，i.e.，the first step from the ground state to the resonance state(2photons)and the second step from the resonance state to the ionization state(2photons)。The nitrogen ions are detected as a signal and its spectra depending on the wavelength of an irradiated laser beam are analyzed to measure the rotational temperature through the Boltzmann plot。The 2R+2N_2-REMPI technique is applied to measure the rotational population in supersonic free molecular nitrogen flows and obtain the non-Boltzmann rotational distribution for P_0·D=15Torr mm(Where P_0is The Source Pressure And D Is The Nozzle Diameter)。The pressure-sensitive paint(PSP)has potential as a diagnostic tool for pressure measurement in the high Knudsen number regime because the principle of the pressure sensitive paint(PSP)technique is based on oxygen quenching of luminescence。Aiming to apply the PSP to micro devices，we have adopted Langmuir-Blodgett(LB)technique to fabricate pressure sensitive molecular films(PSMFs)using PdOEP and PdMP，and have tested these PSMFs to evaluate the feasibility of the pressure measurement around micro devices。Less：Less

To describe the degree of rarefaction, Knudsen number (Kn) is defined by the ratio of the mean free path (λ) divided by the characteristic dimension (L) of the flow. Provided that the Kn exceeds 0.01, we cannot approximate the flow as a continuum one, but have to perceive the flow as an atomic or molecular one. We call these flows with large Kn "High Knudsen number flows," which correspond not only to low density gas flows with large λ, but also to gas flows in micro- or nano-systems with small L. In the case of large λ, there appear the strong non-equilibrium phenomena because of few intermolecular collisions. For extremely small L, on the other hand, the flow field is strongly influenced by interaction of molecules with a solid boundary rather than intermolecular collisions. Experimental analyses of thermo-fluid phenomena related to the high Knudsen number flows need the optical measurement techniques based on atoms or molecules, such as their emission and absorption of photons. Howe … More ver, the experimental techniques are behind in development compared with the molecular simulation techniques.In this study, I introduce a resonantly enhanced multiphoton ionization (REMPI) method and a pressure sensitive molecular film (PSMF). We established the 2R+2 N_2-REMPI technique, in which nitrogen molecules are ionized by two steps, i.e., the first step from the ground state to the resonance state (2 photons) and the second step from the resonance state to the ionization state (2 photons). The nitrogen ions are detected as a signal and its spectra depending on the wavelength of an irradiated laser beam are analyzed to measure the rotational temperature through the Boltzmann plot. The 2R+2 N_2-REMPI technique is applied to measure the rotational population in supersonic free molecular nitrogen flows and obtain the non-Boltzmann rotational distribution for P_0・D=15 Torr mm (where P_0 is the source pressure and D is the nozzle diameter). The pressure-sensitive paint (PSP) has potential as a diagnostic tool for pressure measurement in the high Knudsen number regime because the principle of the pressure sensitive paint (PSP) technique is based on oxygen quenching of luminescence. Aiming to apply the PSP to micro devices, we have adopted Langmuir-Blodgett (LB) technique to fabricate pressure sensitive molecular films (PSMFs) using PdOEP and PdMP, and have tested these PSMFs to evaluate the feasibility of the pressure measurement around micro devices. Less