Pierre Perrier

Mass flow rate measurements in a microchannel, from hydrodynamic to near free molecular regimes

Helium mass flow rates in a microchannel were measured, for a wide Knudsen-number range, in isothermal steady conditions. The flow Knudsen numbers, considered here, cover the range from continuum slip regime to the near free molecular regime. We used a single-channel system involved in an experimental platform more powerful than those previously used. The experimental errors and uncertainties were accurately investigated and estimated. In the continuum slip regime, it was found that the first-order approach is pertinent for Knudsen number between 0.03 and 0.3. Moreover, the slip coefficient was deduced by comparing the experiments with the theoretical first-order slip continuum approach. For Knudsen number between 0.03 and 0.7, a polynomial second-power form is proposed for the mass flow rate expression. Otherwise, the experimental results on the mass flow rate were compared with theoretical values calculated from kinetic approaches over the 0.03-50 Knudsen number range, and an overall agreement appears through the comparison. It was also found, when the Knudsen number increased, that the wall influence on measurement occurred first through the accommodation process in the transition regime followed by the wall influence through the aspect ratio in the free molecular regime.

Mass flow rate measurements in microtubes: From hydrodynamic to near free molecular regime

An experimental investigation of the reflection/accommodation process at the wall in a single silica microtube and isothermal stationary flow conditions was carried out. Several gases and different diameters were studied through various regimes. Especially for helium, the Knudsen number range was investigated as far as the free molecular regime. This kind of investigation requires a powerful experimental platform to measure mass flow rates, which we have carried out. An analytic expression of the mass flow rate, based on the Navier–Stokes equations with second order boundary condition, was used to yield the tangential momentum accommodation coefficient (TMAC) in the 0.003–0.3 Knudsen number range. Otherwise, the experimental results of the mass flow rate were compared with theoretical values calculated from kinetic approaches using variable TMAC as parameter over the 0.3–30 Knudsen number range, and an overall agreement appears through the comparison. Finally, whatever the theoretical approach the TMAC ob...

Measurements of tangential momentum accommodation coefficient for various gases in plane microchannel

Mass flow rate measurements in a single silicon microchannel were carried out for various gases in isothermal steady flows. The results obtained from hydrodynamic to near free molecular regime by using a powerful experimental platform allowed us to deduce interesting information, notably about the reflection/accommodation process at the wall. In the 0–0.3 Knudsen range, a continuum analytic approach was derived from the NS equations, associated with first or second order slip boundary conditions. Identifying the experimental mass flow rate curves to the theoretical ones the tangential momentum accommodation coefficient (TMAC) of various gases was extracted. Over the full Knudsen range [0–30] the experimental results were compared with theoretical values calculated from the kinetic approaches: using variable accommodation coefficient values as fitting parameter, the theoretical curves were fitted to the experimental ones. Whatever the Knudsen range and whatever the theoretical approach, the TMAC values are...

A simulation study of ion kinetic energies during resonant excitation in a stretched ion trap

The trajectories of ions confined individually in a commercial quadrupolar ion trap of stretched geometry and subjected to resonant excitation have been calculated. During resonant excitation, the average ion kinetic energy increases when the ion secular frequency motion is in phase with the resonant excitation and decreases when the phases are opposed. The temporal variation of ion kinetic energy when subjected to resonant excitation exhibits two cyclical forms, one with low ion kinetic energy and one with relatively high ion kinetic energy. The low ion kinetic energy cyclical form is characterized by smoothly rounded profiles at time intervals of ca. 2 ms; the high ion kinetic energy cyclical form is characterized by sharply pointed crests at time intervals of ca. 1 ms. In the low ion kinetic energy cyclical form, the maximum instantaneous ion kinetic energy attained is ca. 16 eV and corresponds to axial excursions of up to 3 mm. In the high ion kinetic energy cyclical form, the maximum instantaneous ion kinetic energy attained increases in value to in excess of 70 eV, with an axial excursion of 6.2 mm, as the resonant excitation frequency is increased. At a critical frequency, ec, there is a discontinuous change from the high to the low ion kinetic energy cyclical form. The maximum instantaneous ion kinetic energy, KEmax, varies as a simple quadratic function of the axial excursion of the ion, so that ion kinetic energy is derived from the main storage field within the ion trap. The asymmetric form observed in the experimental resonance absorption curve, obtained as a function of resonant frequency, has been reproduced qualitatively and the asymmetry can be ascribed to the transition between the two cyclical forms of the temporal variation of ion kinetic energy.

Thermal transpiration flow: A circular cross-section microtube submitted to a temperature gradient

Thermal transpiration is the macroscopic movement of rarefied gas molecules induced by a temperature gradient. The gas moves from the lower to the higher temperature zone. An original method is proposed here to measure the mean macroscopic movement of gas in the case of a long circular cross-section glass microtube onto which a gradient of temperature is applied. The mass flow rate and the thermomolecular pressure difference have been measured by monitoring the absolute pressure evolution in time at both ends of the capillary using high-speed response pressure gauges. Two gases, nitrogen and helium, are studied and three different temperature differences of 50, 60, and 70 °C are applied to the tube. The analyzed gas rarefaction conditions vary from transitional to slip regime.

Time-dependent experimental analysis of a thermal transpiration rarefied gas flow

Thermal transpiration is the macroscopic movement induced in a rarefied gas by a temperature gradient. The gas moves from the lower to the higher temperature zone. An original method is proposed here to measure the stationary mass flow rate of gas created by thermal transpiration in a micro-tube heated at its outlet. In addition, by means of a time-dependent study, parameters such as the pressure variation, the pressure variation speed, and the characteristic time of the system are analyzed. The experimental system is composed of a glass tube of circular cross section and two reservoirs positioned one at the inlet and one at the outlet of the capillary. The reservoirs are connected to two fast response time capacitance diaphragm gauges. By monitoring the pressure variation with time inside both reservoirs, it is possible to measure the macroscopic movement of the gas along the tube. Three gases, nitrogen, argon, and helium, are studied and three temperature differences ΔT = 37, 53.5, and 71 K are applied ...

A dual quadrupole ion trap mass spectrometer

Abstract Two quadrupole ion traps are used to carry out a mass spectrometer. The first concerns ion preparation with possible mass selection functions. The second is used as a mass analysis cell to obtain the secular frequency of simultaneously confined ions. After ion ejection, the secular frequencies are computed from the evolution of time-of-flight (TOF) histograms. Comments and results concerning the ion preparation are given. Then, the metrological parameters of the mass spectrometer prototype are examined: amplitude calibration, visibility, resolution, and mass range.

New operating mode of a quadrupole ion trap in mass spectrometry 4. Simulation studies

Abstract The purpose of this simulation is to understand the contribution of the parameters of the new protocol of ion mass analysis which we have developed in previous papers and to improve the data treatment in order to predict the experimental results. In this first simulation paper, we limit the study to an ion cloud of the same species. The first part describes the formalism chosen to simulate the ion creation, the ion trajectory during confinement, the ion detection by time of flight measurements and the associated treatments. The second part shows the results and explains the influence of the principal parameters. Experimentally, the initial conditions of ion confinement (position and velocity in the axial and radial directions) are not fully controlled and are estimated for the simulation. For the chosen conditions, the results agree with the experimental ones. We show the influence of the different parameters on the intensity of the signal and the uniqueness of the spectral peak, and we confirm the theoretical expressions given in previous papers for the amplitude of the peaks, the signal-to-noise ratio and the resolution. The limit of sensitivity (defined for a signal-to-noise ratio equal to 6), is obtained with statistically 0.35 ion in the trap for 1024 confinement times.

Gas flow through microtubes with different internal surface coatings

An experimental setup based on the constant volume technique is developed to measure the mass flow rate through microtubes under isothermal stationary flow conditions. Four different working gases (helium, nitrogen, argon, and carbon dioxide), and two surface materials (stainless steel and Sulfinert) are considered. The Knudsen number calculated for the experimental conditions varies from ∼10−4 (hydrodynamic regime) to ∼ 5 (transitional regime). In the reduced range (10−4−0.1) corresponding to the hydrodynamic and slip regimes, an approach based on the analytical solution of the Stokes equation subjected to a first order velocity slip boundary condition is used. The velocity slip coefficient and the tangential momentum accommodation coefficient are extracted from the experimental data of the mass flow rate using their analytical expressions. The results are summarized in the tables representing the accommodation coefficients for the corresponding gas-surface material combinations. The influence of the mol...

Rydberg electron-capture mass spectrometry of 1,2,3,4 tetrachlorodibenzo- p -dioxin

A negative-ion creation technique by Rydberg electron capture (REC) is used to ionise 1,2,3,4 tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD). Negative ions are mass-analysed by a commercial quadrupole mass spectrometer and also by a home-made mass spectrometer using a quadrupole ion trap. From spectra of 1,2,3,4-TCDD a comparison between the REC ionisation technique and two other soft ionisation techniques, electron capture chemical ionisation (ECCI) and the electron monochromator (EM), are discussed.