Low-pressure Gas Flow Research Articles

Numerical simulation study on growth rate and gas reaction path of InN-MOCVD with Close-Coupled showerhead reactor

Numerical study on the influence of the carrier gas (H2 and N2), V/III ratio, inlet temperature, and pressure on gas reaction path and growth rate of indium nitride (InN) thin film in metal–organic chemical vapor deposition (MOCVD) with close-coupled showerhead (CCS) reactor was conducted. It was found that the concentrations of precursor for InN film and nanoparticle determine the growth rate and gas reaction path. InN exhibits greater difficulty in undergoing pyrolysis reactions compared to AlN and GaN. Under the conditions of this study, the gas reaction path of InN-MOCVD be dominated by adduct/amide formation path. When H2 is used as the carrier gas, the effect of H radicals on gas reactions is relatively minor, while the effect of NH2 radicals generates more nanoparticles, and significant changes in flow fields are observed compared to using N2 as the carrier gas. Under the conditions of low V/III ratio, low inlet temperature, high pressure, and low gas flow rate, the growth rate is relatively high, but the growth uniformity is decreased. There are different reasons for the effects of the above parameters, such as, altering TMIn flow to change V/III ratio and precursor concentration, varying temperature gradient due to changes in inlet temperature, and increased the particle collision frequency and residence time due to high pressure and low gas flow rate.

Chitosan-TPP microcapsules for controlled drug release

Production of chitosan/sodium tripolyphosphate (CS/TPP) microcapsules via spray drying involves atomizing an emulsion containing CS, TPP, acetic acid (AcOH), and folic acid (FA) into fine droplets exposed to high-temperature, low-pressure gas flow. Solvent evaporation within the drying chamber leads to solid particle formation. Spray drying is valuable for creating solid CS/TPP microcapsules. Precise equipment parameter adjustments, like inlet temperature and gas flow rate, enable the study of microcapsule morphology, size, and properties. This adaptability allows for customization to specific pH dissolution ranges. The production method's impact on CS/TPP microcapsules was studied by modifying spray drier parameters, including inlet temperature and aspirator pressure, to enhance understanding of their behavior in solution under varied production conditions.
 In chitosan delivery systems, various approaches can encapsulate drug agents like folic acid, an analog to the cancer treatment drug methotrexate. Agents can be added to the chitosan solution pre-crosslinking, incorporated into gelation-inducing agents pre-mixing with chitosan, or included in the crosslinking mixture. Experiments were conducted to assess CS/TPP microcapsules' behavior when encapsulating agents like folic acid. Release profiles were analyzed to understand their drug delivery capabilities and potential as controlled release carriers.

Low-pressure gas flow properties of sintered stainless steel microporous media

The gas flows through the low permeable porous media are of great interest, especially in vacuum technology for filtering, separation processes, protection, and flow control. They can combine a high mass flow rate and a high level of rarefaction. The transient experimental technique, developed previously for the mass flow rate measurements through the microchannels [Rojas Cardenas et al., Phys. Fluids 23, 031702 (2011)], is generalized to obtain the permeability and conductance directly from the pressure variation measurements. The present experimental methodology, allowing for step by step data verification, leads to higher accuracy than the similar and commonly used method such as “pulse-decay” techniques [W. F. Brace and R. J. Martin, Int. J. Rock Mech. Min. Sci. 5, 415–426 (1968)]. The measured data are fitted according to the exponential function with the pressure relaxation time as a single fitting parameter. The permeability and conductance of the sintered stainless steel microporous medium are measured for different gases. By using the methodology proposed by Johansson et al. [Int. J. Heat Mass Transfer 142, 118412 (2019)], the characteristic pore size of the sample was determined to be equal to 1.5 micrometers. It was found that free molecular flow constant conductance is achieved at a pressure below 30 mbar for helium. This property makes this kind of porous media particularly suitable as a leak element by taking advantage of the constancy of conductance in the free molecular flow regime, for example, for calibration of ionization gauges or mass spectrometers [Yoshida et al., Measurement 45(10), 2452–2455 (2012)].

Comparison of primary gas flow standard spanning the range from 2 mL/min to 10 L/min

Main textThe CCM.FF-K6.2017 comparison was organised for the purpose of determination of the degree of equivalence of the national standards for low-pressure gas flow measurement over the range 2 mL/min to 10 L/min. Four molbloc-L flow elements and a molbox1+ were used as the transfer standards.Ten laboratories from three RMOs participated between August 2017 and January 2020 - EURAMET: INRIM (Italy); LNE (France); PTB (Germany); METAS (Switzerland); CMI (Czech Republic); SIM: NIST (USA); APMP: NMIJ/AIST (Japan); KRISS (Korea); NMIA (Australia); CMS (Chinese Taipei). The measurements were provided at prescribed reference pressure and temperature conditions. All results were used in the determination of the key comparison reference value (KCRV) and the uncertainty of the KCRV. The reference value was determined at each flow separately following the procedure presented by M G Cox [1]. The degree of equivalence with the KCRV was calculated for each flow and laboratory. This KCRV can now be used in further regional comparisons.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The Traceability Improvement and Comparison of Bell Prover as the Indonesian National Standard of Gas Volume Flow Rate

Traceability is urgent to guarantee the truth of measurement, particularly for National Standard. Although a bell prover facility has established as the national low pressure gas flow standard of Indonesia since 2008, the measurement capability (15 to 1400 L/min, U95 = 0.20%) of the bell prover has not been traceable to SI Units. Moreover, displacement values provided by the bell prover’s manufacturer by rotary encoder method are still used. The limit detector by optical sensor to measure displacement is worthy to achieve dimensional traceability which can be switched by ultrasonic sensor for reasonable solution. The aim of this study is to improve the traceability of the bell prover by reasonable solution and then validate the gas volume flow rate measurement by inter-laboratory comparison. The Center for Measurement Standards (CMS), Industrial Technology Research Institute (ITRI), was invited to participate in the bilateral comparison, and a gas turbine flow meter was used as the transfer standard. The bell prover has been successfully traceable to SI units, particularly displacement measurement through flying start/stop method by limit of ultrasonic sensor (250 to 1200 L/min, U95 = 0.80% passing assessment report). Despite having larger uncertainty than manufacturer specification, the results are better for more in of layer comparison. Because the effect of turbine drift should be a concern, the gap of measurement time for inter-laboratory comparison is recommended to minimize as many as possible. Furthermore, the measurement range of bell prover should be reduced as reasonability purpose.

Mid-Infrared Polarization Spectroscopy Measurements of Species Concentrations and Temperature in a Low-Pressure Flame.

We demonstrate quantitative measurements of methane (CH4) mole fractions in a low-pressure fuel-rich premixed dimethyl ether/oxygen/argon flat flame (Φ = 1.87, 37 mbar) using mid-infrared (IR) polarization spectroscopy (IRPS). Non-intrusive in situ detection of CH4, acetylene (C2H2), and ethane (C2H6) in the flame was realized by probing the fundamental asymmetric C–H stretching vibration bands in the respective molecules in the spectral range 2970–3340 cm−1. The flame was stabilized on a McKenna-type porous plug burner hosted in a low-pressure chamber. The temperature at different heights above the burner (HAB) was measured from the line ratio of temperature-sensitive H2O spectral lines recorded using IRPS. Quantitative measurements of CH4 mole fractions at different HAB in the flame were realized by a calibration measurement in a low-pressure gas flow of N2 with a small admixture of known amount of CH4. A comprehensive study of the collision effects on the IRPS signal was performed in order to quantify the flame measurement. The concentration and temperature measurements were found to agree reasonably well with simulations using Chemkin. These measurements prove the potential of IRPS as a sensitive, non-intrusive, in situ technique in low pressure flames.

Development of MEMS-based thermal mass flow sensors for high sensitivity and wide flow rate range

In the natural gas trade, mass flow metering is preferred to volume flow metering. In order to improve the measurement performance related to sensitivity within wide flow rate range of the mass flow meter, a novel design of a MEMS-based thermal mass flow sensor is proposed. To determine of the correlation between the sensing performance and geometry of sensor components, in this case the heater and the thermopile, models with various designs were fabricated using MEMS technology. Flow characteristic tests of the fabricated models were conducted in the low pressure gas flow standard system of KRISS. The effect of the distance ratio between the heater and thermopiles on the measurement performance of the thermal flow sensor was examined according to the flow rate range. The results presented that the basic models with the different distance ratio show different sensitivity characteristics. The non-uniform model proposed in this study show high sensitivity in both low and high flow rate region compared with models with a certain distance ratio.

Evaluation of the propagation time difference in low-pressure city gas flow using a clamp-on ultrasonic flowmeter

In this paper, we evaluate the suitability of clamp-on ultrasonic flowmeters for measuring gas flow in low-pressure city gas tubing. Thus, the propagation time difference method was used to measure the gas flow velocity in an actual building. The measured gas pressure was almost atmospheric pressure. It was possible to confirm the propagation of the ultrasonic wave through the gas flow inside the metal pipe, with the propagation time difference being measured through this gas flow. The mean measured propagation time difference was found almost identical to the corresponding theoretical value. These results are useful for developing clamp-on ultrasonic flowmeters for low-pressure city gas monitoring.

A low pressure cryogenic trap for cleaning of feed stream in dilution refrigerator

Cryogenic traps are frequently used for removing impurities from gases and conventionally use the cryo-adsorption technique with activated carbon adsorbents. Such purification instruments are often operating at high pressure to aid the adsorption process to its maximum extent. In a system which operates at low pressure and low gas flow rates the residual concentration of the adsorptive gas is determined only by its vapor pressure in relation to the total pressure. In a dilution refrigerator the process gas circulates at sub-atmospheric pressure and it becomes a challenge to remove impurities by cryogenic trap at substantially low pressures. In this paper we describe a simple one column liquid nitrogen cooled cryogenic trap for entrapment of O2 and N2 from the circulating process gas. Two different types of adsorbents, LiLSX and activated carbon were investigated using volumetric adsorption approach and break-through studies.

Numerical interpretation of gas-injection tests at different scales

Abstract To investigate gas-migration processes in saturated low-permeability argillaceous rocks, gas-injection tests under different injection pressures were carried out at different scales: on core samples at the laboratory scale; in the packed-off section of boreholes at the borehole scale (HG-B); and in the sealed microtunnel at the tunnel scale (HG-A) – a 1:2 scale experiment at the Mont Terri Rock Laboratory, Switzerland. All three tests at the Mont Terri Rock Laboratory involved Opalinus Clay. A fully coupled hydromechanical model has been developed that takes account of elastic and plastic anisotropies, anisotropic two-phase flow based on the van Genuchten function, and permeability changes when evaluating the experimental data. Two different flow regimes were studied: two-phase flow under low gas-injection pressure and dilatancy-controlled gas flow under high gas-injection pressure above the confining pressure in the laboratory experiment or the minimal principal stress in situ . When dealing with the dilatancy-controlled gas-flow regime, special consideration was made by applying two permeability approaches in which (i) the permeability change was pore-gas-pressure dependent and (ii) where the permeability change was deformation dependent. Using the parameter values determined by laboratory data, the in situ borehole tests obtained under well-defined hydromechanical conditions could be analysed accordingly. The gas-flow regime in large-scale experiments, as in the case of HG-A, is mainly governed by experimental circumstances: in this case, the excavation-induced fractures around an opening with a permeability four order of magnitude higher than that in the undisturbed rock mass.

Final Report: Comparison of the primary (national) standards of low-pressure gas flow

The EURAMET.M.FF-K6 comparison was organized for the purpose of determination of the degree of equivalence of the primary (national) standards for low-pressure gas flow measurement over the range (2 to 100) m3/h and was performed simultaneously with CCM.FF-K6.2011 with the same transfer standard. A rotary gas meter G65 was used as a transfer standard. The measurements were provided by prescribed reference conditions.Fifteen laboratories from EURAMET participated in this key comparison - SMU, Slovakia; PTB, Germany; CEM, Spain; LNE-LADG, France; VSL, Netherlands; CMI, Czech Republic; BEV, Austria; MKEH, Hungary; GUM Poland; SP, Sweden; METAS, Switzerland; DMDM, Serbia; TUBITAK-UME, Turkey; EIM, Greece; IMBiH, Bosnia-Herzegovina.The EURAMET.M.FF-K6 is linked to the CCM.FF-K6.2011 by correcting the results of three linking laboratories (Slovakia SMU, Germany PTB and France LNE LADG). This correction provides an estimate of what would have been the result from the EURAMET.M-FF-K6 participants, if they had actually participated in CCM.FF-K6.2011.According to the evaluation 93.7 % of the results were consistent with KCRV, 3.4 % of the results were in the warning level and 2.9 % of the results were inconsistent.The results of this comparison can be used for review of the CMC tables.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Final report on CIPM key comparison CCM.FF-K6.2011: Comparison of the primary (national) standards of low-pressure gas flow

The comparison CCM.FF-K6.2011 was organized for the purpose of determination of the degree of equivalence of the national standards for low-pressure gas flow measurement over the range (2 to 100) m3/h. A rotary gas meter was used as a transfer standard. The measurements were provided at prescribed reference conditions. Eleven laboratories from four RMOs participated in this key comparison—EURAMET: PTB, Germany; SMU, Slovakia; LNE-LADG, France; SIM: NIST, USA; CENAM, Mexico; APMP: NMIJ AIST Japan; KRISS, Korea; NMI, Australia; NIM, China; CMS, Chinese Taipei; COOMET: GP GP Ivano-Frankivs'kstandart-metrologia, Ukraine and all participants reported independent traceability chains to the SI. All results were used in the determination of the key comparison reference value (KCRV) and the uncertainty of the KCRV. The reference value was determined at each flow separately following procedure A presented by M G Cox. The degree of equivalence with the KCRV was also calculated for each flow and laboratory. All reported results were consistent with the KCRV. This KCRV can now be used in the further regional comparisons.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

A sensor-equipped microchannel system for the thermal characterization of rarefied gas flows

This paper presents a new MEMS-based experimental design with an integrated measuring system. The foreseen application is the measurement of the temperature profile for pressure driven slip flow of gases in microchannels, but it could also be applied to the characterization of gas flows in other flow regimes. Rarefied gas flow characterization represents a typical case where a local analysis is required to fully understand the systems physical properties. The experimental setup for the low pressure gas flow application is described. The fully integrated measuring system provides temperature sensors, manufactured on top of thin film membranes to retrieve temperature differences between the inner part of a microchannel and its wall. Miniaturized thermistors to monitor the reference substrate temperature have been manufactured, too. The sensor fabrication processes as well as the proposed calibration procedures are reported. Finally, preliminary results for the validation and characterization of the integrated measuring system are given.

Computational Analysis and Studies on Differential Ejector

Studies on differential ejector configuration have been carried out with a view to obtain the optimal entrainment of low pressure gas flow by injecting the motive gas at an appropriate pressure and angle of injection. The length of mixing has been kept constant in one case and varied in another to get results for optimal angle of ejection (between 0 to 90 degrees) for varying mass flow rates between 0.02kg/s and 0.08kg/s, stagnation pressures between 200kPa to 2500kPa and conduit diameter being 50mm. The predictions made are validated employing a versatile code Fluent in 2-d, viscous, turbulent flow formulation. Since the flow is supersonic, compressible form of SIMPLE algorithm is used along with a first order upwinding scheme for correctly predicting the properties inside the flow domain. Various curves have been plotted depicting variation of Mach number with angle of ejection and Mach number with mass flow rate for various pressures and angles of ejection.

Establishment and verification of a primary low-pressure gas flow standard at NIMT

This paper presents the establishment and verification of a primary low-pressure gas flow standard with the capacity of 0.005 L/min to 24 L/min (at 23 °C and 101.325 kPa), newly established at National Institute of Metrology of Thailand (NIMT). This facility is a mercury-sealed piston prover consisting of three precision-machined glass cylinders. Flow measurement can be carried out manually or semi-automatically. The electronics were installed in a separate console to minimize their thermal impact on the gas temperature. Special care was taken in designing the facility to ensure sound and representative gas pressure and temperature measurement. The relative expanded uncertainty of mass flow measurement was evaluated to be less than 0.13%. To verify the measurement capability and performance of the new facility, a bilateral comparison with the piston prover at Center for Measurement Standards (CMS), Taiwan was conducted. The transfer standard used was a set of three critical flow venturis with dedicated thermometers. Eight flow rates of dry air ranging from 42 mL/min to 14.5 L/ min at 0 °C and 101.325 kPa (0.055 g/min to 18.87 g/min) were tested. Comparison results showed that the E n values for the flow measurements at NIMT with reference to CMS were all well less than unity, demonstrating good agreement between the two participants.

Final report on APMP key comparison for low-pressure gas flow: APMP.M.FF-K6

This report presents the results of a key comparison of low-pressure gas flow conducted between six participating institutes during the period January 2007 to August 2008 within the framework of the Asia Pacifica Metrology Program (APMP). A set of four critical flow venturis with dedicated, redundant pressure and temperature sensors was the transfer standard at flows between 4 g min−1 and 183 g min−1. The pilot institute was the National Measurement Institute of Japan (NMIJ), which together with KRISS acted as link laboratories to the CCM.FF-K6 comparison.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Electric spark discharge as an ultrasonic generator in flow measurement situations

In this paper, a gap discharge approach to create acoustic signals for ultrasonic low pressure gas flow measurements is investigated. The objective is to develop an ultrasonic gas flow meter system that is capable of operation in extreme industrial environments. These environments might have extremely high temperatures (1200 °C), moisture, steam, dust, low gas pressure and large transmission distances. Most other types of ultrasonic transducers found show sensitivity to such conditions: their operation suffers, or they may even stop functioning if exposed to such environments. The development of new transducer technology is therefore crucial to allow ultrasonic flow measurements in extreme industrial environments. In this paper, the gap discharge emitter is evaluated as a candidate to be used in these applications. Its capabilities as a sound source are investigated, and its impact on flow meter performance is estimated. It can be concluded that, despite the uncertainties it introduces to a flow meter system, it stands out as a strong candidate to be used as an acoustic emitter in a gas flow meter system for extreme environments.

Characteristics of surface glow discharge in a low-pressure supersonic gas flow

Kinetic particle-in-cell simulations are performed to examine the characteristics of the surface glow discharge in a supersonic nitrogen flow. The gas pressure is varied between 100 and 500 mTorr; the applied voltage, between −500 and −1000 V. The analysis focuses on the effect of boundary conditions at the dielectric barrier surrounding the electrodes on the electron energy distribution function. The potential on the dielectric is found by using a local balance condition for the electron and ion currents to the surface. The results of self-consistent simulations show that a negative potential on the dielectric substantially reduces the rate of high-energy electron loss from the bulk plasma and thus significantly changes the ionization rate, as well as plasma parameters and configuration.

Performance of a Horizontally Mounted Venturi in Low-pressure Wet Gas Flow

The performance of a Venturi tube used in wet gas flow have been explored mainly under higher-pressure condition, but very often, low-pressure test exists in some oil and gas fields in Tianjin Dagang Oil and Gas Field in China. In this study, the performance of horizontally mounted Venturi meters in low-pressure wet gas flow is discussed. Three 50 mm Venturi meters were tested systematically, with β values of 0.4048, 0.55 and 0.70, the operation pressure of 0.15 MPa, 0.20 MPa, 0.25 MPa, the gas densiometric Froude number from 0.6 to 2.0, the modified Lockhart-Maretinelli parameter from 0.0022 to 0.06, and the ratio of the gas liquid mass flow rate from 0.5 to 0.99. The effects of modified Lockhart-Maretinelli parameter, pressure, gas densiometric Froude number, diameter ratio, and gas-liquid mass flow rate ratio to the Venturi tube are analyzed with new independent data. Furthermore, low-pressure performance was compared with that under high pressure.

CIPM key comparison for low-pressure gas flow: CCM.FF-K6

A key comparison between seven national metrology institutes in the area of low-pressure gas flow was organized by the Comité International des Poids et Mesures (CIPM) and the Working Group for Fluid Flow. A set of eight critical flow venturis with dedicated, redundant pressure and temperature sensors was used as the transfer standard at flows between 4.4 g/min and 260 g/min. Preliminary testing in the pilot lab determined temperature operating bounds and corresponding uncertainties. The transfer standard contributed a standard uncertainty of <0.026% to the comparison, primarily due to environmental temperature effects, the pressure sensors, and gas properties (the critical flow function and molecular mass of moist air). Redundant measurements by the transfer standard and the star pattern testing were valuable for maintaining low transfer standard uncertainty. The results supported equivalence between the labs with the largest difference between any two participants at any of the flows tested being 0.308%.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).