Constant pressure primary flow standard for gas flows from 0.01 cm3/min to 100 cm3/min (0.007–74 μmol/s)

We describe a flow standard for gas flows in the range from 0.01 sccm to 100 sccm with a relative standard uncertainty (68% confidence) of 0.03% at 1 sccm (1 sccm≡1 cm³/min of an ideal gas at 101325 Pa and 0 °C ≈ 0.74358 μmol/s). The flow standard calibrates a secondary meter by withdrawing a piston from a cylinder held at constant pressure P while gas flows from the secondary meter into the cylinder. The flow standard can operate anywhere in the range 10 kPa<P<300 kPa, and it can act as a flow source as well as a flow receiver. The flow standard incorporated features that improved its convenience and lowered its cost without sacrificing accuracy, specifically (1) dry sliding seals made with commercially available, easily replaced, o-rings, (2) a compact design based on a commercially available, hollow piston, and (3) a linear encoder with a small Abbe error.     

Water collection techniques at very low flow rates including strong capillary effects

Milli-, micro- and nano-flow calibrations are important in several areas of pharmaceutical, flow chemistry and health care applications where volumetric dosage or delivery at given flow rates are crucial for the process. After developing a facility for the micro-flow range, METAS has developed a facility for flow rates from 50 nL/min up to 400 mL/min. The continuous collection of the flowing water into a beaker on a balance without having droplet formation for a continuous increase of the weighing values is a challenge (dynamic gravimetric method). This technique is often used to determine the flow rate over several orders of magnitude. In this paper, we describe the newly developed METAS piston provers and focus on the water collection techniques used for the flow rate determination of very low flow rates going as low as 50 nL/min by means of the dynamic gravimetric method. One water collection technique is to immerse the outlet needle into the water in the beaker. To reduce evaporation either a saturated environment is created or a layer of oil is added on top of the water. Another water collection technique is applied at the METAS facilities, where the outlet needle is positioned just over glass filters on top of the beaker to collect the water by means of a constant water bridge obtained independently of the flow rate. These two techniques are investigated for comparing the stability of the flow rate determination and the influence of the capillary forces acting due to the water or water-oil surface on the outlet needle and on the water bridge between the outlet needle and glass filters. The technique applied at METAS with the water bridge between outlet needle and glass filter reveals to be more stable for the flow rate determination and corrections due to capillary forces acting on the outlet needle can be neglected compared to the water collection technique with the immersed needle.     

An orifice meter for bidirectional air flow measurements: Influence of gas thermo-hygrometric content on static response and bidirectionality

This paper presents the design and calibration of an ISO non-compliant orifice plate flowmeter whose intended use is for respiratory function measurements in the bidirectional air flow range ±9 L/min.The novelty of the proposed sensor consists of a plate beveled in both upstream and downstream sides: a symmetrical geometry is adopted in order to perform bidirectional measurements of flow rate. A mathematical model is introduced to quantify the influence of temperature on the sensor output. Four different positions of the pressure static taps are evaluated in order to maximize bidirectionality. An index is also introduced in order to quantitatively estimate the anti-symmetry of the sensor's response curve.Trials are carried out to evaluate the influence on sensor output of air temperatures (22 °C, 30 °C and 37 °C) at different values of relative humidity (5%, 55% and 85%). Experimental data show a quite good agreement with the theoretical model (R²>0.98 in each condition).The influence of air temperature on the sensor output is minimized by introducing a correction factor based on the theoretical model leading to measurement repeatability better than 2% in overall range of calibration. The mean sensitivity in the calibration range is about 2 kPa L⁻¹·min allowing to obtain a sensor discrimination threshold lower than 0.2 L/min in both directions. The time constant of the whole measurement system, equal to 2.40±0.03 ms, leads to a bandwidth up to 80 Hz making the sensor suitable for respiratory function measurements.     

Development of a gas micro-flow transfer standard

LNE has ability to calibrate gas micro-flow rates using the dilution method for nitrogen flow rates in the range from 2 µg/s to 200 µg/s or helium ones in the range 0.75–30 µg/s. In addition, a primary constant pressure flowmeter for leak rate measurements from 0.05 µg/s to 35 µg/s is also available. This equipment will be used to validate the dilution method below 30 µg/s. In order to compare these reference facilities, LNE is developing a micro-flow transfer standard (µFTS) in collaboration with ATEQ France, a manufacturer of control equipment for leak testing. The flowmeter consists mainly of an array of three stainless steel capillaries designed to cover the ranges from 0.035 µg/s to 0.35 µg/s, 0.35 µg/s to 3.5 µg/s and 3.5 µg/s to 35 µg/s for nitrogen (0.1–100 ml/h). A dynamic model of the µFTS determines the mass flow rate from the input pressure, the differential pressure of the capillary, the gas temperature, viscosity and density and the length and radius of the capillary. A comparison of both reference methods is carried out with the µFTS from 0.35 µg/s to 35 µg/s.     

Tool wear analysis and improvement of cutting conditions using the high-pressure water-jet assistance when machining the Ti17 titanium alloy

This paper presents experimental results concerning the machinability of the titanium alloy Ti17 with and without high-pressure water jet assistance (HPWJA) using uncoated WC/Co tools. For this purpose, the influence of the cutting speed and the water jet pressure on the evolution of tool wear and cutting forces have been investigated. The cutting speed has been varied between 50 m/min and 100 m/min and the water jet pressure has been varied from 50 bar to 250 bar. The optimum water jet pressure has been determined, leading to an increase in tool life of approximately 9 times. Compared to conventional lubrication, an increase of about 30% in productivity can be obtained.     

An ultra high-pressure test rig for measurements of small flow rates with different viscosities

Within the framework of a research project regarding investigations on a high-pressure Coriolis mass flow meter (CMF) a portable flow test rig for traceable calibration measurements of the flow rate (mass - and volume flow) in a range of 5 g min⁻¹ to 500 g min⁻¹ and in a pressure range of 0.1 MPa to 85 MPa was developed. The measurement principle of the flow test rig is based on the gravimetrical measuring procedure with flying-start-and-stop operating mode. Particular attention has been paid to the challenges of temperature stability during the measurements since the temperature has a direct influence on the viscosity and flow rate of the test medium. For that reason the pipes on the high-pressure side are double-walled and insulated and the device under test (DUT) has an enclosure with a separate temperature control. From the analysis of the first measurement with tap water at a temperature of 20 °C and a pressure of 82.7 MPa an extensive uncertainty analysis has been carried out. It was found that the diverter (mainly due to its asymmetric behaviour) is the largest influence factor on the total uncertainty budget. After a number of improvements, especially concerning the diverter, the flow test rig has currently an expanded measurement uncertainty of around 1.0% in the lower flow rate range (25 g min⁻¹) and 0.25% in the higher flow rate range (400 g min⁻¹) for the measurement of mass flow. Additional calibration measurements with the new, redesigned flow test rig and highly viscous base oils also indicated a good agreement with the theoretical behaviour of the flow meter according to the manufacturers׳ specifications with water as test medium. Further improvements are envisaged in the future in order to focus also on other areas of interest.     

Designing and producing large-volume liquid gamma-ray standard sources for low radioactive pollution measurements of seawater samples by comparison between experimental and simulation results

In order to in-situ measurement of large volume water samples, using of a portable HPGe detector was considered. Because of necessity of efficiency calibration of the detector for the geometry (100 L), the large volume standard sources were prepared. Before making large volume standard sources (100 L), the Monte Carlo method has been applied in order to optimizing the calibration procedures and in agreement with experiment results, has been caused reducing the amount of produced radioactive wastes. First, the efficiency of the portable coaxial P-type HPGe detector for 1 L liquid standard sources in Marinelli beaker geometry was simulated. Then, the experimental efficiency calibration was carried out using the detector for those 1 L liquid standard sources in Marinelli beaker geometry. The detector dead layer was determined by comparison of the simulation and experimental efficiency curve results. Then, a relation between simulation and experimental measurements, that is, between pulse-height per emitted particle, F8 tally, and estimated amount of spiked radioactive solution into the 1 L distilled water in Marinelli beaker was found. Then, the efficiency calibration of the large volume liquid standard sources was simulated. The estimated amount of spiking radioactive solution into the large volume distilled water (100 L) has been taken into account dividing experimental efficiencies (in Marinelli beaker) by the simulated efficiencies (in 100 L). Finally, by spiking the large volume distilled water with the radioactive solution, efficiency calibration of the potable HPGe detector for 100 L geometry was done.     

Influence of tube wall longitudinal heat conduction on temperature measurement of cryogenic gas with low mass flow rates

Longitudinal heat conduction is an important parameter in the cryogenic field, especially in cryogenic heat exchangers. In the present study, the parasitic effect of tube wall longitudinal heat conduction on temperature measurement within the tube has been studied for cryogenic gas with low mass flow rates by finite element method and experimental tests. The effects of various parameters such as tube outlet temperature, tube wall thermal conductivity, mass flow rate, and tube wall thickness have been investigated. Axial positioning errors of temperature sensor due to tube wall longitudinal heat conduction were higher for lower gas flow rates. The results showed that the tube wall thermal conductivity leads to axial heat conduction within the tube wall, but the higher tube wall thermal conductivity does not lead to bigger axial positioning error of temperature sensor at tube outlet. According to data obtained from simulations and experiments, sensor with distance of 5 mm from tube outlet had 14.92% and 8.51% temperature measurement error (with respect to gas flow temperature at tube outlet) for tube wall thermal conductivities of 16 and 400 W m⁻¹ K⁻¹, respectively.     

Atomic force microscope probe calibration by use of a commercial precision balance

In this paper, we investigate the characteristics of a piezoresistive AFM cantilever in the range of 0–1.6 μN by using nano force calibrator (NFC), which consists of a high precision balance with resolution of 1 nN and 1-D fine positioning stage. Brief modeling of the cantilever is presented and then, the calibration results are shown. Tests revealed a linear relationship between the probing force and sensor output (resistance change), but the force vs. deflection is not as linear as the force vs. sensor output curve. The force constant of the cantilever was measured to 0.26 N/m with a standard deviation of 0.01 N/m. It shows that there is big difference between measured and nominal spring constant of 1 N/m provided by the manufacturer’s specifications.     

Development and evaluation of the calibration facility for high-pressure hydrogen gas flow meters

The calibration facility with the multi-nozzle calibrator was developed for the calibration of flow meters to be used with high-pressure, high-flow-rate hydrogen gas. The critical nozzles installed in the multi-nozzle calibrator were calibrated with traceability to the national standard. The relative standard uncertainty of the mass flow rates produced from the calibration facility is 0.09% when the flow rate is between 150 g/min and 550 g/min. In this study, the Coriolis flow meter was calibrated for a pressure range of 15–35 MPa. The relative standard uncertainty of the flow rates obtained from the Coriolis flow meter was 0.44% for the case of the worst fluctuations in the output of the flow meter; based on the calibration curve, this is 0.91%. The present result shows that there is a maximum 3% difference between the output of the Coriolis flow meter and the mass flow rates of the multi-nozzle calibrator, even though the Coriolis flow meter was calibrated using water. Therefore, for the development of a calibration facility that can calibrate a flow meter under the same conditions as those encountered in actual use, it will be important to develop a new flow meter.     

Cutting forces,tool wear and surface finish in high speed diamond machining

We have investigated the cutting forces, the tool wear and the surface finish obtained in high speed diamond turning and milling of OFHC copper, brass CuZn39Pb3, aluminum AlMg5, and electroless nickel. In face turning experiments with constant material removal rate the cutting forces were recorded as a function of cutting speed between v_c = 150 m/min and 4500 m/min revealing a transition to adiabatic shearing which is supported by FEM simulations of the cutting process. Fly-cutting experiments carried out at low (v_c = 380 m/min) and at high cutting speed (v_c = 3800 m/min) showed that the rate of abrasive wear of the cutting edge is significantly higher at ordinary cutting speed than at high cutting speed in contrast to the experience made in conventional machining. Furthermore, it was found that the rate of chemically induced tool wear in diamond milling of steel is decreasing with decreasing tool engagement time per revolution. High speed diamond machining may also yield an improved surface roughness which was confirmed by comparing the step heights at grain boundaries obtained in diamond milling of OFHC copper and brass CuZn39Pb3 at low (v_c = 100 m/min) and high cutting speed (v_c = 2000 m/min). Thus, high speed diamond machining offers several advantages, let alone a major reduction of machining time.     

Air flow rate thermal control system at low pressure drop

Low pressure drop thermal Mass Flow Controllers are generally thought to fulfill needs concerning the realization of a dynamic reference gas mixture generator for accurate gas analysis. A small air flow rate at low pressure drop must be controlled in a stable and precise way in the generator. True operative pressure drop limits, set point reproducibility, calibration needs and flow rate stability during operations were investigated for a low pressure drop thermal Mass Flow Controller. The flow rate bias due to late calibration and flow rate short-term stability were measured and discussed. The Allan method was used to calculate stability during operation. Calibration uncertainty, bias for late calibration, stability and set point reproducibility were composed to calculate the total uncertainty of the flow rate as a function of the operation time. Results show that it is possible to operate below the target uncertainty stated for a dynamic generator of gas mixtures down to 100 Pa pressure drop. Stability gives the main contribution to total uncertainty at very short operation times, while calibration uncertainty gives the main contribution to total uncertainty at normal operation times. The calibration uncertainty at 0.1% is low enough to assure the target uncertainty for operation times over 10 s. Daily verification of calibration enhances the reliability of the measurement. An accurate voltmeter is necessary for the reproducibility of the set point.     

Effect of ozone pretreatment on the physical and mechanical properties of particleboard panels made from bagasse

The main objective of this study was to investigate the applied properties of particleboard panels made from bagasse, which were either treated or not treated with gaseous ozone (O₃). Variable parameters were ozone exposure time (1–3 min) at 9 ppm and storage period (1–5 months). Other parameters such as resin content (12 wt%), hardener content (1 wt%), type of hardener (NH₄Cl), press closing time (5 mm/s), board density (0.70 g/cm³), and press pressure (30 kg/m²) were held constant. The experimental panels were tested for their mechanical properties including modulus of elasticity (MOE), modulus of rupture (MOR); and internal bonding strength (IBS) and physical properties in terms of water absorption (WA) and thickness swelling (TS) according to the procedures defined by EN standards. Overall results showed that all panels made from treated bagasse exceeded the EN standards for MOE, MOR, and IBS. However, WA and TS values decreased after ozone pretreatment compared to the un-treated (control) panels. Application of Duncan’s Multiple Range Test for the mean values of the results showed that the effects of both variables, except their interactions, on the mechanical and physical properties were highly significant (p ⩽ 0.01%). All the mechanical properties of the panels decreased when the treatment duration increased from 1 to 5 months.     

Wear mechanisms of PcBN cutting tools when dry turning ASTM Grade 2 austempered ductile iron under finishing conditions

Experimental studies of dry finish turning of ASTM Grade 2 austempered ductile iron with PcBN cutting tools were carried out at cutting speeds ranging from 50 to 800 m/min, at a feed of 0.05 mm/rev and depth cut of 0.2 mm. The wear mechanisms of PcBN cutting tools were investigated through the examination of the wear surfaces by means of optical, scanning electron and transmission electron microscopes as well as energy dispersive spectroscopy. Flank wear and crater wear were the main wear modes within this range of cutting speeds. Adhesion and adhesion induced abrasion were the main wear mechanisms at cutting speeds less than 150 m/min. Abrasion and wear by thermally activated-diffusion and oxidation-chemical reaction wear were the main wear mechanisms at cutting speeds greater than 150 m/min. A high concentration of Mg, Si, and O on the wear surfaces and a heat-affected zone in the tools suggested that at speeds in excess of 150 m/min, the rate controlling wear mechanism involved chemical reaction between the tools and the operating environment.     

Investigations on pressure dependence of Coriolis Mass Flow Meters used at Hydrogen Refueling Stations

In the framework of the ongoing EMPIR JRP 16ENG01 “Metrology for Hydrogen Vehicles” a main task is to investigate the influence of pressure on the measurement accuracy of Coriolis Mass Flow Meters (CFM) used at Hydrogen Refueling Stations (HRS). At a HRS hydrogen is transferred at very high and changing pressures with simultaneously varying flow rates and temperatures. It is clearly very difficult for CFMs to achieve the current legal requirements with respect to mass flow measurement accuracy at these measurement conditions. As a result of the very dynamic filling process it was observed that the accuracy of mass flow measurement at different pressure ranges is not sufficient. At higher pressures it was found that particularly short refueling times cause significant measurement deviations. On this background it may be concluded that pressure has a great impact on the accuracy of mass flow measurement. To gain a deeper understanding of this matter RISE has built a unique high-pressure test facility. With the aid of this newly developed test rig it is possible to calibrate CFMs over a wide pressure and flow range with water or base oils as test medium. The test rig allows calibration measurements under the conditions prevailing at a 70 MPa HRS regarding mass flows (up to 3.6 kg min⁻¹) and pressures (up to 87.5 MPa).     

Coriolis mass flow metering for three-phase flow: A case study

Previous work has described the use of Coriolis mass flow metering for two-phase (gas/liquid) flow. As the Coriolis meter provides both mass flow and density measurements, it is possible to resolve the mass flows of the gas and liquid in a two-phase mixture if their respective densities are known. To apply Coriolis metering to a three-phase (oil/water/gas) mixture, an additional measurement is required. In the work described in this paper, a water cut meter is used to indicate what proportion of the liquid flow is water. This provides sufficient information to calculate the mass flows of the water, oil and gas components. This paper is believed to be the first to detail an implementation of three-phase flow metering using Coriolis technology where phase separation is not applied.Trials have taken place at the UK National Flow Standards Laboratory three-phase facility, on a commercial three-phase meter based on the Coriolis meter/ water cut measurement principle. For the 50 mm metering system, the total liquid flow rate ranged from 2.4 kg/s up to 11 kg/s, the water cut ranged from 0% to 100%, and the gas volume fraction (GVF) from 0 to 50%. In a formally observed trial, 75 test points were taken at a temperature of approximately 40 °C and with a skid inlet pressure of approximately 350 kPa. Over 95% of the test results fell within the desired specification, defined as follows: the total (oil+water) liquid mass flow error should fall within ±2.5%, and the gas mass flow error within ±5.0%. The oil mass flow error limit is ±6.0% for water cuts less than 70%, while for water cuts between 70% and 95% the oil mass flow error limit is ±15.0%.These results demonstrate the potential for using Coriolis mass flow metering combined with water cut metering for three-phase (oil/water/gas) measurement.     

Improved critical flow factors and representative equations for four calibration gases

The critical flow nozzle is widely used to calibrate flowmeters in gas flow measurement. Its use requires the critical flow factor, C*, a parameter dependent upon the thermophysical properties of the gas at the nozzle throat, and the upstream temperature and pressure. This paper presents C* values for four calibration gases (air, argon, nitrogen and methane), calculated from the most recent reference quality equations of state, over a wider range of temperature and pressure than previously available, 200–600 K and up to 20 MPa. In addition, a new empirical equation has been developed to represent the calculated values accurately, thus eliminating the need for complex calculations or interpolations from tables.     

Torque loss of type C40 FZG gears lubricated with wind turbine gear oils

Five fully formulated wind turbine gear oils were characterised. The gear oils have 320 ISO VG grade and different formulations: ester, mineral, PAO, PAG and mineral+PAMA.A back-to-back FZG test machine, with re-circulating power, was used and a torque-cell was included on the test rig in order to measure the torque loss. Eight thermocouples were included to monitor the temperatures in different locations of the test rig.Tests at 1.13, 2.26 and 6.79 m/s were performed for different FZG load stages: K1, K5, K7 and K9. Both gearboxes were jet-lubricated with an oil flow of 3 l/min. The input flow temperature was kept almost constant (80 ±1 °C).Friction generated between the meshing teeth, shaft seals and rolling bearing losses was predicted.     

Analysis of load-speed sensitivity of friction composites based on various synthetic graphites

The frictional response of a multi-component phenolic-based friction material is highly complex under a set of variable loads and speeds. The present paper discusses the sensitivity of friction coefficient (μ) of friction composites containing synthetic graphite with different particle sizes (with similar crystallinity range) to braking pressure and sliding speed. The friction studies were carried out on a sub scale brake-test-rig, following 4 loads × 3 speeds experimental design. The best combination of performance properties was observed for the composite containing synthetic graphite with an average particle size of 410 μm. Other particle sizes which resulted in good performance were 38 and 169 μm. Very fine particle sizes were not beneficial for desired combination of performance properties. Regression analysis of μ following an orthogonal L₉(3 × 3) experimental design method revealed that the first order influences of sliding speed and braking pressure were significant. When all the combinatorial influences of braking pressure and sliding speed are taken into account together their simultaneous effects would be most effective in the range of graphite particle size ～80–250 μm.     

Application of two-output port fiber coupler as gasoline level sensor

Detection of gasoline level can be done in a safe and simple way using two output port multimode fiber coupler with a structure of 2 × 2 as a sensor. Two output ports (sensing port) are connected with two reflector displacement device (RDD) and functioned as two probes. These probes are placed on the wall of gasoline tank in a storied and work interchangeably or together depending on setting of these probes. Detection mechanism of the system is based on changes in intensity of reflected light from the reflector RDD that shifts due to changes in level of gasoline (hydrostatic pressure principle). Changes in intensity of light coming into the sensing port are then forwarded to the optical detector. Experiments performed by varying the location of the second probe as 45 cm, 50 cm, and 55 cm above the first probe to detect the level of gasoline in the process of filling and emptying the tank. Experimental results show the process of filling and emptying the tank have small differences of 6% with the dynamic range, the linear region, and resolution are 100 cm, 70 cm, and 0.4 cm respectively. Sensor sensitivity in filling and emptying process of the tank are 2.7 mV/cm and 2.8 mV/cm respectively. These results were the best performance of the sensor, which occurs when the level of the second probe was 55 cm above the first probe.