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

Berg, Robert F.; Gooding, Timothy; Vest, Robert E.

doi:10.1016/j.flowmeasinst.2013.12.002

Cited by 19 publications

(14 citation statements)

References 17 publications

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“…The thermal enclosure, which was based on the description given in Berg et al (2014), controlled the temperatures of the humidity generator, the gas manifold, the MFCs, and the pressure gauges near 28 • C. Its height and area were respectively 0.63 m and (1.27 × 0.66) m 2 , and its walls were rigid sheets of 25 mm polyisocyanurate insulation. The temperature was stabilized by a commercial controller (Arroyo Instruments model 5305; see Disclaimer) that drove a thermoelectric cooler (Laird model AA-034-12-22).…”

Section: Thermal Enclosurementioning

confidence: 99%

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Silicone tube humidity generator

2022

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Abstract. We describe the model and construction of a two-flow (or divided-flow) humidity generator, developed at LNE-Cnam, that uses mass flow controllers to mix a stream of dry gas with a stream of humid gas saturated at 28 ∘C. It can generate a wide range of humidity, with mole fractions in the range of 0.7×10-6<x<9000×10-6, without using low temperature or high pressure. This range is suitable for calibrating balloon-borne instruments that measure humidity in the stratosphere, where x∼5×10-6. The generator's novel feature is a saturator that comprises 5 m of silicone tubing immersed in water. Water enters the humid gas stream by diffusing through the wall of the tubing until the gas stream flowing through the tubing is saturated. This design provides a simple, low-cost humidity generator with an accuracy that is acceptable for many applications. The key requirement is that the tubing be long enough to ensure saturation so that the saturator's output is independent of the dimensions and permeability of the tube. A length of only a few meters was sufficient because the tube was made of silicone; other common polymers have permeabilities that are 1000 times smaller. We verified the model of the transition from unsaturated flow to saturated flow by measuring the humidity while using three tube lengths, two of which were too short for saturation. As a more complete test, we used the generator as a primary device after correcting the calibrations of the mass flow controllers that determined the mixing ratio. At mole fractions of 50×10-6<x<5000×10-6, the generator's output mole fraction xgen agreed to within 1 % with the value xcm measured by a calibrated chilled-mirror hygrometer; in other words, their ratio fell in the range xgen/xcm=1.00±0.01. At smaller mole fractions, their differences fell in the range of xgen-xcm=±1×10-6.

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Section: Thermal Enclosurementioning

confidence: 99%

“…Data availability. The laboratory measurements of gas temperature, pressure, and flow rate made in the development of the humidity generator can be found at https://doi.org/10.5281/zenodo.5963596 (Berg et al 2022).…”

Section: A2 Carrier Gas Permeabilitymentioning

confidence: 99%

Silicone tube humidity generator

2022

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“…For each small length dz of the tube, permeation causes water to flow through the tube wall at the following molar flow rate (Crank, 1975):…”

Section: Permeation Of Water Through Siliconementioning

confidence: 99%

“…The permeability  describes the rate at which a given gas diffuses through a given solid. If a gas at pressure pout surrounds a tube of permeability , length L, and outer and inner diameters dout and din contains the same gas at pressure pin, the gas will permeate from the outside to the inside at the molar flow rate (Crank, 1975) (A1)…”

Section: Appendix A: Permeability Of H2o and Ar Through Pdmsmentioning

confidence: 99%

Silicone tube humidity generator

Berg¹,

Chiodo

Georgin

2021

Preprint

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Abstract. We describe the model and construction of a two-flow (or divided-flow) humidity generator, developed at LNE-CNAM, that uses mass flow controllers to mix a stream of dry gas with a stream of humid gas saturated at 28 °C. It can generate a wide range of humidity, with mole fractions in the range 0.7 × 10−6 < x < 9000 × 10−6, without using low temperature or high pressure. This range is suitable for calibrating balloon-borne instruments that measure humidity in the stratosphere, where x ~5 × 10−6. The generator’s novel feature is a saturator that comprises 5 m of silicone tubing immersed in water. Water enters the humid gas stream by diffusing through the wall of the tubing until the gas stream flowing through the tubing is saturated. This design provides a simple, low-cost humidity generator with an accuracy that is acceptable for many applications. The key requirement is that the tubing be long enough to ensure saturation, so that the saturator’s output is independent of the dimensions and permeability of the tube. A length of only a few meters was sufficient because the tube was made of silicone; other common polymers have permeabilities that are 1000 times smaller. We verified the model of the transition from unsaturated flow to saturated flow by measuring the humidity while using three tube lengths, two of which were too short for saturation. As a more complete test, we used the generator as a primary device after correcting the calibrations of the mass flow controllers that determined the mixing ratio. At mole fractions 50 × 10−6 < x < 5000 × 10−6, the generator’s output mole fraction xgen agreed to within 1 % with the value xcm measured by a calibrated chilled-mirror hygrometer; in other words, their ratio fell in the range xgen/xcm = 1.00 ± 0.01. At smaller mole fractions, their differences fell in range xgen − xcm = ±1 × 10−6.

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“…Standard practice with this first bellows flowmeter was (BFM) to measure the outgassing rate of the variable volume and correct the measured flow. This systematic can also limit the uncertainty of the third type of constant pressure flowmeters, those that use a calibrated bellows rather than hydraulics [5,6,7,8,9].…”

Section: Introductionmentioning

confidence: 99%

A constant pressure flowmeter for extremely high vacuum

Eckel,

Barker,

Fedchak

et al. 2021

Preprint

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We demonstrate operation of a constant-pressure flowmeter capable of generating and accurately measuring flows as low as 1 × 10 −13 mol/s. Generation of such small flows is accomplished by using a small conductance element with C ≈ 25 nL/s. Accurate measurement then requires both low outgassing materials (< 10 −15 mol/s) and small volume changes (≈ 70 µL). We outline the present flowmeter's construction, detail its operation, and quantify its uncertainty, which is < 1 % over the entire operating range and better than 0.3 % over a majority. In particular, we present an analysis of its hydraulic system, and quantify the shift and uncertainty due to the slightly compressible oil. Finally, we compare our flowmeter against a NIST standard flowmeter, and find agreement to within 0.61 % (k = 2). Future modifications could achieve a k = 2 uncertainty of 0.2 %.

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

Cited by 19 publications

References 17 publications

Silicone tube humidity generator

Silicone tube humidity generator

Silicone tube humidity generator

A constant pressure flowmeter for extremely high vacuum

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