Air flow rate thermal control system at low pressure drop

Sassi, Guido; Demichelis, Alessia; Sassi, Mariapaola

doi:10.1016/j.flowmeasinst.2013.12.001

Cited by 4 publications

(5 citation statements)

References 5 publications

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“…The typical experimental conditions for reference gas mixture preparation, according to ISO 6145-8, are a 100 kPa nominal total absolute pressure and 3 kPa (above the ambient pressure) for the diffusion vial generation pressure [9].…”

Section: Voc Vapor Pressurementioning

confidence: 99%

“…The D R at the target carrier flow rate D R | φT can be rewritten as equation (9), where c φ is the sensitivity coefficient of D R as a function of the carrier flow rate and φ T is the target carrier flow rate to give a negligible D R decrease:…”

Section: The Carrier Gas Flow Ratementioning

confidence: 99%

“…These two VOC families present a challenge in monitoring due to their reactive nature [3]. Analytical methods are designed to detect and quantify these significant VOC concentration changes; thus, VOC reference mixtures are needed for calibration at the trace level of gas analyzers [4][5][6][7][8][9][10]. The reference mixtures must guarantee the target uncertainty for the methods, analytical instruments and sensor systems.…”

Section: Introductionmentioning

confidence: 99%

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Development of a primary diffusion source of organic vapors for gas analyzer calibration

Lecuna

Demichelis

Sassi

et al. 2018

Meas. Sci. Technol.

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The generation of reference mixtures of volatile organic compounds (VOCs) at trace levels (10 ppt–10 ppb) is a challenge for both environmental and clinical measurements. The calibration of gas analyzers for trace VOC measurements requires a stable and accurate source of the compound of interest. The dynamic preparation of gas mixtures by diffusion is a suitable method for fulfilling these requirements. The estimation of the uncertainty of the molar fraction of the VOC in the mixture is a key step in the metrological characterization of a dynamic generator. The performance of a dynamic generator was monitored over a wide range of operating conditions. The generation system was simulated by a model developed with computational fluid dynamics and validated against experimental data. The vapor pressure of the VOC was found to be one of the main contributors to the uncertainty of the diffusion rate and its influence at 10–70 kPa was analyzed and discussed. The air buoyancy effect and perturbations due to the weighing duration were studied. The gas carrier flow rate and the amount of liquid in the vial were found to play a role in limiting the diffusion rate. The results of sensitivity analyses were reported through an uncertainty budget for the diffusion rate. The roles of each influence quantity were discussed. A set of criteria to minimize the uncertainty contribution to the primary diffusion source (25 µg min−1) were estimated: carrier gas flow rate higher than 37.7 sml min−1, a maximum VOC liquid mass decrease in the vial of 4.8 g, a minimum residual mass of 1 g and vial weighing times of 1–3 min. With this procedure a limit uncertainty of 0.5% in the diffusion rate can be obtained for VOC mixtures at trace levels (10 ppt–10 ppb), making the developed diffusion vials a primary diffusion source with potential to become a new reference material for trace VOC analysis.

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Section: Voc Vapor Pressurementioning

confidence: 99%

Section: The Carrier Gas Flow Ratementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Development of a primary diffusion source of organic vapors for gas analyzer calibration

Lecuna

Demichelis

Sassi

et al. 2018

Meas. Sci. Technol.

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“…The Allan deviation algorithm [11], commonly used in time and frequency metrology to analyse the stability behaviour of reference oscillators, can be employed to evaluate the operative quantity stability at different time scales (observation times). It has been used to calculate the stability of air flow rate provided by flow control systems, in the observation time range of interest [12]. The Allan deviation comes from signal analysis, thus its theoretical approach and practice are robust [9].…”

Section: Introductionmentioning

confidence: 99%

“…The VOC molar fraction can be calculated from the influence quantities, i.e. in dynamic methods: generation flow rate and zero gas purity and flow rate [12]. Zero gas purity depends on the performance of zero gas purification system which in turn depends on purification of operative quantities.…”

Section: Introductionmentioning

confidence: 99%

Molar fraction stability in dynamic preparation of reference trace gas mixtures

Demichelis¹,

Sassi

Lecuna

et al. 2016

IET Science, Measurement & Technology

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Volatile Organic Compounds (VOC) at trace level are common indicators for climate change and ambient air quality. The calibration of detection systems at trace level needs VOC mixtures at nmol/mol level with 5% uncertainty, the dynamic preparation can fulfil it. A source of uncertainty for dynamic generation is the stability of the VOC molar fraction averaged on the sampling time. A general method for the calculation of the relevance of the stability contribution to the total uncertainty is here proposed. VOC molar fraction is here considered as a composed quantity. Threshold values for stability contribution were set to consider it either as negligible and relevant. The stability of the operative quantities of a device, for the dynamic preparation of accurate VOC reference mixtures, was measured at the working conditions by the Allan deviation algorithm. Stabilities of operative quantities were composed to calculate the VOC molar fraction stability and their contribution to total uncertainty of VOC molar fraction. The stability of the air inlet pressure gave the main stability contribution. The stability contribution to the total uncertainty resulted to be negligible for observation times below 60 min for VOC molar fraction uncertainty of 2% at 30 nmol/mol level

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Compact devices for generation of reference trace VOC mixtures: a new concept in assuring quality at chemical and biochemical laboratories

et al. 2018

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Volatile organic compounds (VOCs) in gas mixtures at trace level (nmol/mol) are routinely measured by chemical and biochemical laboratories as climate indicators, indoor air quality pollutants from building materials emissions, contaminants in food and beverages, and biomarkers in body fluids (blood, urine, breath) of occupational exposure or human diseases. Current analytical instruments used for measurements are gas chromatographs equipped with various injector and detector configurations. The assurance of measurement quality is done by using a huge amount of certified liquid VOC standard solutions (or gaseous VOC standard cylinders) with multiple dilutions to reach the required trace level. This causes high standard uncertainty in instrument calibrations, high cost, and high consumption of analysis and laboratory personal time. In this paper, we present the implementation of portable generators producing VOC gas standards at trace level for automatic and direct calibration of VOC detectors employed in various contexts, removing the need for preparation of matrix calibration standards in cylinders. Two compact devices in-house developed by two national metrology institutes-the Istituto Nazionale di Ricerca Metrologica (INRIM) and the Federal Institute of Metrology (METAS)-are here used to dynamically generate reference gas mixtures in an SI traceable way. The two devices are based on different technologies: diffusion and permeation, for INRIM and METAS, respectively. A metrological characterization is given and the practical implementation at chemical and biochemical laboratories is discussed. Graphical abstract Onsite calibration with transportable generation system with similar performances to primary laboratory devices.

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Air flow rate thermal control system at low pressure drop

Cited by 4 publications

References 5 publications

Development of a primary diffusion source of organic vapors for gas analyzer calibration

Development of a primary diffusion source of organic vapors for gas analyzer calibration

Molar fraction stability in dynamic preparation of reference trace gas mixtures

Compact devices for generation of reference trace VOC mixtures: a new concept in assuring quality at chemical and biochemical laboratories

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