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Mina Hoorfar - One of the best experts on this subject based on the ideXlab platform.
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understanding microfluidic based Gas Detectors a numerical model to investigate fundamental sensor operation influencing phenomena and optimum geometries
Sensors and Actuators B-chemical, 2019Co-Authors: Mahyar Mohaghegh Montazeri, Allen Obrien, Mina HoorfarAbstract:Abstract Microfluidic-based Gas Detectors have been developed as an alternative method to GC/MS systems (which are bulky, expensive, and require trained professionals), and electronics noses (which require extensive calibration due to sensor drift). However, the performance of microfluidic-based Gas Detectors requires improvements before being commercially-viable in the Gas monitoring market. Similar to other approaches, this novel technology requires a multitude of tests to calibrate against different compounds, concentrations, and environmental conditions. This paper presents a 3D numerical simulation to study the response of microfluidic-based Gas Detectors across various geometries using Multiphysics modeling of diffusion, surface adsorption/desorption, chemical reactions, and heat and momentum transfer phenomena. By using this model, response curves of different analyte concentrations are generated thereby reducing the need for manual calibration tests and associated costs. In this model, diffusion was demonstrated as the main parameter affecting the response, followed by surface adsorption/desorption and heat and momentum transfer, which had a minimal effect on the response. The model was also used to investigate the effect of the detector’s dimensions (including microchannel length, microchannel height, and sensor housing volume) on sensitivity, selectivity and response/recovery time. Due to an observed trade-off between selectivity and sensitivity, a sum indicator was defined to investigate the best overall performance across various conditions. Results obtained from different geometrical dimensions and Gas concentrations demonstrated that a change in channel length has the most pronounced impact on the sum indicator, especially for low Gas concentrations.
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Selective detection of volatile organic compounds in microfluidic Gas Detectors based on “like dissolves like”
Nature Publishing Group, 2019Co-Authors: Mohammad Paknahad, Carmen Mcintosh, Mina HoorfarAbstract:Abstract This paper studies the effect of channel coating hydrophobicity and analyte polarity on the Gas detection capability of a microfluidic-based Gas detector. Two Detectors with two different channel surface coating combinations (resulting in different levels of hydrophobicity) are fabricated and tested against seven analytes with different polarities (methanol, ethanol, 1-propanol, 2-pentanol, acetone, pentane, and hexane). A feature extraction method is utilized to compare the discrimination capability of each of the fabricated detector. The analysis of the combined feature space presented for both Detectors reveals that the Euclidean distance, which is an indicator of the device discrimination capability between different Gases, between the feature vectors of the two sensors are greater for non-polar Gases compared to those obtained for the polar ones. This shows that the analyte discrimination in microfluidic Gas Detectors is not a purely diffusion-based process, and there are analyte/channel surface interaction parameters involved in enhancing/impeding sensor selectivity. To understand these effects, the surface free energy of each fabricated channel was determined. It is shown that the difference between the solid-liquid surface tension values estimated for the two channel surfaces is higher for the non-polar analytes as compared to the polar analytes. This effect along with the low diffusion coefficients of non-polar analyte magnifies adsorption of the analytes in the diffusion-physisorption process, resulting in a greater difference in Euclidean distances between the features obtained from the two Detectors responses against non-polar analytes as compared to the polar ones. This shows that the choice of the detector’s channel coating material plays a key role in the selectivity of the device between different Gases. As a result, non-polar channel coating surfaces are suggested for better classification of the non-polar Gases, and it is shown in the cases of polar Gases changing the coating surface has less effect
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Diffusion-based humidity control membrane for microfluidic-based Gas Detectors.
Analytica chimica acta, 2018Co-Authors: Mohammad Paknahad, Jannat Singh Bachhal, Mina HoorfarAbstract:Abstract This paper presents a cost-effective and reliable diffusion-based humidity removal membrane for microfluidic-based Gas analyzers. The developed humidity control device reduces the relative humidity of a Gas chamber and also stabilizes the humidity using inexpensive inorganic salts. A 3D-printed microfluidic Gas sensor is used to test four different volatile organic compounds (VOCs) including three alcohols and one ketone in different relative humidity levels ranging from 15% to 80%. To study the effects of humidity on different features of the transient response of the sensor, two different feature extraction methods are used. These methods are (i) normalization method, removing the effect of any changes in the response level for identifying the nature of the Gas, and (ii) integration method, which differentiates between different response levels due to different concentrations or humidity levels. The results show that the sensor fails to differentiate between different VOCs or even between different concentrations of the same Gas when there is a slight change (as small as 5%) in humidity. In essence, the device is vulnerable to the errors occur due to the presence of humidity even after the post processing analysis (feature extraction). Thus, a humidity control and removal membrane is developed in order to minimize the effect of humidity. The selectivity of the sensor with and without the use of the humidity removal membrane is compared and shown to be 36% more in the case of utilizing the humidity removal membrane. The proposed humidity control system successfully removes the effect of humidity on the response pattern of the sensor and can be used for different applications such as breath analyzers for which lowering the level of humidity of the exhaled breath is crucial before analyzing the VOCs of interest.
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characterization of channel coating and dimensions of microfluidic based Gas Detectors
Sensors and Actuators B-chemical, 2017Co-Authors: Mohammad Paknahad, Jannat Singh Bachhal, Ali Ahmadi, Mina HoorfarAbstract:Abstract This paper presents a low-cost, portable, and highly selective 3D-printed Gas detector for sensing different volatile organic compounds (VOCs) and identifying their concentrations. A 3D-printed microfluidic platform is fabricated by integrating a chemoresistor into a microfluidic channel providing a powerful tool for analyzing the kinetic response of the device to the diffused Gas along the channel. Here, the effects of different channel’s coating materials and dimensions on the diffusion-physisorption of Gas molecules are studied based on the diagnostic power as well as the speed of the sensor recovery. This study is resulted in identifying an optimum channel coating and geometry, the combination of which provides high selectivity in differentiating a range of different VOCs as compared to previous microfluidic-based Gas Detectors. The proposed Gas detector also shows a faster recovery time (150 s) compared to those obtained by systems presented in previous studies (10 min). A new feature extraction method is used to quantify the concentration of the analyte. The innovative sensing technology proposed here will advance the state-of-the-art Gas analysis methods by providing real-time sensing with higher selectivity and drastically decreased recovery time.
Carl D Laird - One of the best experts on this subject based on the ideXlab platform.
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a quantitative assessment on the placement practices of Gas Detectors in the process industries
Journal of Loss Prevention in The Process Industries, 2015Co-Authors: A J Benavidesserrano, M S Mannan, Carl D LairdAbstract:Abstract Gas detection is an important safety system with interfaces to several other safety safeguards. However, the generality of the regulations, standards and recommended practices in conjunction with the inherent challenges of the Gas detector placement problem, has resulted in a widespread use of prescriptive and qualitative detector placement strategies. In order to take advantage of the quantitative information provided by dispersion simulations, a stochastic programming formulation (SP-UV) was previously proposed, developed and validated by the authors. This formulation identifies the Gas detector layout that minimizes the expected value of an overall damage coefficient (i.e., the minimization of a risk metric) given a set of dispersion scenarios. Results demonstrated the potential and suitability of numerical optimization to solve the Gas detector placement problem while rigorously considering its inherent uncertainties. In this work, four existing approaches for Gas detector placement were implemented and compared with the previously proposed quantitative optimization-based approach using three different performance metrics in accordance to the objectives of Gas detection systems. Results provide evidence on the effectiveness of the use of dispersion simulations, and mathematical programming, to supplement the Gas detector placement problem.
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a stochastic programming approach for the optimal placement of Gas Detectors unavailability and voting strategies
Industrial & Engineering Chemistry Research, 2014Co-Authors: A J Benavidesserrano, M S Mannan, Sean Legg, Richart Vazquezroman, Carl D LairdAbstract:The task of detector placement is especially difficult due to the large number of variables that influence the risk associated with Gas leaks; these include leak conditions, fluid properties, dispersion characteristics, process equipment geometry, and detection equipment. Existing work on optimal Gas detector placement does not take into account two key considerations associated with Gas detector equipment and policies: the possibility that the detector is not able to perform its intended function and the requirement for a voting logic. Two stochastic Mixed-Integer Linear Programming (MILP) formulations, SP-U and SP-UV, are proposed to address this issue. Formulation results are presented and compared with optimal placement results from a formulation that ignores these two considerations. Unavailability and voting logic considerations result in changes to the optimal detector placement, and significant improvements in the expected time to detection when false positives and false negative alarms are acknow...
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optimal Gas detector placement under uncertainty considering conditional value at risk
Journal of Loss Prevention in The Process Industries, 2013Co-Authors: Sean Legg, A J Benavidesserrano, Chen Wang, Carl D LairdAbstract:Abstract A stochastic programming formulation considering Conditional-Value-at-Risk (CVaR) is developed for the optimal placement of Gas Detectors in petrochemical process facilities. A rigorous Gas dispersion simulator, FLACS, is used to generate release scenario data for a real process geometry. We consider two problem formulations: minimization of expected detection time and minimization of expected detection time subject to a restriction on CVaR across the scenario set. The extensive form of each stochastic program is formulated in Pyomo and solved using CPLEX. Considering all scenarios, we compare key values and histograms of detection times for both formulations. Minimizing the mean detection time only can lead to optimal detector placements with a good expected behavior, but unacceptable worst-case behavior. The formulations that minimize or constraint CVaR produce sensor placements with significantly better worst-case behavior and fewer scenarios having high detection times. Considering these results, a strong case for the use of optimal sensor placement using stochastic programming considering CVaR is made for improving safety systems.
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a stochastic programming approach for Gas detector placement using cfd based dispersion simulations
Computers & Chemical Engineering, 2012Co-Authors: Sean Legg, A J Benavidesserrano, John Daniel Siirola, Jeanpaul Watson, S G Davis, A Bratteteig, Carl D LairdAbstract:Abstract A stochastic programming formulation is developed for determining the optimal placement of Gas Detectors in petrochemical facilities. FLACS, a rigorous Gas dispersion package, is used to generate hundreds of scenarios with different leak locations and weather conditions. Three problem formulations are investigated: minimization of expected detection time, minimization of expected detection time including a coverage constraint, and a placement based on coverage alone. The extensive forms of these optimization problems are written in Pyomo and solved using CPLEX. A sampling procedure is used to find confidence intervals on the optimality gap and quantify the effectiveness of detector placements on alternate subsamples of scenarios. Results show that the additional coverage constraint significantly improves performance on alternate subsamples. Furthermore, both optimization-based approaches dramatically outperform the coverage-only approach, making a strong case for the use of rigorous dispersion simulation coupled with stochastic programming to improve the effectiveness of these safety systems.
Mohammad Paknahad - One of the best experts on this subject based on the ideXlab platform.
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Selective detection of volatile organic compounds in microfluidic Gas Detectors based on “like dissolves like”
Nature Publishing Group, 2019Co-Authors: Mohammad Paknahad, Carmen Mcintosh, Mina HoorfarAbstract:Abstract This paper studies the effect of channel coating hydrophobicity and analyte polarity on the Gas detection capability of a microfluidic-based Gas detector. Two Detectors with two different channel surface coating combinations (resulting in different levels of hydrophobicity) are fabricated and tested against seven analytes with different polarities (methanol, ethanol, 1-propanol, 2-pentanol, acetone, pentane, and hexane). A feature extraction method is utilized to compare the discrimination capability of each of the fabricated detector. The analysis of the combined feature space presented for both Detectors reveals that the Euclidean distance, which is an indicator of the device discrimination capability between different Gases, between the feature vectors of the two sensors are greater for non-polar Gases compared to those obtained for the polar ones. This shows that the analyte discrimination in microfluidic Gas Detectors is not a purely diffusion-based process, and there are analyte/channel surface interaction parameters involved in enhancing/impeding sensor selectivity. To understand these effects, the surface free energy of each fabricated channel was determined. It is shown that the difference between the solid-liquid surface tension values estimated for the two channel surfaces is higher for the non-polar analytes as compared to the polar analytes. This effect along with the low diffusion coefficients of non-polar analyte magnifies adsorption of the analytes in the diffusion-physisorption process, resulting in a greater difference in Euclidean distances between the features obtained from the two Detectors responses against non-polar analytes as compared to the polar ones. This shows that the choice of the detector’s channel coating material plays a key role in the selectivity of the device between different Gases. As a result, non-polar channel coating surfaces are suggested for better classification of the non-polar Gases, and it is shown in the cases of polar Gases changing the coating surface has less effect
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Diffusion-based humidity control membrane for microfluidic-based Gas Detectors.
Analytica chimica acta, 2018Co-Authors: Mohammad Paknahad, Jannat Singh Bachhal, Mina HoorfarAbstract:Abstract This paper presents a cost-effective and reliable diffusion-based humidity removal membrane for microfluidic-based Gas analyzers. The developed humidity control device reduces the relative humidity of a Gas chamber and also stabilizes the humidity using inexpensive inorganic salts. A 3D-printed microfluidic Gas sensor is used to test four different volatile organic compounds (VOCs) including three alcohols and one ketone in different relative humidity levels ranging from 15% to 80%. To study the effects of humidity on different features of the transient response of the sensor, two different feature extraction methods are used. These methods are (i) normalization method, removing the effect of any changes in the response level for identifying the nature of the Gas, and (ii) integration method, which differentiates between different response levels due to different concentrations or humidity levels. The results show that the sensor fails to differentiate between different VOCs or even between different concentrations of the same Gas when there is a slight change (as small as 5%) in humidity. In essence, the device is vulnerable to the errors occur due to the presence of humidity even after the post processing analysis (feature extraction). Thus, a humidity control and removal membrane is developed in order to minimize the effect of humidity. The selectivity of the sensor with and without the use of the humidity removal membrane is compared and shown to be 36% more in the case of utilizing the humidity removal membrane. The proposed humidity control system successfully removes the effect of humidity on the response pattern of the sensor and can be used for different applications such as breath analyzers for which lowering the level of humidity of the exhaled breath is crucial before analyzing the VOCs of interest.
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characterization of channel coating and dimensions of microfluidic based Gas Detectors
Sensors and Actuators B-chemical, 2017Co-Authors: Mohammad Paknahad, Jannat Singh Bachhal, Ali Ahmadi, Mina HoorfarAbstract:Abstract This paper presents a low-cost, portable, and highly selective 3D-printed Gas detector for sensing different volatile organic compounds (VOCs) and identifying their concentrations. A 3D-printed microfluidic platform is fabricated by integrating a chemoresistor into a microfluidic channel providing a powerful tool for analyzing the kinetic response of the device to the diffused Gas along the channel. Here, the effects of different channel’s coating materials and dimensions on the diffusion-physisorption of Gas molecules are studied based on the diagnostic power as well as the speed of the sensor recovery. This study is resulted in identifying an optimum channel coating and geometry, the combination of which provides high selectivity in differentiating a range of different VOCs as compared to previous microfluidic-based Gas Detectors. The proposed Gas detector also shows a faster recovery time (150 s) compared to those obtained by systems presented in previous studies (10 min). A new feature extraction method is used to quantify the concentration of the analyte. The innovative sensing technology proposed here will advance the state-of-the-art Gas analysis methods by providing real-time sensing with higher selectivity and drastically decreased recovery time.
A J Benavidesserrano - One of the best experts on this subject based on the ideXlab platform.
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a quantitative assessment on the placement practices of Gas Detectors in the process industries
Journal of Loss Prevention in The Process Industries, 2015Co-Authors: A J Benavidesserrano, M S Mannan, Carl D LairdAbstract:Abstract Gas detection is an important safety system with interfaces to several other safety safeguards. However, the generality of the regulations, standards and recommended practices in conjunction with the inherent challenges of the Gas detector placement problem, has resulted in a widespread use of prescriptive and qualitative detector placement strategies. In order to take advantage of the quantitative information provided by dispersion simulations, a stochastic programming formulation (SP-UV) was previously proposed, developed and validated by the authors. This formulation identifies the Gas detector layout that minimizes the expected value of an overall damage coefficient (i.e., the minimization of a risk metric) given a set of dispersion scenarios. Results demonstrated the potential and suitability of numerical optimization to solve the Gas detector placement problem while rigorously considering its inherent uncertainties. In this work, four existing approaches for Gas detector placement were implemented and compared with the previously proposed quantitative optimization-based approach using three different performance metrics in accordance to the objectives of Gas detection systems. Results provide evidence on the effectiveness of the use of dispersion simulations, and mathematical programming, to supplement the Gas detector placement problem.
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a stochastic programming approach for the optimal placement of Gas Detectors unavailability and voting strategies
Industrial & Engineering Chemistry Research, 2014Co-Authors: A J Benavidesserrano, M S Mannan, Sean Legg, Richart Vazquezroman, Carl D LairdAbstract:The task of detector placement is especially difficult due to the large number of variables that influence the risk associated with Gas leaks; these include leak conditions, fluid properties, dispersion characteristics, process equipment geometry, and detection equipment. Existing work on optimal Gas detector placement does not take into account two key considerations associated with Gas detector equipment and policies: the possibility that the detector is not able to perform its intended function and the requirement for a voting logic. Two stochastic Mixed-Integer Linear Programming (MILP) formulations, SP-U and SP-UV, are proposed to address this issue. Formulation results are presented and compared with optimal placement results from a formulation that ignores these two considerations. Unavailability and voting logic considerations result in changes to the optimal detector placement, and significant improvements in the expected time to detection when false positives and false negative alarms are acknow...
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optimal Gas detector placement under uncertainty considering conditional value at risk
Journal of Loss Prevention in The Process Industries, 2013Co-Authors: Sean Legg, A J Benavidesserrano, Chen Wang, Carl D LairdAbstract:Abstract A stochastic programming formulation considering Conditional-Value-at-Risk (CVaR) is developed for the optimal placement of Gas Detectors in petrochemical process facilities. A rigorous Gas dispersion simulator, FLACS, is used to generate release scenario data for a real process geometry. We consider two problem formulations: minimization of expected detection time and minimization of expected detection time subject to a restriction on CVaR across the scenario set. The extensive form of each stochastic program is formulated in Pyomo and solved using CPLEX. Considering all scenarios, we compare key values and histograms of detection times for both formulations. Minimizing the mean detection time only can lead to optimal detector placements with a good expected behavior, but unacceptable worst-case behavior. The formulations that minimize or constraint CVaR produce sensor placements with significantly better worst-case behavior and fewer scenarios having high detection times. Considering these results, a strong case for the use of optimal sensor placement using stochastic programming considering CVaR is made for improving safety systems.
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a stochastic programming approach for Gas detector placement using cfd based dispersion simulations
Computers & Chemical Engineering, 2012Co-Authors: Sean Legg, A J Benavidesserrano, John Daniel Siirola, Jeanpaul Watson, S G Davis, A Bratteteig, Carl D LairdAbstract:Abstract A stochastic programming formulation is developed for determining the optimal placement of Gas Detectors in petrochemical facilities. FLACS, a rigorous Gas dispersion package, is used to generate hundreds of scenarios with different leak locations and weather conditions. Three problem formulations are investigated: minimization of expected detection time, minimization of expected detection time including a coverage constraint, and a placement based on coverage alone. The extensive forms of these optimization problems are written in Pyomo and solved using CPLEX. A sampling procedure is used to find confidence intervals on the optimality gap and quantify the effectiveness of detector placements on alternate subsamples of scenarios. Results show that the additional coverage constraint significantly improves performance on alternate subsamples. Furthermore, both optimization-based approaches dramatically outperform the coverage-only approach, making a strong case for the use of rigorous dispersion simulation coupled with stochastic programming to improve the effectiveness of these safety systems.
A. Ulrich - One of the best experts on this subject based on the ideXlab platform.
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The scintillation of liquid argon
EPL (Europhysics Letters), 2010Co-Authors: T. Heindl, T. Dandl, Martin Hofmann, R. Krücken, L. Oberauer, W. Potzel, J. Wieser, A. UlrichAbstract:A spectroscopic study of liquid argon from the vacuum ultraviolet at 110 nm to 1000 nm is presented. Excitation was performed using continuous and pulsed 12 keV electron beams. The emission is dominated by the analogue of the so called 2nd excimer continuum. Various additional emission features were found. The time structure of the light emission has been measured for a set of well defined wavelength positions. The results help to interpret literature data in the context of liquid rare Gas Detectors in which the wavelength information is lost due to the use of wavelength shifters.
