Modelling the effect of aerosol polydispersity on unipolar charging and measurement in low-cost sensors

Low-cost ultrafine aerosol sensors are experimentally calibrated with controlled aerosol sources to provide metrics such as surface area, lung-deposited surface area, mean particle size and/or total concentration from one or more electrical current measurements. However, an aerosol with a large standard deviation in particle size provides a significantly different signal from a monodisperse aerosol with the same median particle size. In this paper, we investigate the effect of particle polydispersity on measurements in devices which employ unipolar charging. The conservation equations are solved for particle/ion charging and transport (convection, diffusion and electrical transport) in laminar, steady-state, incompressible flow. Lognormal particle size distributions are represented by over coupled conservation equations for multiple size bins and discrete charge states and solved numerically for the first time. Modelling results show that integrated electrical current from a polydisperse particle distribution can be represented by a monodisperse distribution characterised by the count mean diameter ( ; unipolar diffusion charging) or diameter of the average surface ( ; photoelectric charging) and total concentration, for a large range of particle distributions and operating conditions offering a convenient simplification for the interpretation of ultrafine particle measurements. The simplification reduces the number of simultaneous conservation equations required, thereby reducing computation time by up to 57 times for a polydisperse particle distribution represented by 16 discrete size bins. The method of analysis is useful to both users and developers of low-cost ultrafine particle sensors to understand the effect of particle polydispersity on measurements.Alphasense Ltd

Systematic review of antiepileptic drugs’ safety and effectiveness in feline epilepsy

Understanding the efficacy and safety profile of antiepileptic drugs (AEDs) in feline epilepsy is a crucial consideration for managing this important brain disease. However, there is a lack of information about the treatment of feline epilepsy and therefore a systematic review was constructed to assess current evidence for the AEDs’ efficacy and tolerability in cats. The methods and materials of our former systematic reviews in canine epilepsy were mostly mirrored for the current systematic review in cats. Databases of PubMed, CAB Direct and Google scholar were searched to detect peer-reviewed studies reporting efficacy and/or adverse effects of AEDs in cats. The studies were assessed with regards to their quality of evidence, i.e. study design, study population, diagnostic criteria and overall risk of bias and the outcome measures reported, i.e. prevalence and 95% confidence interval of the successful and affected population in each study and in total

On the preservation of fibre direction during axisymmetric hyperelastic mass-growth of a finite fibre-reinforced tube

Several types of tube-like fibre-reinforced tissue, including arteries and veins, different kinds of muscle, biological tubes as well as plants and trees, grow in an axially symmetric manner that preserves their own shape as well as the direction and, hence, the shape of their embedded fibres. This study considers the general, three-dimensional, axisymmetric mass-growth pattern of a finite tube reinforced by a single family of fibres growing with and within the tube, and investigates the influence that the preservation of fibre direction exerts on relevant mathematical modelling, as well on the physical behaviour of the tube. Accordingly, complete sets of necessary conditions that enable such axisymmetric tube patterns to take place are initially developed, not only for fibres preserving a general direction, but also for all six particular cases in which the fibres grow normal to either one or two of the cylindrical polar coordinate directions. The implied conditions are of kinematic character but are independent of the constitutive behaviour of the growing tube material. Because they hold in addition to, and simultaneously with standard kinematic relations and equilibrium equations, they describe growth by an overdetermined system of equations. In cases of hyperelastic mass-growth, the additional information they thus provide enable identification of specific classes of strain energy densities for growth that are admissible and, therefore, suitable for the implied type of axisymmetric tube mass-growth to take place. The presented analysis is applicable to many different particular cases of axisymmetric mass-growth of tube-like tissue, though admissible classes of relevant strain energy densities for growth are identified only for a few example applications. These consider and discuss cases of relevant hyperelastic mass-growth which (i) is of purely dilatational nature, (ii) combines dilatational and torsional deformation, (iii) enables preservation of shape and direction of helically growing fibres, as well as (iv) plane fibres growing on the cross-section of an infinitely long fibre-reinforced tube. The analysis can be extended towards mass-growth modelling of tube-like tissue that contains two or more families of fibres. Potential combination of the outlined theoretical process with suitable data obtained from relevant experimental observations could lead to realistic forms of much sought strain energy functions for growth

Soot mass concentration sensor using quartz-enhanced photoacoustic spectroscopy

In this work, a measurement setup for a miniaturized soot sensor with QEPAS is reported. Specifically, measurements of mass concentrations of soot from a miniCAST soot generator are compared with those from an MSS, which is a common method to measure mass concentrations of soot

Characterization of particle number counters based on pulsed-mode diffusion charging

New emission legislation requires number concentration measurements of particles emitted by passenger cars during periodic technical inspections (PTI). For PTI suitable instruments are needed to detect faults, such as diesel particulate filter failures. Diffusion charging is well established as a charging method for particle sensors and is suited to realize low-cost instruments for exhaust particle number measurements in the appropriate size and concentration regime. In order to manufacture affordable instruments, sensors should not only be low cost, but their calibration procedure must be simple and reliable. We experimentally investigated the impact of test aerosol properties—such as material, size, concentration and morphology—on the counting efficiency of two pulsed-mode, unipolar diffusion charging approaches: (i) conventional diffusion charging and (ii) modulated precipitation. By separately characterizing the particle charging process and the overall sensor response with different test aerosols, we found that the modulated precipitation principle shows a very good correlation to particle number concentration, although the method significantly depends on the particle morphology. The conventional approach is not well suited for particle number measurements due to its intrinsic dependency on particle size. We demonstrate that the counting efficiency of the modulated precipitation configuration measured with different tests aerosols stays within 3% for particle sizes up to 80 nm. The difference between a calibration with soot and salt particles with respect to the total solid particle number concentration was estimated to be smaller than 11%. Thus, a calibration according to recently introduced PTI legislation with any of the test aerosols considered is feasible. Tailpipe measurements confirmed the applicability of the modulated precipitation configuration for PTI. As a consequence, the use of diffusion charging based instruments in periodic inspections seems to be suitable due to appropriate sensor response and the simplicity of the calibration process. Copyright © 2020 American Association for Aerosol Research

Open-source modelling of aerosol dynamics and computational fluid dynamics: Nodal method for nucleation, coagulation, and surface growth

Understanding formation, growth and transport of aerosols is critical to processes ranging from cloud formation to disease transmission. In this work, a numerical algorithm of aerosol dynamics including nucleation, coagulation, and surface growth was coupled with flow and heat transfer equations enabling the solution of three-dimensional multi-physics aerosol processes in an open-source platform. The general dynamic equation was solved by a nodal method where the particle size distribution was represented by a finite number of nodes. The models were verified by comparing four test cases, (1) pure coagulation, (2) nucleation and coagulation, (3) pure surface growth, and (4) a general dynamic equation that includes the three mechanisms provided in literature. A high temperature aerosol flow in a cooled pipe is chosen as a tutorial case of coupled computational aerosol and fluid dynamics. The aerosolGDEFoam code is available at https://openaerosol.sourceforge.io and can be further modified under GNU general public licence. Programme summary: Programme title: aerosolGDEFoam CPC Library link to programme files: http://dx.doi.org/10.17632/3s368jpdx2.1 Developer's repository link: https://openaerosol.sourceforge.io/ Licencing provisions: GNU General Public Licence 3 Programming language: C++ Nature of problem: aerosolGDEFoam solves the general dynamic equation coupled with flow and heat transfer equations enabling the solution of three-dimensional multi-physics aerosol processes using the open-source computational platform, OpenFOAM [1]. The general dynamic equation describes changes in aerosols due to e.g. nucleation, coagulation and evaporation/condensation, processes which depend on local conditions such as temperature and humidity. A zero-dimensional form of the general dynamic equation from Prakash et al. [2] has been implemented and verified with previously published examples. Solution method: aerosolGDEFoam employs an explicit time-stepping for the time-dependent source terms for aerosol dynamics. The solution methods and schemes provided by OpenFOAM 6 are used for spatial derivatives. References: [1] OpenFOAM6, OpenFOAM v6, in The OpenFOAM Foundation, https://openfoam.org/, [2] Prakash, A., A.P. Bapat, and M.R. Zachariah, A Simple Numerical Algorithm and Software for Solution of Nucleation, Surface Growth, and Coagulation Problems. Aerosol Science and Technology, 2003. 37(11): p. 892–898

Modelling the effect of aerosol polydispersity on unipolar charging and measurement in low-cost sensors

Low-cost ultrafine aerosol sensors are experimentally calibrated with controlled aerosol sources to provide metrics such as surface area, lung-deposited surface area, mean particle size and/or total concentration from one or more electrical current measurements. However, an aerosol with a large standard deviation in particle size provides a significantly different signal from a monodisperse aerosol with the same median particle size. In this paper, we investigate the effect of particle polydispersity on measurements in devices which employ unipolar charging. The conservation equations are solved for particle/ion charging and transport (convection, diffusion and electrical transport) in laminar, steady-state, incompressible flow. Lognormal particle size distributions are represented by over coupled conservation equations for multiple size bins and discrete charge states and solved numerically for the first time. Modelling results show that integrated electrical current from a polydisperse particle distribution can be represented by a monodisperse distribution characterised by the count mean diameter ( ; unipolar diffusion charging) or diameter of the average surface ( ; photoelectric charging) and total concentration, for a large range of particle distributions and operating conditions offering a convenient simplification for the interpretation of ultrafine particle measurements. The simplification reduces the number of simultaneous conservation equations required, thereby reducing computation time by up to 57 times for a polydisperse particle distribution represented by 16 discrete size bins. The method of analysis is useful to both users and developers of low-cost ultrafine particle sensors to understand the effect of particle polydispersity on measurements

Open-source modelling of aerosol dynamics and computational fluid dynamics: Bipolar and unipolar diffusion charging and photoelectric charging

Electric charging is one of the essential aerosol dynamic mechanisms and is harnessed for detection, capture and control of ultrafine aerosol particles in a range of devices. For simplicity, charging and transport mechanisms are commonly modelled with zero spatial dimensions (0-D) and averaged properties such as mean charge or mean particle diameter. These models often neglect localised effects of the flow distribution, diffusion, discrete charge states, and particle polydispersity, often proving inadequate to explain experimental data. This work aims to provide an open-source three-dimensional (3-D) aerosol charging and transport model including bipolar and unipolar diffusion charging, and photoelectric charging algorithms for use in detailed design and analyses of aerosol systems. The computational model consists of more than 200 particle transport equations for discrete charge states and polydisperse sizes coupled with ion conservation equations in the framework of OpenFOAM, an open-source computational fluid dynamics platform. Three test cases are introduced to verify implementation of three charging models by comparison with published literature: bipolar and unipolar diffusion charging, and photoelectric charging. Tutorial cases, which model three distinct aerosol sensors, are described and demonstrate the capabilities of the 3-D aerosol charging and transport models within the predetermined flow field. The aerosolChargingFoam code is available at https://openaerosol.sourceforge.io for widespread use and can be further modified under the GNU general public licence. Program summary: Program title: aerosolChargingFoam CPC Library link to program files: https://doi.org/10.17632/4pf4n2vg9f.1 Developer's repository link: https://openaerosol.sourceforge.io/ Licensing provisions: GNU General Public License 3 Programming language: C++ Nature of problem: aerosolChargingFoam solves generalised aerosol electrical charging and transport equations coupled with computational fluid dynamics using the open-source computational platform, OpenFOAM [1]. The electric charging algorithm including unipolar diffusion charging, bipolar diffusion charging, and photoelectric charging is verified with zero-dimensional test cases [2-4] and generalized to three-dimensional monodisperse or polydisperse particle distributions for more than 50 particle charge states. aerosolChargingFoam can be straightforwardly coupled with other existing solvers, which enables computations of complex multi-physics aerosol charging processes in practical conditions. Solution method: aerosolChargingFoam employs an explicit time-stepping for the time-dependent source terms for generalised aerosol charging. The solution methods and schemes provided by OpenFOAM 9 are used for solving the spatial and time derivatives in the transport equations. References: [1] OpenFOAM9, OpenFOAM v9, The OpenFOAM Foundation, https://openfoam.org/. [2] W.A. Hoppel, G.M. Frick, Aerosol Sci. Technol. 12 (3) (1990) 471–496. [3] A. Maisels, F. Jordan, H. Fissan, J. Appl. Phys. 91 (5) (2002) 3377–3383. [4] H. Kaminski, T.A.J. Kuhlbusch, H. Fissan, L. Ravi, H.-G. Horn, H.-S. Han, et al., Aerosol Sci. Technol. 46 (6) (2012) 708–716