Model Calculations and Wind Tunnel Testing of an Isokinetic Shroud for High-Speed Sampling

Twohy, Cynthia H.

doi:10.1080/02786829808965568

Cited by 22 publications

(9 citation statements)

References 12 publications

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“…However, concerning the transmission efficiency of the aerosol inlet, only additional wind tunnel studies could provide a complete characterization. Furthermore, in such wind tunnel studies, it should also be investigated whether the use of a shroud would be beneficial (Baumgardner et al, 1991;Murphy and Schein, 1998;Twohey, 1998;Weber et al, 1998). Particle losses inside the inlet system are assumed to be negligible for particle sizes smaller than 500 nm.…”

Section: Discussionmentioning

confidence: 99%

Experimental characterization of the COndensation PArticle counting System for high altitude aircraft-borne application

et al. 2009

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Abstract.A characterization of the ultra-fine aerosol particle counter COPAS (COndensation PArticle counting System) for operation on board the Russian high altitude research aircraft M-55 Geophysika is presented. The COPAS instrument consists of an aerosol inlet and two dual-channel continuous flow Condensation Particle Counters (CPCs) operated with the chlorofluorocarbon FC-43. It operates at pressures between 400 and 50 hPa for aerosol detection in the particle diameter (d p ) range from 6 nm up to 1 µm. The aerosol inlet, designed for the M-55, is characterized with respect to aspiration, transmission, and transport losses. The experimental characterization of counting efficiencies of three CPCs yields d p50 (50% detection particle diameter) of 6 nm, 11 nm, and 15 nm at temperature differences ( T ) between saturator and condenser of 17 • C, 30 • C, and 33 • C, respectively. Non-volatile particles are quantified with a fourth CPC, with d p50 =11 nm. It includes an aerosol heating line (250 • C) to evaporate H 2 SO 4 -H 2 O particles of 11 nm

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Section: Discussionmentioning

confidence: 99%

Experimental characterization of the COndensation PArticle counting System for high altitude aircraft-borne application

et al. 2009

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“…Modifications to the original inlet lip structure and inner CVI geometry have led to increased collection efficiencies at lower particle diameters (Anderson et al, 1993;Schwarzenböck and Heintzenberg, 2000). Further enhancements include the addition of upstream shrouds to aid the alignment of the free stream with the inlet (Twohy, 1998). However, a number of issues still persist.…”

Section: Introductionmentioning

confidence: 99%

Characterisation and airborne deployment of a new counterflow virtual impactor inlet

et al. 2012

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Abstract.A new counterflow virtual impactor (CVI) inlet is introduced with details of its design, laboratory characterisation tests and deployment on an aircraft during the 2011 Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE). The CVI inlet addresses three key issues in previous designs; in particular, the inlet operates with: (i) negligible organic contamination; (ii) a significant sample flow rate to downstream instruments (∼15 l min −1 ) that reduces the need for dilution; and (iii) a high level of accessibility to the probe interior for cleaning. Wind tunnel experiments characterised the cut size of sampled droplets and the particle size-dependent transmission efficiency in various parts of the probe. For a range of counter-flow rates and air velocities, the measured cut size was between 8.7-13.1 µm. The mean percentage error between cut size measurements and predictions from aerodynamic drag theory is 1.7 %. The CVI was deployed on the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter for thirty flights during E-PEACE to study aerosol-cloud-radiation interactions off the central coast of California in July and August 2011. Results are reported to assess the performance of the inlet including comparisons of particle number concentration downstream of the CVI and cloud drop number concentration measured by two independent aircraft probes. Measurements downstream of the CVI are also examined from one representative case flight coordinated with shipboard-emitted smoke that was intercepted in cloud by the Twin Otter.

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“…Deviations from perfect alignment are expected to degrade the performance of the CVI because larger particles that enter the CVI at finite attack angle may directly impact the inner wall of the CVI (Twohy 1992). Recently, a model was developed by Twohy (1998) to study the effect of an isokinetic shroud on the flow field of the CVI. The shroud was shown to improve the alignment between the free stream flow and the CVI inlet.…”

Section: Introductionmentioning

confidence: 99%

Effect of Angle of Attack on the Performance of an Airborne Counterflow Virtual Impactor

Chen

Conant

Rissman

et al. 2005

Aerosol Science and Technology

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A three-dimensional model has been developed within the framework of the commercial computational fluid dynamics program, FLUENT R , to investigate the collection efficiency of an airborne counterflow virtual impactor (CVI). The model assumes steady-state, isothermal, compressible, and turbulent flow. Particle trajectories are computed based on the Lagrangian discrete phase model (DPM). In addition to predicting the effects of flight velocity and counterflow rate on the particle collection efficiency, as do prior models, the model quantifies the effect of flight attack angle on the particle collection efficiency. With an angle of attack as small as 5 • , the CVI collection efficiency drastically degrades at large particle sizes, and only particles with intermediate sizes are collected. Smaller particles do not have sufficient inertia to fight the counterflow, and larger particles tend to impact the CVI inner walls and are lost to the CVI walls. The modeling results show that the alignment between the free stream flow and the CVI inlet is critical to the performance of the CVI.

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Model Calculations and Wind Tunnel Testing of an Isokinetic Shroud for High-Speed Sampling

Cited by 22 publications

References 12 publications

Experimental characterization of the COndensation PArticle counting System for high altitude aircraft-borne application

Experimental characterization of the COndensation PArticle counting System for high altitude aircraft-borne application

Characterisation and airborne deployment of a new counterflow virtual impactor inlet

Effect of Angle of Attack on the Performance of an Airborne Counterflow Virtual Impactor

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