Novel electric thermophoretic sampling device with highly repeatable characteristics

• Published in: Review of scientific instruments 2016-12, Vol.87 (12), p.125108-125108
• Main Authors: Altenhoff, Michael, Teige, Christian, Storch, Michael, Will, Stefan
• Format: Article
• Language: English
• Subjects: Electric motors; Equivalence ratio; Ethylene; High speed; Nanoparticles; Radiance; Samplers; Scientific apparatus & instruments; Soot; Transmission electron microscopy
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/1.4971988

A novel thermophoretic sampling device for probing nanoparticle aggregates in all types of flames as well as in particle-laden gases and aerosols is presented. For the motion of the sampling probe, a tubular electric linear motor is utilized, and its design and operation are described in detail. The spatial and temporal performance is determined from oscilloscope measurements and high-speed recordings of one motion profile featuring three different resident times. Motion sequences offering a minimum residence time of 3 ms and a maximum velocity of 4.1 m s−1 simultaneously providing smooth probe movement and minimal vibrations are feasible. For a stroke length of 100 mm, maximum deviations between sampling and setpoint positions of 0.14 mm in axial, 0.02 mm in horizontal, and 0.36 mm in vertical direction are determined, respectively. The evaluation of standard deviations among individual motion sequences for every time step shows high precision in all directions of movement. The influence of probe invasion on a laminar premixed flame produced using a McKenna burner is characterized employing high-speed recordings. Soot radiance intensities are temporally evaluated in four regions of interest near the sampling probe where maximum changes in the order of 20% are observed. Thermophoretic sampling was performed on the flame at 17 mm height above burner using ethene and ethyne as fuels with an equal equivalence ratio of 2.7. Morphological soot aggregate properties are derived from comprehensive transmission electron microscopy analysis and show satisfying results.