The Development of a New Thermophoretic Precipitator for Scanning Transmission Electron Microscope Analysis of Ultrafine Aerosol Particles

A thermophoretic sampler is designed for the collection of particles smaller than 10 nm. The sampler is composed of heated and cooled surfaces separated by a gap of 0.1 mm; a bypass flow is introduced in the design to minimize the diffusional loss of nanoparticles in the upstream flow channel. Particles may be directly deposited on a 3 mm diameter TEM grid for chemical analysis or on other substrates for other purposes. Calculations show that at an inlet flow rate of 1.5 lpm and thermal gradient of 5 × 10 5 K/m, a maximum collection efficiency of 41% can be achieved for a particle diameter of 1 nm. Ag particles with median size of 6 nm are used to characterize the thermophoretic sampler collection efficiency. The TEM images show that a sizeable number of particles less than 10 nm in diameter are collected, although they are not uniformly distributed on the grid, and the collection efficiency deduced from these deposited particles is much less than the theoretical estimation. Despite this, the efficiency is orders of magnitude higher than previous designs and it is easier to build.

Section: Design Of Thermophoresis Samplermentioning

confidence: 99%

“…To identify the nucleating compounds, we have modified and improved the thermophoretic precipitator designed by Maynard (1995), and have validated its collection efficiency under laboratory conditions.…”

Section: Introductionmentioning

confidence: 99%

Thermophoretic Sampler and its Application in Ultrafine Particle Collection

Wen

Wexler

2007

“…Thermophoretic precipitator can be used for aerosol sampling (Maynard 1995;Bang et al 2003;Lorenzo et al 2007;Wen et al 2007) as well as submicron particle control (Shi and Harrison 2001;Messerer et al 2003). Extensive literature has been published for thermophoretic precipitation in pipe flow (Batchelor and Shen 1985;Montassier et al 1990Montassier et al , 1991Stratmann et al 1994;Chang et al 1995;He and Ahmadi 1998;Romay et al 1998;Lin and Tsai 2003;Lin et al 2004;Tsai et al 2004; Lee et al 2006;Lin et al 2008), in flow between parallel plates (Maynard 1995;Tsai and Lu 1995;Gonzalez et al 2005), and in tube bundle heat exchanger (Messerer et al 2004;Messerer et al 2007). The computational fluid dynamics (CFD) codes was further used to investigate aerosol dynamics (Stratmann and Whitby 1989;Pyykönen and Jokiniemi 2000), thermophoretic deposition in tube flow (Housiadas et al 2001;Housiadas and Drossinos 2003;Housiadas and Drossinos 2005;Munoz-Bueno et al 2005) and in thermophoretic precipitator (Gonzalez et al 2005).…”

Section: Introductionmentioning

confidence: 99%

A New Cross-Flow Tube Bundle Heat Exchanger with Staggered Hot and Cold Tubes for Thermophoretic Deposition of Submicron Aerosol Particles

Chien

Huang

Tsai

2009

A new tube cross-flow bundle heat exchanger has been designed and tested for thermophoretic deposition of submicron aerosol particles. The present design has five columns of hot and cold square tubes, respectively, arranged in a staggered manner to maintain a nearly constant temperature gradient in the direction of the aerosol flow. Each column has four tubes of 4 mm × 4 mm in cross section and the gap between the tube surfaces is 0.5 mm. The precipitator was tested experimentally using monodisperse NaCl test particles ranging from 38 to 397 nm in diameter at the aerosol flow rate of 0.6 and 1.2 L/min, respectively, at different temperature gradients. Results showed that the thermophoretic deposition efficiency increased with decreasing aerosol flow rate and increasing temperature gradient with the maximum thermophoretic deposition efficiency occurred at the aerosol flow rate of 0.6 L/min. The effect of inlet temperature of the aerosol flow on the efficiency was also tested and showed increasing inlet temperature increased the deposition efficiency. Numerical simulation was further conducted to validate the experimental data and good agreement was obtained. An empirical equation was also validated to facilitate the design and scale-up of the precipitator.

“…Thermophoretic aerosol samplers were first employed to assess exposures within the dusty trades, such as mining; these early designs were used primarily as area monitors with sample focused onto a glass slide for analysis by optical microscopy (Watson 1936;Oldham and Roach 1952;Roach 1959). More contemporary designs tend to employ cylindrical (Rogak et al 1993;Wang et al 2012) or plate-to-plate geometries (Tsai and Lu 1995;Wang et al 2012) with sample analysis by electron microscopy (Rogak et al 1993;Maynard 1995;Bang et al 2003;Lorenzo et al 2007). Size distribution measurements made with thermal precipitators tend to agree well with measurements from scanning mobility particle sizers (Boskovic and Agranovski 2012;Miller et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Development of a Transfer Function for a Personal, Thermophoretic Nanoparticle Sampler

Leith¹,

Miller-Lionberg²,

Casuccio³

et al. 2013

Effective assessment of nanoparticle exposures requires accurate characterization of the aerosol. Of increasing concern is personal exposure to engineered nanoparticles that are specifically designed for use in the nanotechnology sector. This manuscript describes the operation and use of a personal sampler that utilizes thermophoretic force to collect nanoparticles onto a standard TEM (transmission electron microscope) grid. After collection, nanoparticles on the TEM grid are analyzed with an electron microscope, and the resultant data used to determine the characteristics of the nanoparticle aerosol sampled. Laboratory experiments were conducted to determine the inlet losses and collection efficiency of the thermophoretic sampler for particles between 20 and 600 nm in diameter. These results are used together with theory for thermophoretic velocity to form a transfer function that relates the properties of the collected particles to the properties of the sampled aerosol. The transfer function utilizes a normalization factor, F(d), which is larger than unity for very small particles but approaches unity for particles larger than about 70 nm.