Thermophoretic Deposition of Particles in Laminar and Turbulent Tube Flows

Abstract

Thermophoretic deposition of aerosol particles (particle diameter ranges from 0.038 to 0.498 µm) was measured in a tube (1.18 m long, 0.43 cm inner diameter, stainless steel tube) using monodisperse NaCl test particles under laminar and turbulent flow conditions. In the previous study by Romay et al., theoretical thermophoretic deposition efficiencies in turbulent flow regime do not agree well with the experimental data. In this study, particle deposition efficiencies due to other deposition mechanisms such as electrostatic deposition for particles in Boltzmann charge equilibrium and laminar and turbulent diffusions were carefully assessed so that the deposition due to thermophoresis alone could be measured accurately. As a result, the semiempirical equation developed by Lin and Tsai in laminar flow regime and the theoretical equation of Romay et al. in turbulent flow regime are found to fit the experimental data of thermophoretic deposition efficiency very well with the differences of less than 1.0% in both flow regimes. It is also found that Talbot's formula for the thermophoretic coefficient is accurate while Waldmann's free molecular formula is only applicable when Kn is greater than about 3.0.

Development and Characterization of a Fast-Stepping/Scanning Thermodenuder for Chemically-Resolved Aerosol Volatility Measurements

“…Thermophoresis will act to focus the particles in the heated section, but de-focus the particle stream as it enters the cooler denuding section. These increased losses at higher temperatures are expected and are within the range of characterizations carried out in previous studies of heated tubes using both theoretical (Housiadas and Drossinos 2005;Stratmann and Fissan 1988) and experimental (Burtscher et al 2001;Tsai et al 2004;Walsh et al 2006) techniques. While diffusion increases greatly as particle size decreases, thermophoretic forces are not strongly sizedependent (Burtscher et al 2001;Hinds, 1999b), but can move particles closer to the walls where diffusion of small particles can be more efficient.…”

Experimental evaluation of the critical local wall shear stress around cylindrical probes fouled by diesel exhaust gases

“…The importance of this deposition mechanism has been exhaustively studied theoretically with models [25], experimentally with latex particles [26], and specifically with soot particles [27]. The authors of these studies have indicated the importance of thermophoresis for small particles.…”

A New Thermophoretic Precipitator for Collection of Nanometer-Sized Aerosol Particles

“…In fact, this phenomenon has been extensively studied both theoretically and experimentally (e.g., Brock 1962;Montassier et al 1991;Stratmann et al 1994;Brown et al 1994;Romay et al 1998;Tsai et al 2004). Thermophoresis has been exploited in the design of thermophoretic precipitators to deposit particles from gas streams.…”