Experimental validation of the TRAP (TheRmophoretic Annular Precipitator) in laminar configuration

- A new TheRmophoretic Annular Precipitator (TRAP) is proposed.
- The TRAP is sized using a laminar deposition model and a CFD numerical simulation.
- Experimental validation of the TRAP with spherical particles is presented.

A TheRmophoretic Annular Precipitator (TRAP) aimed to study the thermophoresis of soot particles is presented in this paper. This device consists of two 0.5 m length concentric tubes together with an inner cylinder and an external envelope. The particles flow through the 1 mm gap created between the inner and outer tubes with imposed temperatures, the inner tube is cooled and the outer one is heated. A thermal gradient is thus created, and particles will deposit by thermophoresis on the inner tube cold wall. This device is based on the so-called penetration method, where the deposition rate on the cold wall is obtained by particles concentration measurements upstream and downstream of the test section. A model developed in this study allowed the conversion of the deposition rates into thermophoretic diffusion coefficients Kth. In this work, the thermophoretic diffusion coefficient in a vertical laminar flow were measured for mono-dispersed spherical PSL particles with particles diameter ranging from 0.1 to 1 μm, and also for poly-dispersed DEP droplets oil with particles diameter from 0.1 to 0.65 μm. The Reynolds number and the thermal gradient values were fixed respectively at 520 and 60,000 K m−1 in order to avoid convective effects that might appear in a laminar configuration. The thermophoretic diffusion coefficients were compared to the theoretical models and other experimental data from the literature. The good agreement found especially with Beresnev and Chernyak (1995) model together with the experimental data validates the use of the TRAP to the on-line determination of the soot particles thermophoretic diffusion coefficients.