Development of a fog droplet sampler with multi-segment structure and specific temperature control

Abstract

Accurate and efficient sampling of fog droplets is a prerequisite for online measurement. The performance of such a sampler relies on the internal flow field, temperature, and humidity. Based on aerodynamics and turbulence theory, we designed a fog droplet sampler with multi-segment structure and specific temperature control. First, we used COMSOL to investigate the effects of key system parameters. The sampling efficiency first increased and then decreased with sampling flow. The reason was that the impact force under reasonable flows maintained particles in suspension, whereas high flows with high turbulence intensity increased the likelihood of particles colliding with the walls. Based on the simulations, we determined the optimal sampling flow (1000 L/min), segment structure (a cylindrical inlet), and segment dimension (25 mm for the optical measurement segment) of the sampler, with a sampling efficiency of 0.87. Subsequently, we investigated the effects of temperature, relative humidity, and sampling flow on the particle size. Size change increased with temperature but decreased with relative humidity and sampling flow. Additionally, temperature control contributed to condensation prevention, and size change was < 1% when the temperature was 15 °C. Finally, we conducted an experiment for verification purposes. The sampling efficiency of the fabricated system was 0.77, i.e., 11.49% lower than for the simulation. Size change was < 1 μm in both the simulations and the experiments, while variation was 6.30% in the experiment, i.e., a difference of 3.97% from the simulation. Hence, the designed fog droplet sampler achieved accurate and efficient sampling of fog droplets.