Characteristics analysis of supercritical CO2 sub-micron particle deposition in heat exchanger channel

Abstract

Better understanding of the dispersion and deposition of sub-micron particles in supercritical CO₂ (SCO₂) is crucial for the safe operation of supercritical thermal equipment. In present study, the numerical simulation was carried out to evaluate the deposition features of sub-micron particles in SCO₂. The anisotropic flow in the gas phase was predicted using the Re-Normalization Group (RNG) k-ε turbulent model and the particle trajectory was tracked using the discrete particle model (DPM). Moreover, the particle deposition under heating and cooling condition were presented. The effects of particle type, wall temperature, inlet flow velocity, temperature and pressure on particle deposition were investigated. The analysis found that the deposition velocity is more applicable to judging the particle deposition than the dimensionless deposition velocity. When SCO₂ is cooled, it promotes particle deposition, and when it is heated, it prevents deposition due to thermophoretic forces. Particles are easily deposited when SCO₂ exceeds the pseudo-critical point in the gaseous-like region. Moreover, stainless steel has greater deposition velocity than graphite due to the large density. The inlet flow velocity has different effects on particle deposition. It promotes the deposition of small particles, medium particles remain stable, and large particles first decrease and then increase. The particle diameter is closely related to the deposition distance. The deposition probability for 1 μm, 10 μm and 50 μm is 63%, 77% and 85% at 0–0.2 m, respectively.