Deposition characteristics of particles in inclined heat exchange channel with surface ribs

Abstract

Ash particles in flue gas flow would deposit on the heat recovery exchanger in the waste heat recovery system (WHRS), which may lead to the reduction of heat transfer efficiency and service life. Understanding of ash particle deposition in the heat exchange channel is crucial for the safe operation of WHRS. In this study, deposition characteristics of ash particles in an inclined heat exchange channel with surface ribs were investigated by using Reynolds stress model combined with discrete phase model. The turbulent fluctuation correction and particle rebound model were developed by using UDF program to improve the prediction accuracy. After grid sensitivity analysis and numerical verification, the flue gas thermal-fluid fields, the 3D particle deposition patterns and deposition efficiency on each ribbed channel surface were obtained and analyzed. Parameter study on the deposition characteristics was conducted by considering flue gas flow velocity, particle size and inclination angle of the ribbed channel. The results showed that significant secondary flow eddies can be observed near the rib windward surfaces and high-value turbulent intensity area appears near the rib crest. The windward surfaces and the crests of the ribs are the main deposition locations in the inclined heat exchange channel. The deposition efficiency in the ribbed channel is obviously changed by the particle diameter and flue gas flow velocity. The inclination angle has little influence on deposition efficiency for small particles (dp<5μm) but great effect on deposition efficiency for large particles (dp>10μm).