Effects of wake dynamics on infrared measurements of particle cloud temperatures in the superheater pendant region of utility boilers

Turbulent particle cloud temperatures in the superheater pendant region are critical in coal-fired utility boilers not only for the interactions between turbulence and radiative heat transfer, but also for the ash deposit slagging and fouling on superheater tubes. The false infrared particle temperature fluctuations due to the pendant wake dynamics may cause large errors in modeling of the radiation transport. This paper presents a model to theoretically analyze the effects of wake dynamics on the false infrared particle cloud temperature fluctuations in the superheater pendant region. The preferred frequency in the power spectra and the root mean square temperature fluctuations are predicted theoretically and the effects of utility boiler operating conditions are analyzed. The preferred frequency is twice the vortex shedding frequency and is proportional to the flue gas velocity, and inversely proportional to the superheater tube diameter. The root mean square temperature fluctuations are proportional to the initial particle volume fraction and inversely proportional to the 1.04 power of the particle mass weighted mean diameter.