Influence of sprayed water temperature on phase changes in droplets slipping in radiative flue gas flow of industrial biofuel boilers

Abstract

This work presents the investigation of phase changes of water droplets with an equivalent diameter of 50–500 μm and initial temperatures of 40 °C and 90 °C in a flue gas flow with a temperature of 200–1200 °C in the case of complex heating, modeled from the application of technological water injection in industrial biofuel boilers. It was assumed that the radiation and multiple reflection of the soot-coated walls in the two-phase flow of droplets and flue gas provide the spectral intensity of blackbody radiation incident on an individual droplet. Convective droplet heating was defined by an initial Reynolds number of 0–200. A numerical scheme based on an iterative algorithm for determining the instantaneous temperature of the droplet surface, which works according to the fastest convergence method, is based on a balance of heat fluxes. It has been highlighted that in a slipping droplet, there is an intense interaction between absorbed radiation and forced convection processes of water, which defines the complex dynamics of the droplet’s thermal and energy state in phase change regimes. It has been justified that the influence of the temperature of the injected water on the equilibrium evaporation of droplets is insignificant, but it has a significant effect on transitional phase changes in droplets. It has been suggested that the thermal state of water be defined using a parameter expressed as the ratio of the equilibrium evaporation temperature to the water temperature, rather than evaluating it based on its sensory temperature.