Transport coefficients and life history of a vaporising liquid fuel droplet subject to retardation in a convective ambience

Abstract

A numerical model has been developed for the process of droplet evaporation in a convective surrounding of high temperature gas. The model is based on numerical solution of unsteady conservation equations of mass, momentum, energy and species for both the gas and liquid phase. The important feature of the work is the consideration of continuous variation in free stream velocity with respect to the drop. This has been made in consideration of varying slip velocity (the velocity of droplet relative to free stream gas) of a moving droplet in a gaseous medium in real situation. The temporal reduction in free stream velocity has been evaluated from the droplet drag determined by the pressure and velocity fields of the gas phase surrounding the droplet. The relationships of drag coefficient and Nusselt number with the controlling variables like Reynolds number and Prandtl number have been established in the case of varying free stream velocity relative to the droplet, and have been compared with the standard laws for constant slip velocity. Other important charcteristics of vaporising droplet, like mass depletion history and temperature response, under the present situation, have been determined as a function of pertinent controlling parameters like initial Reynolds number of the droplet and the ratio of free stream to initial droplet temperature.