Evaporation of Multicomponent Drop Arrays

Abstract

The conventional fuels that are used in the field of transportation are primarily composed of two or more components. Each component evaporates, mixes with hot oxidant gases, ignites, and burns. Since evaporation is the precursor of the sequence of events leading to combustion, the evaporation studies on the multi-component drops are essential for determining the governing parameters of spray evaporation. While single-component drop studies have been carried out extensively in the past, very limited literature exists on the multicomponent array evaporation. The present paper deals with the evaporation of multicomponent fuel droplets in an array using the recently developed point source method (PSM). First, the quasi-steady (QS) evaporation of an isolated, multicomponent droplet is briefly analyzed. The resultant governing equations, along with Raoult’s law and the Cox-Antoine relation, constitute the set of equations needed to arrive at the solutions for: (1) the droplet surface temperature, (2) the evaporation rate of each species, and (3) the vapor mass fraction of each species at the droplet surface. The PSM, which treats the droplet as a point mass source and heat sink, is then adopted to obtain an analytic expression for the evaporation rate of a multicomponent droplet in an array of liquid droplets. Defining the correction factor (η) as a ratio of the evaporation of a drop in an array to the evaporation rate of a similar isolated multi-component drop, an expression for the correction factor is obtained. The results of the point source method (PSM) are then compared with those obtained elsewhere for a three-drop array that uses the method of images (MOI). Excellent agreement is obtained. The treatment is then extended to a binary drop array to study the effect of interdrop spacing on vaporization. When the drops are close to each other, the evaporation rate of the droplet in the array containing the larger percentage of volatiles is higher than the rate under isolated conditions (η>1). The results qualitatively confirm the experimental data reported elsewhere. Parametric results were obtained for the effect of changing the composition on the correction factor and finally critical drop compositions in the binary array are given for which η>1. Even though the results for the average correction factor of the whole array of 2 to 9 drops obtained using PSM are almost the same as the results from MOI, the correction factor of the center drop under severe interaction may deviate from those results obtained with MOI.