A Phenomenological Two-Phase Flow Model of Atomization in an Internally Mixed Liquid Atomizer

Abstract

This paper describes the development and predictions of an engineering model that depicts the two-phase flow within an internally mixed air-assisted liquid atomizer. The main objective of this study is to develop an analytical tool that could be used in the design of improved internally mixed injectors and to predict the injector's flow and spray characteristics under different operating conditions. The developed model assumes that the formation of liquid drops, due to the interaction between the air and liquid flows, occurs inside the injector in an internally mixed atomizer. Basic conservation equations, along with appropriate boundary conditions, are used to model the two-phase air-liquid flow inside the injector. A critical Weber number criterion is used to estimate the mean size of the droplets being produced in the process. A unique solution procedure, using transformation and elimination of variables, is developed to solve this set of equations, which can be readily implemented on a PC. The liquid flow rates and mean droplet sizes, predicted by the model, are compared with the experimentally obtained results and they are found to be in good agreement with each other.

A Heuristic Model of Twin Fluid Internally Mixed Atomization using Distributed Weber Number Criterion

“…Figure 8 shows the dependence of the droplet diameter upon the ALR for a liquid supply pressure of 138 kPa and atmospheric back pressure. While the CCWNM was able to predict only an arithmetic mean diameter [43], the DWN model predicted both, the mean diameter and the SMD. It is evident from Figure 8 the mean droplet diameters predicted by this model are in relatively good agreement with the experimental results and the predicted SMDs also follow the experimental data quite well.…”

“…The model, called the Distributed Weber Number (DWN) model, is developed to predict the behavior of the two-phase air-liquid flow through the investigated, internally mixed, twin fluid, atomizer, which incorporates the formation of a range of sizes of liquid droplets at each location inside the injector. In the Constant Critical Weber Number Model (CCWNM) proposed in [43], it was assumed that the critical Weber number remains constant throughout the flow and that droplets of equal size are present at each location inside the injector. In contrast to the CCWNM, the DWN model assumes that at any given location inside the injector a range of droplets is produced in a manner that satisfies a certain specified Weber number distribution instead of a constant critical Weber number criterion.…”

“…is the rate of work done by the drag force on the droplets of a particular group [43]. The hydraulic diameter corresponding to each droplet group is given by:…”

“…First, the liquid supply pressure, air stagnation temperature, back pressure (P b ) and ALR were provided to the program as inputs. An initial estimate of the liquid mass flow rate was obtained by using the CCWNM [43]. In order to simplify the numerical solution of the model problem, it was assumed that the assumptions of the CCWNM were satisfied by the twophase flow for 0 < ≤ L. Therefore, the droplet diameter and the other flow properties, i.e., V l , V a , P, T a , q a , A a and A l , at x = L were estimated using the CCWNM.…”

A twin-fluid injector for FCC feed injection

“…9 In gas assisted atomizers, a small amount of compressed gas is introduced into the liquid stream before its discharge from the nozzle orifice. Major portion of atomization energy is supplied by the compressed gas in gas-assisted atomizers through the interaction between the two-phases in the confines of the atomizer [10][11][12][13][14][15] resulting in fine atomization. Ferrira et al, 16 have successfully used twin-fluid atomizers to atomize heavy oils and have provided design guidelines for the same.…”