Atomization of liquids is a key component in many natural phenomena and technical processes. For example, combustion in most engines relies on liquid fuel being atomized, evaporated, and mixed with air before chemical reactions can occur. The ensuing combustion generates temperature variations on the order of 1000K. Since all processes occur in a turbulent environment, the atomizing liquid itself is subjected to a broad range of local temperature fluctuations. The direct impact of temperature fluctuations on the phase interface of the atomizing liquid are two-fold. For one, the local evaporation rate depends strongly on the local temperature. Furthermore, surface tension is significantly influenced by the local gas/liquid interface temperature. Tangential variations in surface tension result in Marangoni forces that impact the flow field at the gas/liquid interface, which in turn alter the interfacial temperature distribution via the induced interfacial flow. The Weber number, describing the ratio of global inertial to surface tension forces, is typically large in technical applications (using the diameter of the initial liquid jet as the length scale). However, atomization, which constitutes the first in the sequence of processes leading to combustion, always occurs on small scales (involving droplets which are many orders of magnitude smaller than the diameter of the initial liquid jet). At these scales, surface tension forces are dominant. Variations in temperature, resulting in variations in surface tension forces, can thus influence atomization significantly. Moreover, the developing thermal boundary layers at the gas/liquid interface impact evaporation rates, which in turn alter the local temperature via latent heat effects. Current models describing the atomization process are often based on empirical correlations or over-simplifying assumptions and are unable to truly predict the atomization outcome (in particular, the time variation of the probability density distribution of droplet length scales). Instead, tuning of adjustable parameters has to be performed in order to match experimentally available data. Especially in the later stages of atomization, the so-called secondary atomization, it is common practice to describe the generated liquid structures in a Lagrangian point-particle frame. This approach requires appropriately parameterized models for the drops drag, evaporation, and continued atomization. However, these models neglect the effects of temperature fluctuations on breakup, both in terms of thermal Marangoni flow and evaporation induced effects. A goal of this project is to establish in which regimes temperature fluctuations have to be considered and to develop the necessary enhancements to the secondary drop atomization models.
|Effective start/end date||7/1/08 → 6/30/12|
- National Science Foundation (NSF): $337,118.00