Multimode breakup

In the breakup regimes, a droplet may undergo secondary breakup when the breakup time is reached. The droplet size distribution after bag or multimode breakup may follow the Simmons root-normal distribution pattern 264 with MMD/SMD equal to 1.1,... 

Keywords Bag breakup Breakup mode Breakup time Catastrophic breakup Fragments Fragment size distribution Initiation time Multimode breakup Newtonian drops Non-Newtonian drops Ohnesorge number (Oh) Secondary atomization Secondary breakup Sheet-thinning breakup Total breakup time Vibrational breakup Weber number (We)... 

Multimode breakup occurs at values of We between those of bag- and sheetthinning and resembles a combination of the two breakup modes. Bag formation accompanied by the presence of a core drop results in the formation of a long ligament in the center of the bag, which is referred to as a stamen or plume [1,16], The third image in the second row of Fig. 6.1 illustrates the bag/plume structure. 

In the multimode case, non-Newtonian drops form a much more pronounced stamen that has a much longer lifetime. This stamen eventually forms many large fragments when it finally breaks up. In the sheet-thinning case, non-Newtonian breakup proceeds through two steps - the thinning of the sheet followed by the drop core forming a bag that experiences multimode breakup. 

Z. Dai, G. M. Faeth Temporal Properties of Secondary Drop Breakup in the Multimode Breakup Regime, Inti. J. Multi. Flow 27(2), 217-236 (2001). 

When a droplet breaks up, it results in a group of new droplets with a certain size distribution and mean diameter. The Sauter mean diameter (SMD) is computed for bag breakup and multimode breakup from the following relation ... 

The fine fraction of the droplet fragments is distributed as in bag and multimode breakup regimes based on a reduced SMD which is derived from the Sauter mean diameter dj,z given by (18.15) and the maximum stable diameter by (18.16), as... 

The lognormal distribution function can be interpreted physically as the result of a process of breakup of larger particles at rates that are normally distributed with respect to particle size (Aitchison and Brown, 1957). Approximately lognormal distributions also result when the aerosol size distribution is controlled by coagulation (Chapter 7). In this case the value of the standard deviation is determined by the form of the particle collision frequency function. Multimodal aerosols may result when particles from several different types of sources are mixed. Such distributions are often approximated by adding lognormal distributions, each of which corresponds to a mode in the observed distribution and to a particular type of source. 

Other breakup structures have also been observed to occur in the multimode regime. One example is the plume/sheet-thinning morphology identified in [16], Nevertheless, all of these structures can be thought of as resembling some combination of bag- and sheet-thinning breakup. 

Non-Newtonian liquids also exhibit a transitional multimode regime between bag and sheet-thinning breakup. It is important to note that only bag/plume-type breakup has been observed. Other breakup structures discussed in the Newtonian section have not been observed for non-Newtonian drops. It is unclear if this is due to a lack of available data or some rheological difference. 

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