title: Propagation and breakup of liquid menisci and aerosol generation in small airways.
abstract: BACKGROUND
  Droplets exhaled during normal breathing and not associated with coughing may pose hazardous agents to infective diseases dissemination. The objective is to explore the physical mechanism, which may lead to droplets formation.
  
  
  METHODS
  We hypothesize that liquid menisci occlusions, which may form inside small airways, travel along the airway, may lose mass and finally disintegrate into small droplets. This hypothesis was numerically investigated applying physiologically plausible values of the phenomenological coefficients and geometrical conformations.
  
  
  RESULTS
  We show that three important dimensionless parameters control the motion and disintegration of menisci: the dimensionless mucus layer thickness, the dimensionless menisci initial thickness (all scaled by the airway radius), and the capillary number. Menisci traveling within airways may either remain at equilibrium or diminish or increase in size. Menisci that diminish in size may collapse into the mucus layer; form a large droplet that contains most of the menisci mass before disintegration; or form a larger number of small droplets (we show the forming of three or four droplets in a single occluded airway).
  
  
  CONCLUSIONS
  A critical capillary number for menisci at equilibrium could be defined. It was shown that menisci tend to diminish in size as the capillary number increases above the critical value, and a number of small droplets may be formed during normal breathing.
authors: Technicon, Department of Mechanical Engineering, Haifa, Israel.
authors: Andrei
authors: A
authors: Malashenko
authors: Akira
authors: A
authors: Tsuda
authors: Shimon
authors: S
authors: Haber
mesh_terms: D000336:Aerosols; D000402:Airway Obstruction / Q000209:etiology*; D003141:Communicable Diseases / Q000635:transmission; D045853:Exhalation; D006801:Humans; D008954:Models, Biological; D012119:Respiration; D015656:Respiratory Mechanics
chemical_list: D000336:Aerosols