Laminar jet flow at the microscale: The characteristic sizes and the wave development

Laminar jet flow is an underlying phenomenon used to generate droplets efficiently. However, its hydrodynamics at the microscale remains unknown. This work focuses on the scale effect. We innovatively propose the difference between the jet at the microscale and that at the regular scale is not in the wave development but in the regime of flow pattern, and it’s much more stable at the microscale. The characteristic effect at the microscale due to the intensified gas/liquid/solid–liquid interaction is first reported. The variations of characteristic sizes and hydrodynamics with the kinetic energy, physical property, and structural size at the microscale are analyzed by introducing two key parameters − wave velocity and wave numbers, which are first proposed. The result shows that the kinetic energy determines the hydrodynamics. Viscosity and interfacial tension significantly affect the microscale laminar jet. Using wave numbers, Tyler’s equation is modified, guiding the design of effective microdroplet-generation devices.