Thermal Bubble Jets

There are several ways in which ink jets are created to produce high quality digital printing. One effective technique is to create a vapor bubble of ink that expands pushing ink out a nozzle and then contracts and sucks ink back into the nozzle to pinch off the ejected ink. This fluid dynamic process involves a complex mixture of heat transfer, phase change, and pressure dynamics within both the fluid and vapor.

Bubble Modeling Options

  • Adiabatic Vapor Bubbles—No heat exchange to surroundings
  • Vapor Bubbles with Heat Transfer—Heat is transferred to/from fluid and solids
  • Vapor Bubbles—Heat Transfer and Vaporization/Condensation

Alternative Drop Ejector Architecture from Eastman Kodak

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Comparison between physical experiments (top row) and simulation (bottom row) – Early experimental device configuration. Image courtesy of Eastman Kodak.

The image below shows how a vapor bubble forms when an electric current is pulsed through a heater element in the base of the ejector. The heater’s temperature increases because of Joule heating and once the superheat temperature is reached in the fluid a vapor bubble is formed almost explosively because of the high vapor temperature. Bubble formation by evaporation of ink is governed by a kinetic theory phase-change model. Shortly after the bubble begins to expand and its vapor cools, condensation at the surface of the bubble causes it to collapse, which in turn causes the ink expelled from the nozzle to pinch off. Surface tension and viscous forces largely govern the dynamics of the ink jet and its conversion into discrete drops.

Thermal Bubble Videos