A numerical model has been developed to simulate the firing of an inkjet printhead. The model evaluates the heat generation and diffusion within the thin film structure, the phase change and vapor bubble growth in the ink, and the subsequent flow of ink from the orifice. The heat transfer is modeled numerically throughout the printhead's thin film structure and ink through an asymptotic integration algorithm. The bubble growth and fluid flow are coupled and modeled through conservation of momentum, conservation of energy, and state equations. The heat transfer model has been validated with simple theoretical solutions and ink drop weight and velocity have been compared to empirical data. To test the usefulness of the model as a design tool, parametric studies have been made which characterize pen performance as a function of several system parameters. The results show that although the model does not reflect every detail in the firing process, it is useful for predicting trends and investigating new design concepts. / Graduation date: 1997

During the operation of phase-change ink-jet printers a bubble formation phenomenon often occurs. These bubbles are detrimental to the operation of the printer and substantial efforts are made to remove them. The objective of this research was 1: to develop a fundamental understanding of how bubble or void formation occurs during the phase-change process, and, 2: to develop a simple computer model to simulate this behavior which can then be used as a tool for better design of print-head geometries. Preliminary experimental work indicated the void formation to be a result of the density change accompanying the phase-change process. The commercial numerical code, Flow 3-D, was used to model the phase-change process in print-head geometries and substantiate certain simplifying assumptions. These assumptions included the effect of convection on the process and the effect of the varying material properties. For channel sizes less than 0.5 cm the phase-change process was found to be a pure conduction process. Convection effects are thus negligible and can be eliminated from the model. The variability of density, specific heat and thermal conductivity must be included in the model, as they affect the phase-change process dramatically. Specific heat is the most influential of the properties and determines, along with the conductivity, the rate at which the phase change takes place. The density must be included since it is directly linked to the void formation. / Graduation date: 1994