CFD: Inkjet Model
Fanny Littmarck | October 17, 2012
About a month ago we had a webinar on CFD, and one of the demonstrated examples was the modeling of fluid flow from an inkjet. This technology has many applications and is a great example of how accurate CFD simulation is being used in the design process.
Different Inkjet Applications
It’s probably safe to say most of you have had experience with an inkjet printer at some point or another. These types of printers are widely used as they are both cost efficient and provide high resolution images and text. The basic idea of an inkjet printer is to eject small droplets of liquid from a nozzle onto a sheet of paper.
In addition to printing images onto paper, the inkjet technique is used in 3D printing processes. It can also be observed in scenarios other than printing. For instance, life science applications for diagnosis, analysis, and drug discovery often utilize inkjet instruments. In that case, inkjets are used as part of a larger instrument to deposit microdroplets in a very precise fashion.
The droplet size is a key inkjet design parameter. In order to achieve the desired droplet size it is necessary to optimize the design of the nozzle and the inkjet operating conditions. Simulation helps to understand the physics of the fluid ejection and determine the optimal design.
So what happens inside the nozzle when the liquid is emitted? First, the nozzle fills with fluid. Next, as more fluid enters the nozzle, the existing fluid is forced out of the nozzle. Finally, the injection is halted, which ultimately causes a droplet of liquid to “snap off”. Thanks to the force transmitted to the droplet by the fluid in the nozzle, it travels through the air until reaching its target. In terms of physics, inside the nozzle there is a single-phase fluid flow and when the liquid moves through the air it is experiencing a two-phase flow. Below is a model of the forced jet of a liquid. This is one of the possible mechanisms that can be used to eject a droplet, as seen in our September webinar on CFD. It was created using our CFD and Microfluidics Modules.
Instructions for creating a model of an inkjet nozzle in COMSOL Multiphysics 4.3a can be found in the Model Gallery. In order to view the model documentation, make sure to sign into your COMSOL Access account first. (It’s quick and free to register for Access if you do not already have an account).