Investigation on the Droplet Ejection Process of a Thermal

• Main Authors: Chen, Wen-Cheng, 陳文成
• Other Authors: Chen, Ping-Hei
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/40128303716095521587

博士 === 國立臺灣大學 === 機械工程學系 === 86 === Investigation on the Droplet Ejection Process of a Thermal Bubble Inkjet Printhead Chen, Wen-Cheng Department of Mechanical Engineering National Taiwan University Taipei, Taiwan, R.O.C. Abstract The present study investigated the bubble growth and droplet ejection process of a thermal sideshooter inkjet printhead. The experimental measurement and numerical predictions are both analysis tools in this study. An inexpensive optical system was set up to visualize the transient ink ejection process and measurement of the average mass of one droplet, which mainly consists of a controller with a liquid crystal display (LCD), a pulse generator with a power amplifier, a light emitting diode (LED) stroboscope, a microscope, a charge- coupled device (CCD) camera, and a personal computer with a frame grabber. The shape evolution process of ejected ink have been captured by the CCD camera and stored as files in the computer through the frame grabber. Effects of the electrical heating pulse on the droplet ejection process, the ejected length, the average mass of droplet, and the break-off time of the main drop from the ejected ink were investigated in present study. A theoretical models are presented to analyze heat conduction in the printhead, threshold conditions of stable film boiling in the ink, pressure impulse response curve of the vapor bubble, and heat transfer phenomenon of the flow-ink. The bubble volume, temperature, and pressure under various heating voltages and different ink viscosity were investigated in the theoretical models by numerical predictions. An empirical formulation that can be used to provide good results for predicting the needed minimum voltage for ejection under different heating pulse width was suggested. For investigation of the evolution process of the ejected droplet, the governing continuity and momentum equations were solved by an implicit finite-difference scheme. A comparison is made between the present numerical predictions with experimental results. A good agreement has been found. In addition, the present study shows the effects of the operating voltage of electrical pulse, the ink properties, and the gravity on the evolution process of the droplet, the break-off time of droplet from the ink nozzle exit, and the separation time of the main droplet and satellite droplet from the long tail droplet. Keywords: thermal bubble inkjet printhead; flow visualization; bubble formation; two-phase flow