Browsing by Author "Lai, Jr-Ming"

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Influence of liquid hydrophobicity and nozzle passage curvature on microfluidic dynamics in a drop ejection process
(2010-01-01)
Lai, Jr-Ming
;
Huang, Chang-Yan
;
Chen, Chih-Hao
;
Kung Linliu
;
Lin, Jenn-Der
Employing methods of computational fluid dynamics, we investigated the physical phenomena and fluid dynamics of a microfluid during ejection of a droplet with a designed system of a nozzle plate connected to a flat-plate piezoelectric material. A comparison between experimental measurements and numerical simulations was devised to validate the theoretical model. The volume-of-fluid piecewise linear-interface construction (VOF-PLIC) interface-capturing method was adapted to represent the fluid domain and to track the evolution of its free boundaries whereas the continuous surface force (CSF) mode was chosen to model the interfacial physics. The results show that the curvature of the flow channel affects the velocity, period before disintegration, volume of the droplet and number of satellite drops. Increasing the diameter of the orifice increases the volume and decreases the velocity of the droplet. Increasing the amplitude or frequency of the nozzle plate raises the input energy, so increasing the velocity, decreasing the volume and hastening the disintegration of the droplet, but an increased amplitude or frequency increases the number of satellite drops. At the hydrophobic boundary, the velocity increases, the droplet volume decreases and the period before disintegration is abbreviated because of the decreased adhesive force between the fluid and the boundary surface.
Numerical investigation of the effect of a transducer pulse on the microfluidic control of a piezoelectric printhead
(2010-07-01)
Lai, Jr-Ming
;
Lin, Jenn-Der
;
Kung Linliu
;
機械工程學系
;
Department of Mechanical Engineering
Numerical calculations are performed to investigate the effect of the component of a single transducer pulse on the ejection of a drop for a drop-on-demand ink-jet printhead with a piezoelectric actuator. The flow field is governed by continuity and Navier-Stokes equations. A volume-of-fluid method with a piecewise-linear interface construction is used to track the complicated topological variation of the liquid-gas interface. The computer code is validated with experimental results present in the literature. The volume of the primary drop is closely related to the maximum displacement D(f) of chamber wall induced by the piezoelectric actuator in the forward stoke; the velocity of the primary drop depends on the ratio of Df to the time period of the forward stoke Delta tau(f) . Moreover, the fact that the formation of the primary drop depends weakly on the conditions of the backward stroke is considered. A decreased interval between forward and backward strokes might serve to suppress the formation of satellite drops owing to reducing the liquid thread length l(b) at pinching off to a value less than the upper limit lb l(b)*. The breaking up of the freely flying liquid thread from nozzle outlet has two modes-multiple breaking up and end pinching-and depends on the thread length at pinching off. (c) 2010 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3486201]