Numerical Study of Gas-Liquid Two Phase Flow in TFT-LCD Cleansing Application
Date Issued
2010
Date
2010
Author(s)
Cheng, Kai-Li
Abstract
The gas-liquid droplet two-phase fluid flowing through a de Laval nozzle (converging-diverging nozzle) is essential to spray forming, coating technology, and cleansing process of modern electro-optical industry. In TFT LCD''s (thin film transistor liquid crystal display) industry, a damage-free and easily-assembled cleansing device with high cleansing effectiveness is needed. This study focused on the flow condition in a spray type cleanser and the optimization of cleansing effectiveness.
The flow problem in the nozzle can be treated in a quasi-one-dimensional manner to simulate the entire converging-diverging nozzle flow field of gas entrained with dilute liquid droplets. Given the input condition of gas and liquid droplets, the simulation was started by using the gas-liquid two phase flow model. The governing equations were derived from a generalized one-dimensional gas flow model in a variable area duct, where the behavior of liquid droplets entrained in the gas flow was described by the drag law. The equations were solved by fourth-order Runge-Kutta method. According to the results, the maximum flow speed occurs near the throat of the nozzle under subsonic operation. Since the optimization of a spray type cleanser depends on the exit flow speed in the literature, a spray jet utilizing converging nozzle operating at choking condition was proposed by numerical calculation in this study.
The maximum total energy in the nozzle and the orifice was proposed as another factor of optimization of cleansing effectiveness, and the results showed that the maximum total energy occurs at the same location with the maximum flow speed.
The stand-off distance between the nozzle exit and target surface was determined by the position of minimum flow area where the flow speed reaches minimum. The minimum flow area of orifice flow is defined as vena contracta, which is at the downstream of the exit plane. The exact position of vena contracta was determined by CFD software FLUENT, and the results were in good agreement with experimental data in the literature.
Subjects
Gas-liquid two phase flow
De Laval nozzle
vena contracta
industrial cleansing
Type
thesis
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