Soo-Hong Lee

Comparative study on basis functions for projection matrix of three-dimensional tomographic reconstruction for analysis of dropletbehavior from electrohydrodynamic jet

Three-dimensional optical tomography techniques were developed to reconstruct three-dimensional objects using a set of two-dimensional projection images. Five basis functions, such as cubic B-spline, o-Moms, keys, and cosine functions and Gaussian basis functions, were used to calculate the weighting coefficients for a projection matrix. Two different forms of a multiplicative algebraic reconstruction technique were also used to solve inverse problems. The reconstruction algorithm was examined by using several phantoms, which included droplet behaviors and random distributions of particles in a volume. The three-dimensional volume comprised of particles was reconstructed from four projection angles, which were positioned at an offset angle of 45° between each other. Then, three-dimensional velocity fields were obtained from the reconstructed particle volume by three-dimensional cross correlation. The velocity field of the synthetic vortex flow was reconstructed to analyze the three-dimensional tomography algorithm.

Analysis of electrohydrodynamic jetting behaviors using three-dimensional shadowgraphic tomography

Electrohydrodynamic jetting behaviors of liquid menisci were analyzed experimentally by three-dimensional optical shadowgraphic tomography. The tomographic algorithm was developed after a series of multiplicative algebraic reconstruction techniques updated the objects intensities by using a cubic cosine basis function to determine the weighting coefficients of the projection matrix. The algorithm was evaluated initially by using a synthesized three-dimensional droplet phantom. Three-dimensional reconstructions of several jetting modes were built based on three images of projection data captured by three high-speed cameras, which were positioned at an offset angle of 45° relative to one another.

Study on flow distribution for room air conditioner using visualization technique

Flow distributions of a room air conditioner (RAC) have been analyzed by a visualization technique such as a particle image velocimetry (PIV) in this study. Flow structures have been investigated inside and outside the RAC to improve efficiencies. Accuracies of the measured velocities by the PIV have been confirmed by a Pitot tube at important locations around the RAC. Then, a numerical analysis has been performed by developed computer programs to design parts for the RAC with improved efficiencies. The design guideline has been proposed based on the analyzed results to reduce the condensation problem and increase the flow rate. Finally, shapes of a fan with high flow rates and an outlet with reduced condensation problems have been obtained based on the developed experimental and numerical methods in this study.Graphical Abstract

Numerical analysis of onset voltage for the control of droplet from an electrostatic nozzle

An effect of applied electric potential and physico-chemical parameters on a droplet diameter has been analysed numerically. Smaller droplets can be ejected from a nozzle by applying electrostatic potential between the nozzle and liquids. The droplets have been formed up to the onset value of the electric potential, while unstable liquid jets with multiple satellite droplets have been observed at higher electric potentials. Since the developed equations are appropriate only for limited cases, a numerical analysis has been performed in this study to calculate the droplet diameters and the onset voltages accurately by various parameters.

Study on Droplet Formation With Surface Tension for Electrohydrodynamic Inkjet Nozzle

Droplet ejection from an Electrohydrodynamic (EHD) inkjet nozzle depends on many factors such as an onset voltage, liquid conductivity, surface tension, etc. Since the surface tension has an influence on the contact angle between the nozzle surface and the liquid droplet, the surface tension change should be investigated for the control of the droplet ejection. In this study, surfactant which can weaken the surface tension force was used to analyze the effect of the surface tension. Furthermore, hydrophobic coating of the nozzle surface was considered as another factor for the droplet ejection. Also, a flow visualization technique was developed to observe the droplet formation and ejection from the EHD inkjet nozzle by various surface tension values.Copyright

Analysis of Flow Distribution for Laser Printer Using PIV Technique

Thermal flows inside a laser printer are affected by generated heat from a fuser and boards. Thus, the effect of fans has been investigated to control the thermal flows and behaviors of toners. In order to analyze the phenomena experimentally, a PIV (Particle Image Velocimetry) has been used, and then the flow inside the printer has been predicted by the CFD (Computational Fluid Dynamics) in this study to determine the efficient flow distribution by an optimum design of the printer. The determined optimum design has been confirmed by the developed PIV technique so that the efficiency of the laser printer can be improved by the proposed design.