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As electronic device performance is enhanced, the amount of heat generation is also increased. Electrohydrodynamic (EHD) technology presents a promising alternative solution to address the cooling demands. The EHD flow is generated by a corona discharge, directly converting the electrical energy into kinetic energy, and offers unique advantages over traditional cooling methods. The use of a magnetic field can improve the efficiency of the EHD flow by enhancing the local energy conversion. Experimental results showed that a magnetic field deflected the local velocity distribution, and improved the ionic wind velocity. At a magnetic flux density of 78.1 mT, the energy conversion efficiency was improved by 66.8 %. The convective heat transfer on the surface of high-power light emitting diode (LED) was analyzed. The heat transfer coefficient also increased under the effect of the electromagnetic field. The potential of alternative cooling systems for electronic devices using EHD technology was confirmed. [ABSTRACT FROM AUTHOR]

The importance of equipment technology for semiconductor mass production is growing as well as the exponential increase in demand for semiconductors. A study was conducted to improve the flow condition of a low-pressure chemical vapor deposition (LPCVD) batch-type furnace. Convergent nozzle (C) and divergent nozzle (D) have been adopted to replace the current straight (ST) multi-nozzle system, which was analyzed hydrodynamically without considering the surface chemical reaction. From the result, the D nozzle was not suitable for application due to induced flow oscillation. The flow velocity on the edge of the wafer increased 3.03 % for the C nozzle. In addition, the mass flux was enhanced up to 3 times and the mass flow rate 11.49 % at 3 sections. Therefore, it was expected that the deposition performance of the LPCVD furnace would be improved by the enhanced convective flow when the C nozzle was applied to the multi-nozzle system. [ABSTRACT FROM AUTHOR]

Non-thermal plasma is generated by excitation of the electron in gas or liquid medium. This technique has been applied to many industrial fields, especially for water treatment, because of the byproducts generated electrochemically by high-voltage discharge. Simultaneous production of plasma and bubbles is one of the methods to efficiently reduce the required energy for water treatment. The flow rate of injected gas and supplied electric energy are important parameters. In this study, the characteristics of the continuously generated bubbles with non-thermal plasma discahrge were investigated by experiment. The behavior of bubbles with and without discharge was analyzed by image processing. To verify the water treatment yield of bubbles with plasma generating byproducts, the decomposition of organic dye was investigated and analyzed. Due to the reduction of the surface tension of the interface, the volume of bubble with discharge showed shorter departure time with smaller volume. Bubbles with plasma discharge have faster bubble rising velocity, due to more spherical shape, which lowers the possibility of coalescence between bubbles, and is more effective for water treatment. The higher coalescence probability caused by increased Reynolds number resulted in the reduction of water treatment yield. [ABSTRACT FROM AUTHOR]

Electrohydrodynamic (EHD) flow is an extremely efficient method of using high voltage to generate gas momentum, this approach has various strong points due to the system not having any mechanical component. There has been a lot of research about the locations of discharge points in EHD. However, only one-dimensional shifting has been identified using empirical relations. The Townsend relation between current and voltage shows stable corona discharge into gas. Also, momentum of EHD flow has a linear relationship with the square root of the current an can be expressed by an empirical equation. In this study, two-dimensional shifting of the discahrge point was carried out to uncover the relationship between discharge point and flow, which tackes account of not onlu axial but also lateral distances while using a pin to two cylinder configuration. As a result, the characteristics of EHD flow can be modeled and expressed as a function of a distance parameter. Therefore, an empirical relation of momentum with the experimental variables was derived. [ABSTRACT FROM AUTHOR]

One of the most important design parameters for the inkjet printing device is the inkjet drop velocity, which changes along the falling path from the ejection out of a nozzle to the impact on a substrate. Therefore, in this study, the droplet velocity of the piezoelectric drop-on-demand inkjet was measured. The nozzle diameter was 70 µm and polyethylene glycol aqueous solution was used as ink. The inkjet droplets were generated within a range from 500 to 10000 Hz of frequencies at a reference piezoelectric input voltage. The successive inkjet droplets were captured by the high-speed camera with 100000 fps, then the inkjet droplet velocities were analyzed visually at each falling location. The velocity change of a drop up to its terminal velocity was calculated theoretically to be compared with the experimental results. This study found that the velocity of the continuously ejected droplets depended on the interval of the droplets, as well as the density and diameter of the droplet which are essential factors of the general velocity change of a falling drop. The inkjet droplets with the long interval can be considered as an independent droplet so that it can follow the terminal velocity curve of the general drop. However, the inkjet droplets with short interval have the higher velocity than the general terminal velocity curve. It is considered that each droplet gets into the wake field of the former droplet so that its drag force can decrease and the velocity can increase. [ABSTRACT FROM AUTHOR]

Fog on the automotive windshield interferes with the sight of the driver and causes serious safety problems; thus, removing it rapidly has been a longstanding goal in the automobile industry. In this study, we propose a novel method for improving the defogging performance of the defroster without its structural alteration by using vortex generators (VGs). To optimize the performance of the VGs, we performed particle image velocimetry experiments, an evaporation measurement experiment, and a numerical simulation for visualizing the airflow from the defroster inlet. The dimensions of the VG (height h = δ and length ℓ = 5δ) were selected according to the boundary-layer thickness, δ, of the lowest-flow rate (ulow = 0.33 m/s) used in the defroster inlet. We employed a dimensionless parameter, i.e., the secondary flow intensity (Se), to quantify the intensity of vortices for several angles of attack (30°, 45°, and 60°). The results indicated that the vortices generated from VGs with a 30° angle of attack retained their maximum intensity until they reached the vision area of the driver. Additionally, we explored two different configurations of VGs—co-rotating and counter-rotating—and concluded that the counter-rotating configuration had higher performance than the co-rotating configuration. The optimized VGs were directly inserted in the defroster inlet and improved the defogging performance by approximately 10%. The proposed method is applicable to various automobile models for enhancing the performance of the defroster regardless of the interior volume, air-ventilation performance, and other conditions, such as the number of passengers and outside temperature. [ABSTRACT FROM AUTHOR]

Three-dimensional particle tracking velocimetry (3D-PTV) technique is widely used to acquire the complicated trajectories of particles and flow fields. It is known that the accuracy of 3D-PTV depends on the mapping function to reconstruct three-dimensional particles locations. The mapping function becomes more complicated if the number of cameras is increased and there is a liquid–vapor interface, which crucially affect the total computation time. In this paper, using a shallow neural network model, we dramatically decrease the computation time with a high accuracy to successfully reconstruct the three-dimensional particle positions, which can be used for real-time particle detection for 3D-PTV. The developed technique is verified by numerical simulations and applied to measure a complex solutal Marangoni flow patterns inside a binary mixture droplet. [ABSTRACT FROM AUTHOR]

In this study, we designed a reed valve pump using a piezoelectric device (PZT) as a power source and analyzed its performance. Numerical analysis and preliminary design were carried out in order to construct a pump chamber, and a valve port design was used so as to take advantage of the characteristics of a reed valve. The performance of the manufactured pump was investigated with glycerin solution, a working fluid. As expected, the flow rate of the pump increased with operating frequency as long as sufficient pressure relaxation could be given. From the measured results of the time resolved pressure, the maximum and minimum pressures were determined by the pressure relaxation. The investigation about the duty ratio of the square wave operation probed that the 50 % duty provided the maximum performance, and the duty ratio could be reduced at a high operating frequency without a performance reduction. [ABSTRACT FROM AUTHOR]

When a droplet is placed on an inclined plane, it can slide down the plane by gravitational force. This phenomenon can occur in many industrial applications such as surface coating and printing, as well as in evaluating the characteristics of a surface. The slippery droplet can be analyzed from the balance between the gravitational force and the sum of the capillary and resistance forces. Researchers have suggested various equations of force balance with several hypotheses. To increase the reliability of the force balance correlation, it is important to obtain an accurate inside velocity profile and the three-dimensional (3D) shape of a droplet. In this paper, an analysis system of the slippery droplet was developed which includes optical correction based on a ray tracing method for velocity field measurement and an ellipse fitting method for droplet shape reconstruction. These correction methods were verified by a numerical simulation and applied to a slippery droplet on an inclined plate coated with Poly methyl methacrylate (PMMA). The wall shear force calculated from the velocity field and that calculated from the force balance were in good agreement. [ABSTRACT FROM AUTHOR]

A heat sink for cooling devices using the counter flow of a corona wind was developed in this study. Detailed information about the numerical investigations of forced convection using the corona wind was presented. The fins of the heat sink using the counter flow of a corona wind were also investigated. The corona wind generator with a wire-to-plate electrode arrangement was used for generating the counter flow to the fin. The compact and simple geometric characteristics of the corona wind generator facilitate the application of the heat sink using the counter flow, demonstrating the heat sink is effective for cooling electronic devices. Parametric studies were performed to analyze the effect of the counter flow on the fins. Also, the velocity and temperature were measured experimentally for the test mock-up of the heat sink with the corona wind generator to verify the numerical results. From a numerical study, the type of fin and its optimal height, length, and pitch were suggested for various heat fluxes. In addition, the correlations to calculate the mass of the developed heat sink and its cooling performance in terms of the heat transfer coefficient were derived. Finally, the cooling efficiencies corresponding to the mass, applied power, total size, and noise of the devices were compared with the existing commercial central processing unit (CPU) cooling devices with rotor fans. As a result, it was confirmed that the heat sink using the counter flow of the corona wind showed appropriate efficiencies for cooling electronic devices, and is a suitable replacement for the existing cooling device for high power electronics. [ABSTRACT FROM AUTHOR]

Electrolysis has been applied to many industrial fields because of the simple configuration and various usages. The bubble on the surface of electrodes is one of the most important factors that reduce the transport of electrons in the channel. In this study, the nucleation process of bubbles on electrodes against the time and the characteristics of bubble motion right after departure from the electrode were analyzed according to the Reynolds number of convective electrolytes. To verify the influence of the flow convection, the bubble behavior such as size and motion was analyzed by image processing. For an efficient configuration, the length of the electrode could be designed using empirical equations about the thickness of the bubble layer. [ABSTRACT FROM AUTHOR]