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Inkjet is a well-established technology that has been applied in various applications ranging from graphical printing to functional material printing [...].Inkjet is a well-established technology that has been applied in various applications ranging from graphical printing to functional material printing [...].

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.

The high heat capacity of phase change materials (PCMs) can enhance the thermal performance of oscillating heat pipe (OHP) systems. At the same time, the excellent heat transfer performance of OHPs can improve the thermal performance of PCMs. Firstly, the thermal performance of OHP systems with different numbers of turns (4–6) and filling ratios (FR, 30–90 %) were numerically analyzed. Then, the thermal performance of a PCM/OHP system was compared to an OHP system and a PCM/OHP system without working fluid. The key results are as follows: thermal resistance lowered as the number of turns and FR increased. In the PCM/OHP system, the PCM and OHP worked together symbiotically to improve the system’s overall performance. The PCM helped the OHP achieve a faster thermal response, lower evaporator temperature, and helped ensure continuous operation. In return, the OHP improved the uniformity of the PCM.

Experimental and numerical analysis of the drop-on-demand inkjet was conducted to determine the jetting characteristics and meniscus motion under the control of the ink supply pressure. A single transparent nozzle inkjet head driven by a piezoelectric actuator was used to eject droplets. To control ink supply pressure, the pressure of the air in the reservoir was regulated by a dual valve pressure controller. The inkjet performance and the motion of the meniscus were evaluated by visualization and numerical simulation. A two-dimensional axisymmetric numerical simulation with the dynamic mesh method was performed to simulate the inkjet dynamics, including the actual deformation of the piezoelectric actuator. Numerical simulation showed good agreement with the experimental results of droplet velocity and volume with an accuracy of 87.1%. Both the experimental and simulation results showed that the drop volume and velocity were linearly proportional to the voltage change. For the specific voltages, an analysis of the effect of the ink supply pressure control was conducted. At the maximum negative pressure, −3 kPa, the average velocity reductions were 0.558 and 0.392 m/s in the experiment and simulation, respectively, which were 18.7 and 11.6% less than those of the uncontrolled case of 0 kPa. Therefore, the simulation environment capable of simulating the entire inkjet dynamics, including meniscus movement regarded to be successfully established. The average volume reductions were 18.7 and 6.97 pL for the experiment and simulation, respectively, which were 21.7 and 9.17% less than those of the uncontrolled case. In the results of the meniscus motion simulation, the damping of the residual vibration agreed well with the experimental results according to the ink supply pressure change. Reducing the ink supply pressure reduced the speed and volume, improved the damping of residual vibrations, and suppressed satellite drops. Decreasing ink supply pressure can be expected to improve the stability and productivity of inkjet printing.

Ionic wind, which is generated by a corona discharge, is a promising field that offers significant advantages by directly converting electrical energy into kinetic energy. Because of the electrical characteristics of ionic wind, most studies aiming to improve the performance of ionic wind generators have focused on modifying the geometry of electrode configurations. A mesh-type electrode is one of the electrodes used as a collecting electrode in an ionic wind generator. Using a mesh electrode results in decreased momentum of the ionic wind and increased pressure drop due to frictional loss of the flow. In this study, to minimize the reduction in momentum, a mesh electrode with a central hole was proposed and investigated. Experiments were conducted with the configuration of a needle and mesh with the central hole. These experiments analyzed the effect of the central hole diameter and the distance between the needle and the mesh electrodes on the electrical and physical characteristics of the ionic wind. The addition of the central hole led to a higher average velocity and lower current, thus resulting in increased energy conversion efficiency. The presented configuration offers a simple geometry without electrical and physical interference from complex configurations, and it is considered to have the potential to improve energy conversion efficiency and optimize ionic wind flow.

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.

This study analyzed the characteristics of a small reciprocating pump with a cantilever valve driven by a piezo actuator. Three types of valves were fabricated to investigate the effect of the valve stiffness on the pump performance and to measure the variation in the flow rate according to the frequency. The flow rate increased with the driving frequency until a certain frequency was reached, and then it started to decrease. The rise in the pressure of the pump was found to increase as the stiffness decreased. The pump performance could be clearly distinguished according to the stiffness of the valve. The observation of the valve movements revealed that the valve opening time did not change regardless of the operating frequency, but it changed with the valve stiffness. The delay in time for the outlet valve increased significantly with an increase in the frequency. It seems that the overlap of the opening time of the inlet valve and the outlet valve plays an important role in pump performance. Therefore, it is advisable to use different designs for the inlet and outlet valves, where the shape and stiffness of the valve are adjusted.

A heated junction thermocouple (HJTC) is a device designed to monitor the water level of nuclear reactors to prevent explosions due to overheating. This device consists of heated and non-heated thermocouples. When heat is applied, the temperature rise in HJTC varies depending on whether the device is submerged in water or exposed to air. In this study, we analyzed the thermal characteristics of HJTC through 3D COMSOL simulation. The temperature profile of the cross-section was extracted based on three design parameters: applied heat, heating length of the wound coil, and diameter of the HJTC. The temperature difference between the two thermocouples was more pronounced upon exposure to air. Meanwhile, high applied heat, short coil heating length, and small diameter of the HJTC contributed to a more pronounced temperature difference based on the surrounding environment. These results can aid in the appropriate HJTC design to achieve the desired detection sensitivity.

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.

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.