Jongkwang Lee

A novel micro-mixer with a quasi-active rotor: fabrication and design improvement

In the present paper, a novel micro-mixer with a quasi-active rotor for micro-plant applications is proposed and design considerations for the improvement of the mixing performance of the proposed micro-mixer are derived. The proposed micro-rotor mixer combines an active micro-mixer with a passive micro-mixer. The micro-rotor, which is a moving part of an active micro-mixer, is added to the micro-chamber of a passive micro-mixer. The micro-rotor was rotated by inflows tangential to the chamber, causing strong perturbations. Two models of the micro-rotor mixer were fabricated with six layers of photosensitive glass which were individually fabricated and thermally bonded together. Improvement in the design of the micro-rotor mixer was achieved after the fabrication and experimental testing of the first model. In the design of the second model, the channel width and the rotor diameter were diminished and the number of rotor blades was increased from four to five. Through these design improvements, the micro-rotor started rotating at a lower Reynolds number; the rotor rotated at Re 1000 in the first model, whereas it did so at Re 200 in the second model. The mixing efficiency values of the micro-mixers were measured using an image analysis method. In the results, the mixing performance was dominated by molecular diffusion in the low Reynolds number region. On the other hand, convection flows such as twisted flows and Coanda flows dominated the mixing performance in the higher Reynolds number region. In the upper Reynolds number region, the micro-rotor was rotated and strong perturbations were induced. The mixing efficiency values of the micro-rotor mixers were found to exceed 90% when the rotor was rotated.

A complete power source of micro PEM fuel cell with NaBH 4 microreactor

A complete system of micro fuel cell with NaBH4 microreactor was developed for micro power sources. The micro fuel cell system consists of two main components; one is a micro PEM fuel cell and the other is a microreactor for hydrogen generation from NaBH4 alkaline solution. All of BOP such as a fuel cartridge, a micropump, and an auxiliary battery were integrated for a complete micro power device, and the performance of the micro fuel cell system was measured.

Analysis of Heat and Smoke Flow according to Platform Screen Door and Fan Conditions on Fire in Underground Platform

In this study, a three-dimensional flow analysis of underground subway station was conducted by applying ventilation mode in operation and platform screen door (PSD) opening and closing conditions on fire in underground platform. In order to analyze optimal smoke control and heat removal conditions, the whole underground subway station was set as a model, and a total of eight cases were analyzed by changing the operating conditions of fans for each area under the opening and closing conditions of the PSDs. The analysis results confirmed that the operation mode of supply fan in platform E and I areas located at the third floor underground is more effective than that of exhaust fan in the event of a fire in underground subway station when the PSD is closed. The amount of CO entering a waiting room increased, and the overall CO distribution in the underground subway station was also increased when the PSD is opened. In addition, the CO distributions due to the opening and closing of the PSD were similar to one another when a fire occurred on the platform, which suggests that the operating conditions of the fan affects the formation of CO distribution in the underground subway station rather than the discharge of CO.

Design, Fabrication, and Performance Evaluation of MEMS Solid Propellant Thruster Array

This paper presents the internal ballistic design, fabrication procedure, and performance evaluation of a Micro Electro Mechanical Systems (MEMS) solid propellant thruster array chip. The internal ballistic design was carried out to predict the performance of the thruster. Only the photosensitive glass wafer was used as the bare material for the thruster. We developed the micro igniter with improved structural stability by using a glass membrane with a thickness of tens of microns. The solid propellant was loaded into the propellant chamber without resort to a special technique due to the high structural stability of the glass membrane. An MEMS Solid Propellant Thruster (MSPT) array was fabricated through anisotropic etching of photosensitive glass. Ignition and combustion tests of the fully assembly MEMS thruster were performed successfully. Nomenclature P = pressure t = time R = gas constant T =

Spine-on-a-chip: Human annulus fibrosus degeneration model for simulating the severity of intervertebral disc degeneration

The aetiology of intervertebral disc (IVD) degeneration accompanied by low back pain (LBP) is largely unknown, and there are no effective fundamental therapies. Symptomatic IVD is known to be associated with nerve root compression. However, even in the absence of nerve compression, LBP occurs in patients with IVD degeneration. We hypothesize that this phenomenon is associated with a concentration of pro-inflammatory cytokines such as interleukin (IL)-1β and tumour necrosis factor-alpha (TNF-α), which can lead to altered histologic features and cellular phenotypes observed during IVD degeneration. This study investigated the effects of the concentration of IL-1β and macrophage derived soluble factor including IL-1β and TNF-α on the painful response of human annulus fibrosus (AF) cells using a newly developed spine-on-a-chip. Human AF cells were treated with a range of concentrations of IL-1β and macrophage soluble factors. Our results show that increasing the concentration of inflammatory initiator caused modulated expression of pain-related factors, angiogenesis molecules, and catabolic enzymes. Furthermore, accumulated macrophage derived soluble factors resulted in morphological changes in human AF cells and kinetic alterations such as velocity, dendritic length, cell area, and growth rate, similar to that reported within degenerative IVD. Thus, a better understanding of the relationships between molecular and kinetic alterations can provide fundamental information regarding the pathology of IVD degenerative progression.

Numerical Investigation of Temperature Uniformity and Estimation Accuracy for MEMS-based Black Body System

Output Characteristics of the spaceborn image sensor such as infrared(IR) sensor are varied according to time elapses and sensor repetition on/off operation. As a result, the quality of IR sensor image is decreased. Therefore, spaceborne image sensor require a periodic calibration using a black body system by correcting a non-uniformity of the sensor. In this paper, we proposed a MEMS-based black body system that can implement the high temperature uniformity at various standard temperatures ranging from low to high temperature and easily estimate the representative surface temperature. In addition, it has advantages lightweight, low-power and high accuracy. The feasibility of the proposed MEMS-based black body system was verified through the thermal analysis.Output Characteristics of the spaceborn image sensor such as infrared(IR) sensor are varied according to time elapses and sensor repetition on/off operation. As a result, the quality of IR sensor image is decreased. Therefore, spaceborne image sensor require a periodic calibration using a black body system by correcting a non-uniformity of the sensor. In this paper, we proposed a MEMS-based black body system that can implement the high temperature uniformity at various standard temperatures ranging from low to high temperature and easily estimate the representative surface temperature. In addition, it has advantages lightweight, low-power and high accuracy. The feasibility of the proposed MEMS-based black body system was verified through the thermal analysis.

Thermo-mechanical Design for On-orbit Verification of MEMS based Solid Propellant Thruster Array through STEP Cube Lab Mission

A MEMS solid propellant thruster array shall be operated within an allowable range of operating temperatures to avoid ignition failure by incomplete combustion due to a time delay in ignition. The structural safety of the MEMS thruster array under severe on-orbit thermal conditions can also be guaranteed by a suitable thermal control. In this study, we propose a thermal control strategy to perform on-orbit verification of a MEMS thruster module, which is expected to be the primary payload of the STEP Cube Lab mission. The strategy involves, the use of micro-igniters as heaters and temperature sensors for active thermal control because an additional heater cannot be implemented in the current design. In addition, we made efforts to reduce the launch loads transmitted to the MEMS thruster module at the system level structural design. The effectiveness of the proposed thermo-mechanical design strategy has been demonstrated by numerical analysis.

Performance Evaluation of Components of Micro Solid Propellant Thruster

In this paper research on micro solid propellant thruster is reported. Micro solid propellant thruster has four basic components; micro combustion chamber, micro nozzle, solid propellant and micro igniter. In this research igniter, solid propellant and combustion chamber are focused. Micro igniter was fabricated through typical micromachining and the effect of geometry was evaluated. The characteristic of solid propellant was investigated to observe burning characteristic and to obtain burning velocity. Change of thrust force and the amount of energy loss following scale down at micro combustion chamber were estimated by numerical simulation based on empirical data and through the calculation normalized specific impulses were compared to figure out the efficiency of combustion chamber.