Key Engineering Materials Vols. 364-366

Abstract: Recently the polymeric LOC (lab-on-a-chip) has been developed by the bio technology and the micro electro mechanical system technology. It is possible that biological experiment and analysis is executed rapidly and easily using a simple specimen. Therefore, many researches on LOC are progressing actively in various fields such as medical, biotechnical, environmental aspects etc. Up to the present time, most of polymeric LOC has been manufactured by LIGA (lithograpie galvanofomung abformung) or chemical etching processes. However, these methods have several disadvantages which are the complicated fabrication stages, requirements for various special equipments and limitations of materials. In this study, in order to overcome these difficulties, the possibilities of micro fluidic channel features were executed by micro cutting process for the steel. So the micro mold insert with micro fluidic channel was designed and manufactured by micro cutting process for the injection molding.

Abstract: In this study, stainless steel material (X5CrNi1810) was micromachined by chemical etching method. Ferric chloride was selected as etchant which is the most widely used etchant for iron-based materials. Four different etchant concentrations (32 °Bé, 36 °Bé, 40 °Bé and 44 °Bé) were used at various etching temperature. Moreover, the influence of the addition of hydrochloric acid to main etchant on etching performance was examined. The aim of this study was to investigate the depth of etch and surface roughness affected by etchant concentration, hydrochloric acid addition and etching temperature. It was observed that etching temperature for any etchant concentration is important factor in case of depth of etch and surface roughness. It was also noticed that the addition of hydrochloric acid to main etchant increased depth of etch value at any etching temperature. The optimum etching parameters were obtained for the chemical etching of stainless steel.

Abstract: With advances in micro fuel cell development, the production of hydrogen for micro reformer has become increasingly important. However, some problems regarding the micro reformer are yet to be resolved. These include reducing the size, reducing the quantity of CO and combining the fuel cell, among others. Accordingly, in this investigation, a micro temperature sensor and a heater are combined inside a stainless steel-based micro reformer to measure and control the temperature and thus improve performance and minimize the concentration of CO. In this work, micro-electro-mechanical-systems (MEMS) of the micro channel type are fabricated on a stainless steel substrate to enhance the methanol conversion ratio. The micro temperature sensor and heater are made of gold and placed inside the micro reformer. Although the micro temperature sensor and heater have already been used to measure and control temperature in numerous fields, they have not been employed in micro reformer and commercial products. Therefore, this study presents a new approach for integrating a micro temperature sensor and heater in a stainless steel-based micro reformer to minimize the size and improve performance.

Abstract: This investigation utilizes porous silicon as the gas diffusion layer (GDL) in a micro fuel cell. Pt catalyst is deposited on the surface of, and inside the porous silicon, to improve the performance of a fuel cell, and the Pt metal that remains on the rib is used to form a micro thermal sensor in a single lithographic process. Porous silicon with Pt catalyst replaces traditional GDL, and the relationships between porosity and pore diameter, and the performance of the fuel cell are discussed. In this work, electrochemical etching technology is employed to form porous silicon to replace the gas diffusion layer of a fuel cell. This work focuses on porous silicon with dimensions of tens of micrometers. Porous silicon was applied to the gas diffusion layer of a micro fuel cell. Boron-doped 20 '-cm n-type (100)-oriented doubly polished silicon wafer was used on both sides. The process is performed to etch a fuel channel on one side of a silicon wafer, and then electrochemical etching was adopted to form porous silicon on the other side to fabricate one silicon wafer that combines porous silicon with a fuel channel on a silicon wafer to minimize a fuel cell. The principles on which the method is based, the details of fabrication flows, the set-up and the experimental results are all presented.

Abstract: The temperature and humidity conditions of a membrane electrode assembly (MEA) determine the performance of fuel cells. The volume of traditional temperature and humidity sensors is too large to allow them to be used to measure the distribution of temperature and humidity in the MEA of fuel cells. Measurements cannot necessarily be made where required. They measure only the temperature and humidity distribution outside the fuel cells and yield results with errors that exceed those of measurements made in MEA. Therefore, in this study, micro-electro-mechanical-systems (MEMS) fabrication technology was employed to fabricate an array of micro sensors to monitor in situ the temperature and humidity distributions within the MEA of fuel cells. In this investigation, an array of micro temperature and humidity sensors was made from gold on the MEA. The advantages of array micro gold temperature and humidity sensors are their small volume, which enable them to be placed on MEA and their high sensitivity and accuracy. The dimensions of the temperature and humidity sensors are 180μm × 180μm and 180μm × 220μm, respectively. The experiment involves temperatures from 30 to 100 °C. The resistance varied from 23.084 to 28.196 /. The experimental results reveal that the temperature is almost linearly related to the resistance and the accuracy and sensitivity are less than 0.3 °C and 3.2×10-3/°C, respectively. The humidity sensor showed that the capacitance changed from 15.76 to 17.95 pF, the relative humidity from 20 to 95 %RH, and the accuracy and sensitivity were less than 0.25 %RH and 0.03 pF/%RH.

Abstract: The fuel cell has the potential to become an indispensable source of electric power. However, some problems have not yet been resolved. Measuring the temperature and humidity inside the fuel cells is currently difficult. Accordingly, in this study, micro sensors were fabricated within the fuel cell, in which the temperature and humidity distributions were measured. The substrate of the fuel cell was made of stainless steel (SS-304) and etching was employed to fabricate the channel on the stainless steel substrate. Then micro-electro-mechanical-systems (MEMS) technology was used to fabricate the array micro temperature and humidity sensors on the rib of channel of stainless steel. The advantages of array micro temperature sensors are their small volume, their high accuracy, their short response time, the simplicity of their fabrication, their mass production and their ability to measure the temperature at a precise location more effectively than the traditional thermocouple. The micro humidity sensors were made from gold and titanium as down and up electrodes in the channel. The performance curve of the single cell was operating at 41.54 °C and gas flow rates of H2/O2 at 200/200ml/min. The max power density of the bipolar with micro sensor was 56 mW/cm2.

Abstract: This study used the Al2O3 nano-lubricant produced from the direct synthesis method was used as the experimental samples and the ultrasonic vibration was used for dispersing the nanoparticles into three types of the weight fraction (0.1, 0.2, 0.3%wt). The base solvent was the lubricant of vacuum pump. The objectives of this study were to discuss the dependence of operating temperature of vacuum pump under the various weight fraction of Al2O3 nanoparticles. In this experiment we added Al2O3 nano-lubricant into the direct drive oil sealed rotary vacuum pump, and used the thermocouple measure the temperature on the four test points (cylinder, in-lubricant, case of vacuum pump and discharge pipeline). The results show that the cylinder temperature was reduced by 1.3% and increased by 0.4%, 1.8%, the lubricant temperature was increased by 5.3%, 0.5% and 1.9%, the case surface temperature was reduced by 1.7%, 1.4% and 1.5%, and discharge pipeline temperature was reduced by 0.6%, 2.1% and 3.8% respectively when the sample fractions were 0.1%, 0.2% and 0.3%wt. From the results, it could be realized that the nano-lubricant has more effects on increasing the performance of heat sink than conventional lubricant.

Abstract: The recursive projection schemes used in most existing recursive methods for solid deformable structure dynamic problems in precision manufacturing systems lead to dense coefficient matrices in the acceleration equations and consequently there is a strong dynamic coupling between the joint and elastic coordinates. When the number of elastic degrees of freedom in engineering materials increases, the size of the coefficient matrix in the acceleration equations becomes large and consequently the use of these recursive methods for solving the joint and elastic accelerations becomes less efficient. This paper discusses the problems associated with the recursive projection schemes used in the existing recursive methods, and it is shown that decoupling the joint and elastic accelerations using the nonlinear recursive method requires the factorization of nonlinear matrices whose dimensions are independent of the number of elastic degrees of freedom of the multibody system. An amalgamated formulation that can be used to decouple the elastic and joint accelerations for different multibody manufacturing systems is then proposed. The use of the nonlinear recursive method developed in this paper is demonstrated using the open-loop and closedloop chains in precision manufacturing systems.

Abstract: The liquid flow in nanoscale channel under thermal gradient, or so-called thermal transpiration, is studied by Molecular Dynamics Simulation. The phenomenon was realized in two fluid systems which differed from each other in the methods for applying the temperature gradient. One used heat source and the other wall-heating. The channel was periodic and its walls consisted of two different materials: conducting, high energy wall and non-conducting slip wall. It is shown that the liquid in a periodic channel can effectively be driven by the thermal transpiration. Various characteristics of the flow are discussed that include the temperature gradient, velocity profile and liquid structure in the channel.

Abstract: Due to lack of desirable mechanical properties of silicon substrate; the current trend of micro-fabrication technology is towards metallic materials. In this study, the electrochemical micromachining (EMM) technology is developed to fabricate micro-scale flow channels on thin metallic 316L stainless steel plate. The cathode electrode, the tool, is the mirror image of flow channels. It was produced by the MEMS and UV-LIGA technology and the size is 200μm in width and 500μm in height for the intension to fabricate a serpentine flow channel of 200μm in both depth and width. Because of the electrode size, the process control parameters and geometrical features surpassed conventional and CMOS methods. The flow channels on 0.6mm thick SS 316L plates were fabricated by EMM process within 30 seconds with effective area of 625mm2. The dimensions of flow channel were varying from 1504m to 5004m in width and about 2004m in depth. The results demonstrate the EMM technology produces good quality metallic flow channels efficiently.