Sukkee Um

Performance measurement and analysis of a thermoelectric power generator

The thermoelectric power generation with various thermal conditions is examined. An analysis model considered the manufacturing factors and the pellet size is presented to predict the performance characteristics of thermoelectric generators. The theoretical analysis shows that the maximum power output is produced when the electrical internal resistance is identical to the external load resistance. The overall performance is significantly increased with the temperature difference between cold and hot sides of thermoelectric generator. Under the fixed temperature difference, the thermoelectric generator produces the identical voltage, current and power outputs regardless of the operating temperature since the assumption of the constant thermoelectric properties is adopted in the analysis model. However, the experimental results obtained disclose that the effect of the operating temperature appears in the overall performance of the thermoelectric generator. Thus, the experimental correction of electrical internal resistance is adopted in the modified analysis model. Considerations are focused on the explicit role of the temperature-dependent electrical internal resistance for a method of accurate performance prediction. The modified analysis model is shown to be consistent with the experimental results in terms of the voltage output, current output and power outputs.

Analysis of Film Flow Around Rotating Roller Partially Immersed in Ink

This study is intended to analyze the effect of thin ink-film thickness around rotating printing roll on the printing quality in the gravure printing process which is used for making electronics circuit like a RFID tag with a conductive ink. The present work numerically estimates the film thickness around rotating roller partially immersed in ink for which the volume of fluid (VOF) method was adopted to figure out the film formation process around rotating roller. Parameter studies were performed to compare the effect of ink properties (viscosity, surface tension), operating condition (roller rotating speed, initial immersed angle) on the film thickness. The result indicates that the film thickness has a strong dependency on the rotating speed, while the surface tension has negligible effect.

Sub-zero temperature thermo-electrochemical energy harvesting system using a self-heating negative temperature coefficient CNT-vanadium oxide cathode

In this study, we report for the first time a simple method that directly converts heat into electrical energy at sub-zero ambient temperatures. The thermo-electrochemical cell was constructed with negative temperature coefficient (NTC) carbon nanotube-vanadium oxide (CNT-VOx) self-heating cathode, which provided thermal energy through an induced Joule effect. The electrical energy was obtained by creating in situ temperature difference between the electrodes (ΔT) and with subsequent redox reactions. A decrease in the cell resistance with an increase in the ΔT, and enhanced electrical energy conversion through a charge-transfer mechanism (i.e., Faradaic redox reaction) was observed. In addition, the advantage of using NTC CNT-VOx cathode as a self-heating source at various ΔT (i.e., without the support of any external source) in a thermo-electrochemical system for sub-zero temperature energy conversion is presented.Graphical Abstract

Development and Performance Investigation on a 60kW Induction Motor for EV Propulsion

This paper summarizes the development process and the investigation of 60kW induction motor for electric vehicle. In the traction motor, performance improvement of an induction motor using copper die-casting based on multi-gate process is presented. The copper die-casting motors can reduce the size of motors, the loss of rotor, and material costs. The electromagnetic, thermal, mechanical design and analysis results are also introduced to satisfy the design and the performance requirements. In order to analyze losses accurately of induction motor, commercial finite element analysis is done considering PWM voltage and thermal characteristics by using lumped-circuit parameters. The experimental tests are also carried out for the validity of EV traction motor design.

Loss and Heat Transfer Analysis for Reliability in High Speed and Low Torque Surface Mounted PM Synchronous Motors

It is essential to predict the coil temperature under over load and over speed conditions for reliability in high speed low torque surface mounted PM synchronous motors(SPM). In the present study, the losses and coil temperature are measured under rated condition and calculated under over speed and over load conditions in the three different motors with 35PN440, 25PN250 and 15HTH1000. The heat transfer modeling has been performed based on acquired losses and temperature. The difference of coil temperature between heat transfer modeling and experiment is less than 6.4% under no load, over speed and over load conditions. Subsequently, the coil temperature of the motor with 15HTH1000 is 84.4% of the coil temperature of the motor with 35PN440 when speed is 0.9 and load is 3.0. The output of motor with 15HTH1000 is 85.2% greater than the output of the motor with 35PN440 when the dimensionless coil temperature is 1.0.

The analysis of film flow around rotating roller partially immersed ink

This study is intended to analyze the effect of thin ink-film thickness around rotating printing roll on the printing quality in the gravure printing process which is used for making electronics circuit like a RFID tag with a conductive ink. The present work numerically estimates the film thickness around rotating roller partially immersed in ink, in which the volume of fluid (VOF) method was adopted to figure out the film formation process around rotating roller. Parameter studies were performed to compare the effect of ink viscosity, surface tension, roller rotating speed and immersed angle on the film thickness. The result indicates that the film thickness has a strong dependency on the fluid viscosity, while the surface tension effect becomes negligible.

The Operating Characteristics in an Air-Breathing PEMFC

Air-breathing polymer electrolyte membrane fuel cells (PEMFC) are highly promising particularly for small-power applications up to tens watts class. A distinctive feature of the air-breathing PEMFC is its simple system configuration in which axial fans operate for dual purposes, supplying both oxidant and coolant in a single manner. In the present study, a nominal 80W air-breathing PEMFC system is developed and investigated to determine the optimal operating strategy through parametric studies (i.e., reactant humidity, and fan-blowing flow rate). The cell voltage distributions are examined as a function of time to evaluate the system performance under various operating conditions.Copyright

Performance Loss & Heat Transfer Characteristics of Synchronous Motors under Various Driving Conditions

Core loss has a major effect on heat generation in synchronous motors with surface-mounted permanent magnets (SPMs). It is essential to perform heat transfer analysis considering core loss in SPM because core loss is seriously affected by torque and speed of motors. In the present study, mechanical loss, core loss and coil loss are evaluated by measuring input and output energies under various driving conditions. For a better understanding heat transfer paths in synchronous motors, we developed a lumped thermal system analysis model. Subsequently, heat transfer analysis has been performed based on acquired energy loss, temperature data and thermal resistance with three types of SPM. It is shown that the torque constants decrease by Max. 10% as speed increase. At the rated torque, the core loss is Max. 10.9 times greater than the coil loss and the hysteresis loss of magnets is dominant in total loss.

An Experimental Study of Synthesis and Characterization of Vanadium Oxide Thin Films Coated on Metallic Bipolar Plates for Cold-Start Enhancement of Fuel Cell Vehicles

The enhancement of the cold-start capability of polymer electrolyte fuel cells is of great importance in terms of the durability and reliability of fuel-cell vehicles. In this study, vanadium oxide films deposited onto the flat surface of metallic bipolar plates were synthesized to investigate the feasibility of their use as an efficient self-heating source to expedite the temperature rise during startup at subzero temperatures. Samples were prepared through the dip-coating technique using the hydrolytic sol-gel route, and the chemical compositions and microstructures of the films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. In addition, the electrical resistance hysteresis loop of the films was measured over a temperature range from -20 to using a four-terminal technique. Experimentally, it was found that the thermal energy (Joule heating) resulting from self-heating of the films was sufficient to provide the substantial amount of energy required for thawing at subzero temperatures.

An Improved Design of Microchannel Fuel Processors

This paper focuses on a new systematic configuration of micro-channel fuel processors, particularly designed for portable applications. An alternative integration method of the micro-channel fuel processors is attempted to overcome the serious thermal unbalance and to minimize the system volume by introducing the direct contact method of the sub-components. An integrated micro-channel methanol processor was developed by assembling unit reactors, which were fabricated by stacking and bounding micro-channel patterned stainless steel plates, including fuel vaporizer, catalytic combustor and steam reformer. Commercially available Cu/ZnO/Al2 O3 catalyst (ICI Synetix 33-5) was coated inside micro-channel of the unit reactor for steam reforming. The steam reforming reaction was conducted in the temperature range of 200°C to 260°C in the basis of reformer side end-plate and the temperature was controlled by varying methanol feeding into the combustor. More than 99% of methanol was converted at 240°C of reformer side temperature. A mechanism-based numerical model aimed at enhancing physical understanding and optimizing designs has been developed for improved micro-channel fuel processors. A two-dimensional numerical model in the reformer section created to model the phenomena of species transport and reaction occurring at the catalyst surface. The mass, momentum, and species equations were employed with kinetic equations that describe the chemical reaction characteristics to solve flow-field, methanol conversion rate, and species concentration variations along the micro-channel. This mechanism-based model was validated against the experimental data from the literature and then applied to various layouts of the micro-channel fuel processors targeted for the optimal catalyst loading and fuel reforming purpose. The computer-aided models developed in this study can be greatly utilized for the design of advanced fast-paced micro-channel fuel processors research.Copyright