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國立清華大學工程與系統科學系
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工科研究聚焦(論文精選) - 低碳能源

 



Nuclear Energy

Fossil fuels such as oil, coal, and natural gas would lead to the production of carbon dioxide when they are consumed for thermal energy. Adopting a low-carbon energy source is therefore a more reasonable, responsible and environmentally friendly choice to alleviate the global warming impact. Among currently available low-carbon energy sources, nuclear energy is relatively efficient and stable in terms of power density and output. National Tsing Hua University was re-established in 1956 in Hsinchu, and the first academic program re-instated then at the University was the graduate institute of nuclear science. For growing demands on nuclear education and research, the construction project of Tsing Hua Open-pool Reactor (THOR) started in 1958. THOR reached its first criticality on April 13th of 1961. It has been a long and endeavoring history contributing to the development of nuclear energy at College of Nuclear Science. Our college offers one of the largest and complete higher education programs on nuclear science and engineering in the world. Subjects continuously studied at College of Nuclear Science include nuclear safety, reactor physics, and nuclear materials and water chemistry.

 


Introducing PCTRAN as an evaluation tool for nuclear power plant emergency responses

Yi-Hsiang Cheng, Chunkuan Shih, Show-Chyuan Chiang, and Tung-Li Weng

Annals of Nuclear Energy, 2012, 40, 122


 

Protecting the public from radiation exposure is important if a nuclear power plant (NPP) accident occurs. Deciding appropriate protective actions in a timely and effective manner can be fulfilled by using an effective accident evaluation tool. In our earlier work, we have integrated PCTRAN (Personal Computer Transient Analyzer) with the off-site dose calculation model. In this study, we introduce PCTRAN as an evaluation tool for nuclear power plant emergency responses. If abnormal conditions in the plant are monitored or observed, the plant staffs can distinguish accident/incident initiation events. Thus, the responsible personnel can immediately operate PCTRAN and set up those accident/incident initiation events to simulate the nuclear power plant transient or accident in conjunction with off-site dose distributions. The evaluation results consequently help the responsible organizations decide the rescue and protective actions. In this study, we explain and demonstrate the capabilities of PCTRAN for nuclear emergency responses, through applying it to simulate the postulated nuclear power plant accident scenarios.

 



Dose evaluation for an independent spent fuel storage installation using MAVRIC

Rong-Jiun Sheu, Yen-Fu Chen, Shiang-Huei Jiang, Jeng-Ning Wang, and Uei-Tyng Lin

Nuclear Technology, 2011, 175, 335


A cutaway view of the ISFSI layout at the NPP1 and total dose rate (cSv/h) distribution around the ISFSI site due to the fuel neutron source in 30 standard casks.

The first Nuclear Power Plant (NPP1) of Taiwan Power Company (TPC) has been commercially operated for more than 30 years. The capacity of the spent fuel storage pool has been near exhausted even after double re-rackings. In order to solve the impending shortage problem of spent fuel storage, TPC is currently constructing an independent spent fuel storage installation (ISFSI) in the plant site to maintain the normal plant operation and mitigate public concern on the safety of spent fuel storage. A complete radiation shielding analysis of an ISFSI facility involves many difficulties: source terms and geometry modeling, deep penetration calculation, radiation streaming through air inlets/outlets of a cask, and also skyshine evaluation. To make a complicated and deep-penetration Monte Carlo simulation computationally practical, efficient variance reduction techniques are indispensable. In contrast to a two-step cask-by-cask method adopted in the safety analysis report, this study directly resorts to a one-step whole-site approach to evaluate the dose rates at the site boundary. This full-scale calculation method of analyzing the site boundary doses is straightforward without many approximations but too challenging for conventional Monte Carlo simulations. Using a hybrid deterministic/Monte Carlo method, the computing time for this problem starts to become affordable to us using off-the-shelf computers. The results and some experiences learned from this study will be valuable to the design and analysis of other ISFSI facilities.

 


Corrosion behavior of Alloy 625 in supercritical water environments

Kai-Hsiang Chang, Jih-Hsuan Huang, Cun-Bin Yan, Tsung-Kuang Yeh, Fu-Rong Chen, and Ji-Jung Kai

Progress in Nuclear Energy (2012), in press, doi:10.1016/j.pnucene.2011.12.015


TEM bright field images, EDS analyses, and diffraction patterns for the samples tested at 600 °C for (a) 300 h, (b) 600 h, and (c) 1000 h.

For a better understanding on the corrosion behavior of Alloy 625, samples fabricated from this alloy were exposed to supercritical water (SCW) environments with 8.3 ppm dissolved oxygen at 400 and 600 °C and 24.8 MPa (3600 psi) for various periods of time up to 1000 hours. Pits were found on the surfaces of the samples after the corrosion tests, and the formation of these pits could be attributed to metal carbide inclusions in the as-received Alloy 625. Mass changes (w) in the samples as a function of exposure time (t) could be fitted by an equation of w2.21= 1.4×10-5t, indicating that the mass change approximately followed the parabolic law in the specified SCW environment. In addition, oxides with a double-layer structure were observed on the samples. The outer layer of the oxides consisted mainly of sub-micron spinels of Ni(Cr,Fe)2O4, and the compact inner layer was mixed Ni(Cr,Fe)2O4 and Cr2O3 with a grain size of tens of nanometer.




Solar Cells

A solar cell (also called photovoltaic cell or photoelectric cell) is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect. In 2011, the International Energy Agency said that "the development of affordable, inexhaustible and clean solar energy technologies will have huge longer-term benefits. It will increase countries’ energy security through reliance on an indigenous, inexhaustible and mostly import-independent resource, enhance sustainability, reduce pollution, lower the costs of mitigating climate change, and keep fossil fuel prices lower than otherwise. These advantages are global.

In the Department of Engineering and System Science, solar cells have three major research directions, including Dye-sensitized solar cells (DSSCs), Organic solar cells, and Si-based Solar cells. The following research classification depicts the representative research on solar cells in ESS department.

1. Dye-sensitized solar cells (DSSCs): DSSCs promise the lower production costs with simple fabrication and environment-friendly. DSSCs are composed of transparent conductive glasses (fluorine-doped SnO2, FTO), nanoporous TiO2 film immersed with monolayer of dye, redox couple electrolyte and counter electrode. The studies of Department of Engineering and System Science (ESS) include using the gel and solid-state electrolyte to replace liquid electrolyte for improving DSSC lifetime, and applying the Ag nanowire & carbon nanotube (CNT) embedded in the porous TiO2 film for enhancing the electron conduction.

2. Organic solar cells: It is a photovoltaic cell that uses organic semiconductor materials. It is a branch of organic electronics that deals with conductive organic polymers or small organic molecules for light absorption and charge transport. The plastic itself has low production costs in high volumes. ESS currently develops the molecular engineering (e.g. changing the length and functional group of polymers) for high efficiency and long lifetime solar cells.

3. Si-based Solar cells: Due to low cost and high efficiency requirements, Si solar cells with hetero-junction and intrinsic layer (HIT) structure and selective emitter are studied. On the other hand, in Si thin film solar cells studies, ESS intends to develop two important processes (a) multiple run Aluminum-induced crystallization process and (b) back contact electrode: Ni-Al alloy film in order to fabricate Si based thin-film PV device onto a cheap ceramics substrate for building-integrated photovoltaic (BIPV) applications.

 


Fabrications of quasi-solid state flexible dye-sensitized solar cells

Po-Ya Hsu, Hsin-Fang Lee, Jhih-Lin Wu, Fan-Yi Ouyang and Ji-Jung Kai

The 6th Aceanian Conference on Dye-sensitized and Organic Solar Cells (DSC-OPV-6), Oral (2011)


Several attempts have been made to fabricate highly efficient flexible dye-sensitized solar cells based on quasi-solid state electrolytes. Quasi-solid electrolytes by employing 17wt% TiO2 nanoparticles into liquid electrolytes and assembled DSCs were prepared. Three different kinds of the titanium dioxide (20nm pure anatase, P25 and ST01) were dispersed in solvent to prepare binder-free nanocrystalline TiO2 pastes. Incorporation of large nanoparticles (100 nm) has been employed as light-scattering centers to increase the optical length in the film, and an enhanced light-harvesting has effect by scattering. A static mechanical compression technique as the post-treatment is employed to the flexible ITO/PEN photoelectrodes in order to enhance the particles connection. A solar cell with platinum-coated FTO glass counter electrode and ITO/PEN photoelectrode, prepared by an ethanol based low-temperature TiO2 paste composed of a mixture of P25 (25nm, 25% rutile and 75% anatase) and 100 nm anatase

TiO2 particles, yielded highest conversion efficiencies of 6.53% under 1 sun illumination. All plastic DSC with Pt-sputtered ITO/PEN counter electrode yields a light to electricity conversion efficiency of 4.4% under 1 sun illumination.

 


Nanostructured penetrating anode Electrodes Based on Chemically-treated Single-walled Carbon Nanotubes for Performance Improvement in Organic Solar Cells

C.-Y. Su, A.-Y. Lu, Y.-L. Chen, C.-Y. Wei, P.-C. Wang, and C.-H. Tsai

Journal of Materials Chemistry, 2010, 20, 7034.

P.-C. Wang, Y.-C. Liao, Y.-L. Lai, Y.-C. Lin, C.-Y. Su, C.-H. Tsai and Y.-J. Hsu

Carbon, 2012, 50, 1650


Research Highlight

We fabricated and characterized organic photovoltaic (OPV) devices with hybrid composite anodes containing single-walled carbon nanotube (SWCNT) networks sandwiched between ITO and PEDOT : PSS. The SWCNTs used were initially grown on silicon wafers by a surfactant-free process based on ACCVD (alcohol catalytic chemical vapor deposition), and then transferred to glass substrates with pre-patterned indium-tin-oxide (ITO) electrodes for the fabrication of our OPV devices. We also integrated H2SO4/HNO3-treated and N2H4-treated SWCNT networks into OPV devices to investigate the effect of chemically-treated SWCNTs on OPV devices’ performance. We found that open-circuit voltage (Voc) of our OPV devices was insensitive to SWCNTs’ work function shifting caused by the employed chemical treatments, while their short-circuit current (Jsc) and power conversion efficiency (PCE) both varied in the order of: reference devices < devices with pristine SWCNT networks < devices with H2SO4/HNO3-treated SWCNT networks < devices with N2H4- treated SWCNT networks. In particular, we found that integration of N2H4-treated SWCNTs into the hybrid composite anode could enhance Jsc by 12% to 20% in P3HT : PCBM OPV devices (with PCE up to 4.02%). The improved performance in devices integrated with N2H4-treated SWCNTs can be attributed to (i) better crystallinity of the P3HT polymer, and (ii) increased hole-transport efficiency of the hybrid composite anode, both induced by the penetration/digitation of SWCNTs into the P3HT polymer layer.

 


Optimization of Amorphous Si/Crystalline Si Heterojunction Solar Cells by BF2 Ion Implantation

Tzong-Han Tsai, Yung-Chun Wu, Shih-Sian Yang, and Chun-Hao Chen

Japanese Journal of Applied Physics, in press, 2012


In this study we evaluated two approaches to improving the efficiency of amorphous Si/crystalline Si (a-Si/c-Si) heterojunction solar cells by BF2 ion implantation. First, emitter layer formation was compared for the cases of B and BF2 ion implantation when using the same 7° tilt angle. Second, emitter layer formation was compared between a 7° tilt angle and a 60° tilt angle when using BF2 ion implantation. The experimental results reveal that the fluorine in BF2 passivates the defects at the a-Si and a-Si/c-Si interface, and ion implantation at a high 60° tilt angle forms a shallow solar cell junction. The emitter layer formed by BF2 ion implantation with a 60° tilt angle in an a-Si/c-Si heterojunction solar cell achieves the highest short circuit current density (JSC) of 36.85 mA/cm2 with a conversion efficiency (η) of 14.41%.

 



Hydrogen Energy and Fuel Cells

Hydrogen energy is one of the promising green energy sources, and the practical application of hydrogen energy would most likely rely on fuel cell systems. Among the various fuel cell systems, the proton exchange membrane fuel cell (PEMFC) is one of the most adopted systems, which generates electricity by the electrochemical reaction of hydrogen and oxygen. However, commercial applications of PEMFCs are limited by their insufficient energy densities and by the difficulties of hydrogen storage and transportation. Potential candidates for resolving these issues are being studied worldwide, and the reforming-type PEMFC, using the hydrogen produced by the reformation reaction of methanol, are deemed as a promising solution. In the development of reformed methanol fuel cell (RMFC), our research topics mainly focus on improving the efficiency of methanol reformation and decreasing the working temperature of methanol-reforming catalyst to below 200 ℃. To pursue a useful reforming-type PEMFC, our research team is to target on the development of low-temperature and low-CO-sensitive catalysts. Furthermore, it is necessary to develop a high-temperature resistant membrane for the operation of PEMFC at a temperature closer to that of the reformer. The integration of all the components in a nano/micro-fabricated fluidic system is realized by optimizing the size and performance with the micro electromechanical system (MEMS) technique. Finally, to provide essential knowledge of heat and water managements in the reforming-type PEMFC, the details of the transportation phenomena are also studied for a real device design. With the integration of single cells, a 10-100 W level low-temperature methanol reforming-type Low-CO-sensitive PEMFC is expected to be realized in the near future.



The effect of gold on the copper-zinc oxides catalyst during the partial oxidation of methanol reaction

Yuh-Jeen Huang, Ke-Lun Ng, and Hsiao-Yu Huang

International Journal of Hydrogen Energy, 2012, 36,15203


Hydrogen production resulting from the partial oxidation of methanol (POM) was investigated using copper-zinc-supported gold catalysts. The influence of oxygen concentration on activity and initiation temperature (Ti) over Au4.3CZ (ca. 4.3 wt.% Au, 32.3 wt.% Cu and 63.4 wt.% Zn) catalysts was compared with CZ (ca. 31.7 wt.% Cu and 68.3 wt.% Zn) catalysts.

The Au4.3CZ catalyst was able to react at temperatures lower than 195 , while CZ catalyst could not be initiated without pre-activation. In addition, Au4.3CZ performed higher hydrogen selectivity and lower carbon monoxide selectivity than CZ catalyst. The addition of gold might induce a change in the reducibility of copper species and result in the more active species, Cu0 and Cu+, on the catalytic surface and, especially, enhance the adsorption of oxygen and methoxy group at low temperature. These adsorbed oxygen atoms could be removed as CO2, which speed up the rate-determining step of POM. It might influence initiation temperature and catalytic performance, i.e. the POM reaction can be initiated at Ti: 120 , with catalytic performance at 95% methanol conversion, 97% hydrogen selectivity, and 5.5% carbon monoxide selectivity at 190 over Au4.3CZ without pre-activation.



Highly efficient platinum nanocatalysts synthesized by an open-loop reduction system with a controlled temperature loop

Yi-Shiuan Wu, Shin-Mei Gong, Chun-Hsien Wang, Tsung-Kuang Yeh, Ming-Chi Tsai, Chuen-Horng Tsai, Yu-Chuan Su, and Fan-Gang Tseng

Electrochimica Acta, in press, 2012


Top-view SEM images of (a) the raw CNTs and the Pt catalysts deposited on the CNTs at different reduction temperatures: (b) 110, (c) 120, (d) 130, (e) 140, and (f) 160 oC, and the corresponding TEM insets (b)-(f). The red arrows indicate the agglomeration of Pt nanoclusters on the CNTs.

In the present study, highly homogeneous platinum nanocatalysts with enhanced electrocatalytic activity were uniformly deposited on carbon nanotubes directly grown on a silicon plate (Pt/CNTs/Si) as the electrode catalysts for direct methanol fuel cells (DMFCs) by a novel homemade open-loop reduction system (OLRS). Compared with a traditional reflux system that maintains the ratio of water to ethylene glycol (EG) at 160 oC for 4 h, the gradual concentration increase of EG in the precursor solution can be accomplished by distilling off water in the OLRS while increasing the temperature to 130 oC. This process with simultaneous increases in precursor concentration and in reaction temperature rendered high-quality Pt nanoparticles to precipitate with a high-density dispersion on the pretreated CNTs. The OLRS is not only able to only shorten the reduction time (<1.5 h) but is also able to enhance the electrocatalytic activity of the electrodes by creating a preferential orientation of Pt (111) facets for the methanol oxidation reaction (MOR). Cyclic voltammetry and electrochemical impedance spectroscopy were conducted to evaluate the mass activity (MA) and charge transfer resistance (Rct) of the prepared electrodes for the MOR. Compared with the electrodes prepared by traditional Pt reductions (MA: 100-360 A g−1 and Rct: 40-80 Ω-cm2), the Pt/CNTs/Si-based electrodes prepared at 130 oC in the OLRS exhibited superior electrocatalytic properties, including an MA of 435 A g−1 and an Rct of 30 Ω-cm2.




Li-ion Batteries

Li-battery is an emerging technology for today’s energy saving business. It can be applied on electric vehicles (EV), 3C appliances and even smart cards. The EV business is huge in order to reduce the emission of CO2 and gasoline free for all the cars on the road. It is a short term roadmap for many governments in the world to replace the gasoline consumption with either batteries or fuel cells. High power Li-battery and high capacity Li-battery is a major and urgent research today. The big high capacity Li-battery can also be used in the storage of electricity power when the solar cells can not functioning during the night or to stabilize the energy generated by wind power.  In the Department of Engineering and System Science, Professor Chih-Hao Lee’s group using synchrotron radiation X-ray and neutron beam technique to study the correlation between the battery performance and the crystallographic microstructures. The major research right now is to study the LiFePO4 battery doped with different ions. The storage capacity was known to be increased by doping the ions in this cathode material while the detailed structure and the mechanism of capacity increase is still unknown. To understand the mechanism how the performance can be improved is a key leads to a future new battery design. Using the in-situ synchrotron radiation X-ray and neutron beam diffraction, the structure change of cathode materials during the charge and discharge cycles were measured to understand that the phase change and delay of phase change at high charge/discharge rate. The ion diffusion and migration in the crystallographic change of cathode materials is also important and the key to fully understand this battery behavior. X-ray absorption spectroscopy together with X-ray and neutron diffractions were used to probe the local location of ion dopants in the LiFePO4 cathode, which reveals the interplay among the Li-diffusion and defects migrations created by dopants.

 



Magnetic Cooling

The magnetic cooling is an emergent developing technology to replace the traditional refrigerator business. Magnetic cooling using the principle of reducing the entropy of a magnetic material under applied magnetic field to generate heat and to absorb heat when the applied field is removed. The efficiency of the cooling in this way can be two times higher than the tradition refrigerator using compressing gas, which was believed to be a big energy saving in the world of refrigerator. In the Department of Engineering and System Science, a team to study this issue was formed. Major studies involve in the study of the magnetocaloric effect of magnetic material from the microstructural and crystallographic point of view (Prof. Chih-Hao Lee), the new optimized design of rotary magnet (Prof. K. C. Leou) and thermodynamics of heat flow studied by Prof. Y. C. Su.  The current research is to simulate the cooling cycle by finite element method using COMSOL and CFD code. The magnet design applied MAXWELL code to optimalize the best performance to the material weight. The optimal parameters of the scaling dimension, the cycling time of applied magnetic field and recirculation time of coolant. The scaling of the system is to be studied and the coefficient of performance of the system will be estimated. In order to have a major breakthrough, a composite material system will be estimated in order to take advantage of material properties of each single substance, then, a proto-type of rotary type magnetic cooling system using permanent magnet will be built and tested to verify the idea. The key issue is the active magnetic material itself. The atomistic structure and electronic structure related with the lattice dynamics and magnetic properties will be studied using Taiwan synchrotron radiation X-ray source, and neutron scattering technique in the near future. One of current simulation result is by adding the nanoparticles to the water coolant to increase the thermal conductivity resulting a higher efficiency of the cooling. Similar researches using nano-composition materials will be studied in the near future.

 



Thermal Management

Since 1993, the Advance Cooling Laboratory (ACL) at the ESS Department of National Tsing Hua University has established for more than 20 years. The Wind Tunnel T.I.M. K Value Measurement Instrument & T.R.I. (Thermal Resistance Measurement Instrument) developed in the laboratory had been widely use in the cooler manufacturer in Taiwan. Other facilities such as the performance test of the heat pipe; CPL; vapor chamber and spread thermal resistance test are developed at the ACL. In 2007, the first vacuum pressure measurement instrument for the forming heat pipe is successful developed in the lab. Recently, the LED Junction Temperature measurement technical, integrating sphere measurement technical and LED thermal structure analysis technical for LED device has been established as well.

 


Experimental analysis of the reservoir effects to capillary pumped loop in one unit server

Hung-Wen Lin and Wei-Keng Lin

Applied Thermal Engineering, 2007, 27, 2086


This paper aims to study the capillary-pumped loop (CPL) vapor line temperature distributions. A simple axial heat transfer method is developed to predict the vapor line temperature from evaporator outlet to condenser inlet. CPL is a high efficiency two-phase heat transfer device. Since it does not need any other mechanical force such as pump, furthermore, it might be used to do the thermal management of high power electronic component such as spacecraft, notebook and computer servers. It is a cyclic circulation pumped by capillary force, and this force is generated from the fine porous structure in evaporator. A novel semi-arc porous evaporator to CPL in 1U server is designed on the ground with a horizontal position and scale down the whole device to the miniature size. From the experimental results, the CPL could remove heat 90 W in steady-state and keep the heat source temperature about 70 C. Finally, a good agreement between the simulation and experimental values has been achieved. Comparing with experiment and simulation results, the deviation values of the distributions of the condenser inlet temperature are less than 8%.

 

 

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