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Highlights • A simple nonlinear model for a supercritical uniformly heated channel is developed. • Parametric effects on the system stability are performed. • Complex nonlinear phenomena could appear in this supercritical heated system. • A route from various periodic oscillations to chaotic oscillations is identified. • unimaginable periodic nonlinear oscillations could occur in the unstable region. Abstract This study develops a simple nonlinear dynamic model of a supercritical uniformly heated channel by dividing the channel into three regions coupled with linear profile approximations between flow enthalpy and flow density. Stability map, nonlinear characteristics and parametric effects of a uniformly heated channel with supercritical water are investigated. The results indicate that the nonlinear oscillations between inlet flow velocity and outlet flow velocity tend to present out-of-phase in the supercritical heated system. The parametric studies on system stability suggest that increasing inlet flow resistance or enlarging the channel diameter would stabilize the system, while increasing outlet flow resistance or lengthening the channel length would destabilize the system. In addition, complex nonlinear phenomena, i.e. supercritical Hopf bifurcations and period-doubled bifurcations, could exist in this supercritical uniformly heated channel system. In the deep unstable region of high pseudo-subcooling number, various periodic oscillations through a series of period-doubled bifurcations would eventually lead to chaotic oscillations. The appearance of period three (P-3) oscillation deduces that unimaginable periodic types of nonlinear oscillations could occur in the limited unstable space of this system. [ABSTRACT FROM AUTHOR]

Highlights • Nonlinear model for parallel supercritical uniformly heated channels is developed. • Three region methodology with polynomial profile approximations is employed. • The present model can explore the stability of parallel uniformly heated channels. • Nonlinear characteristics of the system with supercritical water are investigated. • Parametric effects on the stability of parallel three channel system are discussed. Abstract This study develops a nonlinear dynamic model of parallel supercritical uniformly heated channels based on three-region methodology coupled with polynomial profile approximations between flow density and flow enthalpy. The validation results against the experimental data indicate that the present model has the capability to investigate the stability issues of parallel uniformly heated channels with supercritical water. Nonlinear characteristics, stability maps and parametric effects of three uniformly heated channels with supercritical water are investigated. The results illustrate that channel-to-channel interactions among three channels will drive the system more unstable due to a more asymmetric power distribution. In addition, the hottest channel with the highest steady state flow rate would oscillate with the largest amplitude and out-of-phase with the other less heated channels under constant total inlet flow rate condition. This study also reveals that the nonlinear oscillations between inlet flow velocity and outlet flow velocity in each channel tend to present out-of-phase. It could demonstrate that increasing the pressure drop of heavy fluid region (region 1) would stabilize the system, while increasing the pressure drop of light fluid region (region 3) would destabilize the system. The parametric studies on system stability of three uniformly heated channels suggest that increasing inlet flow resistance or enlarging the channel diameter would stabilize the system, while increasing outlet flow resistance or lengthening the channel length would destabilize the system. [ABSTRACT FROM AUTHOR]

In this study, experimental tests were carried out to investigate the feasibility of heat transfer enhancement by ultrasonic vibration under a subcooled pool condition. A commercial stainless-steel heater was utilized along with a water tank, and three ultrasonic transducers were attached underneath the tank bottom to generate ultrasonic vibration with a frequency of 40 kHz and total power of 150 W. For demonstrating the effectiveness, the tests were performed with and without ultrasonic vibration under a constant water temperature of 30°C and pressure of 1 atm. The heights of heater were set at 15, 22, and 33 mm from the tank bottom, and the heat flux was operated from 7800 to 70800 W/m2, which covered the regimes of single phase natural convection and subcooled nucleate boiling. Instantaneous signals of temperature and heat flux were recorded during the experiment, and the heat transfer coefficients were determined for each condition. The results show that the heat transfer coefficient can increase up to 3880 W/m2K and the enhancement ratio can reach up to 284% by ultrasonic vibration. Trends of heat transfer increments and enhancement ratios against heat flux and height were presented. This study successfully demonstrated the feasibility of heat transfer enhancement by ultrasonic vibrations. [ABSTRACT FROM AUTHOR]

After Fukushima Daiichi disaster, the safety analysis of severe accidents became one of the safety concerns in Taiwan. At the same time, Taiwan Power Company built up an event basis strategy called Ultimate Response Guideline (URG) to cope with the accident like Fukushima. The analysis of the effectiveness of URG also became the most popular issue in Taiwan. However, the beyond design basis accident was very complicate and combined with many different aspects. Although researchers in Taiwan did lots of analysis of URG using different codes with different aspects, the differences of codes in the severe accident analysis were not mention in any of those studies. Thus, a Fukushima-like accident of Chinshan Nuclear Power Plant (NPP) was done by four codes in this study: MELCOR2.1, TRACE, PCTRAN and MAAP5.03. All four codes shared the same boundary conditions in the accident simulations. The crosswalk of these codes was discussed in detail and showed the similarity and differences among these codes. Those similarity and differences can help the improvement of URG analysis and make that this kind of analysis has more reliability. Also, the application field of each code can be clearly distinguished and help the improvement of code use in future NPP safety analysis. [ABSTRACT FROM AUTHOR]

An experimental investigation of horizontal forced vibration effect on void fraction variation of subcooled boiling flow was carried out in this study. In order to simulate the fuel assembly subchannel of a boiling water reactor (BWR), an annular test section with inner and our diameters of 19.1 and 38.1 mm was utilized for subcooled boiling tests under atmospheric pressure. The annular test section was attached to an eccentric-cam vibrator, which was driven by a low-speed motor and can produce horizontal forced vibrations with frequency up to 20 Hz and maximum displacement of 22.2 mm. The inlet liquid velocity and subcooling were set as v f , in = 0.25–1.00 m/s and Δ T Sub = 5–20 °C. Different heat fluxes of q ″ = 0.058–0.193 MW/m 2 were loaded through the center heater rod, and the void fraction and fluid temperature were measured during the tests under stationary (no vibration) and vibration conditions. Test results show that in the subcooled boiling region, the void fraction and fluid temperature can vary under horizontal forced vibrations, and the variation trends were presented in N Zu - N Sub and v f , in -〈 α 〉 plots. These variations can be explained by the potential changes of thermal boundary layers (TBL) and the heat transfer enhancement under vibrations. In addition, no significant change of void fraction and fluid temperature was found in or near the saturated boiling conditions under vibrations. [ABSTRACT FROM AUTHOR]

In order to investigate the potential seismic vibrations effect on two-phase flow in an annular channel, experimental tests with air-water two-phase flow under horizontal vibrations were carried out. A low-speed eccentric-cam vibration module capable of operating at motor speed of 45–1200 rpm ( f  = 0.75–20 Hz) was attached to an annular channel, which was scaled down from a prototypic BWR fuel sub-channel with inner and outer diameters of 19.1 mm and 38.1 mm, respectively. The two-phase flow was operated in the ranges of 〈 j f 〉 = 0.25–1.00 m/s and 〈 j g 〉 = 0.03–1.46 m/s with 27 flow conditions, and the vibration amplitudes controlled by cam eccentricity ( E ) were designed for the range of 0.8–22.2 mm. Ring-type impedance void meters were utilized to detect the area-averaged time-averaged void fraction under stationary and vibration conditions. A systematic experimental database was built and analyzed with effective maps in terms of flow conditions (〈 j g 〉-〈 j f 〉) and vibration conditions ( E - f and f - a ), and the potential effects were expressed by regions on the maps. In the 〈 j g 〉-〈 j f 〉 maps, the void fraction was found to potentially decrease under vibrations in bubbly flow regime and relatively lower liquid flow conditions, which may be explained by the increase of distribution parameter. Whereas and the void fraction may increase at the region closed to bubbly-to-slug transition boundary under vibrations, which may be explained by the changes of drift velocity due to flow regime change from bubbly to slug flows. No significant change in void fraction was found in slug flow regime under the present test conditions. [ABSTRACT FROM AUTHOR]

Heat pipes and two-phase heat transfer devices are widely used in electronics cooling, and the thermal resistance is a key issue to ensure the system performance and reliability. In this study, the traditional one dimensional (1D) and quasi-two dimensional (Q2D) methods were utilized to analyze the thermal resistance of the previous boiling experiments of evaporator tests with silicon (Si) and copper (Cu) micro channel structures as well as the existing flat-plate heat pipe tests with aluminum micro channels as wick structures. The temperature distributions and variations under different test conditions were collected, and the 1D and Q2D methods were applied to calculate the overall thermal resistance for evaporator tests and heat pipe tests and compared with the experimental data. The results showed that the Q2D method can predict the overall thermal resistance for the evaporator region and the whole heat pipe with a higher accuracy because the spreading resistance was significant and should be considered under small heater area (hot spot) conditions. Detailed distributions of thermal resistance and the calculated errors of each test sample under different heat loads were presented and compared. For present tests, the Q2D method can reach a lower average error (about 10%) and is recommended for calculations. Furthermore, the spreading resistance of Q2D method is further applied to calculate the selected test cases to investigate the wall thickness effects. The spreading resistance of the selected evaporator tests and heat pipe tests may decrease and increase, respectively, as wall thickness increases due to different evaporative heat transfer conditions. The present results demonstrate the applicability of the Q2D methods for both evaporator and heat pipe tests, and the present analyses can be a reference for future thermal management and electronic cooling designs. [ABSTRACT FROM AUTHOR]

This study integrates a single nuclear-coupled boiling channel model previously developed by the authors with the external force method to illustrate the qualitative dynamic behaviors of a two-phase flow system subject to external vertical accelerations. With the normal operating condition of an ABWR as a reference case, the effect of external vertical acceleration on the system transients may depend on their imposed amplitudes and frequencies. Periodic and quasi-periodic oscillations can appear in the system as the frequency ratios between two vertical waves. The parametric effects on the seismic-induced oscillations are performed in the present system without nuclear coupling. The resonance oscillations could be triggered if the external vibration frequency is equal to the system natural frequency. The strength of resonance effect may depend on the inherent stability characteristics of the initial states for both the thermal-hydraulic and nuclear-coupled boiling systems. Complex seismic-induced oscillations can be predicted in the nuclear-coupled boiling system with strong void-reactivity feedback. The seismic-induced oscillations can experience various types of oscillations, from periodic ones to chaos, as the inlet subcooling is increased with the reference void-reactivity coefficient being doubled. [ABSTRACT FROM AUTHOR]

Abstract: In a low-speed linear cascade wind tunnel, effects of boundary layer suction on the flow characteristic in a highly-loaded compressor cascade with a stator clearance are studied experimentally, and two types of clearance including “long clearance” and “short clearance” are considered separately. In particular, hole-type suctions with different locations and distributions on the endwall are applied to control clearance flow and loss. The nature of flow separation is described by analyzing the properties of the limiting streamlines, based on the ink-trace flow visualizations on the cascade surface and lower endwall. The configuration of suction holes was associated with the kinetic energy of a clearance flow and the interaction of tip clearance flow with the endwall boundary layer and the suction surface boundary layer. The separation line and reattachment line form the base of a separation structure for corners with clearance. The results show that the clearance flow can be greatly improved and the losses reduced to some extent when boundary layer suction is adopted appropriately. The maximum amplitude of the loss reduction in different schemes with clearance is 32%. [Copyright &y& Elsevier]

Abstract: A one-dimensional drift-flux model was developed and benchmarked with existing models in the present study. Different from existing empirical correlations, this newly developed 1-D drift-flux model started from the variations of two-phase flow distribution parameter C 0 for non-dimensional superficial gas velocity from low to high, which represents the variation of phase distribution patterns. Due to a combination of small-scale sub-channel effect and large-scale casing effect in a rod bundle, the Hibiki–Ishii’s drift velocity was introduced to describe the relative motion between two phases. A clear boundary of distribution parameter, C 0, can be found when the non-dimensional superficial gas velocity is closed to 0.5. A linearly increasing trend and an exponentially decreasing trend of C 0 were found in the lower and higher gas sides divided by this boundary, respectively. Through the present model, one dimensional area-averaged gas velocity and void fraction can be determined for rod bundles in pool conditions. The prediction results were compared with several existing models and experimental data. The present model shows a good agreement with the existing experimental data and can be applied to both boiling and adiabatic air–water two-phase flows. In order to explain the peak values of C 0 in low superficial gas velocity conditions, several possible superficial velocity and void fraction profiles were examined by considering the recirculation flow/void distributions. [Copyright &y& Elsevier]

Abstract: In order to establish a reliable rod bundle database under pool conditions and to benchmark the existing models, a well-scaled 8×8 rod bundle test loop was designed based on the scaling criteria and a series of experiments was carried out with adiabatic air–water two-phase flow. Experiments for pool conditions covered the area-averaged void fraction 〈α〉 range of 0.12–0.93. Existing models and experimental data including boiling and air–water two-phase flow were compared and analyzed. Experimental results show that differences exist between large and small casing rod bundles as the flow structure changes with the casing scale. In addition, traditional drift-flux models for pipes may reflect the casing scale effect, but cannot be directly applied to the rod bundle geometry in pool conditions. Among the existing models for rod bundles, the give relatively better predictions in most regions. All benchmark results of existing models are tabulated in terms of void fraction prediction error for the present database. [Copyright &y& Elsevier]

Abstract: Micro-grooves with various feature sizes ranged form 200 to 500μm were fabricated as micro-wick structures by two different processes, including chemical etching and precision milling, for the experimental investigation and visualization on capillary and boiling limits. Pure water was employed as the working fluid, and the surfaces of the micro-wick structures were cleaned to ensure the hydrophile and the same surface conditions of these samples before testing. Various heat fluxes were then applied to these micro-wick structures to measure their thermal performances and capillary and boiling limits by both temperature measurement and experimental visualization. In addition, the experimental results were compared with the simplified analytical models. This study proposes a simple method to determine working limits and thermal performance of micro-structures for designing wick and selecting process. [Copyright &y& Elsevier]

Abstract: A series of organotin (IV) compounds of the type [R3SnL]2, R is Me (1), Bu (2), [R2SnL]2, R is Ph (3), Me (4), Bu (5), L is pyruvic acid thiophene-2-carboxylic hydrazone, and R2SnL, R is Me (6), Bu (7), Ph (8), L is salicylaldehyde thiophene-2-carboxylic hydrazone have been synthesized in 1:1 molar ratio. All compounds were characterized by elemental analysis, IR, 1H NMR, 13C NMR and 119Sn NMR spectra. The crystal structure of compounds 1, 3, 4, 8 have been determined by X-ray single crystal diffraction analyses, study found that the compounds 1 and 3 are rendered one-dimensional chain structure and the tin atoms are five-coordinated in a distorted trigonal-bipyramidal geometry. The compound 4 has a dimeric structure and the central tin atom is rendered seven-coordinate in a distorted pentagonal-bipyramid configuration. While the compound 8 is a monomer in which the tin atom adopts five-coordinated in distorted trigonal-bipyramidal geometry. [Copyright &y& Elsevier]

Abstract: Seven Schiff base adducts of organotin(IV), RSnLCl2, which L is o-vanillin-2-thiophenoylhydrazone, and R is n-C4H9 (1), Me (2), Ph (3), and [R2SnL], which L is o-vanillin-2-thiophenoylhydrazone, R is n-C4H9 (4), Me (5), Ph (6), PhCH2 (7) have been synthesized. Those products were characterized by elemental analysis, IR, 1H, 13C and 119Sn NMR spectra. The crystal and molecular structures of compounds 1, 4, and 6 have been determined by X-ray single crystal diffraction. In the crystal of compound 1 the tin atom is rendered six-coordinate in a distorted octahedral configuration by coordinating with the N atom of the Schiff base ligand, in compounds 4 and 6 the central tin atoms are five-coordinate in distorted trigonal-bipyramidal geometry and the comparison of the IR spectra reveal that disappearance of the bands assigned to carboxyl unambiguously conforms the ligand coordinate with the tin atom in enol form. [Copyright &y& Elsevier]

• Air-water two-phase flow tests were carried out in a 3 × 3 rod bundle channel. • Global and local void fraction data were measured, benchmarked and validated. • PDF, FFT, averages and standard deviations were obtained for dynamic analysis. • Local/global void distributions under different flow conditions were presented. • A set of empirical correlations for estimating local void fractions were proposed. In this study, the vertical upward air–water two-phase flow tests have been carried out to investigate the distribution of local and global void fractions in a rod bundle channel under low-flow conditions. The height of the rod bundle channel is about 5 m, and the channel cross section is comprised of a 52 × 52 mm rectangular casing and 3 × 3 circular rods. The rods with a diameter of 11.5 mm and a pitch of 15.4 mm were set as a rectangular array. Four sets of non-intrusive conductivity sensors were built to measure the local and global void fractions of various gaps within the rod bundle channel. The tests were operated at low flow conditions: j g = 0.016–0.92 m/s and j f = 0.02–0.05 m/s, which covered the possible flow regimes of bubbly, cap-bubbly and cap-turbulent flows. The measured global void fraction were benchmarked with existing one-dimensional drift-flux model, and the local void fractions have been summed up by regions and compared with the global void fraction for validation. The dynamic characteristics of local/global void fractions have been analyzed with probability density function (PDF) and fast Fourier transform (FFT), and the distributions and variations of averaged void fraction against test conditions have been presented. Furthermore, the empirical correlations for estimating the local void fractions have been proposed, which can successfully estimate the local void distribution from global void fraction with limited errors. The present results and correlations can be a reference for future development and modification of detailed two-phase flow models in the rod bundle geometry. [ABSTRACT FROM AUTHOR]

By adopting the external force method to consider the impact of seismic vibration on the two-phase flow system, this study integrates the nonlinear dynamic model of a nuclear-coupled boiling parallel-channel natural circulation loop (NCL) developed previously by the authors with the external vertical seismic accelerations to investigate the qualitative dynamic behaviors of the seismic-induced oscillations in the NCL. The methodology employed in this study could simulate a real vertical seismic acceleration and address the major nonlinear characteristics of seismic-induced oscillations by the comparisons between the results caused by the real vertical seismic acceleration and the simulated wave. The seismic-induced oscillations are found to be highly consistent with the resonance effect in different natural circulation stable states. The resonance part of the seismic waves would dominate the nonlinear phenomena of the system under vertical seismic accelerations imposed. The vertical seismic motion could cause in-phase mode of oscillation among boiling channels in this NCL system. In addition, some parametric effects on the seismic-induced oscillations are performed in the present NCL system. The natural circulation system with a higher subcooling may trigger a more prominent resonance phenomenon, due to the inherent stability characteristics of the initial states, and thus lead to a more dramatic seismic-induced oscillation in the cases studied. [ABSTRACT FROM AUTHOR]

Seismic vibration can induce additional interphase forces acting on bubbles and change flow characteristics in two-phase flow system. Local measurements of air-water two-phase flow parameters, namely void fraction, interfacial area concentration and Sauter mean diameter, were conducted in a vibrating annulus. The vibration acceleration ranged from 0.05 g to 0.24 g. Nine inlet flow conditions were selected, which covered bubbly and slug flows. No significant difference was observed in the time-averaged flow parameters between reference and vibration experiments. During vibration cycle, the radial two-phase flow distribution varied continuously with vibration phase. The change in non-dimensional line-averaged void fraction decreased with the increase of void fraction. As the vibration amplitude increased from 3.04 mm to 10.08 mm, the vibration effects on variations of local flow parameters were greatly enhanced with the mean relative variation (MRV) of void faction reached up to 55%. The study on MRV of local parameters showed that the vibration effects were strongly related to specific flow conditions. With the increase of superficial gas velocity and void fraction, the vibration effects were reduced and the MRV of void fraction decreased from 55% to 18%. [ABSTRACT FROM AUTHOR]

An experimental study on air-water two-phase flow under vibration condition has been conducted using double-sensor conductivity probe. The test section is an annular geometry with hydraulic diameter of 19.1 mm. The vibration frequency ranges from 0.47 Hz to 2.47 Hz. Local measurements of void fraction, interfacial area concentration (IAC), and Sauter mean diameter have been performed along one radius in the vibration direction. The result shows that local parameters fluctuate continuously around the base values in the vibration cycle. Additional bubble force due to inertia is used to explain lateral bubble motions. The fluctuation amplitudes of local void fraction and IAC increase significantly with vibration frequency. The radial distribution of local parameters at the maximum vibration displacement is specifically analyzed. In the void fraction and IAC profiles, the peak near the inner wall is weakened or even disappearing and a strong peak skewed to outer wall is gradually observed with the increase of vibration frequency. The nondimensional peak void fraction can reach a maximum of 49% and the mean relative variation of local void fraction can increase to more than 29% as the vibration frequency increases to 2.47 Hz. But the increase of vibration frequency does not bring significant change to bubble diameter. [ABSTRACT FROM AUTHOR]

This study employs the nonlinear dynamic model developed previously by the authors to investigate the effect of void-reactivity feedback on the bifurcation phenomena and nonlinear characteristics of a single nuclear-coupled boiling channel in an advanced boiling water reactor. The parametric effects on the system stability are evaluated by nonlinear analyses as well. The effects of void-reactivity feedback and outlet flow resistance will both destabilize the system, while the inlet flow resistance will generate a stable effect on the system. The strength of void-reactivity feedback has a great influence on the bifurcation phenomena and nonlinear dynamics of the single nuclear-coupled boiling channel. The system can evolve from stable state, limit cycle, periodic to chaotic oscillation through supercritical Hopf and period-doubled bifurcations as the increase in the absolute value of void-reactivity coefficient. In addition, the system can experience a series of period-doubled bifurcation to present various types of oscillations, from periodic ones to chaos, in the unstable region as the controlling parameter of steady phase change number or subcooling number under some specific conditions with a relatively strong void-reactivity coefficient of C α = - 0.38 $ / % . The appearance of a periodic cycle of three suggests that there may be immeasurable periodic types of nonlinear oscillations in the limited unstable space of this system. [ABSTRACT FROM AUTHOR]

Highlights: [•] Recirculating flow patterns may affect drift flux parameters in rod bundles. [•] A drift-flux correlation is developed considering low pressure and low liquid flow. [•] Improvement over earlier correlations is demonstrated with a performance analysis. [•] The new correlation is demonstrated as scalable to high pressure conditions. [Copyright &y& Elsevier]

Highlights: [•] Systematic two-phase flow data is collected at low pressure and low liquid velocity. [•] Gravitational forces are more significant at low pressure conditions. [•] The effect of recirculation patterns may be observed in the new data. [•] Uncertainty in earlier correlations may be attributed to secondary flow patterns. [Copyright &y& Elsevier]

Abstract: Reactions of pyruvic acid hydrazone series [pyruvic acid thiophenecarbonyl hydrazone (L1), pyruvic acid 4-hydroxybenzoylhydrazone (L2), pyruvic acid salicyloylhydrazone (L3), pyruvic acid benzoylhydrazone (L4)], or salicylaldehyde hydrazone Schiff base ligand [salicylaldehyde isonicotinoylhydrazone (L5)] with different alkyltin salts result in six new organotin(IV) compounds, {(n-Bu)2Sn[2-SC4H3CON2C(CH3)CO2](HOC3H7-i)}2 (1), [{(n-Bu)2SnCl(O)(n-Bu)2 Sn(O)[C6H4CON2C(CH3)CO2]Sn(n-Bu)2(HOCH3)}2]∞ (2), {(o-ClBz)2Sn[4-HOC6H4CON2C(CH3) CO2] (HOC2H5)}2 (3), {(n-C8H17)2Sn[2-HOC6H4CON2C(CH3)CO2](H2O)}2 (4), {(n-Bu)2Sn[C6H5 CON2C(CH3)CO2][HOSn(n-Bu)3]}2 (5), and {[(n-C4H9)SnCl2]−[4-NHC5H4CON2CH (C6H4O-2)]+ (6), which have been characterized by single crystal X-ray diffraction, elemental analysis, IR, 1H and 119Sn NMR. In compounds 1, 3, 4, weak-bridged dimers are found, in which the two tin atoms are linked by a pair of monodentate bridges. Each pyruvic acid hydrazone ligand serves as an enolic tridentatic ligand. Compound 2 contains dimeric units of {Sn6(L2)2(n-Bu)6(HOCH3)2} that are further connected by two pairs of monodentate bridges into an 1D weak-bridged polymeric chain, in which there also exists a fascinating dichlorodistannoxane ladder structure. Studies show that the bulk and steric hindrance of the alkyl groups and the coordinated solvent molecule bonding to Sn center have little effect on the geometry of the weak-bridge for compounds 1–4. A similar weak-bridged dimeric structure is also found in compound 5; in this case, however, there is no coordinated solvent molecule and the corresponding coordination site is replaced by the trialkyltin hydroxide. Compound 6 exhibits a rare 1D supermolecular chain constructed from the zwitterionic {Sn(L5)(n-Bu)Cl2} units connected by the intermolecular N–H⋯Cl hydrogen bonds. The thermal stability of compound 1 was also studied. [Copyright &y& Elsevier]

The technique of laser-assisted nanoimprinting lithography (LAN) has been proposed to utilize an excimer laser to irradiate through a quartz mold and melts a thin polymer film on the substrate for micro- to nano-scaled fabrications. This study introduces optical multiple reflection theory to demonstrate both analytical and numerical modeling during the LAN process and to predict the thermal response theoretically. Furthermore, the capability of energy absorption for polymer resist is examined herein. The temperature of polymer resist with the capability of energy absorption is much higher than that without energy absorption. This study demonstrates the characteristics of the energy absorption for polymer materials could improve the performance of the LAN process for the reason that the thermally affected region is extremely limited. [ABSTRACT FROM AUTHOR]

The reserves of krypton are abundant, and it has become an important high specific impulse substitute for Hall thrusters as its physical properties are closest to xenon. However, it has been found that the plasma beam of a Hall thruster has weak plume-focusing characteristics and the half-divergence angle is large when using krypton as a propellant. In this paper, the thrust, specific impulse, efficiency, and plume half-divergence angle of a Hall thruster under different propellant supply flow rates are measured. In addition, the influences of the magnetic field configuration and cathode heating power on the beam-focusing characteristics are researched. The results show that the magnetic field mainly affects the beam-focusing characteristics by the bending direction of the magnetic field lines, thus causing the divergence, focusing, and overfocusing phenomena of the plasma plume. Excessive cathode heating power changes the low-frequency discharge amplitude of the Hall thruster, affects the ionization distribution and the width of the main ionization region, and thereby changes the plume focusing state. [ABSTRACT FROM AUTHOR]

In this paper, we extensively review the status and projection of the Filtered Containment Venting Systems (FCVSs) in the Nuclear Power Plants (NPPs) in Asia. As an important strategy to mitigate the Severe Accidents (SAs) in NPPs, FCVS is designed to prevent the containment overpressure failure by providing containment venting through a filtration system. The 2011 Fukushima Daiichi nuclear accident brought a negative impact to the public faith on the nuclear safety, the accident has led regulatory authorities and policy makers to re-evaluate safety criteria and reinforce safety supervision. As a result, the mitigation of SAs regains attention of nuclear community. Many investigation and research works were initialized or resumed, particularly about the enhancement of FCVS on robustness and filtration efficiency. Presently, Asia is a region where nuclear energy grow fast. To ensure nuclear safety, the FCVS is being taken into account in the SA mitigation strategy by regulatory authorities. Chinese nuclear safety administration requires NPPs to have adequate and reliable containment venting system. Thus FCVS is either equipped or about to be equipped on most reactors operating or under construction in China. Nuclear companies and research institutions are conducting research and engineering works about FCVS design and function. In South Korea, a government funded project was carried out during 2013–2017, aimed to design a domestic FCVS technology. Confirmatory tests have been performed to evaluate the function of designed FCVS. In Japan, Tokyo Electric Power Company started installing FCVS on the NPPs since 2013. Related research work is performing in Japanese universities and institutions. Taiwan’s Atomic Energy Council also requests utility companies to reexamine the present emergency operation procedures and study the strategies such as the addition of required facilities for SA prevention and mitigation in each NPP. It is noticed that India is also investigating the options to mitigate the SAs, including FCVS. [ABSTRACT FROM AUTHOR]

In this study, the model of Lungmen ABWR NPP (nuclear power plant) using RELAP5 with the interface SNAP was established. This RELAP5/SNAP model performed the mitigation strategy simulation and study. The main systems of the mitigation strategy are RCIC (Reactor Core Isolation Cooling System), ADS (Automatic Depressurization System), and AC-Independent Water Addition System (ACIWA). This research focuses to assess the usefulness of the mitigation strategy under Fukushima-like conditions. There are three steps in this study. The first step is the establishment of Lungmen NPP RELAP5/SNAP model using the systems data, startup tests reports, and FSAR. The second step is the mitigation strategy simulation and analysis under Fukushima-like conditions using the RELAP5/SNAP model. In this step, the case without mitigation strategy was also performed to evaluate the mitigation strategy effectiveness. Finally, the FRAPTRAN analysis with the interface SNAP was performed in this study. This can evaluate the mechanical property and integrity of fuel rods. According to the RELAP5 results under Fukushima-like conditions, the mitigation strategy can maintain the PCT (peak cladding temperature) below the criteria (1088.7 K). And the FRAPTRAN results also present that the mitigation strategy can keep the fuel rods integrity. It indicates that Lungmen NPP would be in a safe situation when Lungmen NPP performs the mitigation strategy. [ABSTRACT FROM AUTHOR]

In this research, the TRACE and MAAP5 model of Chinshan BWR/4 nuclear power plant (NPP) has been established for the simulation and analysis of ultimate response guideline (URG). The main actions of URG are the depressurization and low pressure water injection of the reactor and containment venting. This research focuses to assess the usefulness of the URG under Fukushima-like conditions. This study consists of three steps. The first step is the establishment of Chinshan NPP TRACE and MAAP5 model. The second step is the URG simulation and analysis under Fukushima-like conditions by using Chinshan NPP TRACE and MAAP5 model. In this step, the base case without URG case was also performed in order to evaluate the URG effectiveness of Chinshan NPP. In order to confirm the mechanical property and integrity of fuel rods, the final step is FRAPTRAN analysis. According to TRACE and MAAP5 analysis results under Fukushima-like conditions, the URG can keep the peak cladding temperature (PCT) below the criteria 1088.7 K. It indicates that Chinshan NPP can be controlled in a safe situation. If under Fukushima-like conditions Chinshan NPP does not perform the URG, the water level may drop below the TAF (top of active fuel) which means a fuel melt safety issue may exist. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of heat transfer enhancement with liquid-gas two-phase segmented microchannel flows by utilizing a novel technique of molecule-based temperature sensors. A serpentine microchannel was constructed and steady liquid and gas segments of ethanol and air were successfully produced at various flow rates. A molecule-based temperature sensor made of Tris(2,2′-bipyridyl) ruthenium was utilized in the liquid segments by dissolving in ethanol as temperature-sensitive fluid and mixing in a dope to produce temperature-sensitive paint in order to retrieve fluid and surface temperature data, respectively. Three cases of different liquid and gas flow rates were tested. The heat transfer enhancements of these three cases were carefully examined under constant heat flux thermal boundary conditions, and the increased heat transfer was evaluated in comparison with the single-phase flow, where only liquid was injected in the microchannel. An improvement of up to 30% in the averaged Nu number of the microchannel flow was determined for Case 3, with a high gas flow rate and short liquid segments. Velocity and vorticity profiles in the liquid segments at different gas and liquid flow rates were also studied using a micro-particle image velocimetry technique. Stronger circulation was observed in Case 3, which confirmed the results from the heat transfer analysis, namely that more efficient heat transfer occurs with strong circulation in short liquid segments when a high gas flow rate is applied. The results of the present study provide detailed temperature profiles in segmented flow as well as the evolution of the Nu number from the entrance to the exit of a serpentine microchannel. [ABSTRACT FROM AUTHOR]

After Fukushima Daiichi disaster, the safety analysis of severe accidents became one of the safety concerns in Taiwan. The Emergency Operating Procedure (EOP) cannot cope with a multiple system failure situation under a severe accident since it is a “Symptom-basis” procedure. To deal with that, Taiwan Power Company built up a new strategy for Fukushima-like accident called Ultimate Response Guideline (URG). It is a simple strategy with three main conditions: loss of regular motor driven injection system, loss of all AC power and tsunami/earthquake warning. If two of three happen, the operating procedure will change from EOP to URG and start the main works by following the strategy. There are three main works in URG: controlled-depressurization, line up low pressure injection water and prepare containment venting. In this study, MELCOR2.1 was used to calculate the cases of URG and checked the goal of the strategy that prevents the accident or not. There were three steps in this research. First, a model of Chinshan nuclear power plant (NPP) was built. Second, one was the case with URG and the other was not by using the above MELCOR model. The results were compared to MAAP5.0, TRACE and PCTRAN. Finally, some sensitivity studies of depressurization and water injection rate were done. [ABSTRACT FROM AUTHOR]

Abstract: Experiments were performed to examine the spreading thermal resistance of centrally positioned heat sources and the thermal performance of a water charged, gravity assisted flat vapor chamber to be used for electronic cooling. Parametric studies including different heat fluxes and operating temperatures were conducted, and the effect of the relevant parameters on the cooling performance in terms of the spreading resistance was presented and discussed. The present vapor chamber heat spreader showed a heat removal capacity of 220W/cm2 with a thermal spreading resistance of 0.2°C/W. [Copyright &y& Elsevier]

Abstract: A three dimensional analytical solution using product solutions via the separation of variables for spreading thermal resistances of centrally positioned heat sources of a vapor chamber heat sink with and without a partition for electronic cooling is presented. Parametric study including partition thickness and height was performed, and the effect of the relevant parameters on the heat transfer performance in terms of the base spreading resistance was examined. [Copyright &y& Elsevier]

In the title compound, C30H28N2S4, the S—S bond length is 1.9910 (13) Å. In the absence of classical hydrogen bonds and π–π inter­actions, the crystal packing is stabilized by van der Waals forces. [ABSTRACT FROM AUTHOR]