To determine the thermodynamic temperature of a solid surface from the electron energy distribution measured by photoelectron spectroscopy, it is necessary to accurately evaluate the energy ...broadening of the photoelectron spectrum and investigate its temperature dependence. Broadening functions in the photoelectron spectrum of Au(110)’s surface near the Fermi level were estimated successfully using the relationship between the Fourier transform and the convolution integral. The Fourier transform could simultaneously reduce the noise of the spectrum when the broadening function was derived. The derived function was in the form of a Gaussian, whose width depended on the thermodynamic temperature of the sample and became broader at higher temperatures. The results contribute to improve accuracy of the determination of thermodynamic temperature from the photoelectron spectrum and provide useful information on the temperature dependence of electron scattering in photoelectron emission processes.
•Constitutive equations for a vertical rod bundle are reviewed.•Dependence of distribution parameter on flow conditions is discussed.•1D momentum equation by considering void fraction distribution is ...discussed.•Effect of channel size on interfacial area concentration is discussed.
In view of the quality assurance of two-phase flow simulations, CSAU (Code Scalability, Applicability, and Uncertainty) methodology and code V & V (Verification and Validation) have been proposed. The estimation of simulation uncertainty is indispensable in using best-estimate computational codes. A key of successful two-phase flow simulations is to use the state-of-the-art constitutive equations to close the mathematical system used in two-phase flow analyses. The advanced constitutive equations should be developed based on “physics” behind phenomena and should consider scaling parameters which enable their application beyond test conditions used for a code validation. Two-phase flow simulations in a rod bundle is important in various industrial apparatuses such as heat exchangers and nuclear reactors. Constitutive equations for two-phase flows in a vertical rod bundles have been advanced in recent five years. In view of this, this paper provides a comprehensive review of most advanced constitutive equations for two-phase flow analyses in a vertical rod bundle. The constitutive equations of two-phase flow parameters reviewed in this paper are flow regime map, void fraction, void fraction covariance and relative velocity covariance, interfacial area concentration and wall friction. In addition, an exact formulation of one-dimensional momentum equation in two-fluid model considering void fraction distribution is discussed.
The EPRI (1991) and the Clark et al. (2014) drift-flux correlations implemented in RELAP5/MOD3 code were benchmarked against the low-pressure void fraction data collected by Clark et al. (2014) at ...Purdue University and the high-pressure data collected by Anklam and Miller (1982) at ORNL. The Clark et al. correlation (2014) was found to perform best at low pressures of Clark et al. tests (2014), but the accuracy was deteriorated at higher pressures of Anklam and Miller tests (1982). To account for this effect, a pressure scaling factor has been added to the distribution parameter correlation to reduce the distribution parameter peaking at high pressures. This factor is dependent on the density ratio and it eliminates the distribution parameter enhancement effect for pressures over 0.5 MPa. It was confirmed that the new correlation with the correction improved the void fraction prediction performance at a higher pressure of Anklam and Miller tests (1982). The new correlation provides a transition between the Clark et al. correlation (2014) at low pressures and the correlation of Ozaki et al. (2013) and Ozaki and Hibiki (2015) at high pressures, which is excellent both in physical characteristics and scalability of two-phase flow in rod bundles.
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•A hybrid PECVD/sputtering system was developed for the synthesis of carbon catalysts.•Fe-N-doped carbon catalysts are directly synthesized on carbon papers as fuel cell ...electrode.•The synthesized catalysts exhibit high ORR activity with the onset potential of 0.84V at 10μA.•The high ORR activity is associated with Fe-N coordination bonds in the synthesized carbon catalysts.
A hybrid plasma-enhanced chemical vapor deposition (PECVD)/sputtering system was developed to prepare iron (Fe)-nitrogen (N)-doped carbon catalysts for oxygen reduction reaction (ORR). This hybrid system combines PECVD effective for the synthesis of nanocarbons with sputtering technique for the doping of metals such as Fe where the amount of the doping can be independently controlled during synthesizing nanocarbons. By using this system, Fe-N-doped carbon catalysts are directly synthesized on carbon papers which have been widely used as a gas diffusion layer in fuel cells. The synthesized catalysts with carbon papers exhibit high ORR activity. This is attributed to Fe-N coordination bonds which are stably formed in the synthesized catalysts.
► Adiabatic two-phase flow experiments in an 8×8 rod bundle were performed under pool conditions. ► An extensive database of adiabatic/boiling two-phase flows in pool rod bundle systems was ...collected. ► Effect of large casing on two-phase flow structure was observed in experimental data for medium 〈jg+〉 conditions. ► Existing rod bundle models were benchmarked with the present database. ► All of the void fraction prediction errors of each model are tabulated.
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 Murase’s model (1986), Kamei’s model (2008) and Ishizuka’s model (1995) 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.
•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.
An experiment has been performed to measure void fraction at stagnant to low liquid flow conditions in a rod bundle. An 8×8 rod bundle test facility scaled from a boiling water reactor design was utilized at atmospheric pressure with air and water as working fluids. Superficial liquid velocity ranged from 0 to 1.0m/s and superficial gas velocity ranged from 0.03 to 10.0m/s. Area-averaged measurements of superficial liquid velocity, superficial gas velocity, and void fraction are used to calculate distribution parameter from a kinematic constitutive equation of the drift-flux model. Results indicate a significant increase in distribution parameter when mixture volumetric flux is relatively low. This observation may be attributed to recirculating flow patterns. An investigation is conducted for existing rod bundle drift-flux correlations because they may not appropriately consider these mechanisms at low liquid flow and low pressure conditions. Results suggest that improvements may be made if the effects of recirculating flow are taken into consideration.
Numerical simulations were done to evaluate countercurrent flow limitation (CCFL) characteristics in a pressurized water reactor (PWR) hot leg with the diameter of 750 mm by using a volume of fluid ...(VOF) method implemented in the CFD software, FLUENT6.3.26. The calculated CCFL characteristics agreed well with known values including the UPTF data at 1.5 MPa. Sensitivity analyses for system pressures up to 8 MPa showed that the calculated CCFL characteristics in the Wallis diagram were slightly mitigated from 0.1 MPa to 1.5 MPa with increasing system pressure, but they did not change from 1.5 MPa to 8MPa. Using the CCFLs calculated in this study and values measured under air-water and steam-water conditions, a CCFL correlation and its uncertainty were derived.
•Thermodynamic temperature measured via area ratio of photoelectron spectrum.•Fermi–Dirac distribution obtained to determine thermodynamic temperature.•Photoelectron spectra near Fermi level measured ...on Au(110) surface at 3 temperatures.•Accuracy of temperature determination less than 1 K for all temperature ranges.•It enables calibration-free multifunctional simultaneous measurement.
The Fermi–Dirac (FD) distribution describes the occupancy of electronic states in a material at thermal equilibrium as a function of the thermodynamic temperature. By measuring the electron energy distribution using photoelectron spectroscopy, we can obtain the FD distribution and determine the thermodynamic temperature. This study proposes a method for determining the thermodynamic temperature, which involves calculating the area ratio between the photoelectron spectra above and below the Fermi level. This thermometric technique offers several advantages, including surface selectivity, noncontact measurement, and coordination with other measuring devices commonly used in surface analysis and nanoscale measurements under ultrahigh vacuum conditions. In this study, we measured the photoelectron spectra near the Fermi level on an Au (110) surface at three different temperatures: liquid nitrogen, liquid helium, and room temperatures. Using the area ratio method, we successfully determined the thermodynamic temperatures with an accuracy of less than 1 K.
A novel retarding type electron energy analyzer implementing an electrostatic lens system to achieve a high energy resolution sufficient to measure thermodynamic temperature has been investigated ...based on the electron trajectory analysis. The energy resolution of the analyzer depends linearly on the retarding energy with a modulus of 0.05 %. The voltages to be applied to the electrodes in the analyzer are found to be controllable linearly against the retarding voltage. The analyzer has threshold energies, whose effect can be excluded in practical measurements.
In reflux cooling, the steam generated in the reactor core and the water condensed in a steam generator form a countercurrent flow in a hot leg. In order to investigate flow patterns in the hot leg ...under countercurrent flow conditions, countercurrent air-water tests were previously conducted using a 1/15th scale model of a PWR hot leg. Numerical simulation results for the tests using a three-dimensional two-fluid model in FLUENT6.3.26, implemented with an appropriate set of correlations for the gas-liquid interfacial friction, were in good agreement with the measured data. In the present study, further numerical simulations were carried out for a full-scale hot leg under PWR plant conditions to investigate the effects of pipe diameter and fluid properties. The predicted countercurrent flow limitation characteristics were well correlated with the Wallis parameters and agreed well with the measured data from the 1/15th scale air-water tests as well as the full-scale steam-water UPTF tests. The results indicate that the set of correlations for the gas-liquid interfacial friction can be utilized to simulate countercurrent flows in the full-scale PWR hot leg.
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