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We experimentally investigated the effects of thermal aging and cold work on the microstructure, mechanical properties, and primary water stress corrosion cracking (PWSCC) initiation time for Alloy 182 welds. The effects of thermal aging and cold work on the PWSCC initiation time of Alloy 182 were modeled based on the plastic energy concept and the PWSCC initiation data of this study and previous reports by considering censored data. Based on the results, it is estimated that the PWSCC resistance of the Alloy 182 weld firstly increases and then decreases with thermal aging time when the applied stress is kept constant.

Smart islands have focused on renewable energy sources, such as solar and wind, to achieve energy self-sufficiency. Because solar photovoltaic (PV) power has the advantage of less noise and easier installation than wind power, it is more flexible in selecting a location for installation. A PV power system can be operated more efficiently by predicting the amount of global solar radiation for solar power generation. Thus far, most studies have addressed day-ahead probabilistic forecasting to predict global solar radiation. However, day-ahead probabilistic forecasting has limitations in responding quickly to sudden changes in the external environment. Although multistep-ahead (MSA) forecasting can be used for this purpose, traditional machine learning models are unsuitable because of the substantial training time. In this paper, we propose an accurate MSA global solar radiation forecasting model based on the light gradient boosting machine (LightGBM), which can handle the training-time problem and provide higher prediction performance compared to other boosting methods. To demonstrate the validity of the proposed model, we conducted a global solar radiation prediction for two regions on Jeju Island, the largest island in South Korea. The experiment results demonstrated that the proposed model can achieve better predictive performance than the tree-based ensemble and deep learning methods.

Carbon capture and storage is a popular CO2-reduction technology, and carbon capture and utilization (CCU) technology has been reported frequently over the years. However, CCU has certain disadvantages, including the requirement of high energy consumption processes such as mineral carbonation. In addition, stable metal sources are required to fix CO2. This study used concentrated seawater to supply metal ions. In addition, the selected 5 wt % amine solution changed CO2 into aqueous CO2 to reduce the additional energy required to form the metal carbonate under moderate conditions. As a result, precipitates were formed because of the reaction of carbonate radicals with metal ions in the seawater. These precipitates were analyzed by X-ray diffraction and field-emission scanning electron microscopy, and they were found to mostly consist of CaCO3 and NaCl. Furthermore, it was verified that the conversion solution maintained its CO2-loading capacity even after the solids and liquid were filtered twice. Therefore, the proposed method permits a substantial reuse of CO2 and waste seawater when sufficient metal ions are supplied. Therefore, methods to improve their purity will be developed in future studies.

Abstract Ocean energy is a promising renewable energy resource. In particular, South Korea is a country with a large amount of tidal current energy needed for the economically and technically feasible development of a tidal current power plant. In this study, the environmental conditions including the bathymetry and tidal conditions for Uldolmok Strait and previous studies carried out in Uldolmok Strait are first briefly reviewed, and the optimal design of the blade shape and performance of an optimally designed horizontal axis rotor for a 200-kW class tidal current turbine are discussed. For the optimal blade shape design, the design code, the Horizontal Axis Rotor Performance Optimizer developed by the National Renewable Energy Laboratory in the United States, is utilized, and the performance is investigated with respect to the number of blades (two or three) and the pitch control algorithms (variable or fixed). The results indicate that a variable speed fixed pitch turbine with three blades showed the best performance. However, the performances of four alternative cases did not show significant differences. Considering the advantages in terms of maintenance, we also conducted an analysis under various rotor and cut-in speed conditions. Hence, to select the final design, it is necessary to consider the structural integrity related to fatigue, as well as the economic feasibility in manufacturing the blades.

Abstract A CANDU-6 reactor has 380 fuel channels of a pressure tube type, which provides an independent flow passage, and each pressure tube contains twelve fuel bundles horizontally. The CHF of a CANDU fuel bundle in a horizontal fuel channel is one of the important parameters determining the thermalhydraulic safety margin as well as the trip set point of the Regional Overpower Protection (ROP) system. Hence, the CHF enhancement of a CANDU fuel bundle has been an issue for a long time and can be affected by the geometric configuration of the fuel elements as well as several appendages such as the end-plates, bearing pads, and spacers attached to the fuel elements. It is known that the first CHFs of a standard 37-element fuel bundle preferably occur at the peripheral subchannels of the center rod, owing to the relative small flow area or high flow resistance under high flow conditions or the normal operating conditions of a CANDU reactor. An increase of the inner ring radius of a standard 37-element fuel bundle without any changes in the fuel bundle or element sizes is introduced to enhance the CHF in consideration of the CHF characteristics of a standard 37-element fuel bundle for a CANDU reactor. Subchannel analysis techniques using the ASSERT-PV code were applied to investigate the local CHF characteristics according to the inner ring radius variation for the original diameter of the pressure tube. It was found that the modification of the inner ring radius is very effective in enhancing the dryout power of the fuel bundle through an enthalpy re-distribution of the subchannels and change in the local locations of the first CHF occurrences.

Carboxylic acid functionalized alloxazine (alloxazine-COOH) and ferrocyanide are utilized as active species for aqueous redox flow battery (ARFB), and the effect of operating temperature on the performance of ARFB was investigated. Based on electrochemical characterization, although ferrocyanide is in a quasi-reversible state at room temperature, the state becomes irreversible as temperature increases. By the use of carbon felt (CF) containing carbon-oxygen functional groups, the activity of ferrocyanide is enhanced without side effect, such as irreversible redox reactivity. This is because the hydrophilic (charge-dipole) interaction between dipole groups (hydroxyl and carbonyl groups) onto CF and ferricyanide ions promotes the oxidation reaction of ferricyanide. Though alloxazine-COOH coated on glassy carbon electrode shows irreversible state compared to ferrocyanide as temperature increases, the activity of alloxazine-COOH is also enhanced by using the hydrophilic group doped CF. To prove whether the redox reactivity of the two active species is improved with increase in temperature, the performance of ARFBs using them was evaluated in the different temperature conditions. When the temperature of both anolyte and catholyte is 45 °C, average discharge capacity and state of charge are 24 Ahr·L−1 and 90%, and the values are reduced to 23 Ahr·L−1 and 86% in ARFB of only catholyte heating, 22 Ahr·L−1 and 82% in ARFB of only anolyte heating and 21.3 Ahr·L−1 and 80% with no heating. Based on that, it is speculated that the operation temperature can be a factor in determining the performance of ARFB.

A humidification–dehumidification (HDH) desalination system requires thermal energy to desalt seawater. An environmentally friendly approach to obtain thermal energy is to utilize solar energy using solar collectors. Either seawater or air (or both) are typically preheated by HDH desalination systems before these fluids are conveyed to the humidifier column. Compared with preheating only air or water, preheating both is preferred because improved performance and higher productivity are achieved. Many researchers have proposed dual preheated HDH systems utilizing two separate solar heaters/collectors for simultaneous air–seawater preheating. In this study, dual-fluid preheating is achieved using a single solar collector. The proposed simultaneous air–water solar heater (SAWSH) is a modified flat-plate collector designed for simultaneously preheating air and seawater before the fluids reach the humidifier. A thermodynamic study was conducted using formulated mathematical models based on energy and mass conservation principles. Then, the dual-fluid heating HDH system is compared with HDH systems in which only air or only water is heated. This work found that the former outperformed the latter. The daily and monthly performance levels of the system in terms of the outlet temperatures of air and water, distillate rate, and gain output ratio were calculated using the weather data of the hot and humid climate of Jeddah City, Saudi Arabia.

Abstract Sodium-promoted vanadium oxide catalysts supported on MCM-41 and TiO 2 (anatase) were investigated for the partial oxidation of ethanol to acetaldehyde. The catalysts were prepared by incipient wetness impregnation with a vanadium oxide content of 6 wt.%. The experimental characterization was performed by X-ray diffraction (XRD), N 2 adsorption, temperature-programmed reduction (TPR), and diffuse reflectance UV–vis. Temperature-programmed oxidation (TPO) was also used to identify carbon deposits on the spent catalysts. The presence of sodium plays a strong role in the dispersion and reducibility of the vanadium species as detected by TPR analysis and optical absorption spectroscopy. While sodium addition increases the dispersion of the VO x species, its presence also decreases their reducibility. Additionally, TPO of the spent catalysts revealed that an increase in the Na loading decreases the carbon deposition during reaction. In the case of the catalysts supported on MCM-41, these modifications were mirrored by a change in the activity and selectivity to acetaldehyde. Additionally, on the VO x /TiO 2 catalysts the catalytic activity decreased with increasing sodium content in the catalyst . A model in which sodium affects dispersion, reducibility and also acidity of the supported-vanadia species is proposed to explain all these observations.