[en] The land-sea contrast in turbulent surface fluxes on small flat islands offers a real-world scenario that regularly results in organised convection. This contrast results in a thermally driven circulation that tilts downwind of the island, leaving a warm plume in the wake of the island. Convection that forms in the warmed wake of the island is organised into a band aligned parallel to the flow. These thermally forced convective bands, or ‘cloud trails’, have been observed to extend more than 100 km downwind of islands in a wide range of environments. For example, Bermuda in the Subtropical Atlantic and Nauru in the Tropical Pacific. Cloud trails are found to be controlled by a combination of low-level humidity which controls the height of the lifting condensation level, and the land-sea contrast in turbulent surface fluxes which controls the strength of thermal circulation (i.e. lift) downwind of the island. Convective precipitation within a cloud trail, or in the background environment, results in cold pools that can act against the organisation due to the thermally forced island circulation. In the present study, idealised simulations at high (100 m) resolution are performed. Analysis aimed at a deeper exploration into the lifecycle of cloud trails and the processes involved in the initiation of convection and the maintenance of convective organisation are presented. (author)

[en] The following study aimed to determine the effect of nanofluid concentration and the inclusion of porously filled channels on the thermal performance of highly porous open-cell foam metals. The study considered variable heat flux, nanofluid concentration and considered porously filled channels and bulk porous media. The nanofluid used in the experimental and numerical work was γ-Al₂O₃ nanoparticles suspended in water. The foam metal used was composed of 6061-T6 aluminum with a porosity of 0.91 and a permeability of 3.36e − 8 m². The nanofluid concentrations used for the study were 0.1%, 0.3%, and 0.6% by volume. The experimental and numerical work showed good agreement with a maximum relative error between numerical and experimental temperature of 4.8% and an average error of 3.0%. The thermal performance of the system was evaluated based on Nusselt number and an index of performance including pressure effects. The results indicate that the optimal conditions for system operation are 0.6% with porously filled channels when pumping power is not considered of importance. However, should the pumping power be considered as an essential operating parameter then the optimal system conditions are 0.3% with bulk porous media.

[en] The ESR spin-label method has been used for studies on molecular dynamics in polymers. Advanced computer simulation for the dynamics and a novel technique (microwave power saturation method) for determination of T_g by ESR are introduced here. These techniques reveal the polymer dynamics at the specific sites and in specific environments. (author)

[en] The Joint UK Land Environmental Simulator (JULES) was run offline to investigate the sensitivity of land surface type changes over South Africa. Sensitivity tests were made in idealised experiments where the actual land surface cover is replaced by a single homogeneous surface type. The vegetation surface types on which some of the experiments were made are static. Experimental tests were evaluated against the control. The model results show among others that the change of the surface cover results in changes of other variables such as soil moisture, albedo, net radiation and etc. These changes are also visible in the spin up process. The model shows different surfaces spinning up at different cycles. Because JULES is the land surface model of Unified Model, the results could be more physically meaningful if it is coupled to the Unified Model.

[en] Highlights: • A propane-nitrogen two-phase expander cycle is proposed for natural gas liquefaction. • The proposed process improves the energy efficiency significantly. • The proposed process remains the low global warming potential. • Particle swarm algorithm is used for optimization with exergy analysis. Nitrogen (N₂) expander liquefaction process has the highest ecological and safety advantages over different types of available commercial natural gas liquefaction processes. However, its relatively low energy efficiency is a major issue. In this context, the optimum flow rate of propane as a high-boiling component with low-global warming potential was mixed with conventional refrigerant N₂, resulting in a two-phase single mixed refrigerant appearing at the suction point of the conventional turbo expander. The potential application of a two-phase cryogenic expander was investigated to generate a cooling effect through the expansion of the high-pressure two-phase propane-nitrogen refrigerant. The proposed study was modeled using Aspen Hysys® and optimized by adopting a MATLAB coded particle swarm optimization approach that was linked to Aspen Hysys® using the ActiveX (also known as COM) functionality. The results revealed that the specific energy consumption and required refrigerant flow rate for liquefied natural gas (LNG) production can be reduced up to 46.4% and 27.7%, respectively, in comparison with the conventional N₂ single expander LNG process. Furthermore, the overall energy can be reduced from 79.2% to 29.5% as compared to previously reported N₂ single expander LNG processes, depending on feed conditions, composition, and design parameters. An exergy analysis of the proposed LNG process revealed that the compressors and LNG heat exchanger have the highest exergy loss, i.e., 34.0% and 29.7%, respectively.

[en] Highlights: • Simple, compact and energy-efficient SMR processes were proposed. • Proposed process showed a synergetic advantage of enhancing energy efficiency. • Energy saving of 30.6% can be accomplished by a knowledge-inspired optimization. • Energy requirement is reduced significantly lowering the intercooler temperature. - Abstract: This study examined the enhancement of the single mixed refrigerant (SMR) natural gas liquefaction process. The effects of the main parameters, such as mixed refrigerant (MR) composition and operating pressures on the compression energy requirement were investigated. A process knowledge inspired decision-making method was exploited for liquefied natural gas process optimization. The results showed that the proposed optimization methodology is simple and effective in determining the optimal operating conditions and could save up to 30.6% in terms of the compressor duty compared to the base case. In addition, the proposed optimization methodology provides process understanding, which is essential to process engineers. Another benefit of the proposed methodology is that it can be applied to any MR liquefaction cycle. The use of heavier refrigerants, such as isobutane and isopentane, and the addition of a NG compressor were examined to improve the energy efficiency of the SMR process. The effect of the intercooler outlet temperature on energy saving was also considered. The synergistic effects of those modifications on improving the performance of the liquefaction process were investigated.

[en] Highlights: • Practical method for finding optimum refrigerant composition is proposed for LNG plant. • Knowledge of boiling point differences in refrigerant component is employed. • Implementation of process knowledge notably makes LNG process energy efficient. • Optimization of LNG plant is more transparent using process knowledge. - Abstract: Mixed refrigerant (MR) systems are used in many industrial applications because of their high energy efficiency, compact design and energy-efficient heat transfer compared to other processes operating with pure refrigerants. The performance of MR systems depends strongly on the optimum refrigerant composition, which is difficult to obtain. This paper proposes a simple and practical method for selecting the appropriate refrigerant composition, which was inspired by (i) knowledge of the boiling point difference in MR components, and (ii) their specific refrigeration effect in bringing a MR system close to reversible operation. A feasibility plot and composite curves were used for full enforcement of the approach temperature. The proposed knowledge-based optimization approach was described and applied to a single MR and a propane precooled MR system for natural gas liquefaction. Maximization of the heat exchanger exergy efficiency was considered as the optimization objective to achieve an energy efficient design goal. Several case studies on single MR and propane precooled MR processes were performed to show the effectiveness of the proposed method. The application of the proposed method is not restricted to liquefiers, and can be applied to any refrigerator and cryogenic cooler where a MR is involved

[en] Highlights: • Hybrid friction stir welding for Al alloy and Ti alloy joint has been carried out. • Mechanical strength of dissimilar joint by HFSW and FSW has been compared. • Microstructure of dissimilar joint by HFSW and FSW has been compared. - Abstract: Hybrid friction stir butt welding of Al6061-T6 aluminum alloy plate to Ti–6%Al–4%V titanium alloy plate with satisfactory acceptable joint strength was successfully achieved using preceding gas tungsten arc welding (GTAW) preheating heat source of the Ti alloy plate surface. Hybrid friction stir welding (HFSW) joints were welded completely without any unwelded zone resulting from smooth material flow by equally distributed temperature both in Al alloy side and Ti alloy side using GTAW assistance for preheating the Ti alloy plate unlike friction stir welding (FSW) joints. The ultimate tensile strength was approximately 91% in HFSW welds by that of the Al alloy base metal, which was 24% higher than that of FSW welds without GTAW under same welding condition. Notably, it was found that elongation in HFSW welds increased significantly compared with that of FSW welds, which resulted in improved joint strength. The ductile fracture was the main fracture mode in tensile test of HFSW welds

[en] Highlights: • Uncertainty quantification and sensitivity analysis for LNG process. • Standard Monte Carlo (MC) method is utilized. • Relative percentage of the Sobol total effect indices for DMR LNG process. • Probability distribution of the approach temperature for DMR liquefaction process. • Global sensitivity analysis with less computational effort. -- Abstract: The dual mixed refrigerant (DMR) liquefaction process is complicated and sensitive compared to the competitive propane pre-cooled mixed refrigerant liquefied natural gas (LNG) process. When any uncertainty is introduced to the process operation conditions, it is necessary for the DMR process to be re-optimized to maintain efficient operation at a minimal cost. However, in actual operation, re-optimization is a challenging task when the process operational input variables are varied, typically owing to the lack of information regarding the nature, impact, and levels of uncertainty. Within this context, this study investigates the uncertainty levels in the overall energy consumption and minimum internal temperature approach (MITA) inside LNG heat exchangers with variations in the operational variables of the DMR processes. Moreover, a global sensitivity analysis is conducted to identify the influence of random inputs on the process performance parameters. The required energy is significantly influenced by the variations in the variables in the cold mixed refrigerant (approximately 63%), while changes in the warm mixed refrigerant (WMR) section only slightly affect the uncertainty of the required specific energy. Furthermore, the probability distribution of the approach temperature (MITA1) inside the WMR exchanger is mainly affected by changes in the compositions of methane, ethane, and propane, as well as the high pressure of the cold mixed refrigerant (approximately 97%). Conversely, the flow rate of ethane and low pressure of the WMR significantly affect the uncertainty of the approach temperature (MITA2) inside the cold mixed refrigerant exchanger.

[en] In this study, we suggest a new concept design of GBS (Gravity Based Structure) type ONPP (Offshore Nuclear Power Plants) using the SMART (System integrated Modular Advanced Reactor) model, which is the most recent SMR (Small Modular Reactor) model in Korea. Because floating and submerged types of NPPs (Nuclear Power can easily be affected by severe ocean environments such as tsunamis and storms, a new GBS type ONPP using the APR1400 model, the largest NPP model in Korea, was proposed in our previous work. We expand this concept for the SMART model and suggest a new concept with design parameters, design requirements, and the new total GA (General Arrangement) based on modularization. We discuss its structural safety features. We believe that the proposed GBS type ONPP design concept based on the SMART model can be a robust alternative to the original land based SMART. (authors)