Phase change material (PCM) laden with nanoparticles has been testified as a notable contender to increase the effectiveness of latent heat thermal energy storage (TES) units during charging and discharging modes. In this study, a numerical model is developed and implemented based on the coupling between an advanced two-phase model for the nanoparticles-enhanced PCM (NePCM) and the enthalpy-porosity formulation for the transient behavior of the phase change. Therefore, a porosity source term is added to the nanoparticles transport equation to account for the particles' frozen state in regions occupied by solid PCM. This two-phase model includes three main nanoparticles’ slip mechanisms: Brownian diffusion, thermophoresis diffusion, and sedimentation. A two-dimensional model of a triplex tube heat exchanger is considered and different charging and discharging configurations are analyzed. Compared to pure PCM, results show a substantial heat transfer enhancement during the charging and discharging cycle in which a homogeneous distribution of nanoparticles is considered as the initial condition. For this case, the two-phase model predictions are superior to the ones obtained with the classical single-phase model. In the case of multi-cycle charging and discharging, a significant deterioration of the heat transfer rate is observed using the two-phase model while such assessment is senseless using the single-phase mixture model due to the physical assumptions upon which this model is formulated. The two-phase model results reveal that, for a NePCM with high nanoparticles concentration (> 1%), the melting performance during the second charging cycle is reduced by 50% compared to the first one. This performance degradation is attributed to a noteworthy non-homogeneous distribution of the nanoparticles at the beginning of the second charging cycle. The dominant nanoparticles migration mechanism, in this scenario, is the one resulting from sedimentation effects.
Nuclear power and modern agriculture are two crucial sectors for sustainable development in the United Arab Emirates (UAE). As these industries mature rapidly in the country, their long-term inter-compatibility needs monitoring with local data on transfer of radionuclides from arid sandy soils to farm products. Date palms, main crop from the Arabian Peninsula, remain largely unstudied for radioecological impact assessments. This paper reports the first measurement of soil to UAE date palms concentration ratios for natural radionuclides. Representative samples of soils, fruits, and leaves from seven palms in Abu Dhabi have been studied using gamma-spectrometry. Average activity concentrations in the soils are around 278.9 Bq kg−1 for 40K, 15.5 Bq kg−1 for 238U, and 8.3 Bq kg−1 for 232Th. The latter two decay chains, in the plant samples, are close to detection limits, signifying their lower levels in the UAE flora and the need for upgrading analytical techniques. The geometric means of soil to fruit concentration ratios are 1.12 for 40K, but negligibly low for the others—approximately 0.08 for 238U and 0.17 for 232Th chains. The respective ratios for the leaves are approximately 0.13, 0.36, and 0.77. Personal radiation doses due to soils and dates are very low, posing no danger to the public.
The current numerical investigation is carried out to assess the possibility of integrating a latent heat thermal energy storage (TES) in a nuclear power plant (NPP) system. This would allow improving the capability of such plants to operate in a load-following mode by eliminating the gap between energy supply and energy demand by the grid. In contrary to previously published TES designs, the phase change material (PCM) triplex-tube containers are vertically oriented in the present study to take advantage of melting/solidification enhancements induced by the buoyancy forces. In addition, two different fluids simultaneously co-circulating within the storage, hence, allowing for this component to operate as a storage system (under extreme charging/discharging conditions) or as simple heat exchanger (under normal steady-state conditions). The computational domain, in this study, is reduced from the full TES geometry to a single triplextube container owing to the homogeneous triangular positioning of the annular tubes within the storage vessel. The results show that the time required to fully melt the solid PCM is around 27 hours during charging mode, thus, allowing for a relatively long-time margin even under an extreme postulated accident scenario consisting in the inability of the secondary loop to remove heat from the system. In the opposite discharging mode, the time needed to fully solidify the 100% liquid PCM is 17 hours. During the simultaneous charging and discharging (SCD) mode, with constant load, the fraction of liquid PCM is nearly fixed with time. Hence, TES in this mode is said to take the role of a standard heat exchanger. Finally, simulations conducted for the SCD mode, with variable load, demonstrate that the coupled system can follow the daily variations in the grid demand without having any significant impact on the constant operation of the reactor. In this operating mode, the PCM is changing phases from solid to liquid and vice versa to adapt to the energy demand variations as anticipated.
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