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[en] Here we have studied locally rotationally symmetric Bianchi-V Universe in the presence of modified theory for gravitation [f(R,T)theory] and for that, we considered a perfect fluid with heat conduction as the energy source. We used the law of variation for the deceleration parameter (DP) to solve field equations, as it gives a constant value of DP and is related to the average scale factor metric. Also, we have discussed the physical and geometrical properties of the model in detail. (author)
[en] We demonstrate a simple, low-cost, and passive radiative cooler based on a monolithic design consisting of thin nanoporous anodic alumina (NAA) films grown on aluminium sheets. The NAA/Al structure maintains a high broadband reflectivity close to 98% within the solar spectrum (0.4–2.2μm) and simultaneously exhibits a high average emissivity of 88% within the atmospheric infrared (IR) transmission window of 8–13μm with the peak IR emission approaching 99% at a wavelength of 10μm. Optical modelling of the system using optical parameters of the materials confirms that the high solar reflectance arises due to the transparent nature of NAA and high reflectivity of bottom Al, while the large thermal IR emissivity arises from the interference effects of the NAA film and the high absorption of IR light due to phonon resonances in alumina at wavelength larger than 10μm. Further, we estimate the average cooling power of NAA/Al to be about 136 W m−2 at ambient temperature even after including the contribution to heat input from external non-radiative processes. This robust and light weight NAA/Al can be projected as an excellent alternative to optical solar reflectors used in spacecraft for thermal heat management and rooftop cooling green technologies. (author)
[en] In general, Primary Heat Transport System (PHTS) chemistry for pressurized heavy water reactors (PHWRs) is stable and believed to be well understood. The current narrow-band control to minimize feeder wall thinning and hydrogen addition to maintain reducing conditions are effective chemistry control strategies to maximize component lifetimes and minimize degradation and activity transport processes in the PHTS circuit. However, recent laboratory-scale investigations, ongoing evaluations of available reactor chemistry data and the increased availability of on-line analyses are providing more detailed insights into PHTS chemistry in operating plants that may allow future refinements to operating practices. This paper will provide an overview of recent work related to PHTS chemistry from CNL. (author)
[en] The present study analyses the phenomena of entropy generation of magneto third-grade fluid flow through the microchannel. The significance of Joule heating, viscous heating and internal heat source is also scrutinised. The non-dimensional forms of the corresponding governing equations of the physical phenomenon with the associated boundary conditions for third-grade fluid flow and heat transfer has been solved using finite element method. The impact of various parameters on the flow and heat transfer behaviour, entropy generation and Be jan number is explained using graphs. The obtained results are examined through the plots. The results showed that an increase in the fluid parameter reduces the activity of the fluid flow and, as a result, the temperature is diminished. An enhancement in fluid motion and temperature is obtained by increasing the viscosity index. We noted that the effect of Hartmann number on the rate of local entropy generation and Be jan number is sinusoidal in nature. (author)
[en] The history behind CANDU heat transport pH control is briefly discussed along with the rationale. The journey progresses from early 1950s into the new millennium. pH specifications, where possible, are identified along with the rationale for changes. Equipment malfunctions are discussed along with challenges presented by unit outages. (author)
[en] This paper deals with a detailed investigation of the effects of various metal oxide nanoparticles on unsteady stagnation point flow of a hybrid base fluid impinging on a flat surface. The ‘single-phase’ nano fluid model,i.e., the Tiwari and Das model, is considered for the study. We consider water and ethylene glycol in 1:1 ratio as the base fluid and four different types of metal oxides, namely, CuO, TiO2, ZnO and MgO as the nanoparticles.Using similarity transformations, the conservation equations are transformed into self-similar ordinary differential equations. Dual and unique similarity solutions are obtained for certain set of values of parameters. The analysis explores many important findings. Dual self-similar solutions exist up to a certain critical value of the decelerating unsteady parameter and the critical value is independent of the type of metal oxide nanoparticles considered. The strongest surface drag force is observed for the nano fluid with CuO nanoparticles, while the weakest is for the nano fluid with MgO nanoparticles. The heat transfer rate is highest for the nano fluid with CuO nanoparticles and lowest for the nano fluid with TiO2 nanoparticles. Also, the boundary layer is thickest for the nano fluid with multiprocessing MgO nanoparticles. (author)
[en] Fuel pool cooling is an essential task in the scope of nuclear power applications. During the first years of commercial nuclear power implementation robust fuel pool cooling systems have been developed and used for several decades. Two decades ago the development of a new cooling technology/concept was initiated to ensure prevention of accidents, including fuel damage. The so-called advanced cooling technology offers a modular design system which enables tailor-made robust and cost efficient cooling solutions. However, all the advanced cooling systems feature an indispensable and distinctive fall back option of a passive heat removal in case of a station blackout as most important feature. In contradiction to conventional cooling systems the advanced cooling solutions use immersed heat exchangers to establish an additional safety barrier inside the heat removal chain. This results in the necessity of a free convective heat transfer on pool water side. This in turn requires a special design approach and methodology. Because of the huge nominal heat load and the size of the heat removal systems itself full size test are under economical aspects nearly impossible. In this paper a purpose-built simulation and design methodology is presented, which has been developed and proved in the scope of several first-of-a-kind projects during the last years.
[en] Providing useful information on optimized chemistry control for pressurized heavy water reactors (PHWRs), this publication presents up to date knowledge on the topic including corrosion phenomena observed in the primary heat transport system and consequent effects on fuel reliability in PHWRs. Specifically, it describes the national practices on coolant chemistry control under various operating conditions and research and development programmes aiming to understand the corrosion phenomena (formation and transport) and related chemistry control. Crud deposit on the fuel cladding, the influence on fuel fitness-for-service in the primary heat transport system, as well as the technical basis for remedial actions to ensure reliable fuel performance in PHWRs are considered.
[en] A novel high-speed photodiode (PD) with an InGaAs/Si structure fabricated by atomic-diffusion bonding (ADB) is proposed with the aim of improving the heat transfer. The fabricated PD shows a responsivity of 0.42 A W and a 3 dB bandwidth of over 50 GHz. The maximum damage-threshold photocurrent, or high-power tolerance, is higher than that of a conventional PD on an InP substrate, thanks to the high thermal conductivity of Si used as the collector in the PD. (© 2020 Wiley‐VCH GmbH)
[en] CARPT technique is widely applied to studies on the dynamics of fluids and solids in the design phase of industrial equipment. This study describes the simulation, using MCNP code, of a CARPT-based methodology and uses a reduced-scale model of the Brazilian Multipurpose Reactor as reference for the simulations. The goal is to evaluate the applicability of this methodology to the study of natural circulation passive safety systems in medium-scale experiments, such as the one modelled here, by comparing previously simulated trajectories for a radioactive particle and the trajectories calculated by the methodology under the same conditions. The methodology described was proposed by VIEIRA (2009) and has the advantages of being cost-effective and easy to implement, but it was initially designed considering small-scale experiments. Different configurations for the system were tested and correspondence between simulated trajectories and those reconstructed by applying the technique was analyzed for each of them; efficiencies and errors were also discussed. Comparison between simulated and reconstructed trajectories showed similar trends between them for each configuration, but the errors found were not negligible. Configurations’ parameters that promoted the best fit between trajectories were listed and possible improvements were suggested. This is the first study on the application of CARPT technique for research reactors safety systems. (author)