117,413 research outputs found
Numerical analyses of concrete thermal energy storage systems: effect of the modules’ arrangement
No full textThis paper is focused on modularized concrete sensible thermal energy storage systems with thermal oil as heat transfer fluid; the thermal storage systems have been conceived to be integrated into a concentrated solar power plant. This work is mainly focused on the effect of the modules’ arrangement on the overall performance of the thermal energy storage system. Series and parallel arrangements are investigated, to determine the most performant solutions in terms of exchanged thermal energy as a function of the main operating conditions: oil mass flow rate and pressure drop, both in heating and cooling phase. Two different boundary conditions are considered: adiabatic and diabatic external walls. The simulations are carried out using an extended version of a model proposed by the present authors for a single concrete block, that was validated with experimental data. The exchanged thermal energy, the oil mass flow rate, the pressure drops, and the duration of the process are changed to evaluate the storages under different operating conditions. The best thermal energy storage configuration is determined by a thermal energy assessment: it coincides with the first one that reaches the asymptotic values with the minimum number of elements. Furthermore, in the diabatic case, the loss heat flux toward the environment has a significant role and highlights the differences between charging and discharging phases, its presence contributed to a more aware choice of the most suitable and performant modularized system
Studio sperimentale sul deflusso di una soluzione LiBr-H2O irrorata su una colonna di tubi
No full textNumerical simulation through experimental validation of latent and sensible concrete thermal energy storage system
No full textA new type of concrete with PCM (Phase Change Material) thermal energy storage system is presented. The system, developed for industrial applications, is supposed to operate with a temperature up to 400 °C and the PCM added mixture presents enhanced thermal performances. A binary mixture of salts was used as PCMs, composed of 40% of KNO3 and 60% of NaNO3, and they were absorbed by diatomite, a porous fossil flour. A stainless-steel pipe is inserted in the centre of a concrete cylinder, the whole system is insulated. The experimental tests studied two concrete mixtures, with 5% PCM in weight and without it. The charging stage is carried out via Joule's effect and the module is then cooled with compressed air through the pipe. The two mixtures were tested under the same operating conditions. The module was numerically simulated and the results were compared with previous experimental tests to calibrate the model. Further numerical simulations were conducted to test other PCM percentages, under the same conditions as the experimental tests and with thermal oil as heat transfer fluid, to evaluate a possible working scenario. The results showed that the PCM integration into the storage system led to an impressive improvement in thermal performance. The amount of stored and released thermal energy increased with the PCM integration, coming to double its original value with the highest PCM percentage integration simulated, which corresponds to 40%
RMT: evoluzione delle conoscenze e valutazione dei saperi matematici, Atti delle giornate di studio sul Rally matematico transalpino, Siena 1999 - Neuchâtel 2000,
No full textCostruzione del concetto di equazione: dalla messa in formula alla risoluzione di equazioni e sistemi lineari
No full textCostruzione del concetto di equazione: dalla messa in formula alla risoluzione di equazioni e sistemi lineari
No full textThis article presents some problems suitable for the introduction of the concept of equation and linear system. It contains the report of some of these experiments. In students from 12 to 14 years old the expèeriment was aimed to bring out any spontaneous pre-algebraical strategies. In students from 15 to 16 years old the goal was to introduce the concept of linear system and its procedures for solutions
Dare significato ai concetti di equazione e di sistema: attività in classe con i problemi del RMT
No full textWater Pool boiling on Aluminum Metal Foams
No full textWith current growth in electronic systems, their physical sizes decrease, and the spacing between components decreases, both the total amount of heat generated and the power density increase significantly. There is a general agreement in the scientific community that current air-cooling technologies are asymptotically approaching their intrinsic limits. Pool boiling is widely used in many different engineering systems, but most of these applications have a common limitation: the maximum heat flux that can be rejected by the cooling systems under safe, reliable, and efficient operation. In this paper experimental data pertinent to deionized water pool boiling across 10 mm thick aluminum foams are presented. Three foam samples with different pore densities, 5, 10, and 40 PPI, yet with an identical mean porosity of 0.92 are tested. Compared to a heated flat plate, the foams offer higher heat transfer area albeit at induced bubble escaping resistance. The tradeoff between these two effects is investigated. Through the use of high speed video camera recording, bubble generation, trajectory and growth rate were analyzed and critically discussed
Natural and forced convection in high temperature PCM embedded in a 3D periodic structure realized via additive manufacturing
No full textThe interest in Phase Change Materials (PCMs) is continuously growing, since they have been identified as a suitable way of storing large quantities of thermal energy. There are many PCMs available on the market, nevertheless almost all present a relatively low thermal conductivity, which limits the efficiency and the convenience of their use inside Latent Thermal Energy Storages (LTES). This work proposes a novel method to overcome the low thermal conductivity drawback, the additive manufacturing was used to realize innovative 3D metallic periodic structures to be filled with a suitable PCM. The samples were experimentally tested by analyzing the temperature field in a paraffin wax having a melting temperature of around 70 °C and by collecting several videos and images during the charging (i.e. heating and melting) process, obtained by electrical heating (power from 30 W to 60 W were applied) and the discharging (i.e. solidification and cooling) one where the heat was rejected by natural or by forced convection with ambient air. The coupling of PCMs and aluminum structures was demonstrated to enhance both the charging and the discharging processes
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