Browsing by Keyword "Nanofluid"
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Item Effect of Al2O3 nanoparticles on laminar, transient and turbulent flow of isopropyl alcohol(2019-03) Nikulin, A.; Moita, A. S.; Moreira, A. L.N.; Murshed, S. M.S.; Huminic, A.; Grosu, Y.; Faik, A.; Nieto-Maestre, J.; Khliyeva, O.; VALORIZACIÓN DE RESIDUOSThe laminar, transient and turbulent heat transfer and hydrodynamic of a new nanofluid isopropanol/Al2O3 is investigated in a closed flow loop with a horizontal mini-channel test section (3.5 mm inner diameter) under uniform heat flux conditions. The experiments performed at various inlet temperatures (15, 25, 35 °C), mass flow rates (from 0.00076 to 0.041 kg/s) and nanoparticle concentrations (0.387, 0.992, 3.12, 4.71 mass%). We found that despite the pressure drop increases with Reynolds number and nanoparticles mass fraction the dependence of friction factor for the isopropanol/Al2O3 nanofluid remains the same as for the base fluid. The heat transfer performance of isopropanol/Al2O3 nanofluid was evaluated in two ways (i) depending on the Reynolds number and (ii) product of the mass flow rate and specific heat capacity. The first approach indicates to significant enhancement of the heat transfer coefficient with addition of nanoparticles in all range of experimental parameters. The second approach shows no effect of nanoparticles on the heat transfer coefficient in laminar flow and its deterioration in transient and turbulent flows. Both effects of nanoparticles on the heat transfer are attributed to change in intensity of the turbulence in nanofluids compared to the base fluids. Finally, an influence of nanoparticles on the start of laminar-turbulent transition was examined.Item Molten salt-based nanofluids as efficient heat transfer and storage materials at high temperatures. An overview of the literature(2018-02) Muñoz-Sánchez, Belén; Nieto-Maestre, Javier; Iparraguirre-Torres, Iñigo; García-Romero, Ana; Sala-Lizarraga, Jose M.; Tecnalia Research & Innovation; VALORIZACIÓN DE RESIDUOSThe research in the field of nanofluids has experienced considerable advances from their discovery two decades ago. These liquid mixtures with tiny quantities (< 10% in volume) of nanometric size solid particles (< 100 nm) in suspension have a great potential for thermal management applications due to their excellent thermophysical properties. The so-called traditional nanofluids (based on water or industrial oils) have been extensively studied so far with a special focus on the enhancement observed in their thermal conductivity. Experimental results, mechanisms and models regarding these materials have been published and reviewed on a large number of articles. A new kind of nanofluids based on inorganic salts has been developed in the last few years with the aim of storing and transferring thermal energy at high temperatures. These Molten Salt-Based Nanofluids (MSBNFs) are characterized by a considerable increase of their specific heat due to the presence of particles at the nanometric scale. On the contrary, the specific heat of the traditional nanofluids is lower compared to that of the base fluid. This surprising behaviour has caused an opened debate in the scientific community, which is currently dealing with these controversial results and the lack of theories and models for these materials. This article reviews the published scientific contributions on MSBNFs. The influence of several facts on the specific heat is deeply analysed, as well as the synthesis methods. Other important aspects related to the behaviour and development of the MSBNFs such as the stability of the NanoParticles (NPs) in the molten salt, their latent heat, viscosity and thermal conductivity, have also been reviewed in this article. Finally, the difficulties and challenges concerning the further development of these materials have been summarized and the main conclusions have been listed.Item Rheology of Solar-Salt based nanofluids for concentrated solar power. Influence of the salt purity, nanoparticle concentration, temperature and rheometer geometry(2018-03) Muñoz-Sánchez, Belén; Nieto-Maestre, Javier; Veca, Elisabetta; Liberatore, Raffaele; Sau, Salvatore; Navarro, Helena; Ding, Yulong; Navarrete, Nuria; Juliá, J. Enrique; Fernández, Ángel G.; García-Romero, Ana; Tecnalia Research & Innovation; VALORIZACIÓN DE RESIDUOSSolar Salt-based nanofluids have attracted significant scientific interest in recent years due to their improved thermal properties, making them strong candidates as thermal energy storage materials and/or heat transfer fluids in CSP plants. There have been reports on increased specific heat due to the addition of nanoparticles, however, there is a lack of comprehensive information on other essential properties affecting the heat transfer, such as the viscosity. This article concerns the rheological behaviour of nanofluids made of Solar Salt (mass percentage at 60% NaNO3 – 40% KNO3) as the base fluid and silica or alumina nanoparticles as additives. The evolution of these nanofluids viscosity as a function of the shear rate (1–1000 s−1) at a temperature range of 250–400 °C was measured and analysed. The impact of the salt purity (refined or industrial grade), the nanoparticle concentration (0.5–1.5 wt%) and the rheometer measuring configuration (coaxial cylinder or parallel plate) are examined. The results showed in general a Newtonian behaviour of the nanofluids with independency of the rheometer configuration. The relationship between the viscosity and the temperature follows an Arrhenius model. The influence of the nanoparticle concentration on the viscosity of the refined grade Solar Salt is analysed according to the Maron-Pierce and Kriegher-Dougherty models for the nanofluids containing alumina and silica nanoparticles respectively, due to their different shape.