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Project titleNanofluids for renewable heat applications
Project LeadBalakin Boris
AffiliationNational Research Nuclear University MEPhI (Moscow Engineering Physics Institute),
Implementation period2019 - 2021
Research area 09 - ENGINEERING SCIENCES, 09-402 - Hydropower engineering, new and renewable power sources
Keywordsnanofluid, solar collector, radiation, heat pump, numerical modelling
The urban population of Russia intensively grows and therefore requires domestic heat supply systems operating with greater efficiency and environmental friendliness. The strategy of scientific development of Russia promotes technological shift to renewable sources of heat, from where the solar energy, the geothermal energy and the waste heat are among the most promising resources. This energy is harvested by solar collectors and heat pumps from the wells, where the most challenging part of the process is to extract the low-temperature heat without much energy lost. Another important problem is to preserve the harvested solar heat in geothermal seasonal storage, i.e. combining the solar collector with the heat pump technology. This project aims to improve the thermal performance of the wells developing a new type of heat transfer fluid: a "renewable" nanofluid, i.e. a stable suspension of solid nanoparticles (metals, carbon or silicon) in a liquid base. These fluids, being similar to liquid metals in terms of their thermal parameters (high thermal conductivity, the ability of magnetic convection) and perfectly absorbing solar thermal radiation, have been demonstrating superior thermal performance in different technical systems, improving heat transfer by up to 50%. Several countries (Australia, India, Norway, UAE, USA) have demonstrated sufficient progress in the development of direct absorption solar collectors with nanofluids. However, the reported laboratory systems have not yet been implemented into industrial operation. Moreover, there are no nanofluids developed for geothermal applications at the moment. The project is after a comprehensive study of the use of the nanofluid in the renewable heat systems. The project goes in several stages, starting from the development of a theory and a numerical model to describe the process of heat transfer in the direct absorption solar collectors and the wellbore heat exchangers. The model is further used for a parametric analysis of the nanofluid composition, i.e. selecting the most optimum particle size, their material, and concentration, type of the base fluid. The next stage of the project is the production of the nanofluids using the materials, available from the domestic suppliers. The nanofluids will be tested in the prototypes of the renewable energy systems, developed and constructed in-house. We are going to consider how an external magnetic field influences the heat transfer. The produced nanofluids will be tested in-situ using a commercial solar concentrator of Russian design.
In this project we are planning to obtain the following results: 1) laboratory method to synthesize nanofluids for more efficient (up to 30% over existent solutions) utilization of solar and geothermal heat and efficient storage of solar heat in a well. There are no such systems existent in Russia. 2) prototypes of nanofluid-based renewable energy systems: direct absorption solar collector, wellbore heat exchanger, seasonal storage of solar heat. The prototypes will be equipped with a magnetic system aimed to establish magnetic convection and so to improve the heat transfer and to reduce their size. There is no information on similar systems in the research literature. 3) validated full-scale and real-time CFD-PBM models of the direct absorption solar collector, the wellbore heat exchanger and the seasonal storage of solar heat. There is no information on the models of such complexity in the research literature. 4) guidelines on the use of the developed “renewable” nanofluids in the coupled seasonal storage of solar heat in a well. An analysis of environmental safety for the designed solution comes in addition. 5) economic analysis on the use of the nanofluids in the renewable heat systems. 6) nanofluid erosion maps for the materials, which are most frequently used in renewable heat applications. 7) research articles, conference reports and publications in professional journals according to the project roadmap. According to our preliminary estimates based on interpolation of statistical information from 2003-2011, increasing the thermal efficiency by means of utilization of nanofluids will facilitate harvesting of 9.1 MWth/year in addition to current generation, just improving the existing renewable energy facilities in Russia. Economically this will result in 2 mln.euro spared (without account for capital costs). In case Russia explores renewable resources extensively in the future, these numbers will rise by at least two orders, which will become equivalent to 2.3 Mt CO2 emissions prevented.
Annotation of the results obtained in 2019
The following results were obtained after the first year of the project: 1) the nanofluid-based prototype of the direct absorption solar collector (DASC) designed and constructed. The collector was tested in the surface absorption mode using the aqueous coolant. The area of the prototype is 1.9 sq.m. and the thermal efficiency of the surface-based modification was in the interval 72...85% that is comparable with the commercial solar collectors. 2) we built two supplementary test rigs for the wet slurry test with nanoparticles and the measurement of the nanofluid heat transfer coefficient. 3) the transparent receiver of solar radiation for the helioconcentrator-based study of the nanofluid was developed. The operation pressure of the vessel is 2 bar. 4) we developed a theory and a multiphase CFD-PBM model of DASC. The model was validated against the available experimental data. 5) as it followed from the numerical simulations, the optimum composition of the nanofluid was set when the thickness of the collector was proportional to the optical depth of the fluid, which was 0.05 wt% for the collector of our design. 6) we produced stable nanofluids with carbon nanotubes and iron oxide, the size of the nanoparticles in the fluid was below 400 nm 7) the multiphase numerical model of the bottom part of the geothermal heat exchanger was developed using the Lagrangian technique and empirical correlations. The theoretical optimization of the nanofluid was conducted for the standard collector geometry and the nanoparticles of aluminum oxide. The optimum was found in the interval 5-6 vol. %. The model predicted the formation of a bottom deposit of the particles, the volume of the deposit is below 15% of the entire volume of the nanoparticles in the system. 8) the numerical model of erosion in the standard geometry of the 90-degree bend was developed using the Lagrangian model. The model produced the erosion maps for the bend and predicted that the erosion rate was maximum when the nanoparticles agglomerated to the size of about 1 μm.
1. A. Kosinska, B.V. Balakin, P. Kosinski Theoretical analysis of erosion in elbows due to flows with nano- and micro-size particles Powder Technology, v. 364, pp. 484-493 (year - 2020).
2. R. Bårdsgård, D.M. Kuzmenkov, P. Kosinski, B.V. Balakin Eulerian CFD Model of Direct Absorption Solar Collector with Nanofluid Journal of Renewable and Sustainable Energy, - (year - 2020).
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