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Project Number17-79-10481

Project titlePhoto-thermal boiling of nanofluid in solar collector: optimization and prototype development

Project LeadBalakin Boris

AffiliationNational Research Nuclear University MEPhI (Moscow Engineering Physics Institute),

Implementation period2017 - 2018

Research area 09 - ENGINEERING SCIENCES, 09-402 - Hydropower engineering, new and renewable power sources

Keywordsnanofluid, solar collector, boiling, thermal radiation, numerical modelling



This project is aimed at optimization of the process of nanofluid evaporation under external solar radiation and further prototype development of a solar nano steam generator for the production of electric energy in micro-CHP systems. The core idea of the method is in concentration of sunlight on a nanofluid rather than at a continuous dark surface, found in conventional solar generators. In this case, the nanoparticles, dispersed in liquid, are accumulating the sunlight and heating the liquid with greater intensity, acting as a cloud of mobile nano-sized heaters. When the liquid gets to saturation, the steam bubbles nucleate and grow directly at the particles, rather than in a limited space between the micron-sized asperities of the continuous surface (conventional case), enhancing vaporization due to the larger total area of the particle-fluid interphase. The most optimum composition of such a "solar" nanofluid is however unknown. There are very few independent research groups (USA, China, Norway) which succeed to maintain the process under natural solar irradiation or equivalent artificial lightning. It follows from those studies that the concentration of nanoparticles ought to be lower than in the nanofluids used as coolers in microelectronics. Moreover, it is unclear whether the target nanofluid to be stabilized with surfactants. Unorthodox boiling of this type is described by a number of complex inter-connected phenomena driven by combination of optics, fluid dynamics and thermal physics of the system. The proposed optimization is therefore hardly possible without a reliable theoretical descritpion of the process. The first stage of the project is after the development of a multiphase CFD-model of the process. The model will be validated by three independent experimental datasets from those mentioned in close collaboration with foreign research groups. As it follows from previous studies, the most intensive evaporation takes place in case the nanoparticles are located in the mostly irradiated zone of the system, i.e. their mobility due to natural convection of the fluid is limited. Here in this project we propose to prolong exposure of nanoparticles by an externally-generated magnetic field and induction of thermomagnetic convection within the zone; this will be tested using the model developed. The validated model is further used for the parametric analysis by altering the main process determinants. The research literature lacks information on whether any modelling, similar to one proposed here, has been ever performed. From the practical point of view, the first stage of the project will enable definition of the system operation point, i.e. the most optimum: - geometry of the boiler within solar collector; - material, concentration and size of the nanoparticles; - type of the carrier fluid; - the degree of sun concentration; - parameters of magnetic field. The second stage of the process is focused on development and construction of a pilot prototype of the solar nano steam generator for micro-CHP (up to 2kWe). The generator includes the solar dish collector with the boiler (photo-thermal reactor) mounted in its focal zone, the steam turbine and an infrastructure, required for the establishment of closed turbine cycle: condenser, feed pump, electric generator and the sensor-pipe network to enable regulation. Preliminary market research allows to pin-point commercial solutions for these units even at the application stage. For example, a potential turbine alternative could be QuasiTurbine when employed in organic Rankine cycle. The nanofluid will be produced in Russia with the use of nanoparticles produced in-house in collaboration with domestic research groups. The efficiency and dynamics of the prototype will be evaluated at the end of the project. Dependently on the season, an artificial thermal radiation will be produced from an array of lamps with minimum 1 sun capacity; the natural sun tests to be run during aestival season. As it follows from literature, there is only one solar collector of this type in the world, though the turbine cycle is not arranged there and it is utilized solely for the production of steam.

Expected results
The first stage of the present project is aimed at the development of a theory of photo-thermal boiling in nanofluids and numerical tests of the model proposed. An opportunity to intensify the process in the field of external magnetic field of moderate strength will be considered as well as numerical optimization of the process performed. Similar studies has not been presented yet in the research literature and it is proposed to publish four articles (totally over the entire project) in ACS Nano, HMT, Energy&Fuels and AIChE. At the end of entire project it is also planned to write a monograph on the integrated results of the study. Practical outcomes of the project include: - methods for the "solar" nanofluid production; - pilot prototype of the solar steam generator with the design documentation. According to preliminary estimated, a system of this type occupies 6 times less space and is 30% cheaper than a comparable photovoltaic system. It is also produced w.o. involvement of the large-scale industrial chemical plants; - a probability to apply for a patent exists since the design of this system and the composition of the nanofluid is different from the closest analogue developed at Rice University.



Annotation of the results obtained in 2018
During the second year of the project we have obtained the following experimental results: 1) two experimental rigs were developed and constructed: * a lab-scale flow loop, closed at a transparent volume, where the nanofluid was evaporated under external artificial radiation; * a real-scale prototype of a solar generator, based on a solar concentrator with the effective area of 5 sqr.m. 2) two types of nanofluids were produced using graphite (up to 500 nm) and iron oxide (100 nm) nanoparticles. The nanoparticles were produced in-house (graphite) and ordered from a Russian manufacturer (iron oxide) 3) using the lab-scale experimental rig, we screened the composition of the nanofluids, looking at an optimum volume fraction of nanoparticles, which was found approximately 1% for both fluids. For the first time, to our knowledge, we succeeded in the establishment of a steam turbine cycle, driving a model turbine with the nanofluid-generated "luminate" steam. 4) it was found that the volumetric, photo-thermal boiling of aqueous nanofluids produces 70% more steam than a classical boiling of water at an opaque surface at the same heat flux 5) we have recently launched the real-scale prototype of the nanofluid-driven solar generator and detected a 3-fold increase of the steam production compared to the lab-scale prototype. The theoretical results include: 1) a full-scale, 3D and three-phase, transient CFD-model of the photothermal steam generator. The model of this type has never been reported in the literature. 2) the CFD-model was used for parametric optimization of the system, focusing at: * orientation of receiver in the filed of gravity; * geometry of the process, i.e. the shape, the size, and the condensate return line position. The optimized system produces 30% more solar steam. 3) the CFD-model was validated using several independent benchmarks from the research literature and our in-house experiments.



1. Улсет Э.Т., Косински П., Забеднова Ю., Жданеев О.В., Стручалин П.Г., Балакин Б.В. Photothermal boiling in aqueous nanofluids Nano Energy, 50, 339-346 (year - 2018).

2. Балакин Б.В., Косинска А., Куценко К.В. Pressure drop in hydrate slurries: Rheology, granulometry and high water cut Chemical Engineering Science, 190, 77-85 (year - 2018).

3. Балакин Б.В., Куценко К.В. Magnetic enhancement of photothermal heating in ferrofluids Journal of Physics: Conference Series, 1133, 012011 (year - 2018).

4. Косинска А., Балакин Б.В. Numerical analysis of erosion due to nanoparticles in a pipe elbow Journal of Physics: Conference Series, 1133, 012045 (year - 2018).

5. Балакин Б.В.,Жданеев О.В., Косинска А.,Куценко К.В. Direct absorption solar collector with magnetic nanofluid: CFD model and parametric analysis Renewable Energy, Volume 136, Pages 23-32 (year - 2019).

6. Кузьменков Д.М.,Куценко К.В., Делов М.И., Карелова Д.Г., Балакин Б.В. Numerical studies of boiling in nanofluids exposed to thermal radiation AIP Conference Proceedings, - (year - 2019).

7. - Sun and Nanofluids: MEPhI Launches Unique Power Generation System сайт НИЯУ МИФИ, - (year - ).

Annotation of the results obtained in 2017
During the first year of the project we have obtained following theoretical results: 1) a theory of photo-thermal boiling in aqueous nanofluids was developed. The technique may be used for calculation of temperature and flow rate of the steam depending on the concentration of nanoparticles, their size and the geometry of the photo-thermal system. 2) the accuracy of this analytical approach was further increased applying a newly developed numerical model, which was capable to simulate motion of a growing individual steam bubble within a hot "boundary layer", where most of the thermal radiation is consumed. Applying the model we detected that 5 μm was the most optimum particle size that resulted with the maximum efficiency of the process. 3) we have also developed a multiphase 3D CFD model of a direct adsorption collector with nanofluid. This model, first of its kind (to our knowledge), being studied parametrically, drove us to conclusions, that: - the efficiency of the collector may be increased by 6% due to nanofluid convection if the sunlight is re-directed from the top towards the bottom of the collector; - the nanofluid convection plays very important role. Increasing the Rayleigh number of the system by 420 we obtained 1.5-fold efficiency rise; - applying external magnetic field of very moderate capacity we manage to simulate the process of thermomagnetic convection in this collector for the case when ferromagnetic nanoparticles were used (MnZn-ferrite). The magnetic convection increases the efficiency by 20% when gradient of magnetic field over the system was 300 mG/m. The numerical models and the theory (p.1) were validated against experiments. 4) applying the mechanistic model, developed for the steam bubble (p.2), and going through a dimensional analysis of the process, we have introduced a correlation that relates a dimensionless frequency of bubble formation with a number of dimensionless criteria, which determine the process. A systematic experimental study of the photo-thermal boiling was conducted in collaboration with the Norwegian research group: 1) two different types of the nanofluids were produced. They were made by ultrasonic dispersion in water the nanoparticles of carbon black (51 nm) and iron oxide (184 nm); 2) an optimum concentration of the nanoparticles was found looking for a maximum of the process efficiency. This volume fraction was in the interval 1.3-1.9% for both nanofluids. The observed value was in fact 3-4 times greater than the optimum concentrations, reported in other experimental works for the process of natural convection (w.o. radiation and boiling) and adsorption of solar radiation (w.o. boiling). We have also found that when using a surfactant (SDS), the efficiency of the photo-thermal boiling was increased by 5%. An experimental video is available at our website: 3) the degree of the "luminate" steam contamination was examined. The steam was surprisingly free of the “light” hydrophobic particles yet polluted with “heavy” hydrophilic particles. 4) next we evaporated the carbon black nanofluid in-situ, using a mid-scale parabolic dish concentrator at 0.76 sun. The solar steam was superheated by 25 K which exceeded the conventional boiling curve value for the experimental heat flux. The efficiency of the process was 73%. This was the first, to our knowledge, documented record of the solar steam production in northern conditions. Another video from this test is found at: Finally, we have conducted a theoretical parametric study of the solar generator with nanofluid, selecting its operation point. According to calculations, we are planning to use an aqueous nanofluid at 2 barg. The most important elements of the solar generator were selected basing on the performed analysis: a parabolic dish collector and a steam engine, both from the Russian suppliers.



1. - SolarNano совместный интернет-сайт нашей и норвежской научной групп, We acknowledge support from: I. Russian Science Foundation (project 17-79-10481) (year - ).

2. E.T. Ulset, P. Kosinski, B.V. Balakin Solar steam in an aqueous carbon black nanofluid Applied Thermal Engineering, - (year - 2018).

3. M. Lucas, P. Kosinski, B.V. Balakin Eulerian-Eulerian model for photo-thermal energy conversion in nanofluids AIP Conference Proceedings, - (year - 2018).

4. Балакин Б.В., Делов М.И.,Кузьменков Д.М.,Лаврухин А.А., Стручалин П.Г., Улсет Э.Т. Кипение наножидкости под действием теплового облучения Сборник трудов XIII международной научно-практической конференции "Будущее атомной энергетики", стр. 152-154 УДК 621.039:5 (year - 2017).