scholarly journals Aqueous Nanofluid as a Two-Phase Coolant for PWR

2012 ◽  
Vol 2012 ◽  
pp. 1-6
Author(s):  
Pavel N. Alekseev ◽  
Yury M. Semchenkov ◽  
Alexander L. Shimkevich
Keyword(s):  
Thermal Conductivity ◽  
Hydrogen Bonds ◽  
Liquid Water ◽  
Water Clusters ◽  
Density Fluctuations ◽  
Solid Particles ◽  
Two Phase ◽  
Gaseous Oxygen ◽  
Alternative Approach ◽  
Solubility Of Oxygen

Density fluctuations in liquid water consist of two topological kinds of instant molecular clusters. The dense ones have helical hydrogen bonds and the nondense ones are tetrahedral clusters with ice-like hydrogen bonds of water molecules. Helical ordering of protons in the dense water clusters can participate in coherent vibrations. The ramified interface of such incompatible structural elements induces clustering impurities in any aqueous solution. These additives can enhance a heat transfer of water as a two-phase coolant for PWR due to natural forming of nanoparticles with a thermal conductivity higher than water. The aqueous nanofluid as a new condensed matter has a great potential for cooling applications. It is a mixture of liquid water and dispersed phase of extremely fine quasi-solid particles usually less than 50 nm in size with the high thermal conductivity. An alternative approach is the formation of gaseous (oxygen or hydrogen) nanoparticles in density fluctuations of water. It is possible to obtain stable nanobubbles that can considerably exceed the molecular solubility of oxygen (hydrogen) in water. Such a nanofluid can convert the liquid water in the nonstoichiometric state and change its reduction-oxidation (RedOx) potential similarly to adding oxidants (or antioxidants) for applying 2D water chemistry to aqueous coolant.

scholarly journals On Clustering Impurities by Liquid Density Fluctuations

2010 ◽  
Vol 2010 ◽  
pp. 1-5
Author(s):  
Alexander L. Shimkevich
Keyword(s):  
Thermal Conductivity ◽  
Colloidal Particles ◽  
Fractal Structure ◽  
Density Fluctuations ◽  
Liquid Density ◽  
Particle Loading ◽  
Two Phase ◽  
New Class ◽  
Recent Developments ◽  
Natural Mechanism

Recent developments in liquid technology have created a new class of fluids called “nanofluids” which are two-phase mixtures of a non-metal-liquid matrix and addon particles usually less than 100 nm in size. It is reputed that such liquids have a great potential for application. Indeed, many tests have shown that their thermal conductivity can be increased by almost 20% compared to that of the base fluids for a relatively low particle loading (of 1 up to 5% in volume). It is confirmed by experimental data and simulation results. In this study, the author considers an effect of impurity clustering by liquid density fluctuations as a natural mechanism for stabilizing microstructure of the colloidal solution and estimates the effect of fractal structure of colloidal particles on thermal conductivity of water. The results of this study may be useful for motivating choosing the composition of heat-transfer suspension and developing technology for making the appropriate nanofluid.

A Study on Uncertainties in Estimations of Thermal Conductivity of Alumina Nanofluids

2015 ◽  
Vol 809-810 ◽  
pp. 525-530 ◽  
Author(s):  
Madalina Georgiana Moldoveanu ◽  
Alina Adriana Minea
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Performance ◽  
Unsolved Problem ◽  
Volume Fraction ◽  
Solid Particles ◽  
Two Phase ◽  
Polymeric Particles ◽  
Semi Empirical ◽  
Thermal Conductivities

An innovative way of improving the thermal conductivities of fluids is to suspend small solid particles in the fluids. Various types of powders such as metallic, non-metallic and polymeric particles can be added into fluids to form slurries. The thermal conductivities of fluids with suspended particles are expected to be higher than that of common fluids. Application of nanoparticles provides an effective way of improving heat transfer characteristics of fluids. By suspending nanophase particles in heating or cooling fluids, the heat transfer performance of the fluid can be significantly improved. Moreover, the thermal conductivity of nanofluid is strongly dependent on the nanoparticle volume fraction. So far it has been an unsolved problem to develop a sophisticated theory to predict thermal conductivity of nanofluids, although there are some semi empirical correlations to calculate the apparent conductivity of two-phase mixture. In this article few correlations were considered and differences were noted between different theories. In conclusion, a lot of uncertainties in determining thermal conductivity were noticed.

scholarly journals Capabilities and Limitations of 3D-CFD Simulation of Anode Flow Fields of High-Pressure PEM Water Electrolysis

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 968
Author(s):  
Christoph Haas ◽  
Marie-Gabrielle Macherhammer ◽  
Nejc Klopcic ◽  
Alexander Trattner
Keyword(s):  
High Pressure ◽  
Liquid Water ◽  
Single Phase ◽  
Cfd Simulation ◽  
Flow Analysis ◽  
Two Phase ◽  
Gaseous Oxygen ◽  
Geometry Model ◽  
Exact Geometry ◽  
Phase Liquid

In this work, single-phase (liquid water) and two-phase (liquid water and gaseous oxygen) 3D-CFD flow analysis of the anode of a high pressure PEM electrolysis cell was conducted. 3D-CFD simulation models of the anode side porous transport layer of a PEM electrolyzer cell were created for the flow analysis. For the geometrical modelling of the PTL, two approaches were used: (a) modelling the exact geometry and (b) modelling a simplified geometry using a porosity model. Before conducting two-phase simulations, the model was validated using a single-phase approach. The Eulerian multiphase and the volume-of-fluid approaches were used for the two-phase modelling and the results were compared. Furthermore, a small section of the PTL was isolated to focus on the gas bubble flow and behaviour in more detail. The results showed plausible tendencies regarding pressure drop, velocity distribution and gas volume fraction distribution. The simplified geometry using the porous model could adequately replicate the results of the exact geometry model with a significant reduction in simulation time. The developed simulation model can be used for further investigations and gives insight into two-phase flow phenomena in the PTL. Additionally, the information obtained from simulation can aid the design and evaluation of new PTL structures.

scholarly journals On Water Density Fluctuations with Helices of Hydrogen Bonds

2011 ◽  
Vol 2011 ◽  
pp. 1-5 ◽  
Author(s):  
Alexander Shimkevich ◽  
Inessa Shimkevich
Keyword(s):  
Hydrogen Bonds ◽  
Liquid Water ◽  
Condensed Matter ◽  
Matter Density ◽  
Density Fluctuations ◽  
Point Of View ◽  
Spectral Series ◽  
Adaptive Model ◽  
Water Density ◽  
The One

An adaptive model is developed here for the liquid water density fluctuations as momentary dense clusters with helices of hydrogen bonds and nondense tetrahedral clusters of ice. This model can be useful for explanation of liquid water structural anomalies including the high quantity of hydrogen bonds with quasitetrahedral orientation in the nonordered liquid water. The topology of such clusters is essentially differed from the one of the crystalline ice. From this and only this point of view, the liquid water can be considered as a two-structural fluid by dynamic forming the two topological kinds of clusters as a consequence of condensed-matter density fluctuations. Another feature of the dense-water-part clusters is helical ordering of protons which can realize coherent vibrations. A spectral series of such vibrations is determined as a function of the number of molecules into the helical cluster.

Reciprocal Polarizable Embedding with a Transferable H2O Potential Function II: Application to (H2O)n Clusters & Liquid Water

2019 ◽  
Author(s):  
Asmus Ougaard Dohn ◽  
Elvar Jónsson ◽  
Hannes Jonsson
Keyword(s):  
Density Functional Theory ◽  
Liquid Water ◽  
Density Functional ◽  
Water Clusters ◽  
Theory Model ◽  
Coupling Scheme ◽  
Functional Theory ◽  
Total Polarization ◽  
Electrostatic Embedding ◽  
Polarizable Embedding

The manuscript analyzes the accuracy of our recently developed reciprocal polarizable embedding scheme, where a density functional theory model of the QM region is coupled to a dipole- and quadrupole polarizable water potential of the MM region. We present calculations of water clusters and liquid water where we analyze the energy, atomic forces and total polarization to demonstrate that artifacts in energy and polarization introduced by the QM/MM coupling are small and well-behaved. Furthermore, our methodology improves the consistency of the structure of optimized water hexamer geometries when compared to results obtained with models that neglect polarization. Additionally, the manuscript provides evidence that our coupling scheme eliminates artifacts in the structure of liquid water obtained with simpler electrostatic embedding models.

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