Development of conjugate heat transfer coupling model for supercritical water flowing in 2 × 2 ballooning ATF rod bundles

Evaluation and development of heat transfer model for supercritical water flowing in 2 × 2 rod bundles with spacer grid

<p>The method is developed to calculate soil water content W, evapotranspiration Ev and other water and heat regime (WHR) characteristics of agricultural regions for vegetation season (VS). The base of the method is the physical-mathematical model of vertical water and heat transfer in the “Soil-Vegetation-Atmosphere” system (SVAT), suitable for utilizing satellite-retrieved estimates of vegetation and meteorological characteristics such as vegetation index NDVI, emissivity E, vegetation cover fraction B, leaf area index LAI, precipitation, and land surface temperature LST. These estimates were built under thematic processing satellite data obtained by radiometers AVHRR/NOAA, SEVIRI/Meteosat-10, -11, -8; MSU-MR/Meteor-M No 2 in visible and IR ranges. Soil and vegetation characteristics were the model parameters and meteorological characteristics were considered to be the input variables.</p><p>The case study was carried out for forest-steppe territory of 227,300 km<sup>2</sup> located in the Central Black Earth Region of European Russia, for steppe black earth Rostov region of 100,000 km<sup>2</sup>, and for arid steppe territory of the Saratov and Volgograd Trans-Volga region of 66,600 km<sup>2</sup> for VS of 2017-2018.</p><p>Estimates of daily, ten-day and monthly precipitation sums were carried out using the Multi Threshold Method for detecting cloudiness, identifying its types, allocating precipitation zones and determining rainfall intensity maximum. The key point of the method is the transition from assessing the rainfall intensity to estimating its daily sums.Comparing calculated daily, ten-day and monthly rainfall sums with each other for all sensors and with similar ground-based data showed the coincidence of the satellite-detected and actual precipitation zones in 75-85% of cases for each radiometer.</p><p>Satellite LST estimates were retrieved by the Generalized Split-Window method using the regression equations for the satellite-measured radiation temperature. Comparison of these estimates with each other for all radiometers, with the model calculation results and with ground-measured air temperature values for named VS showed their differences to be within acceptable limits.</p><p>Because of the different climatic conditions in the study areas, the empirical formulae to calculate B and LAI were analyzed and their detailed estimates were made, the errors of which were about 15 and 20%, respectively.</p><p>The possibility to use soil surface moisture estimates obtained from the scatterometer ASCAT/MetOp data in the microwave range for modeling is shown (to select initial conditions when calculating W and to assess evaporation from soil surface).</p><p>To calculate W, Ev and other WHR components the developed procedures to assimilate satellite-retrieved B, LAI, precipitation and LST estimates in the model were adapted to the territories under study. These procedures included replacing ground-based estimates of these values by their satellite-retrieved estimates in all computational grid nodes at each time step. The efficiency of these procedures was confirmed by comparing modeled and measured values of W and Ev. The final modeling results are distributions of W, Ev and other WHR components over the areas of interest. Estimation errors for W (10-15%) and Ev (20-25%) (even for the arid Trans-Volga region) are acceptable values.</p><p>As a conclusion, the developed method can be used to assess water resource components for vast agricultural regions.</p>

Heat transfer characteristics of supercritical water in a 2 × 2 rod bundle – numerical simulation and experimental validation

This study investigates the differences between the predictions of various properties of rigid and flexible simple point charge water models at supercritical conditions. Molecular dynamics simulations were conducted for supercritical water in a temperature range of 773-1073 K and densities in the range 115-659 kg/m3. We present thermodynamic data, pair correlation functions, selfdiffusivity, power spectra, dielectric constants, and variaous measures of hydrogen bonding at different state conditions. The flexible water model performs better in predicting the pressures along the supercritical isotherms simulated. Agreement between experimental and calculated dielectric constants is superior for the flexible water model, particularly at high densities. The flexible model exhibits a greater degree of hydrogen bonding and more persistent hydrogen bonds than does the rigid model. The structural features of supercritical water at high densities are identical for the two water models. At low densities, however, the flexible potential exhibits pair correlation functions with enhanced peaks. Inclusion of flexibility in the potential model does not result in a significant shift in the position of the rotational/librational peak in the power spectrum. The self-diffusivities obtained from the simulations are within the accuracy of the experimental values for both the rigid and flexible models. On balance the inclusion of flexibility improves agreement with the properties of real supercritical water while incurring little or no additional

We report results of molecular dynamics (MD) simulations of the limiting conductances of MgCl2 and CaCl2 in supercritical water as a function of water density using the SPC/E model for water. The limiting conductances of Mg2+, Ca2+ and Cl- over the whole range of water density considered exhibits a linear dependence of the limiting conductance on the water density. In the cases of Mg2+ and Ca2+, a solventberg picture for the behavior of small divalent cation emerges from our studies. From the view of the solventberg picture, the ion and its shell moving together as an entity interacts with the second hydration shell water molecules, and its mobility is restricted mostly by the number of the second hydration shell water which is proportional to the water density of the whole system. In the case of Cl-, the range of water density considered in this study belongs to the higher-density region (above 0.45 g/cm3) in which the effect of the number of hydration water molecules around ions dominated. As the water density increases, the water molecules of the first hydration shell restrict the mobility of Cl- and the limiting conductance of Cl- decreases nearly linearly. Significant different dependence on the water density is observed between the calculated limiting conductances of MgCl2 and CaCl2 at 673 K and the experimental results over the water density of 0.60–0.90 g/cm3. Possible limitation of the extended simple point charge (SPC/E) model with regard to this difference should be pointed out and the use of a more precise model like the revised polarizable (RPOL) model is indispensable for a further MD study to gain a complete picture of the chemical circumstance around the ions.

A 1/4-scale hot-water model of industrial 107-tonne steel ladles was established in the laboratory. With this physical model, thermal stratification phenomena due to natural convection in steel ladles during the holding period before casting were investigated. By controlling the cooling intensity of the water model to correspond to the heat loss rate of steel ladles, which is governed by dimensionless numbers Fr and βΔT, temperature distributions in the water model can simulate those in the steel ladles. Consequently, the temperature profile in the hot-water bath in the model can be used to deduce the thermal stratification phenomena in liquid steel bath in the ladles. In addition, mathematical simulations on fluid flow and heat transfer both in the water model and in the prototype steel ladle were performed using a computational fluid dynamics (CFD) numerical method. The CFD model was validated against temperatures measured in the water model. Comparisons between mathematically simulated temperature profiles in the prototype steel ladle and those physically simulated by scaling-up the measured temperature profiles in the water model showed a good agreement. Therefore, it can be concluded that, as long as accurate heat loss information is known, it is feasible to use a 1/4-scale water model to non-isothermally simulate fluid flow and heat transfer in steel ladles during the holding period before casting.

Summary In Nordic regions water infiltration into soil is controlled by soil moisture content and frozen soil conditions, which are regulated by soil temperature. For long‐term model predictions of the effects of climate change, models need to be tested with long‐term data to assess model sensitivity to parameter uncertainties under both typical and exceptional conditions. Ten‐year (2002–2011) daily soil moisture and temperature data at different depths in glacial till soils in central Finland were used to assess the sensitivity of a coupled heat and water transfer model, COUP, to model parameters. The model was most sensitive to the parameters controlling snow accumulation and melt, the thermal conductivity of frozen soil and soil water retention characteristics. Observed time series for soil temperature and moisture at different depths were matched reasonably well by model simulations, although the model performance with respect to moisture dynamics in the topsoil was relatively poor. The model was not able to simulate accurately exceptional winter conditions, such as mid‐winter snowmelt events. This study showed that the main characteristics of long‐term variation in soil temperature for till‐derived soil in a cold climate can be resolved by a coupled water and heat transport model. Better characterization of infiltration in cold climates would require measurement of water fluxes, and soil frost occurrence and penetration. Highlights Ten‐year soil temperature and moisture observations are predicted with coupled heat and water model. Snow processes and soil thermal and water retention properties proved critical in our simulations. Exceptional winter conditions pose a challenge in parameterization of the model. Studies measuring water fluxes and soil frost occurrence are needed for advances in modelling.

An adaptive force matching (AFM) scheme using the nonlinear optimization to reparametrize the three-site, flexible, and polarizable single-point-charge (SPC) water model is reported. We compare the radial distribution functions of the intermolecular oxygen-oxygen, oxygen-hydrogen, and hydrogen-hydrogen distances with the recent scattering experiments, the previous AFM-fitting water model (MP2f), and the atomic multipole expanded AMOEBA model. Our nonpolarizable SPC-3f(0) model captures the feature of the first solvation shell of bulk water. With the ad hoc inclusion of the isotropic polarizability, the polarizable SPC-3f(0.6) water model recovers the many-body effect of the second solvation shell. In the n-body decomposition analysis, the SPC-3f(0) model predicts the best agreement with MP2/aug-cc-pVTZ calculations with the use of the low-dimensional (H2O)4-ring and (H2O)6-ring clusters. For the comparison using the three-dimensional (H2O)6-prism and (H2O)16-4444a clusters, SPC-3f(0.6) predicts the results consistent with those of AMOEBA and MP2 levels. For simulating a water-cluster-dominant system such as supercritical water, SPC-3f(0) well characterizes the combination mode of bending and stretching at 5300 cm-1.

Heat transfer in rod bundles cooled by supercritical water – Experimental data and correlations

In the continuous casting process, the fluid flow of molten steel in the tundish is in a non-isothermal state. Because of the geometric shape and process parameters of a multi-strand tundish, the fluid flow behavior of each strand is quite inhomogeneous, and the difference in temperature, composition and inclusion content between each strand is great, which directly affects the quality of the steel products. In this paper, the fluid flow, heat transfer phenomena and inclusion trajectories in a four-strand tundish with and without flow-control devices (FCDs) are investigated using a water model and numerical simulation in isothermal and non-isothermal conditions. The results show that natural convection has a significant influence on the flow pattern and temperature distributions of molten steel in the tundish. Without FCDs, the average residence times of the molten steel in the tundish obtained by the isothermal water model, non-isothermal water model and non-isothermal mathematical model were 251.2 s, 263.3 s and 266.0 s, respectively, and the dead zone volumes were 21.51%, 29.26% and 28.21%, respectively. With FCDs, the average residence times of the molten steel obtained by the isothermal water model, non-isothermal water model and non-isothermal mathematical model were 293.0 s, 304.0 s and 305.2 s, respectively, and the dead zone volumes were 43.98%, 50.23% and 52.78%, respectively. The flow characteristics of the molten steel in the tundish were different between the isothermal and non-isothermal conditions. Compared with isothermal conditions, the numerical simulation results were closer to the water model results in non-isothermal conditions. The trial results showed that the fluid flow in a tundish has a non-isothermal characteristic, and the results in non-isothermal conditions can better reflect the actual fluid flow and heat transfer behaviors of molten steel in a tundish.

The Canadian supercritical water-cooled reactor was selected as one of the Generation IV International Forum initiatives for reactor design. It uses supercritical light water as a coolant under operating conditions of 25 MPa (250 bar) and 623–898 K. However, the simulation codes used to assess the performance and safety of such a design depend upon the accuracy of available nuclear data parametrizations, which currently do not include models of light water in the supercritical regime. In this paper, we present a study of supercritical water (SCW) through molecular dynamics simulations. Flexible variants of the TIP4P/2005 and simple point charge models for H2O are assessed to determine their ability to reproduce experimental measurements of SCW properties, and their suitability for the future development of nuclear data parametrizations for thermal neutron scattering from SCW. Planned experiments measuring thermal neutron scattering from SCW to inform nuclear data development are also summarized.

The configuration of a tundish for a two-strand horizontal continuous caster was designed and optimized using water modeling, mathematical modeling and industrial trials. Five designs were studied: the original tundish without flow control devices, the tundish with a turbulence inhibitor at the bottom, the tundish with a deep inlet launder and a tilted dam at the end of the inlet launder, the tundish with two dams with holes, and the tundish with a shallow inlet launder and a high dam in the main chamber. Water modeling was used to measure residence time and investigate dead zone fractions and fluid flow patterns. In the mathematical modeling, fluid flow, heat transfer and inclusion motion and removal were calculated. In industrial trials, the total oxygen, nitrogen pick-up, and inclusions in steel samples taken from the tundish and the billets were analyzed. The results indicated that the tundish with an inlet launder and a dam either at the end of the chamber or in the main chamber was the best design.

The computationally efficient classical MARTINI model is extended to simulate heat transfer simulations of water. The current MARTINI model, variations of it and other coarse grain water models focus on reproducing the thermodynamic properties below or at room temperature, hence making them unsuitable for studying high temperature simulations especially evaporation at . In this work, the MARTINI model is reparametrised using a combination of Genetic Algorithm, Artificial Neural Network and Nelder–Mead optimisation technique to match the phase equilibrium properties of water. The reparametrised model (MARTINI-E) accurately reproduces density, enthalpy of vaporisation and surface tension at and outperforms other leading coarse grain water models. The model is also validated using the energy conservation and enthalpy change due to latent heat in a lamellar system. This new water model can be used for simulating phase change phenomena, thin film evaporation and other energy transport mechanisms accurately.

The quantity of available water resources have been recognized as limiting factors in development of most of the arid regions. Therefore, sustainable use of water resources is key problem for development of these areas. In the present paper, Hetao irrigation district, one of the largest irrigation districts in the Yellow River basin, is selected as the research area. The sustainable utilization coupled management model for water resources is established by dynamically coupling numerical simulated model for ground water with optimal allocation model. In the coupled model, the groundwater level is adopted as the constraint condition and the optimal conjunctive utilization quantity of surface water and groundwater is set as the objective function. Finally, the coupled model is applied to calculate the optimal water supply quantity of surface water and groundwater and optimal sustainable utilization scheme of water resources in 2020 and 2030 of Hetao irrigation district. The results indicate that the water imported from the Yellow River can be reduced to the national limited amount of 4.0 × 109 m3/a, with adjusting well-canal irrigated area and industry structure appropriately as well as using the ground water reasonably. The research result can offer a valuable reference to efficiently use water resources and prevent the salinization for other similar regions.

We report results of molecular dynamics simulations of the limiting conductance of Na2+, Cl2−, Na°, and Cl° in supercritical water using the SPC/E model for water in conjuction with our previous study (Lee et al., Chem. Phys. Lett. 293, 289 (1998)). The behavior of the limiting conductances of Na2+ and Cl2− in the whole range of water density shows almost the same trend as those of Na+ and Cl−, but the deviation from the assumed linear dependence of limiting conductances of Na2+ and Cl2− on the water density is smaller than that of Na+ and Cl−. The ratio of the limiting conductance of the divalentions to that of the corresponding monovalentions over the whole range of water density is almost constant. In the cases of Na2+ and Cl2−, the dominating factor of the number of hydration water molecules around ions in the higher-density region and the dominating factor of the interaction strength between the ions and the hydration water molecules in the lower-density region are also found as was the cases for Na+ and Cl−. These factors, however, are not so strong as for the corresponding monovalent ions because the change in the energetics, structure, and dynamics are very small mainly due to the strong Coulomb interaction of the divalent ions with the hydration water molecules. The diffusion coefficient of Na° and Cl° monotonically increases with decreasing water density over the whole range of water density. The increase of the diffusion coefficient with decreasing water density is attributed only to the dramatic decrease of the hydration number of water in the first solvation shell around the uncharged species. Among the two important competing factors in the limiting conductance of Na+ and Cl−, the effect of the number of hydration water molecules around the uncharged species is the only existing factor over the whole range of water density since the interaction strength between the uncharged species and the hydration water molecules very small through the LJ interaction. This result has confirmed the dominating factor of the number of hydration water molecules around ions in the higher-density region in the explanation of the limiting conductance of Na+ and Cl− in supercritical water at 673 K.