Improvements in technology for the production of microbial biomass from natural gas, which have been gaining importance in recent years, require the development and optimization of energy‐efficient ...bioreactor designs. The most advanced methods for developing and scaling up industrial biotechnological processes rely on detailed hydrodynamic modeling, in addition to classical approaches, as the main tool for analysis and large‐scale transfer of experimental information. This paper presents the results of a simulation of flows in a bioreactor circuit using the latest mathematical methods and numerical flow analysis tools for two‐phase bubble flows based on experimental data.
Previously, the authors of this article proposed a 3D Euler-Eulerian model of raw materials spraying and evaporation in the heat-carrier gas flow in the carbon production reactor. The raw materials' ...droplets fragmentation and evaporation are considered as the carrier and dispersed phase interaction. The continuous phase is a heat carrier gas whose motion is described by the Navier-Stokes equations. Dispersed phase (droplets of raw material and products of its evaporation) motion is described using a non-uniform convective-diffusion equation for the particle concentration. The model was tested with water as a raw material. In this work, hydrocarbons are specified as raw materials. It is proposed next to solve the inverse problem with the target functional providing zero contact of the unevaporated raw materials with the reactor wall. Then the number of solid coke particles in the final product will be minimal. An analysis is made of the unevaporated raw material area sensitivity to the inlet velocity of the heat-carrier gas flow. This parameter has the most impact on the distribution area of the unevaporated raw materials and is assumed to be varied in the optimization problem.
An approach to numerical analysis of thermo-hydraulic processes proceeding in a fast-neutron reactor is described in the given article. The description covers physical models, numerical schemes and ...geometry simplifications accepted in the computational model. Steady-state and dynamic regimes of reactor operation are considered. The steady-state regimes simulate the reactor operation at nominal power. The dynamic regimes simulate the shutdown reactor cooling by means of the heat-removal system. Simulation of thermo-hydraulic processes is carried out in the FlowVision CFD software. A mathematical model describing the coolant flow in the first loop of the fast-neutron reactor was developed on the basis of the available geometrical model. The flow of the working fluid in the reactor simulator is calculated under the assumption that the fluid density does not depend on pressure, with use a $k-\varepsilon$ turbulence model, with use of a model of dispersed medium, and with account of conjugate heat exchange. The model of dispersed medium implemented in the FlowVision software allowed taking into account heat exchange between the heat-exchanger lops. Due to geometric complexity of the core region, the zones occupied by the two heat exchangers were modeled by hydraulic resistances and heat sources. Numerical simulation of the coolant flow in the FlowVision software enabled obtaining the distributions of temperature, velocity and pressure in the entire computational domain. Using the model of dispersed medium allowed calculation of the temperature distributions in the second loops of the heat exchangers. Besides that, the variation of the coolant temperature along the two thermal probes is determined. The probes were located in the cool and hot chambers of the fast-neutron reactor simulator. Comparative analysis of the numerical and experimental data has shown that the developed mathematical model is correct and, therefore, it can be used for simulation of thermo-hydraulic processes proceeding in fast-neutron reactors with sodium coolant.
This work presents the model of heat wall functions FlowVision (WFFV), which allows simulation of nonisothermal flows of fluid and gas near solid surfaces on relatively coarse grids with use of ...turbulence models. The work follows the research on the development of wall functions applicable in wide range of the values of quantity y+. Model WFFV assumes smooth profiles of the tangential component of velocity, turbulent viscosity, temperature, and turbulent heat conductivity near a solid surface. Possibility of using a simple algebraic model for calculation of variable turbulent Prandtl number is investigated in this study (the turbulent Prandtl number enters model WFFV as parameter). The results are satisfactory. The details of implementation of model WFFV in the FlowVision software are explained. In particular, the boundary condition for the energy equation used in high-Reynolds number calculations of non-isothermal flows is considered. The boundary condition is deduced for the energy equation written via thermodynamic enthalpy and via full enthalpy. The capability of the model is demonstrated on two test problems: flow of incompressible fluid past a plate and supersonic flow of gas past a plate (M = 3). Analysis of literature shows that there exists essential ambiguity in experimental data and, as a consequence, in empirical correlations for the Stanton number (that being a dimensionless heat flux). The calculations suggest that the default values of the model parameters, automatically specified in the program, allow calculations of heat fluxes at extended solid surfaces with engineering accuracy. At the same time, it is obvious that one cannot invent universal wall functions. For this reason, the controls of model WFFV are made accessible from the FlowVision interface. When it is necessary, a user can tune the model for simulation of the required type of flow. The proposed model of wall functions is compatible with all the turbulence models implemented in the FlowVision software: the algebraic model of Smagorinsky, the Spalart-Allmaras model, the SST $k-\omega$ model, the standard $k-\varepsilon$ model, the $k-\varepsilon$ model of Abe, Kondoh, Nagano, the quadratic $k-\varepsilon$ model, and $k-\varepsilon$ model FlowVision.
The article submits wall functions model "FlowVision". The model allows simulating turbulent flows of fluid and gas over solid impermeable surfaces on different grids. Four turbulence models are ...considered: $k-\varepsilon$ FlowVision, $k-\varepsilon$ Standard, SST $k-\omega$, SA. Details of implementation of turbulence models in FlowVision software are discussed. Calculations of two test cases are demonstrated.
The article provides a development of recently published turbulence model KEFV. The submitted version of this model allows modeling transition in a separated flow. The model includes an adjustable ...mechanism for specifying generation of turbulence in laminar zones with high velocity gradients. The model is implemented in the FlowVision CFD software. Simulation of the air flow around low-Reynolds airfoil Eppler-387 is discussed in the article. The flow conditions are characterized by the Reynolds number Re = 200 000.
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