Incompressible Ideal Gas Research Articles

CFD analysis of spent fuel dry cask storage system for High burnup nuclear fuel

Storage of nuclear spent fuel and cooling of the fuel assembly is one of the vital requirements for nuclear safety. This engineering technology involves a dynamic thermo-fluid phenomenon in the dry storage casks. Therefore, this study investigated HI-STORM 100 dry cask storage container for thermal-fluid with sensitivity analysis using 3D Computational Fluid Dynamics (CFD) simulations. It is a vertical concrete cylindrical structure (6.09 m height and 3.36 m diameter) containing a welded stainless-steel sealed barrel multi-purpose canister (MPC) for storing the fuel components replaced by the reactor. MPC-32 storage barrel (4.85 m height, 1.78 m outer diameter) and Westinghouse 17 × 17 high burnup (45GWd/MTU) Pressurized Water Reactor (PWR) fuel assembly is selected in this research. 2D and 3D models of this assembly were simulated using CFD with porous media assumption. Further, Boussinesq approximation and incompressible ideal gas models are adopted in simulation; and standard k-ε and k-ω Shear Stress Transport (SST) turbulence models were also compared under natural convection. The internal flow and temperature of the MPC by the incompressible ideal gas model were found to be in line with the actual situation. The standard k-ε model can cause abnormal results at the high-temperature position. The sensitive factors are analyzed to predict the temperature distribution and flow field characteristics of the system during 10–55 cooling years. During this period, the decay thermal power of nuclear waste, the maximum temperature of the system and shell; the air outlet temperature and the volumetric flowrate decreased. Under non-uniform thermal conditions, the heat dissipation performance was studied defining the decay heat ratio (X). The heat dissipation performance of the system was found better when X ≥ 1, and the maximum temperature of the fuel assembly rise when X < 1.

Numerical study on the flow and heat transfer characteristics of natural convection in CFETR cryostat

The cryostat in the China Fusion Engineering Testing Reactor (CFETR) provides vacuum and low temperature operating conditions for the superconducting magnet system. A high pressure in the cryostat can increase the Rayleigh number (Ra) and cause the natural convection within the continuous hypothesis. A three-dimensional model, using incompressible ideal gas model and realizable k-ε model, is built to simulate the natural convection between the superconducting magnet system and the thermal shield within the temperature range of 4.5-80 K. The distributions of velocity field and heat flux on different surfaces of superconducting magnet system are obtained under different Rayleigh number conditions. The results show that the areas with large natural convection velocity mainly locate near the Central Solenoid (CS) coils and at the bottom of vacuum chamber. When the Rayleigh number ranges from 104 to 1010, the maximum velocity of helium gas decreases, while the heat flux on walls of superconducting magnets increases rapidly, and the heat flux on walls of PF-1, CS and TF coils is more affected by pressure, which needs to be considered in designing the safety system.

О НАДЕЖНОСТИ ОЦЕНКИ ТЕПЛОВОГО РЕЖИМА ПОДЗЕМНОГО ОБЪЕКТА ХРАНЕНИЯ ОТРАБОТАВШЕГО ЯДЕРНОГО ТОПЛИВА НА БАЗЕ ЧИСЛЕННОГО МОДЕЛИРОВАНИЯ

The results of checking the reliability of a previously performed assessment of the thermal mode of an underground facility for long-term storage of spent nuclear fuel in a variant of an integrated reinforced concrete structure on three calculation grids (Coarse, Normal, Fine) are presented. The test was performed on a previously developed three-dimensional computer model in the COMSOL program. The mathematical basis of the model is following: continuity equation, Navier-Stokes equations averaged by Reynolds, standard turbulence model and general heat transfer equation. The consideration of mixed convection conditions was implemented in the "incompressible ideal gas" approximation. It was shown that when using computational grids with high resolution (Normal, Fine), some characteristics may be predicted. They are: temperature increase inside the built-in structure and at the boundary "rock mass - built-in structure" no more than 1°C; a significant change in the structure of the spatial distribution of temperature and an increase in maximum temperatures by about 1°C on the surface of the built-in structure. The duration of calculations in variants with small grids increased approximately 3.4 (Normal) and 7.7 (Fine) times, respectively

Numerical simulation of the thermal regime of an underground spent fuel storage facility (built-in structure variant)

The results of a numerical simulation of the thermal regime of an underground facility for long-term storage of spent nuclear fuel in a built-in reinforced concrete structure are presented. Two computer models were constructed in a three-dimensional formulation in the COMSOL programme. The first model is based on the incompressible fluid approximation, while the second model is based on the "incompressible ideal gas" approximation. The mathematical basis of models: the continuity equation, Navier - Stokes equations averaged by Reynolds, the standard (k - ε) turbulence model, and the general heat transfer equation. Consideration of mixed convection conditions is implemented in the "incompressible ideal gas" approximation, where the air density is a function of temperature only. The most thermally stressful arrangement of spent fuel placement is investigated: U-Zr - defective - U-Be. The air rate is varied in the range from 21 to 0.656 m3/s. Numerical experiments were performed for up to 5 years of fuel storage. The principal difference between the non-stationary structure of the velocity fields predicted in the "incompressible ideal gas" model and the "frozen" picture of the aerodynamic parameters in the incompressible fluid model is emphasized. It is shown that the requirements for exceeding the temperature limit values are met when the object operates under conservative ventilation conditions (rate 0.656 m3/s) with a minimum of costs for organizing ventilation. The dynamics of heat flows directed into the rock mass through the base and from the surface of the built-in structure of the U-Zr fuel compartment to the air environment are analyzed. The predominance of the heat flow from the surface of the structure and the different times when the curves of the heat flow dynamics reach their maximum values are noted. The heat flow to the array reaches its maximum significantly faster than to the air.

Forecast of the thermal regime of an underground storage facility for heat-generating materials under mixed convection conditions

The paper presents the results of a study based on numerical simulation methods of the thermal regime of an underground facility for long-term spent nuclear fuel storage in the version of a built-in reinforced concrete structure. A multiphysical computer model was constructed in a two-dimensional setting by means of the COMSOL software. The mathematical model was based on the continuity equations, Navier-Stokes equations and the general heat transfer equation. The conditions of mixed convection were taken into account in the ‘incompressible ideal gas’ approximation, in which the thermophysical properties of air were a function of temperature only. For two parameters of the model, the following values were taken: the air flow rates providing the velocity at the inflow boundary = 0.01, 0.03 and 0.05 m/s, and the effective heat conductivity coefficients of the material of the built-in structure = 1.0 and 2.0 W/(m×K). Numerical experiments were performed for a period of up to 5 years of fuel storage. Special emphasis was given to the fundamental difference between the non-stationary structure of the velocity fields forecasted in the model of an ‘incompressible ideal gas’ and the ‘frozen’ picture of aerodynamic parameters in the model of an incompressible fluid. An analysis was made of the dynamics of spatial temperature field distributions in different areas of the model. It was shown that the criterion temperature control requirements were met when the facility was operated under conservative ventilation conditions in terms of the air flow rate and the heat conductivity coefficient of the built-in structure material. The dynamics of heat flows directed into the rock mass through the base and from the surface of the built-in structure into the air was analyzed. The heat flow dominance from the structure surface was also noted. Finally, the influence of the effective heat conductivity coefficient of the built-in structure material and the air flow rate on the values of heat flows directed into the air and rock mass was demonstrated.

Turbulent thermal characteristics and air flow patterns in a naturally ventilated tunnel with roof openings

Air flow is a major characteristic in the tunnel ventilation design, to avoid severe disasters like smoke suffocation problems in tunnel and fire accidents. Tunnels are best ways to reduce distance between two adjacent places. It may be underground or above ground, depending upon the usage of it. There are different types of tunnel ventilation, e.g. roof vents, side vents, mechanical ventilation, naturally ventilated etc. This paper majorly focuses on roof vents mass extraction with different sizes of the heat sources and it also records the horizontal and normal velocity for different sizes of heat sources. The Reynolds Number is low but still turbulence occurs when we deal with buoyant smoke keeping density as incompressible ideal gas. Ratio of height by width is taken into account and the transient air flow is simulated for 10 seconds, and mass flow is recorded at each time step of 0.1 seconds using Large Eddy turbulence Model to capture the flow physics. It is observed that with changing the heat source size, mass flow rate from each vent changes significantly and it drastically affects the air flow patterns and heat transfer characteristics inside the tunnel.

CFD simulations on high-buoyancy gas dispersion in the wake of an isolated cubic building using steady RANS model and LES

As the use of emergency generators for buildings increases, the near-field dispersion of high-temperature and high-buoyancy exhaust gas is becoming a concern. We conducted computational fluid dynamics (CFD) simulations using steady Reynolds-averaged Navier-Stokes (RANS) model and large eddy simulation (LES) on the near-field dispersion of high-buoyancy exhaust gas emitted from a building's wake and validated using a wind tunnel experiment. Realizable k-ε 2-layer and wall-adapting local eddy viscosity (WALE) models were used in RANS and LES, respectively. The density difference between the light gas and ambient air in the experiment was reproduced as the temperature difference by an incompressible ideal gas model. RANS model exhibited good agreement with the experimental flow field values for the time-averaged velocity but underestimated the turbulent kinetic energy. LES accurately predicted both the time-averaged velocity and turbulent kinetic energy. For the concentration field, RANS model predicted the region of high time-averaged concentration near the exhaust port but overestimated ground-level values. Meanwhile, LES adequately predicted time-averaged and fluctuating concentrations. Additionally, an investigation of the effect of the turbulent Schmidt number Sct in RANS model demonstrated that a small Sct increased the overall prediction accuracy, while a large Sct compensated for the overestimation on ground-level time-averaged concentrations.

Numerical modeling of heat losses in a line focusing solar compound parabolic concentrator with planar absorber

In this work, a three-dimensional steady state thermal model is developed for a compound parabolic concentrator of 2× concentration considering the effects of surface radiation and wall conduction. The performance of the compound parabolic concentrator is modeled to obtain the convective and radiative heat loss under the influence of different parameters such as absorber temperature, absorber emissivity, ambient temperature, external heat loss coefficient, aspect ratio and concentrator tilt. The turbulent natural convection in the concentrator is modeled using standard two equation k-ε turbulent model with enhanced wall treatment. For the surface radiation inside the concentrator, discrete ordinate radiation model is used. The thermo physical properties of air inside the cavity are assumed to be constant except the density which is modeled as incompressible ideal gas. The conduction at the walls is accounted by setting suitable wall thickness for reflectors, glass cover and end walls in the solver. This work clearly demonstrates the need for a three dimensional numerical simulation and coupled natural convection and radiation to exactly reproduce the velocity fields as would be obtained in experiments. The convective Nusselt number, radiative Nusselt Number and thermal stratification are obtained from the parametric study. This study on estimation of heat losses in compound parabolic concentrator is applicable to both solar thermal and solar photo-voltaic collectors with a view of modifying the concentrator design to optimize its thermal performance.

Predictive accuracy of Boussinesq approximation in opposed mixed convection with a high-temperature heat source inside a building

The density model of Boussinesq approximation has been extensively used in mixed convection. Literature have investigated the validity of Boussinesq approximation in natural convection; however, there is no related study in mixed convection. This work aims to investigate the accuracy of Boussinesq approximation in mixed convection. In this paper, mixed convection is generated by a thermal plume from a heat source (natural convection) and a downward air jet from the inlet (forced convection). An experiment is set up to validate the computational fluid dynamics (CFD) simulations for the Boussinesq approximation and incompressible ideal gas density models. Results indicate incompressible ideal gas model can be used as a comparative reference to quantitatively investigate the predictive accuracy of the Boussinesq approximation in simulations. Then, simulation results show the accuracy of Boussinesq approximation in mixed convection correlates with Archimedes number, not temperature difference. Accuracy trends are different for forced convection dominated flow, comparable mixed convection, and natural convection dominated flow. This work is of fundamental importance for the application of Boussinesq approximation in mixed convection with a high-temperature heat source, especially in industrial buildings.

Development of Modified Incompressible Ideal Gas Model for Natural Draft Cooling Tower Flow Simulation

The article deals with the development of incompressible ideal gas like model, which can be used as a part of mathematical model describing natural draft wet-cooling tower flow, heat and mass transfer. It is shown, based on the results of a complex mathematical model of natural draft wet-cooling tower flow, that behaviour of pressure, temperature and density is very similar to the case of hydrostatics of moist air, where heat and mass transfer in the fill zone must be taken into account. The behaviour inside the cooling tower is documented using density, pressure and temperature distributions. The proposed equation for the density is based on the same idea like the incompressible ideal gas model, which is only dependent on temperature, specific humidity and in this case on elevation. It is shown that normalized density difference of the density based on proposed model and density based on the nonsimplified model is in the order of 10-4. The classical incompressible ideal gas model, Boussinesq model and generalised Boussinesq model are also tested. These models show deviation in percentages.

수치 해석을 통한 비행체 내부 압력 예측과 실험적 검증

In this study, a numerical analysis for predicting the internal pressure of the flight vehicle system with relief valve and N2-injection type cooler was conducted to operate the system safely in an unsteady-state condition. By adopting an incompressible ideal gas equation to computational domain at each time step, internal pressure was calculated without iteration. To increase the accuracy of the numerical analysis results, numerical model was correlated by modifying the volume of the computational domain. To modify the volume of computational domain, internal pressure along time was compared with experimental results. It showed good agreement within system operating time. Air mass flow rate at the relief valve is calculated by interpolating the performance curve data. For accurate and rapid calculation of the internal pressure in an unsteady-state condition, time step size convergence study was conducted additionally. By using a correlated numerical model, Pcr of the relief valve is conducted to remain the flight vehicle system within an internal pressure range of 0.6-2.0 atm, in each flight profile. Finally, specific Pcr of relief valve was applied to the system and the experimental results showed that the internal pressure remained in a safe range.

Numerical Study of Temperature and Air Velocity Distribution In Oil Filling Factory

This paper describes the use of CFD modeling to analyze the thermal comfort in the oil filling factory which has an area of 3000 m 2. the need for this analysis comes from an uncomfortable condition that is felt by the workers of the factory. A 3D simulation using FLUENT software 6.3.26 conducted to analyze the temperature and velocity distribution in the plant room. The water is assumed as an incompressible ideal gas, steady flow, turbulence models used k-e standard, the SIMPLE algorithm and second order upwind discretisation. Analysis was conducted on existing models and propose models, whereby on a model propose, the diffuser is installed above the workers with a height of 4,2 m above the floor, the velocity of supply air diffuser is varied from 1,5 m/s, 2 m/s, and 2,5 m/s. The simulation results show that the temperature distribution in the existing conditions in the range of about 34-36 ° C, this value exceeds the thermal comfort standards specified by ASHRAE. The simulation results show that the proposed model better temperature distribution, where the temperature is generated in the range of ASHRAE thermal comfort criteria, ranging from 24-26 °C, and the supply air velocity at the diffuser inlet of 1,5 m/s recommended for use in AHU system. For the 20 units of the diffuser with inlet velocity of 1,5 m / s, the mass flow rate that should be handled by a cooling device is 9 kg/s and require a cooling capacity of 0,128 MW. This is 58% more efficient than cooling the entire room factory.

Computational fluid dynamics modeling patterns and force characteristics of flow over in-line four square cylinders

The flow over four square cylinders in an in-line, square arrangement was numerically investigated by using the finite volume method with CFD techniques. The working fluid is an incompressible ideal gas. The length of the sides of the array, L, is equal. The analysis is carried out for a Reynolds number of 300, with center-to-center distance ratios, L/D, ranging from 1.5 to 8.0. To fully understand the flow mechanism, details in terms of lift and drag coefficients and Strouhal numbers of the unsteady wake frequencies are analyzed, and the vortex shedding patterns around the four square cylinders are described. It is concluded that L/D has important effects on the drag and lift coefficients, vortex shedding frequencies, and flow field characteristics.

회전원판형 CVD 장치의 유동 재순환을 억제하는 출구부 형상 설계를 위한 전산해석

A numerical design analysis is conducted to search for an optimal shape of outlet in a rotating-disk CVD reactor. The goal is to suppress flow recirculation that has been found in a reactor having a sudden expansion of flow passage outside of the rotating disk. In order to streamline gas flow, the sidewall at which the flow in the Ekman layer is impinged, is tilted. The axisymmetric laminar flow and heat transfer in the reactor are simulated using the incompressible ideal gas model. For the conventional vertical sidewall, the flow recirculation forming in the corner region could be expanded into the interior to distort the upstream flow. The numerical results show that this unfavorable phenomenon inducing back flow could be dramatically suppressed by tilting the sidewall at a certain range of angle. The assessment of deviation in deposition rate based on the characteristic isotherm illustrates that the sidewall tilting may expand the domain of stable plug-like flow regime toward higher pressure. A physical interpretation is attempted to explain the mechanism to suppress flow recirculation.

배전용 몰드변압기의 온도특성 파악을 위한 열유동해석

In this paper, the temperature characteristics of mold transformer for the distribution power system have been analyzed by using computational fluid dynamics(CFD). The model has been modeled by coil, cores, insulating materials and frames about 3MVA grade mold transformer and analyzed the temperature distribution of the structure with a heat fluid. The fluid, which is incompressible ideal gas, is analyzed as a turbulent flow phenomenon on the assumption that it is natural cooling of transformer cooling system. Through this study, by examining the temperature distribution and hot-spot of the structure field of the mold transformer, cooling design and temperature distribution information, which are demanded for designing are estimated.

Estimation of convective heat transfer coefficient in a single-slope solar still: a numerical study

ABSTRACT The intention of this work is to investigate the natural convection effect in a 2-D single-slope solar still. The flow is assumed as steady, laminar, and incompressible ideal gas. A numerical model based on SIMPLEC algorithm is used for the solution of mass, momentum, energy, and concentration equations. The solutions are performed for several values of aspect ratio and Rayleigh number between 2.5 and 5.5 and between 5 × 106 and 5 × 107, respectively. Moreover, a new correlation for estimating the convective heat transfer coefficient has been obtained, which has a good agreement with published well-known models. The results show that, for a given aspect ratio, Rayleigh number has a direct effect on Nusselt number. On the other hand, for a fixed Rayleigh number, the value of Nusselt number decreases when the aspect ratio increases. Furthermore, it is found that the maximum heat transfer coefficient is in the area where flow directed downward from glass to water.

Gas mixing enhancement in minichannels using a rotationally oscillatory circular cylinder

Oscillating structures and actuators can induce flow kinematics that enhances mixing. This approach is specifically effective for mixing enhancement in meso-scale channels, where the flow kinematics can be actively controlled using micro-electro-mechanical-systems (MEMS). In this paper, numerical results for mixing of two incompressible ideal gas (Schmidt number of 1.0) streams through a 2D minichannel via a rotationally oscillating circular cylinder are presented and discussed. Simulations are performed for blockage ratio of D/H=l/3 and Reynolds number of 100 and oscillation amplitudes of π/3, 2π/3,π/2 and π for subharmonic (F < 1), harmonic (F = 1) and superharmonic (F > 1) regimes. Numerical results indicate that mixing performance is improved by about 70% compare to the plane channel at oscillation amplitude of π and excitation frequency of 25% higher than the natural frequency of vortex shedding of a stationary cylinder. It is shown that the mixing efficiency is increased by increasing of amplitude in all the cases except at very low excitation frequencies. This study also shows that when the excitation frequency is equal to the vortex shedding frequency the maximum power is required for mixing of two gases.

Application of CFD Simulation in the Development of a New Generation Heating Oven

This paper deals with the application of Computational Fluid Dynamics simulation in the development of a new generation cooking appliance in Gorenje concern. As the oven is multifunctional, radiation, conduction, natural and forced convection mechanisms of heat transfer are used. The Discrete Ordinate (DO) model is used for radiation. The density of air is described by incompressible ideal gas equation in a natural convection model. The intention was to create the best possible baking conditions for different heating systems. Several discrete models were created. The influence of geometry change and boundary conditions variations to the velocity and temperature field distribution in the oven cavity was analyzed. The results of numerical simulations are validated with measurements taken from an oven prototype. The agreement was good. After successfully passing the standard tests, the oven came into serial production and was launched on the market.

Numerical and experimental studies of heat transfer in particle-laden gas flows through a vertical riser

This paper presents numerical and experimental studies of gas–solid flow with heat transfer during pneumatic transport. The experimental work investigates the flow with two different cases of inlet thermal conditions namely; hot gas with cold solid particles, while the second case is cold gas with hot particles. Crushed limestone particles with different sizes are used in the experimental study. The Eulerian–Lagrangian approach is utilized to simulate the process under consideration. In the present study, the SIMPLE algorithm is extended to compressible flow. The model takes into account the effects of particle–particle and particle wall collisions, gas phase turbulence modulation and turbulence dispersion (i.e., four-way coupling). The effect of wall roughness is simulated using the virtual-wall model. The model is validated with available published experimental data for high speed gas–solid flow and a good agreement is obtained. Also, the model predictions are found to be in a good agreement with the present experimental measurements. The present results show that pressure drop increases in dilute phase and decreases in dense phase pneumatic conveying when hot particles are introduced in cold gas flow, and an opposite effect is obtained when cold particles is introduced in a hot gas stream. In addition, it is noticed that the equilibrium temperature and the distance required to reach equilibrium are greatly affected by the flow conditions. Furthermore, the present results show that gas–solid flows with heat transfer can be accurately modeled using incompressible ideal gas law for low conveying speed, while for high conveying speed; the full compressible model should be used.