Tobias Stromgren | KTH Royal Institute of Technology (original) (raw)

Papers by Tobias Stromgren

The goal of this work is to design a nozzle system around the Reactor Pressure Vessel (RPV) of a ... more The goal of this work is to design a nozzle system around the Reactor Pressure Vessel (RPV) of a VVER-1000 nuclear reactor which would ensure successful melt retention during a severe accident. Simulations were performed with a multiphase model in ANSYS Fluent 19.1 to determine this. The results suggest that an efficient cooling can be achieved by inducing a flow rising parallel to the RPV walls in the flooded reactor cavity. In order to do this, it is proposed to use one central nozzle below the RPV and a ring of 32 nozzles 0.5 m above the RPV bottom. Assuming a 2 bar pressure, injection of 750 m 3 /h water at 80 o C through the nozzles led to little steam production and a heat flux below the critical value.

A turbulent two-phase flow model using kinetic theory of granularflows for the particle phase is ... more A turbulent two-phase flow model using kinetic theory of granularflows for the particle phase is developed and implmented in afinite element code. The model can be used for engineeringapplications. However, in this thesis it is used to investigateturbulent gas-particle flows through numerical simulations. The feedback from the particles on the turbulence and the meanflow of the gas in a vertical channel flow is studied. In particular,the influence of the particle response time, particle volumefraction and particle diameter on the preferential concentration ofthe particles near the walls, caused by the turbophoretic effect isexplored. The study shows that when particle feedback is includedthe accumulation of particles near the walls decreases. It is also foundthat even at low volume fractions particles can have a significant impacton the turbulence and the mean flow of the gas. The effect of particles on a developing turbulent vertical upward pipeflow is also studied. The development length is found to substantiallyincrease compared to an unladen flow. To understand what governs thedevelopment length a simple estimation was derived, showing that itincreases with decreasing particle diameters in accordance with themodel simulations. A model for the fluctuating particle velocity in turbulentgas-particle flow is derived using a set of stochastic differentialequations taking into account particle-particle collisions. Themodel shows that the particle fluctuating velocity increases whenparticle-particle collisions become more important and that increasingparticle response times reduces the fluctuating velocity. The modelcan also be used for an expansion of the deterministic model for theparticle kinetic energy.

The upward turbulent gas-particle flow in a channel was studied usingan Eulerian-Eulerian two-pha... more The upward turbulent gas-particle flow in a channel was studied usingan Eulerian-Eulerian two-phase model taking into account the feedbackfrom the particles on the gas-phase. The objective is to study theinfluence of particles with different diameters and volume fractionson the ...

Annular gas-liquid flow is one of the last flow regimes in boiling channels. It is characterized ... more Annular gas-liquid flow is one of the last flow regimes in boiling channels. It is characterized by a core flow of steam and liquid droplets and a thin liquid film wetting the wall of the channel. This type of flow can be encountered in many different industrial applications including boiling tubes, moisture separators, distillation towers and in particular nuclear Boiling Water Reactors.

European Journal of Mechanics B-fluids, May 1, 2011

The correlation between the fluctuating particle and gas velocity in isotropic turbulence is stud... more The correlation between the fluctuating particle and gas velocity in isotropic turbulence is studied with a set of stochastic differential equations taking into account both particle-particle collisions and the particle feedback on the turbulence. The principal aim of this work is to use the Langevin equations to formulate closures for two-fluid gas-particle flow models. Using Itô calculus we derived solutions for the turbulent kinetic energy of the particle phase and the particle-gas velocity correlations. If particle-particle collisions and particle feedback on the turbulence are neglected the new relations approach the ones derived by Tchen and Hinze but if these effects are included additional terms in the relations appear. In this study we only use a very simple model for the particle-particle collisions. The new relation and the classical relation of Tchen and Hinze for the particle turbulent kinetic energy as well as a relation based on the kinetic theory of granular flows have been implemented in a two-fluid model for turbulent gas-particle flow in a channel in order to make comparison for different particle Stokes numbers. Results show that while the two-fluid model using Hinze's relations only gives good results for small Stokes numbers, the new relation yields significant improvements for a large range of Stokes numbers.

Flow, turbulence and combustion, Mar 5, 2011

An Eulerian turbulent two phase flow model using kinetic theory of granular flows for the particl... more An Eulerian turbulent two phase flow model using kinetic theory of granular flows for the particle phase was developed in order to study evolving upward turbulent gas particle flows in a pipe. The model takes the feedback of the particles into account and its results agree well with experiments. Simulations show that the pipe length required for particle laden turbulent flow to become fully developed is up to five times longer than an unladen flow. To increase the understanding of the dependence of the development length on particle diameter a simple model for the expected development length was derived. It shows that the development length becomes shorter for increasing particle diameters, which agrees with simulations up to a particle diameter of 100 μm. Thereafter the development length becomes longer again for increasing particle diameters because larger particles need a longer time to adjust to the velocity of the carrier phase.

In the present article, the predictions of two models describing turbulent gas-particle flow in a... more In the present article, the predictions of two models describing turbulent gas-particle flow in a vertically oriented backward-facing step are compared to each other and with literature data. The first model is an Eulerian approach based upon the kinetic theory of granular flow, ...

A turbulent two-phase flow model using kinetic theory of granular flows for the particle phase is... more A turbulent two-phase flow model using kinetic theory of granular flows for the particle phase is developed and implmented in a finite element code. The model can be used for engineering applications. However, in this thesis it is used to investigate turbulent gas-particle flows through numerical simulations. The feedback from the particles on the turbulence and the mean flow of the gas in a vertical channel flow is studied. In particular, the influence of the particle response time, particle volume fraction and particle diameter on the preferential concentration of the particles near the walls, caused by the turbophoretic effect is explored. The study shows that when particle feedback is included the accumulation of particles near the walls decreases. It is also found that even at low volume fractions particles can have a significant impact on the turbulence and the mean flow of the gas. The effect of particles on a developing turbulent vertical upward pipe flow is also studied. The development length is found to substantially increase compared to an unladen flow. To understand what governs the development length a simple estimation was derived, showing that it increases with decreasing particle diameters in accordance with the model simulations. A model for the fluctuating particle velocity in turbulent gas-particle flow is derived using a set of stochastic differential equations taking into account particle-particle collisions. The model shows that the particle fluctuating velocity increases when particle-particle collisions become more important and that increasing particle response times reduces the fluctuating velocity. The model can also be used for an expansion of the deterministic model for the particle kinetic energy.

A filter system to be used in order to reduce the radioactive pollution when reducing the pressur... more A filter system to be used in order to reduce the radioactive pollution when reducing the pressure in the containment in case of a severe accident is developed. The radioactive pollution will be captured in the vessel that acts as a bubble column. To be able to maximize the water content in order to ensure that the radioactive pollution is captured it is of importance to predict the swelled water level in the vessel. In this study is three different methods to predict the gas holdup is presented and compared to experimental results; empirical correlations, thermal-hydraulic codes and Computational Fluid Dynamics (CFD). The advantages and disadvantages with the different methods are discussed.Both Computational Fluid Dynamics and the thermal hydraulic code (Gothic) show good predictions of the water level. Using empirical models it is crucial to have knowledge of the two-phase flow region in the bubble column.Copyright © 2014 by ASME

Powder Technology, Jul 1, 2012

An Eulerian model was developed for turbulent gas-particle flow that takes into account the influ... more An Eulerian model was developed for turbulent gas-particle flow that takes into account the influence of particles on the gas-phase turbulence. For the description of the particle-phase stress the kinetic theory of granular flow and the simpler Hinze model were adopted. A K-ω model was used as the gas phase turbulence model. The difference between one-and two-way coupling was investigated for different particle volume fractions and particle diameters. It was found that particles with a much higher density than the fluid substantially affect the gas-phase in turbulent channel flow for particle volume fractions as low as 10 − 4. The models with the particle-phase stress described by the kinetic theory of granular flow and the simpler Hinze model produce similar results for particles with small response times but deviate for larger response times. The study shows that two-way coupling and the turbophoretic effect must be taken into account in models even at relatively low particle volume fractions.

Two different advection schemes, Flux Corrected Transport (FCT) scheme (Zalesak, 1979) and increm... more Two different advection schemes, Flux Corrected Transport (FCT) scheme (Zalesak, 1979) and incremental remapping (Dukowicz and Baumgardner, 2000) have been tested in a two-dimensional test program where an initial cylindrical tracer distribution was advected in a circular velocity field. Evaluation of the tests showed that incremental remapping preserved the shape of the tracer distribution better than FCT. However, incremental remapping is computationally efficient first when many tracers are used. In addition, it has been developed for only two-dimensions so far. Consequently, it was decided to implement FCT into the Rossby Centre Ocean model (RCO) (Meier et al., 1999). Model simulations with RCO for the period November 1902 to December 1998 were done with FCT as advection scheme. This model simulation was compared to a model simulation with modified split-quick (Webb et al., 1997) advection scheme (Meier and Kauker, 2003). Modified split-quick isa third order scheme and is the current advection scheme in RCO. The advection of salinity and temperature was compared between the two model simulations. FCT was applied without explicit diffusion whereas modified split-quick needs explicit diffusion to eliminate subgrid-scale noise caused by the non-monotonicity of the scheme. Consequently, the simulation utilizing FCT was less diffusive. This is positive because as little implicit diffusion as possible is desirable, especially for long integrations. At sharp gradients modified split-quick may result in under- or overshooting. For example at the outflow of Neva and Kernijoki rivers a Sharp salinity gradient causes salinity to become negative for modified split-quick. FCT was shown to handle sharp gradients very well, no negative values for the salinity occurs with FCT as advection schem

A numerical study into the physical characteristics of dilute gasparticle flows over a square-sec... more A numerical study into the physical characteristics of dilute gasparticle flows over a square-sectioned 90 • bend is reported. Two approaches, namely the Lagrangian particle tracking model and Eulerian two fluid model are employed to predict the gas-particle flows. Renormalization Group based k-model is used as the turbulent closure for both the approaches; however, for the Eulerian model, additional transport equations are solved to account for the combined gas-particle interactions and the turbulence kinetic energy of the particulate phase.

An Eulerian-Eulerian model for dilute gas-particle turbulent flows is developed for engineering a... more An Eulerian-Eulerian model for dilute gas-particle turbulent flows is developed for engineering applications. The aim is to understand the effect of particles on turbulent flows. The model is implemented in a finite element code which is used to perform numerical simulations. The feedback from the particles on the turbulence and the mean flow of the gas in a vertical channel flow is studied. In particular, the influence of the particle response time and particle volume fraction on the preferential concentration of the particles near the walls, caused by the turbophoretic effect is explored. The study shows that the particle feedback decreases the accumulation of particles on the walls. It is also found that even a low particle volume fraction can have a significant impact on the turbulence and the mean flow of the gas. A model for the particle fluctuating velocity in turbulent gas-particle flow is derived using a set of stochastic differential equations. Particle-particle collisions were taken into account. The model shows that the particle fluctuating velocity increases with increasing particle-particle collisions and that increasing particle response times decrease the fluctuating velocity.

Flow Turbulence and Combustion, 2011

Abstract An Eulerian turbulent two phase flow model using kinetic theory of granular flows for th... more Abstract An Eulerian turbulent two phase flow model using kinetic theory of granular flows for the particle phase was developed in order to study evolving upward turbulent gas particle flows in a pipe. The model takes the feedback of the particles into account and its results ...

Powder Technology, 2012

An Eulerian model was developed for turbulent gas-particle flow that takes into account the influ... more An Eulerian model was developed for turbulent gas-particle flow that takes into account the influence of particles on the gas-phase turbulence. For the description of the particle-phase stress the kinetic theory of granular flow and the simpler Hinze model were adopted. A K-ω model was used as the gas phase turbulence model. The difference between one-and two-way coupling was investigated for different particle volume fractions and particle diameters. It was found that particles with a much higher density than the fluid substantially affect the gas-phase in turbulent channel flow for particle volume fractions as low as 10 − 4 . The models with the particle-phase stress described by the kinetic theory of granular flow and the simpler Hinze model produce similar results for particles with small response times but deviate for larger response times. The study shows that two-way coupling and the turbophoretic effect must be taken into account in models even at relatively low particle volume fractions.

Flow, Turbulence and Combustion, 2011

European Journal of Mechanics - B/Fluids, 2011

European Journal of Mechanics B-fluids, May 1, 2011

Flow, turbulence and combustion, Mar 5, 2011

A turbulent two-phase flow model using kinetic theory of granular flows for the particle phase is... more A turbulent two-phase flow model using kinetic theory of granular flows for the particle phase is developed and implmented in a finite element code. The model can be used for engineering applications. However, in this thesis it is used to investigate turbulent gas-particle flows through numerical simulations. The feedback from the particles on the turbulence and the mean flow of the gas in a vertical channel flow is studied. In particular, the influence of the particle response time, particle volume fraction and particle diameter on the preferential concentration of the particles near the walls, caused by the turbophoretic effect is explored. The study shows that when particle feedback is included the accumulation of particles near the walls decreases. It is also found that even at low volume fractions particles can have a significant impact on the turbulence and the mean flow of the gas. The effect of particles on a developing turbulent vertical upward pipe flow is also studied. The development length is found to substantially increase compared to an unladen flow. To understand what governs the development length a simple estimation was derived, showing that it increases with decreasing particle diameters in accordance with the model simulations. A model for the fluctuating particle velocity in turbulent gas-particle flow is derived using a set of stochastic differential equations taking into account particle-particle collisions. The model shows that the particle fluctuating velocity increases when particle-particle collisions become more important and that increasing particle response times reduces the fluctuating velocity. The model can also be used for an expansion of the deterministic model for the particle kinetic energy.

Powder Technology, Jul 1, 2012

Flow Turbulence and Combustion, 2011

Powder Technology, 2012

An Eulerian model was developed for turbulent gas-particle flow that takes into account the influ... more An Eulerian model was developed for turbulent gas-particle flow that takes into account the influence of particles on the gas-phase turbulence. For the description of the particle-phase stress the kinetic theory of granular flow and the simpler Hinze model were adopted. A K-ω model was used as the gas phase turbulence model. The difference between one-and two-way coupling was investigated for different particle volume fractions and particle diameters. It was found that particles with a much higher density than the fluid substantially affect the gas-phase in turbulent channel flow for particle volume fractions as low as 10 − 4 . The models with the particle-phase stress described by the kinetic theory of granular flow and the simpler Hinze model produce similar results for particles with small response times but deviate for larger response times. The study shows that two-way coupling and the turbophoretic effect must be taken into account in models even at relatively low particle volume fractions.

Flow, Turbulence and Combustion, 2011

European Journal of Mechanics - B/Fluids, 2011