Modelling the evaporation of cryogenic liquids in storage tanks

Cryogenic liquids are substances with a normal boiling point below -150°C. Recently, the interest in cryogenic liquids has skyrocketed because of their role in the energy transition, particularly for LNG and liquid hydrogen. Cryogenic liquids are stored in highly insulated tanks, which are nevertheless subject to heat ingress from the surroundings. The heat ingress drives thermal stratification, natural convection, pressure build-up and evaporation. Managing the evaporated cryogen, denominated boil-off gas (BOG), pose techno-economic, safety and environmental challenges. To facilitate the design and operation of cryogenic storage tanks, new models for cryogenic liquids evaporation have been developed. For isobaric storage, a 1-D model has been developed. The model includes wall heating, heat conduction and advection in the vapour phase. The model shows that advection dominates vapour heat transfer. A 2-D CFD model has been developed to validate the assumptions of the 1-D model. The CFD model validates the 1-D model assumption of one-dimensional advective flow. Additionally, the CFD model shows that thermal stratification dampens natural convection in the vapour. Analytical solutions of the 1-D model valid for the pseudo-steady state have been developed. The analytical solutions constitute an easy-to-use tool for practitioners to improve BOG management. For non-isobaric storage, a 1-D model that considers wall heating, heat conduction and wall boiling has been developed. The 1-D model demonstrates that wall boiling is relevant even for low heat fluxes. The 1-D model predictions were in good agreement with experimental pressure and vapour temperature profiles. The assumptions of the 1-D model have been validated by developing a new single-phase CFD model. A multiphase model has been developed to investigate interfacial transport phenomena. It shows that interfacial momentum transfer slightly enhances liquid heat transfer, and that vapour heating dominates pressure build-up at the beginning of the storage period.Open Acces

Turbulence modelling of fluid-particle interaction

The accurate prediction of turbulent fluid-particle behaviour has been a complex and elusive topic for researchers for several decades. The momentum and energy exchange between the fluid and particles, across the whole spectrum of spatial and temporal scales, leads to an abundance of rich physical behaviour which has ensured that significant advances in the area have proven challenging. This contribution seeks to shine a small ray of light on a vast and murky abyss in which the true nature of turbulent fluid-particle flows may allude us for some time still. This thesis presents a multi-scale continuum approach to modelling fluid-particle flows i.e. Eulerian-Eulerian (E-E). A fully-coupled Reynolds-Averaged Two-Fluid Model (RA-TFM) for turbulent fluid-particle flow, with particular emphasis on the near-wall region, is developed. The coupling is provided both mathematically i.e. the fluid-particle momentum and energy coupling across all spatial and temporal scales and numerically i.e. the RA-TFM governing equations are solved within a block-coupled matrix. The RA-TFM is derived, applied and validated against a plethora of benchmark experimental and Direct Numerical Simulation data in which a wide range of physical processes are present. Finally, the RA-TFM’s implementation within the open-source CFD toolbox OpenFOAM is detailed

A CFD-DEM solver to model bubbly flow. Part I: Model development and assessment in upward vertical pipes

[EN] In the computational modeling of two-phase flow, many uncertainties are usually faced in simulations and validations with experiments. This has traditionally made it difficult to provide a general method to predict the two-phase flow characteristics for any geometry and condition, even for bubbly flow regimes. Thus, we focus our research on studying in depth the bubbly flow modeling and validation from a critical point of view. The conditions are intentionally limited to scenarios where coalescence and breakup can be neglected, to concentrate on the study of bubble dynamics and its interaction with the main fluid. This study required the development of a solver for bubbly flow with higher resolution level than TFM and a new methodology to obtain the data from the simulation. Part I shows the development of a solver based on the CFD-DEM formulation. The motion of each bubble is computed individually with this solver and aspects as inhomogeneity, nonlinearity of the interfacial forces, bubble-wall interactions and turbulence effects in interfacial forces are taken into account. To develop the solver, several features that are not usually required for traditional CFD-DEM simulations but are relevant for bubbly flow in pipes, have been included. Models for the assignment of void fraction into the grid, seeding of bubbles at the inlet, pressure change influence on the bubble size and turbulence effects on both phases have been assessed and compared with experiments for an upward vertical pipe scenario. Finally, the bubble path for bubbles of different size have been investigated and the interfacial forces analyzed. (C) 2017 Elsevier Ltd. All rights reserved.The authors sincerely thank the ''Plan Nacional de I + D+ i" for funding the project MODEXFLAT ENE2013-48565-C2-1-P and ENE2013-48565-C2-2-P.Peña-Monferrer, C.; Monrós Andreu, G.; Chiva Vicent, S.; Martinez-Cuenca, R.; Muñoz-Cobo, JL. (2018). A CFD-DEM solver to model bubbly flow. Part I: Model development and assessment in upward vertical pipes. Chemical Engineering Science. 176:524-545. https://doi.org/10.1016/j.ces.2017.11.005S52454517

Two-phase flow properties upscaling in heterogeneous porous media

The groundwater specialists and the reservoir engineers share the same interest in simulating multiphase flow in soil with heterogeneous intrinsic properties. They also both face the challenge of going from a well-modeled micrometer scale to the reservoir scale with a controlled loss of information. This upscaling process is indeed worthy to make simulation over an entire reservoir manageable and stochastically repeatable. Two upscaling steps can be defined: one from the micrometer scale to the Darcy scale, and another from the Darcy scale to the reservoir scale. In this thesis, a new second upscaling multiscale algorithm Finite Volume Mixed Hybrid Multiscale Methods (Fv-MHMM) is investigated. Extension to a two-phase flow system is done by weakly and sequentially coupling saturation and pressure via IMPES-like method

Interstitial-Scale Modeling of Packed-Bed Reactors

Packed-beds are common to adsorption scrubbers, packed bed reactors, and trickle-bed reactors widely used across the petroleum, petrochemical, and chemical industries. The micro structure of these packed beds is generally very complex and has tremendous influence on heat, mass, and momentum transport phenomena on the micro and macro length scales within the bed. On a reactor scale, bed geometry strongly influences overall pressure drop, residence time distribution, and conversion of species through domain-fluid interactions. On the interstitial scale, particle boundary layer formation, fluid to particle mass transfer, and local mixing are controlled by turbulence and dissipation existing around packed particles. In the present research, a CFD model is developed using OpenFOAM: www.openfoam.org) to directly resolve momentum and scalar transport in both laminar and turbulent flow-fields, where the interstitial velocity field is resolved using the Navier-Stokes equations: i.e. no pseudo-continuum based assumptions. A discussion detailing the process of generating the complex domain using a Monte-Carlo packing algorithm is provided, along with relevant details required to generate an arbitrary polyhedral mesh describing the packed-bed. Lastly, an algorithm coupling OpenFOAM with a linear system solver using the graphics processing unit: GPU) computing paradigm was developed and will be discussed in detail

Numerical Simulation of Viscoelastic Multiphase Flows Using an Improved Two-phase Flow Solver

The production of uniformly-sized droplets has numerous applications in various fields including the biotechnology and chemical industries. For example, in the separation of mixtures based on their relative absorbency, an optimal arrangement of monodispersed droplets in columns is desired for an effective separation. However, very few numerical studies on the formation of viscoelastic droplets via cross-flow shear are available, none of which have considered the case when the flow of the continuous phase is Couette. In this work, a new solver capable of automatic mesh refinement is developed for the OpenFOAM CFD toolbox to solve viscoelastic two-phase flow problems. The finite volume method is used to discretize the governing equations while employing the Volume of Fluid (VOF) coupled with the level set method to accurately describe the interface. The fourth-order least squares method is applied to the reinitialization of the level set function. Mesh refinement and coarsening procedure is based on a specified range of the volume fraction field. To validate the numerical technique, two-dimensional numerical simulation is conducted for a drop under static conditions, drop deformation in shear flow, the rise of a Newtonian drop in a Giesekus liquid and formation of viscoelastic droplet in a microfluidic T-junction. Furthermore, the effect of flow type and fluid elasticity on drop size and droplet formation dynamics was investigated in a viscoelastic-Newtonian system. The results obtained show good qualitative agreement with experimental work. In both cases where the flow of the continuous phase is pressure-driven (P-flow) and plane Couette (C-flow), there was a decrease in drop size as the cross-flow shear rate increased. However, for a fixed average shear rate, the drop sizes generated in C-flow were found to be smaller than that in P-flow. It was also found that the influence of elasticity on drop size became accentuated as the cross-flow shear increased. An increase in elasticity was accompanied by a decrease in drop size

DYNAMIC MESHING AROUND FLUID-FLUID INTERFACES WITH APPLICATIONS TO DROPLET TRACKING IN CONTRACTION GEOMETRIES

The dynamic meshing procedure in an open source three-dimensional solver for calculating immiscible two-phase flow is modified to allow for simulations in two-dimensional planar and axisymmetric geometries. Specifically, the dynamic mesh refinement procedure, which functions only for the partitioning of three-dimensional hexahedral cells, is modified for the partitioning of cells in two-dimensional planar and axisymmetric flow simulations. Moreover, the procedure is modified to allow for computing the deformation and breakup of drops or bubbles that are very small relative to the mesh of the flow domain. This is necessary to avoid mass loss when tracking small drops or bubbles through flow fields. Three test cases are used to validate the modifications: the deformation and breakup of a two-dimensional drop in a linear shear field; the formation and detachment of drops in a two-dimensional micro T-junction channel; and an axisymmetric bubble rising from a pore into a static liquid. The tests show that the modified code performs very well, giving accurate results for much less computational time when compared to corresponding simulations without dynamic meshing. The modified code is then applied to study drop breakup conditions inside a spray nozzle when an emulsion is sprayed to produce a powder. This is done by tracking droplets of various sizes through the flow field within the nozzle and determining conditions under which they break up. The particular interest is in determining the largest drop sizes for which breakup does not occur. The effects of viscosity ratio, capillary number, shear rate, and fluid rheology on the critical drop sizes are determined. Although the code modifications performed for this research were implemented for dynamic mesh refinement of cells close to fluid-fluid interfaces, they may be adapted to other regions in the domain and for other types of flow problems