The use of risk information in establishing code and standard requirements enables: (1) An adequate and appropriate level of safety; and (2) Deployment of hydrogen facilities are as safe as gasoline facilities. This effort provides a template for clear and defensible regulations, codes, and standards that can enable international market transformation.
A series of experiments consisting of vessel-to-vessel transfers of pressurized gas using Transient PVT methodology have been conducted to provide a data set for optimizing heat transfer correlations in high pressure flow systems. In rapid expansions such as these, the heat transfer conditions are neither adiabatic nor isothermal. Compressible flow tools exist, such as NETFLOW that can accurately calculate the pressure and other dynamical mechanical properties of such a system as a function of time. However to properly evaluate the mass that has transferred as a function of time these computational tools rely on heat transfer correlations that must be confirmed experimentally. In this work new data sets using helium gas are used to evaluate the accuracy of these correlations for receiver vessel sizes ranging from 0.090 L to 13 L and initial supply pressures ranging from 2 MPa to 40 MPa. The comparisons show that the correlations developed in the 1980s from sparse data sets perform well for the supply vessels but are not accurate for the receivers, particularly at early time during the transfers. This report focuses on the experiments used to obtain high quality data sets that can be used to validate computational models. Part II of this report discusses how these data were used to gain insight into the physics of gas transfer and to improve vessel heat transfer correlations. Network flow modeling and CFD modeling is also discussed.
Part I of this report focused on the acquisition and presentation of transient PVT data sets that can be used to validate gas transfer models. Here in Part II we focus primarily on describing models and validating these models using the data sets. Our models are intended to describe the high speed transport of compressible gases in arbitrary arrangements of vessels, tubing, valving and flow branches. Our models fall into three categories: (1) network flow models in which flow paths are modeled as one-dimensional flow and vessels are modeled as single control volumes, (2) CFD (Computational Fluid Dynamics) models in which flow in and between vessels is modeled in three dimensions and (3) coupled network/CFD models in which vessels are modeled using CFD and flows between vessels are modeled using a network flow code. In our work we utilized NETFLOW as our network flow code and FUEGO for our CFD code. Since network flow models lack three-dimensional resolution, correlations for heat transfer and tube frictional pressure drop are required to resolve important physics not being captured by the model. Here we describe how vessel heat transfer correlations were improved using the data and present direct model-data comparisons for all tests documented in Part I. Our results show that our network flow models have been substantially improved. The CFD modeling presented here describes the complex nature of vessel heat transfer and for the first time demonstrates that flow and heat transfer in vessels can be modeled directly without the need for correlations.
Detailed herein are the results of a validation comparison. The experiment involved a 2 meter diameter liquid pool of Jet-A fuel in a 13 m/s crosswind. The scenario included a large cylindrical blocking object just down-stream of the fire. It also included seven smaller calorimeters and extensive instrumentation. The experiments were simulated with Fuego. The model included several conduction regions to model the response of the calorimeters, the floor, and the large cylindrical blocking object. A blind comparison was used to compare the simulation predictions with the experimental data. The more upstream data compared very well with the simulation predictions. The more downstream data did not compare very well with the simulation predictions. Further investigation suggests that features omitted from the original model contributed to the discrepancies. Observations are made with respect to the scenario that are aimed at helping an analyst approach a comparable problem in a way that may help improve the potential for quantitative accuracy.
This report documents activities performed in FY2006 under the ''Gas-Powder Two-Phase Flow Modeling Project'', ASC project AD2006-09. Sandia has a need to understand phenomena related to the transport of powders in systems. This report documents a modeling strategy inspired by powder transport experiments conducted at Sandia in 2002. A baseline gas-powder two-phase flow model, developed under a companion PEM project and implemented into the Sierra code FUEGO, is presented and discussed here. This report also documents a number of computational tests that were conducted to evaluate the accuracy and robustness of the new model. Although considerable progress was made in implementing the complex two-phase flow model, this project has identified two important areas that need further attention. These include the need to compute robust compressible flow solutions for Mach numbers exceeding 0.35 and the need to improve conservation of mass for the powder phase. Recommendations for future work in the area of gas-powder two-phase flow are provided.
An experimental investigation is made into the fluid mechanics and heat transfer of a circular cylinder immersed in a wall-bounded turbulent mixed-convection flow of water. The cylinder is oriented spanwise to the forced channel flow and within the thermal boundary layer of the heated lower wall. The flow channel is capped with a cold, near-adiabatic upper wall producing a fully turbulent gap Rayleigh number of 108. A low-speed crossflow is applied to advect the turbulent thermal plumes over the cylinder surface. We present spatially resolved cylinder-surface heat-flux data alongside 2-D PIV imaging of the streamwise and wall-normal velocity components for two flow conditions in the mixed-convection heat-transfer regime. The measured cylinder-wake flowfield reflects the complex coupling between the separated wake flow, the highly turbulent freestream and the buoyant wall and cylinder boundary layers. A method for measurement of spatially resolved surface heat fluxes based on the measured cylinder-surface temperature distribution and a well-posed two-dimensional solution to the conduction problem in the cylinder wall is presented. The resulting spatially resolved flux measurements show enhanced surface heat transfer, which results from the intense buoyancy generated free-stream turbulence and mixing in the cylinder wake. This work extends the literature on thermal convection with crossflow well into the turbulent regime and is, to our knowledge, the first investigation of surface heat-transfer to an object of engineering importance placed in this type of turbulent mixed-convection flowfield. The data are currently being utilized for validation of mixed-convection turbulence models at Sandia and comparisons between the computational and experimental results are presented.
An experimental investigation is made into the fluid mechanics and heat transfer of a circular cylinder immersed in a wall-bounded turbulent mixed-convection flow of water. The cylinder is oriented spanwise to the forced channel flow and within the thermal boundary layer of the heated lower wall. The flow channel is capped with a cold, near-adiabatic upper wall producing a fully turbulent gap Rayleigh number of 10{sup 8}. A low-speed crossflow is applied to advect the turbulent thermal plumes over the cylinder surface. We present spatially resolved cylinder-surface heat-flux data alongside 2-D PIV imaging of the streamwise and wall-normal velocity components for two flow conditions in the mixed-convection heat-transfer regime. The measured cylinder-wake flowfield reflects the complex coupling between the separated wake flow, the highly turbulent freestream and the buoyant wall and cylinder boundary layers. A method for measurement of spatially resolved surface heat fluxes based on the measured cylinder-surface temperature distribution and a well-posed two-dimensional solution to the conduction problem in the cylinder wall is presented. The resulting spatially resolved flux measurements show enhanced surface heat transfer, which results from the intense buoyancy generated free-stream turbulence and mixing in the cylinder wake. This work extends the literature on thermal convection with crossflow well into the turbulent regime and is, to our knowledge, the first investigation of surface heat-transfer to an object of engineering importance placed in this type of turbulent mixed-convection flowfield. The data are currently being utilized for validation of mixed convection turbulence models at Sandia and comparisons between the computational and experimental results are presented.
Two-dimensional processes of nickel electro-deposition in LIGA microfabrication were modeled using the finite-element method and a fully coupled implicit solution scheme via Newton's technique. Species concentrations, electrolyte potential, flow field, and positions of the moving deposition surfaces were computed by solving the species-mass, charge, and momentum conservation equations as well as pseudo-solid mesh-motion equations that employ an arbitrary Lagrangian-Eulerian (ALE) formulation. Coupling this ALE approach with repeated re-meshing and re-mapping makes it possible to track the entire transient deposition processes from start of deposition until the trenches are filled, thus enabling the computation of local current densities that influence the microstructure and functional/mechanical properties of the deposit.
This report documents the efforts and accomplishments of the LIGA electrodeposition modeling project which was headed by the ASCI Materials and Physics Modeling Program. A multi-dimensional framework based on GOMA was developed for modeling time-dependent diffusion and migration of multiple charged species in a dilute electrolyte solution with reduction electro-chemical reactions on moving deposition surfaces. By combining the species mass conservation equations with the electroneutrality constraint, a Poisson equation that explicitly describes the electrolyte potential was derived. The set of coupled, nonlinear equations governing species transport, electric potential, velocity, hydrodynamic pressure, and mesh motion were solved in GOMA, using the finite-element method and a fully-coupled implicit solution scheme via Newton's method. By treating the finite-element mesh as a pseudo solid with an arbitrary Lagrangian-Eulerian formulation and by repeatedly performing re-meshing with CUBIT and re-mapping with MAPVAR, the moving deposition surfaces were tracked explicitly from start of deposition until the trenches were filled with metal, thus enabling the computation of local current densities that potentially influence the microstructure and frictional/mechanical properties of the deposit. The multi-dimensional, multi-species, transient computational framework was demonstrated in case studies of two-dimensional nickel electrodeposition in single and multiple trenches, without and with bath stirring or forced flow. Effects of buoyancy-induced convection on deposition were also investigated. To further illustrate its utility, the framework was employed to simulate deposition in microscreen-based LIGA molds. Lastly, future needs for modeling LIGA electrodeposition are discussed.
A phenomenological model was developed for multicomponent transport of charged species with simultaneous electrochemical reactions in concentrated solutions, and was applied to model processes in a thermal battery cell. A new general framework was formulated and implemented in GOMA (a multidimensional, multiphysics, finite-element computer code developed and being enhanced at Sandia) for modeling multidimensional, multicomponent transport of neutral and charged species in concentrated solutions. The new framework utilizes the Stefan-Maxwell equations that describe multicomponent diffusion of interacting species using composition-insensitive binary diffusion coefficients. The new GOMA capability for modeling multicomponent transport of neutral species was verified and validated using the model problem of ternary gaseous diffusion in a Stefan tube. The new GOMA-based thermal battery computer model was verified using an idealized battery cell in which concentration gradients are absent; the full model was verified by comparing with that of Bernardi and Newman (1987) and validated using limited thermal battery discharge-performance data from the open literature (Dunning 1981) and from Sandia (Guidotti 1996). Moreover, a new Liquid Chemkin Software Package was developed, which allows the user to handle manly aspects of liquid-phase kinetics, thermodynamics, and transport (particularly in terms of computing properties). Lastly, a Lattice-Boltzmann-based capability was developed for modeling pore- or micro-scale phenomena involving convection, diffusion, and simplified chemistry; this capability was demonstrated by modeling phenomena in the cathode region of a thermal battery cell.