Clifford K. Ho

Gas transport in porous media

Table of Contents 1. Introduction C.K. Ho and S.W. Webb Part 1: Processes and Models 2. Gas Transport Mechanisms S.W. Webb 3. Vapor Transport Processes C.K. Ho 4. Solid/Gas Partitioning S.K. Ong 5. Two-Phase Gas Transport S.W. Webb 6. Conservation Equations S. Whitaker 7. Gas-Phase Dispersion in Porous Media M.S. Costanza-Robinson and M.L. Brusseau 8. Gas Injection and Fingering in Porous Media M. Sahimi, M. Reza Rasaei, and M. Haghighi 9. Unstable and Fingering Gas Flow in Fractures P. Persoff 10. Natural Convection Gas Transport in Porous Media K. Khanafer and K. Vafai 11. Scaling Issues in Porous and Fractured Media V.C. Tidwell 12. Numerical Codes for Continuum Modeling of Gas Transport in Porous Media K. Pruess 13. Lattice Boltzmann Method for Calculating Fluid Flow and Dispersion in Porous and Fractured Media H.W. Stockman Part 2: Measurement and Monitoring 14. Experimental Determination of Transport Parameters O. Solcova and P. Schneider 15. Air Permeability Measurements in Porous Media V.C. Tidwell 16. Analyzing Barometric Pumping to Characterize Subsurface Permeability J. Rossabi 17. Subsurface Flow Measurements J. Rossabi 18. Measurement of Vapor Concentrations C.K. Ho, M. Kelly and M.T. Itamura 19. In-Situ Measurement of InducedContaminant Flux A. Tartre Part 3: Applications 20. Radon Transport B.W. Arnold 21. Gas Transport Issues in Landmine Detection J. Phelan 22. Environmental Remediation of Volatile Organic Compounds R. Falta 23. Yucca Mountain Heater Tests Y.Y.W. Chang 24. Impact of Gas Generation on the Performance of the Waste Isolation Pilot Plant P. Vaughn 25. Oil and Gas Industry Applications of Gas Flow in Porous Media D.J. Borns 26. Geological Carbon Sequestration: CO2 Transport in Depleted Gas Reservoirs C.M. Oldenburg 27. Industrial Gas Transport Processes Involving Heat Transfer O.A. Plumb Index

Review of Chemical Sensors for In-Situ Monitoring of Volatile Contaminants

Sandia National Laboratories has sponsored an LDRD (Laboratory Directed Research and Development) project to investigate and develop micro-chemical sensors for in-situ monitoring of subsurface contaminants. As part of this project, a literature search has been conducted to survey available technologies and identify the most promising methods for sensing and monitoring subsurface contaminants of interest. Specific sensor technologies are categorized into several broad groups, and these groups are then evaluated for use in subsurface, long-term applications. This report introduces the background and specific scope of the problem being addressed by this LDRD project, and it provides a summary of the advantages and disadvantages of each sensor technology identified from the literature search.

Development and Evaluation of a Prototype Solid Particle Receiver: On-Sun Testing and Model Validation

A prototype direct absorption central receiver, called the solid particle receiver (SPR), was built and evaluated on-sun at power levels up to 2.5 MW th at Sandia National Laboratories in Albuquerque, NM. The SPR consists of a 6 m tall cavity through which spherical sintered bauxite particles are dropped and directly heated with concentrated solar energy. In principle, the particles can be efficiently heated to a temperature in excess of 900°C, well beyond the stability limit of existing nitrate salt formulations. The heated particles may then be stored in a way analogous to nitrate salt systems, enabling a dispatchable thermal input to power or fuel production cycles. The focus of this current effort was to provide an experimental basis for the validation of computational models that have been created to support improved designs and further development of the solid particle receiver. In this paper we present information on the design and construction of the solid particle receiver and discuss the development of a computational fluid dynamics model of the prototype. We also present experimental data and model comparisons for on-sun testing of the receiver over a range of input power levels from 1.58―2.51 MW th . Model validation is performed using a number of metrics including particle velocity, exit temperature, and receiver efficiency. In most cases, the difference between the model predictions and data is less than 10%.

Characterization of Pyromark 2500 Paint for High-Temperature Solar Receivers

Pyromark 2500 is a silicone-based high-temperature paint that has been used on central receivers to increase solar absorptance. The radiative properties, aging, and selective absorber efficiency of Pyromark 2500 are presented in this paper for use as a baseline for comparison to high-temperature solar selective absorber coatings currently being developed. The solar absorptance ranged from ∼0.97 at near-normal incidence angles to ∼0.8 at glancing (80°) incidence angles, and the thermal emittance ranged from ∼0.8 at 100 °C to ∼0.9 at 1000 °C. After thermal aging at temperatures of ∼750 °C or higher, the solar absorptance decreased by several percentage points within a few days. It was postulated that the substrate may have contributed to a change in the crystal structure of the original coating at elevated temperatures.

Performance assessment model development and analysis of radionuclide transport in the unsaturated zone, Yucca Mountain, Nevada

This paper describes the development and use of a particle-tracking model to perform radionuclide-transport simulations in the unsaturated zone at Yucca Mountain, Nevada. The goal of the effort was to produce a computational model that can be coupled to the projects calibrated 3D site-scale flow model so that the results of that effort could be incorporated directly into the Total System Performance Assessment (TSPA) analyses. The transport model simulates multiple species (typically 20 or more) with complex time-varying and spatially varying releases from the potential repository. Water-table rise, climate-change scenarios, and decay chains are additional features of the model. A cell-based particle-tracking method was employed that includes a dual-permeability formulation, advection, longitudinal dispersion, matrix diffusion, and colloid-facilitated transport. This paper examines the transport behavior of several key radionuclides through the unsaturated zone using the calibrated 3D unsaturated flow fields. Computational results illustrate the relative importance of fracture flow, matrix diffusion, and lateral diversion on the distribution of travel times from the simulated repository to the water table for various climatic conditions. Results also indicate rapid transport through fractures for a portion of the released mass. Further refinement of the model will address several issues, including conservatism in the transport model, the assignment of parameters in the flow and transport models, and the underlying assumptions used to support the conceptual models of flow and transport in the unsaturated zone at Yucca Mountain.

Software and codes for analysis of concentrating solar power technologies.

This report presents a review and evaluation of software and codes that have been used to support Sandia National Laboratories concentrating solar power (CSP) program. Additional software packages developed by other institutions and companies that can potentially improve Sandias analysis capabilities in the CSP program are also evaluated. The software and codes are grouped according to specific CSP technologies: power tower systems, linear concentrator systems, and dish/engine systems. A description of each code is presented with regard to each specific CSP technology, along with details regarding availability, maintenance, and references. A summary of all the codes is then presented with recommendations regarding the use and retention of the codes. A description of probabilistic methods for uncertainty and sensitivity analyses of concentrating solar power technologies is also provided.

Capillary barrier performance in heterogeneous porous media

The effects of heterogeneities on the performance of capillary barriers is investigated by numerically simulating three systems comprised of a fine soil layer overlying a coarse gravel layer with (1) homogeneous, (2) layered heterogeneous, and (3) random heterogeneous property fields. The amount of lateral diversion above the coarse layer under steady state infiltration conditions is compared among the simulations. Results indicate that the performance of capillary barriers can be significantly influenced by the spatial variability of hydraulic properties. In the layered heterogeneous systems, realizations with highly stratified regions within the fine layer performed best and resulted in localized capillary barriers that delayed breakthrough into the coarse layer. In contrast, realizations of the random heterogeneous system performed worst because of channeled flow that produced numerous localized regions of breakthrough into the coarse layer. Results of the homogeneous model were comparable to the mean results of the layered heterogeneous realizations, but homogeneous results underpredicted the frequency and amount of breakthrough for all realizations of the random heterogeneous system. These results indicate that homogeneous models can be used to estimate the average behavior of layered heterogeneous systems with reasonable accuracy. In addition, engineered capillary barriers may be improved through emplacement and packing methods that induce highly stratified features within the fine layer of a capillary barrier system.

Characterization of the ability of polymeric chemiresistor arrays to quantitate trichloroethylene using partial least squares (PLS): effects of experimental design, humidity, and temperature

Polymeric chemiresistors are a class of chemical sensor that have promise for being practical in situ sensors of volatile organic compounds (VOC) in various environmental monitoring applications. However, these devices may undergo changes in response due to changes in temperature or humidity that must be taken into consideration when developing calibration models. The devices can also display significant hysteresis effects after exposure to VOC vapor. These effects are complicated by the fact that each sensor within an array is coated with a different polymer, each with a different response to temperature, humidity, and VOC exposure. It is shown that partial least squares (PLS) can provide quantitative predictions of trichloroethylene (TCE) using an array of chemiresistors through appropriate experimental design. Effects of humidity and temperature on the response of chemiresistor arrays and predictive ability of PLS are also discussed. It is also shown that to truly assess the quality of a calibration model it must be first tested through prediction of a test set at a time separated from the acquisition of the calibration data. Using only leave-one-out cross-validation results from the calibration can lead to unwarranted confidence in a model that is not stable with respect to changing environmental conditions and device drift.

Incorporating Uncertainty into Probabilistic Performance Models of Concentrating Solar Power Plants

A method for applying probabilistic models to concentrating solar-thermal power plants is described in this paper. The benefits of using probabilistic models include quantification of uncertainties inherent in the system and characterization of their impact on system performance and economics. Sensitivity studies using stepwise regression analysis can identify and rank the most important parameters and processes as a means to prioritize future research and activities. The probabilistic method begins with the identification of uncertain variables and the assignment of appropriate distributions for those variables. Those parameters are then sampled using a stratified method (Latin hypercube sampling) to ensure complete and representative sampling from each distribution. Models of performance, reliability, and cost are then simulated multiple times using the sampled set of parameters. The results yield a cumulative distribution function that can be used to quantify the probability of exceeding (or being less than) a particular value. Two examples, a simple cost model and a more detailed performance model of a hypothetical 100-MW e power tower, are provided to illustrate the methods.

Improved High Temperature Solar Absorbers for Use in Concentrating Solar Power Central Receiver Applications

Concentrating solar power (CSP) systems use solar absorbers to convert the heat from sunlight to electric power. Increased operating temperatures are necessary to lower the cost of solar-generated electricity by improving efficiencies and reducing thermal energy storage costs. Durable new materials are needed to cope with operating temperatures >600 C. The current coating technology (Pyromark High Temperature paint) has a solar absorptance in excess of 0.95 but a thermal emittance greater than 0.8, which results in large thermal losses at high temperatures. In addition, because solar receivers operate in air, these coatings have long term stability issues that add to the operating costs of CSP facilities. Ideal absorbers must have high solar absorptance (>0.95) and low thermal emittance (<0.05) in the IR region, be stable in air, and be low-cost and readily manufacturable. We propose to utilize solution-based synthesis techniques to prepare intrinsic absorbers for use in central receiver applications.