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CFD analysis of LLNL downdraft table

Description: This study examines the airflow and contaminant transport in an existing room (89 inch x 77 inch x 98 inch) that houses a downdraft table at LLNL. The facility was designed and built in the 1960's and is currently being considered for redesign. One objective of the redesign is to reduce airflow while maintaining or improving user safety. Because this facility has been used for many years to handle radioactive material it is impractical to conduct extensive experimental tests in it. Therefore, we have performed a Computational Fluid Dynamic (CFD) analysis of the facility. The study examines the current operational condition and some other cases with reduced airflow. Reducing airflow will lead to savings in operating costs (lower fan power consumption), and possible improvements in containment from reduced turbulence. In addition, we examine three design (geometry) changes. These are: (1) increasing the area of the HVAC inlet on the ceiling, (2) adding a 15{sup o} angled ceiling inlet and (3) increasing the area of the slot in the doorway. Of these three geometry modifications, only the larger doorway slot leads to improved predicted containment.
Date: October 1, 2003
Creator: Finlayson, Elizabeth U.; Jayaraman, Buvana; Kristoffersen, Astrid R. & Gadgil, Ashok J.
Partner: UNT Libraries Government Documents Department

Tracer Gas Transport under Mixed Convection Conditions in anExperimental Atrium: Comparison Between Experiments and CFDPredictions

Description: We compare computational fluid dynamics (CFD) predictions using a steady-state Reynolds Averaged Navier-Stokes (RANS) model with experimental data on airflow and pollutant dispersion under mixed-convection conditions in a 7 x 9 x 11m high experimental facility. The Rayleigh number, based on height, was O(10{sup 11}) and the atrium was mechanically ventilated. We released tracer gas in the atrium and measured the spatial distribution of concentrations; we then modeled the experiment using four different levels of modeling detail. The four computational models differ in the choice of temperature boundary conditions and the choice of turbulence model. Predictions from a low-Reynolds-number k-{var_epsilon} model with detailed boundary conditions agreed well with the data using three different model-measurement comparison metrics. Results from the same model with a single temperature prescribed for each wall also agreed well with the data. Predictions of a standard k-{var_epsilon} model were about the same as those of an isothermal model; neither performed well. Implications of the results for practical applications are discussed.
Date: January 1, 2006
Creator: Jayaraman, Buvaneswari; Finlayson, Elizabeth U.; Sohn, MichaelD.; Thatcher, Tracy L.; Price, Phillip N.; Wood, Emily E. et al.
Partner: UNT Libraries Government Documents Department

THERM 2.1 NFRC simulation manual

Description: This document, the ''THERM 2.1 NFRC Simulation Manual'', discusses how to use THERM to model products for NFRC certified simulations and assumes that the user is already familiar with the THERM program. In order to learn how to use THERM, it is necessary to become familiar with the material in the THERM User's Manual. In general, this manual references the THERM User's Manual rather than repeating the information. If there is a conflict between the THERM User's Manual and the THERM 2.1 NFRC Simulation Manual, the THERM 2.1 NFRC Simulation Manual takes precedence. The CD that is included with the manual includes all sample files that are referenced in the manual as well as some additional samples.
Date: July 1, 2000
Creator: Mitchell, Robin; Kohler, Christian; Arasteh, Dariush; Finlayson, Elizabeth; Huizenga, Charlie; Curcija, Dragan et al.
Partner: UNT Libraries Government Documents Department

Pollutant dispersion in a large indoor space: Part 2 -Computational Fluid Dynamics (CFD) predictions and comparison with ascale model experiment for isothermal flow

Description: This paper reports on an investigation of the adequacy of Computational fluid dynamics (CFD), using a standard Reynolds Averaged Navier Stokes (RANS) model, for predicting dispersion of neutrally buoyant gas in a large indoor space. We used CFD to predict pollutant (dye) concentration profiles in a water filled scale model of an atrium with a continuous pollutant source. Predictions from the RANS formulation are comparable to an ensemble average of independent identical experiments. Model results were compared to pollutant concentration data in a horizontal plane from experiments in a scale model atrium. Predictions were made for steady-state (fully developed) and transient (developing) pollutant concentrations. Agreement between CFD predictions and ensemble averaged experimental measurements is quantified using the ratios of CFD-predicted and experimentally measured dye concentration at a large number of points in the measurement plane. Agreement is considered good if these ratios fall between 0.5 and 2.0 at all points in the plane. The standard k-epsilon two equation turbulence model obtains this level of agreement and predicts pollutant arrival time to the measurement plane within a few seconds. These results suggest that this modeling approach is adequate for predicting isothermal pollutant transport in a large room with simple geometry.
Date: October 1, 2002
Creator: Finlayson, Elizabeth U.; Gadgil, Ashok J.; Thatcher, Tracy L. & Sextro, Richard G.
Partner: UNT Libraries Government Documents Department

Infiltration heat recovery in building walls: Computational fluid dynamics investigations results

Description: Conventional calculations of heating (and cooling) loads for buildings assume that conduction heat loss (or gain) through walls is independent of air infiltration heat loss (or gain). During passage through the building envelope, infiltrating air substantially exchanges heat wall insulation leading to partial recovery of heat conducted through the wall. The Infiltration Heat Recovery (IHR) factor was introduced to quantify the heat recovery and correct the conventional calculations. In this study, Computational Fluid Dynamics was used to calculate infiltration heat recovery under a range of idealized conditions, specifically to understand factors that influence it, and assess its significance in building heat load calculations. This study shows for the first time the important effect of the external boundary layers on conduction and infiltration heat loads. Results show (under the idealized conditions studied here) that (1) the interior details of the wall encountered in the leakage pa th (i.e., insulated or empty walls) do not greatly influence the IHR, the overall relative location of the cracks (i.e., inlet and outlet locations on the wall) has the largest influence on the IHR magnitude, (2) external boundary layers on the walls substantially contribute to IHR and (3) the relative error in heat load calculations resulting from the use of the conventional calculational method (i.e., ignoring IHR) is between 3 percent and 13 percent for infiltrating flows typically found in residential buildings.
Date: August 5, 2002
Creator: Abadie, Marc O.; Finlayson, Elizabeth U. & Gadgil, Ashok J.
Partner: UNT Libraries Government Documents Department

Protecting Buildings From a Biological or Chemical Attack: Actions to Take Before or During a Release

Description: This report presents advice on how to operate a building to reduce casualties from a biological or chemical attack, as well as potential changes to the building (e.g. the design of the ventilation system) that could make it more secure. It also documents the assumptions and reasoning behind the advice. The particular circumstances of any attack, such as the ventilation system design, building occupancy, agent type, source strength and location, and so on, may differ from the assumptions made here, in which case actions other than our recommendations may be required; we hope that by understanding the rationale behind the advice, building operators can modify it as required for their circumstances. The advice was prepared by members of the Airflow and Pollutant Transport Group, which is part of the Indoor Environment Department at the Lawrence Berkeley National Laboratory. The group's expertise in this area includes: tracer-gas measurements of airflows in buildings (Sextro, Thatcher); design and operation of commercial building ventilation systems (Delp); modeling and analysis of airflow and tracer gas transport in large indoor spaces (Finlayson, Gadgil, Price); modeling of gas releases in multi-zone buildings (Sohn, Lorenzetti, Finlayson, Sextro); and occupational health and safety experience related to building design and operation (Sextro, Delp). This report is concerned only with building design and operation; it is not a how-to manual for emergency response. Many important emergency response topics are not covered here, including crowd control, medical treatment, evidence gathering, decontamination methods, and rescue gear.
Date: January 29, 2003
Creator: Price, Phillip N.; Sohn, Michael D.; Gadgil, Ashok J.; Delp, William W.; Lorenzetti, David M.; Finlayson, Elizabeth U. et al.
Partner: UNT Libraries Government Documents Department