Thomas K. Blanchat

Experimental study of the flow field in and around a one meter diameter methane fire

Abstract Simultaneous temporally and spatially resolved, 2-D velocity fields are obtained using Particle Image Velocimetry (PIV) in a one-meter diameter methane fire. The flow rate of methane is 0.066 kg/m2-s, comparable to fuel burning rates in a large JP8 pool fire. Raw PIV images are recorded with 35 mm cinematography at 200 images/s. They are digitized and post-processed to obtain velocity data for a region ∼0.8 m high by 1 m wide centered on the centerline of the flame and extending from just above the surface of the burner to include the fuel core, near-field combusting zones, and surrounding air. The data cover 11 puff cycles of the fire. Instantaneous, phase-, and time-averaged 2-D velocity plots (103 × 82 vectors) are obtained for each of 1331 time-planes (121 time-planes per puff cycle) spaced 5 ms apart. Each vector represents a statistical estimate of the velocity in 2.1 cm by 2.1 cm by 0.8 cm volumes, which are overlapped by 50% in the vector plots. Time-averaged turbulent statistics ( u′ 2 , v′ 2 , & u′v′ ) are also presented. Boundary conditions have been carefully measured and the results are intended for validation of numerical simulations of the fire behavior. The results clearly show the dominant effect of puffing, measured at 1.65 cycles/s for this fire, on the temporal and spatial development of the velocity field.

Sandia Heat Flux Gauge Thermal Response and Uncertainty Models

The San&a Heat Flux Gauge (HFG) was developed as a rugged, cost-effective technique for performing steady state heat flux measurements in the pool fire environment. The technique involves reducing the time-temperature history of a thin metal plate to an incident heat flux via a dynamic thermal model, even though the gauge is intended for use at steady state. In this report, the construction of the gauge is reviewed. The thermal model that describes the dynamic response of the gauge to the f~e environment is then advanced and it is shown how the heat flux is determined from the temperature readings. This response model is based on first principles, with no empirically adjusted constants. A validation experiment is presented where the gauge was exposed to a step input of radiant heat flux. Comparison of the incident flux, determined from the thermal response model, with the known flux input shows that the gauge exhibits an noticeable time lag. The uncertainty of the measurement is analyzed, and an uncertainty model is put forth using the data obtained from “the experiment. The uncertainty model contains contributions from seventeen separate sources loosely categorized as being either from uncontrolled variability, missing physics, or simplifying assumptions. As part of the missing physics, an empirical constant is found that compensates for the gauge time lag. Because this compensation is incorporated into the uncertainty model instead of the response model, this information can be used to advantage in analyzing pool fire data by causing large uncertainties in non-steady state situations. A short general discussion on the uncertainty of the instrument is presented along with some suggested design changes that would facilitate the determination and reduction of the measurement uncertainty.

Well-characterized open pool experiment data and analysis for model validation and development.

Four Well-Characterized Open Pool fires were conducted by Fire Science and Technology Department. The focus of the Well-Characterized Open Pool fire series was to provide environmental information for open pool fires on a physics first principal basis. The experiments measured the burning rate of liquid fuel in an open pool and the resultant heat flux to a weapon-sized object and the surrounding environment with well-characterized boundary and initial conditions. Results presented in this report include a general description of test observation (pre- and post-test), wind measurements, fire plume topology, average fuel recession and heat release rates, and incident heat flux to the pool and to the calorimeters. As expected, results of the experiments show a strong correlation between wind conditions, fuel vaporization (mass loss) rate, and incident heat flux to the fuel and ground surface and calorimeters. Numerical fire simulations using both temporally- and spatially-dependant wind boundary conditions were performed using the Vulcan fire code. Comparisons of data to simulation predictions showed similar trends; however, simulation-predicted incident heat fluxes were lower than measured.

Analysis of hydrogen depletion using a scaled passive autocatalytic recombiner

Hydrogen depletion tests of a scaled passive autocatalytic recombine (pAR) were performed in the Surtsey test vessel at Sandia National Laboratories (SNL). The experiments were used to determine the hydrogen depletion rate of a PAR in the presence of steam and also to evaluate the effect of scale (number of cartridges) on the PAR performance at both low and high hydrogen concentrations.

Hydrocarbon characterization experiments in fully turbulent fires : results and data analysis.

As the capabilities of numerical simulations increase, decision makers are increasingly relying upon simulations rather than experiments to assess risks across a wide variety of accident scenarios including fires. There are still, however, many aspects of fires that are either not well understood or are difficult to treat from first principles due to the computational expense. For a simulation to be truly predictive and to provide decision makers with information which can be reliably used for risk assessment the remaining physical processes must be studied and suitable models developed for the effects of the physics. The model for the fuel evaporation rate in a liquid fuel pool fire is significant because in well-ventilated fires the evaporation rate largely controls the total heat release rate from the fire. This report describes a set of fuel regression rates experiments to provide data for the development and validation of models. The experiments were performed with fires in the fully turbulent scale range (> 1 m diameter) and with a number of hydrocarbon fuels ranging from lightly sooting to heavily sooting. The importance of spectral absorption in the liquid fuels and the vapor dome above the pool was investigated and the total heat flux to the pool surface was measured. The importance of convection within the liquid fuel was assessed by restricting large scale liquid motion in some tests. These data sets provide a sound, experimentally proven basis for assessing how much of the liquid fuel needs to be modeled to enable a predictive simulation of a fuel fire given the couplings between evaporation of fuel from the pool and the heat release from the fire which drives the evaporation.

Experiments and Modeling of Large-scale Benchmark Enclosure Fire Suppression:

This article presents a series of experiments on benchmark fire suppression. The experiments were performed in a controlled environment, utilizing a cylindrical object or calorimeter centered above a 2 m diameter pan filled with kerosene-based hydrocarbon fuel, JP8. The experimental setup and procedure for gathering data on water suppression performance are presented. The characteristics of the nozzles used in the experiments are presented as well. The experimental results provide the boundary condition and temporal data necessary for validation of the fire suppression models used. The article also includes simulation results on the fire suppression experimental tests. The suppression simulations were carried out using a numerical model based on a Temporally Filtered Navier-Stokes (TFNS) formulation coupled with a Lagrangian model for droplets, which includes detailed descriptions of the interaction between the water droplets and the fire plume. The results from both experiments and simulations suggest that the criterion for complete suppression depends on a combination of factors including the mass flow rate (or nozzle diameter), nozzle operating pressure, and calorimeter presence. A critical regime which distinguished the regions of suppression and no-suppression in the domain of the mass flow rate versus operating pressure is found.

A validation quality heat flux dataset for large pool fires.

A series of experiments has been performed in the Sandia National Laboratories FLAME facility with a 2-meter diameter JP-8 fuel pool fire. Sandia heat flux gages were employed to measure the incident flux at 8 locations outside the flame. Experiments were repeated to generate sufficient data for accurate confidence interval analysis. Additional sources of error are quantified and presented together with the data. The goal of this paper is to present these results in a way that is useful for validation of computer models that are capable of predicting heat flux from large fires. We anticipate using these data for comparison to validate models within the Advanced Simulation and Computing (ASC, formerly ASCI) codes FUEGO and SYRINX that predict fire dynamics and radiative transport through participating media. We present preliminary comparisons between existing models and experimental results.Copyright

Testing a Passive Autocatalytic Recombiner in the Surtsey Facility

Performance tests of a scaled passive autocatalytic recombiner (PAR) were performed in the Surtsey test vessel at Sandia National Laboratories. Measured hydrogen depletion rate data were obtained and compared with previous work. Depletion rate is most likely proportional to PAR scale. PAR performance in steamy environments (with and without hydrophobic coating) was investigated. The tests determined that the PAR startup delay times decrease with increasing hydrogen concentrations in steamy environments. Tests with placement of the PAR near a wall (as opposed to a center location) yielded reduced depletion rates. Tests at low oxygen concentrations also showed a reduced recombination rate. The PAR repeatedly ignited hydrogen at ~6 mol% concentration with a catalyst temperature near 940 K. Velocity data at the PAR exhaust were used to calculate the volumetric flow rate through the PAR as a function of the vessel hydrogen concentration.

Experiments to investigate DCH phenomena with large-scale models of the Zion and Surry nuclear power plants

The Surtsey Test Facility and the Containment Technology Test Facility (CTTF) at Sandia National Laboratories (SNL) have been used to perform scaled experiments for the Nuclear Regulatory Commission (NRC) that simulate high-pressure melt ejection (HPME) accidents in a nuclear power plant (NPP). These experiments are designed to investigate the effects of direct containment heating (DCH) phenomena on the containment load. High-temperature, chemically reactive alumino (thermitic) melt is ejected by high-pressure steam into a scale model of either the Zion or Surry NPP. Integral effects tests under prototypic conditions have been performed to investigate the effects of dispersal of molten core materials on DCH loads, and to study the effects of Westinghouse plant configurations on DCH loads. In Westinghouse plants, there is (1) an intermediate compartment that is large compared with the reactor cavity but small compared with the main containment volume, and (2) no significant line-of-sight pathway for debris transport from the cavity to the main containment volume. Containment compartmentalization is the dominant mitigating feature for Zion, Surry, and most other pressurized water reactors. Experimental results will be used to further assess the applicability of existing DCH models to Westinghouse plants on DCH loads.

Large-Scale Open Pool Experimental Data and Analysis for Fire Model Validation and Development.

Four large-scale open pool fire experiments were performed with well-characterized boundary and initial conditions. Results presented include a general description of test observations, wind measurements, fire plume topology, fuel recession and heat release rates, incident heat flux to the pool, surrounding terrain, and calorimeters. All initial and boundary condition data required as necessary inputs to computation models are also presented. The large physical scale, the experimental design, the use of independent measurement techniques, and the attention to data quality provide a unique dataset to support numerical fire model validation.