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Publication Citation: Minimum Mass Flux Requirements to Suppress Burning Surfaces With Water Sprays (NISTIR 5795)

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Author(s): Jiann C. Yang; C I. Boyer; William L. Grosshandler;
Title: Minimum Mass Flux Requirements to Suppress Burning Surfaces With Water Sprays (NISTIR 5795)
Published: April 01, 1996
Abstract: Experimental measurements of extinguishment times of burning solid fuels using water were conducted using a prototype micronozzle array and a piezoelectric droplet generator. Solid fuels considered included solid white pine, polymethylmethacrylate, and polystyrene foam. External heat flux was applied to the sample surface during burning. The effects of drop size, sample orientation with respect to the nozzle, and nozzle distance from the sample surface on extinguishment time were examined. The extinguishment time was found to decrease with increasing water flow rate. For a given water flow rate, significant reduction in extinguishment time was observed when smaller droplets were used. At low water flow rates, the extinguishment time decreased when the nozzle was positioned further from the sample surface. At high flow rates, the extinguishment was independent of the nozzle-to-sample distance. When the droplet stream was 45DG relative to the sample, the extinguishment time was not affected by the nozzle-to-sample distance. The other component of the project was to evaluate a commercial low pressure, high momentum pendant water mist nozzle using an optical array probe droplet analyzer. The pendant nozzle used in this study is currently being evaluated by listing organizations for fire suppression in residential and light hazard occupancies. The objective of this study was to determine drop size and velocity distributions at various locations in the spray. Experiments were conducted at delivery pressures of 621 kPa + 14 kPa (90.0 psi + 2.0 psi) and 448 kPa + 14 kPa (65.0 psi + 2.0 psi). The droplet diameters from the experiments were found to range from less than 36 mm to 1230 mm for the experiments conducted at 448 kPa + 14 kPa (65.0 psi + 2.0 psi,) and to range from less than 36 mm to 1155 mm for the experiments conducted at 621 kPa + 14 kPa (90.0 psi + 2.0 psi). The velocities of the water droplets were calculated based on the time required for each individual drop to pass through the probe image field. The range of droplet velocities was found to be approximately 0.19 m/s to 1.58 m/s (0.62 ft/s to 5.18 ft/s) from the experiments conducted at 448 kPa + 14 kPa (65.0 psi + 2.0 psi). For the measurements taken at 621 kPa + 14 kPa (90.0 psi + 2.0 psi), the droplet velocities ranged from approximately 0.25 m/s to 1.9 m/s (0.82 ft/s to 6.23 ft/s).
Citation: NIST Interagency/Internal Report (NISTIR) - 5795
Pages: 50 pp.
Keywords: drop sizes; extinguishment times; fire suppression; mist; sprays; polymethyl methacrylate; polystyrene foams; wood
Research Areas: Building and Fire Research
PDF version: PDF Document Click here to retrieve PDF version of paper (2MB)