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Investigation of Droplet Penetrations Through Complex Openings of Compartments.


pdf icon Investigation of Droplet Penetrations Through Complex Openings of Compartments. (5560 K)
Yao, S. C.; Hung, L. S.

NIST GCR 98-759; 78 p. November 1998.

Sponsor:

National Institute of Standards and Technology, Gaithersburg, MD

Available from:

National Technical Information Service
Order number: PB99-105132

Keywords:

compartments; droplets; penetration; computational fluid dynamics; fire suppression; water mist

Abstract:

The use of fine water mist as one of the possible Halon 1301 replacements has been identified for certain fire suppression situations in equipment compartments. One current research effort is to apply the water mist sprays to suppress the fire occurring in hidden location behind obstructions or inside the equipment compartments. Since the mist usually contains a spectrum of drop sizes, the smaller mist droplets may follow the gas streams closely and penetrate directly through the slots of the obstructions while the larger droplets may be intercepted or impacted by the obstructions. When the mist droplets are approaching the structures, the overall penetrating process of the mist flow through the obstruction depends strongly on the transport of the mist droplets in the gas streams, the ability of the droplets flowing through the obstruction, and the behavior of droplets subsequent to the impaction. The present research presents an integrated approach to model the penetration of water mist through the obstructions for fire suppression applications. Firstly, numerical investigations employing the two-phase Navier-Stokes equations are achieved using computational fluid dynamics (CFD) to evaluate the overall transport of droplets in the vicinity of the openings, which include rectangular strips and a 3-D screen object. In particular, the motions of the droplets coupled with the gas flow field around the objects are analyzed. The deposition of droplets on the objects and their penetration through the spacing of the objects are also formulated. Then, experimental investigations are performed to address the actual impacting phenomena of droplets on objects. Droplet generators are designed to generate droplets in a variety of operating conditions. Structures such as cylindrical wires and mesh screens are examined in the impaction experiments. Images of the impacting phenomena are analyzed through digital image processing. Non-dimensional regime maps and the correlations of the impaction outcome are also developed. The conclusions from both the numerical and experimental investigations are integrated to provide an overall understanding to the complex interaction phenomena and to establish a procedure for predicting the outcome of similar processes.