Atomization and Dispersion Measurements in Fire Sprinkler Sprays

Abstract

Water sprays are commonly used in fire suppression applications for cooling the fire environment. This cooling is achieved through the evaporation of droplets (dispersed in the fire gases) and through the wetting of surfaces (from hot or burning materials), inhibiting both the growth and spread of the fire. The suppression performance of these sprays is determined by their ability to penetrate the fire (i.e., the induced flow) to reach burning surfaces below, while dispersing water throughout the hot environment. Spray penetration and dispersion are governed by the initial drop size and velocity characteristics of the spray, which depend on the injection conditions and nozzle configuration. In many fire suppression devices, such as sprinklers, a jet is injected onto a deflector to generate the water spray. Although there are many variations on this basic concept, most sprinklers include a central boss surrounded by a deflector having both tines and spaces. To study the essential physics of the atomization process, discharge characteristics from simplified nozzles were measured. These measurements were compared with those from a more realistic sprinkler configuration. Flow visualization experiments revealed that the canonical impinging jet configuration produces a radially expanding sheet. While similar atomization mechanisms were observed, the realistic sprinkler configuration produces a three-dimensional sheet with two distinct flow streams generated by the tines and spaces of the nozzle. Comprehensive experiments were conducted to describe atomization (e.g., sheet breakup locations and initial drop sizes) and dispersion (e.g., volume density and local drop size profiles) in these sprays.

Unraveling Fire Suppression Sprays

“…These analytical results compared favorably to some limited experimental data obtained by using high speed flash (i.e., short exposure time) photography. Since these break-up modes have been observed in sprinkler spray generation [25,26,28] for a wide range of operating conditions, Dombrowski and Hooper's analysis among others provides insight for sprinkler sprays, despite differences in nozzle configuration. Correspondingly, Huang utilized a high-speed motion photographic technique to study the break-up mechanisms of liquid sheets formed by the impingement of two co-axial jets [29].…”

“…Most recently, Blum [21], Do, [22], and Ren [23] have performed a series of spray characterization studies on laboratory and actual fire sprinkler configurations which are summarized in the current paper. These studies have evaluated the topology of the initial spray revealing different spray characteristics in the vicinity of the tines and slots [24][25][26]. These initial spray features were characterized and analyzed with unprecedented detail.…”

“…We −1 over a relatively narrow and small We (1000 to 2000). Unfortunately, little data is available for the high We regime relevant to fire sprinkler operating conditions (3 × 10 3 to 2 × 10 5 ) [25]. A series of detailed experiments have been performed at the University of Maryland to quantify the discharge characteristics from laboratory configurations (i.e.…”

“…A series of detailed experiments have been performed at the University of Maryland to quantify the discharge characteristics from laboratory configurations (i.e. a solid deflectors similar to Clanet and Villermaux) and actual fire sprinkler configurations in this high We regime [24][25][26].…”

Comparison of PIV Experiment and Numerical Simulation on the Velocity Distribution of Intermediate Pressure Jets with Different Nozzle Parameters

“…However, these parameters are connected with the distribution of the external flow field. Many scholars have studied the flow velocity for high‐pressure jets (Glezer and Amitay, ; Jabbal and Zhong, ; Zhang and Zhong, ; Santangelo et al ., ; Ren et al ., ), but there are problems that need to be solved in intermediate pressure jets in order to get the break‐up characteristics for irrigation.…”