Jets in Confined Spaces

2 Experimental Studies of Isothermal Horizontal Jets in Confined Spaces Airflow Pattern, Throw, Velocities 

The first experimental data on confined air jets used for ventilation date back to 1939, when Baturin and Hanzhonkov studied air supply method with 

FIGURE 7.35 Jet flow in a room oj short room (b) long room. Reproduced from Etheridge and Sandberg.  

Studies by Nelson and Stewart,Bromley, - and Gunes provide experimental data on air velocities and temperature distribution for this method of air supply at different room configurations, locations of air supply outlets, and velocities and temperatures of air supply. 

The effect of the room length and position and shape of the air supply outlets was studied by Linke. These studies show that there is a maximum room length that can be effectively ventilated by the supply air jet (Fig. 7.36 2). For the 

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FIGURE 7.38 Schematic of air jet in confined space proposed by N. N. Sadovskaya. Reproduced from Grimitlyn. ... 

Other experimental and analytical studies of nonisothermal inclined jets in confined spaces were carried out by Zhivov. Experimental studies were conducted on the physical models. The ratio of the model dimensions L x B x H was changed so that the value H/B was from 0.3 to 3.0 and L/ B xH) = 2.4-4.9. 

Karimipanah, T. 1996. Turbulent jets in confined spaces. Ph.D. thesis. Royal Institute of Technology, Center for Built Environment, Gavle, Sweden. 

The effect of supply air temperature on jet behavior in confined spaces was studied by Miillejans. Studies of cooled air jets were conducted in rooms with a size from 1.0 m x 1.0 m x 1.6 m to 2.27 m x 3.33 m x 5.31 m with an air supply through the slot (b = or rectangular opening (h B. . Numerous smoke photographs were taken reflecting supply situa-... 

Air supplied in confined space by downward vertical jets creates a similar flow pattern as in the case of air supply by horizontal nonattached jets. With vertical air supply, the occupied zone is ventilated directly by air jets. Grimitlyn suggests that the area of occupied zone ventilated by one jet be sized based on the jet s cross-sectional area at the point it enters the occupied zone. The jet cross-sectional area and configuration depend upon the height of the air supply, the type of air jet, and diffuser characteristics ( K, and K, ). 

Steam jet systems. These are used to smotlier some fires in closed containers or in confined spaces. 

Pressure Development Overpressure in a UVCE results from turbulence that promotes a sudden release of energy. Tests in the open without obstacles or confining structures do not produce damaging overpressure. Nevertheless, combustion in a vapor cloud within a partially confined space or around turbulence-producing obstacles may generate damaging overpressure. Also, turbulence in a jet release, such as may occur with compressed natural gas discharged from a ruptured pipehne, may result in blast pressure. 

It is assumed in the above-mentioned methods that the influence of confined space on the supplied jet can be described by the reduction of the axial component and the value as for jet development in the counterflow. The value of i/,. is assumed to be the same throughout each cross-section but variable along the jet length. The value of can be found from the continuity equation, which in the case of jet distribution in a space of cylindrical shape can be presented as... 

Shepelev, L A., and M. D. Tarnopolsky. 1965. Turbulent air jet spreading in the confined space. In Heat-, Gas Supply and Ventilation Proceedings of the Conference. Budivelnik, Kiev. 

Grimitlyn, M. 1., and G. M. Pozin. 1973. Determination of parameters of the jet developing iri a confined space and following a blocked or through-motion pattern. In Proceedings of VTsNliOT VTsSPS 91. Profizdat, Moscow. 

Evacuate danger area immediately Consult an expert Ventilation. Absorb remaining liquid in sand or inert absorbent and remove to safe place. Do NOT wash away into sewer. NEVER direct water jet on liquid. Prevent from entering confined spaces. Do NOT let this chemical enter the environment (extra personal protection gas-tight chemical protection suit including self-contained breathing apparatus). 

Detailed experimental data were obtained by Sadovskaya on a physical model in isothermal conditions. She has found that the confined air jet has two critical cross-sections (Fig. 7.38). In the first cross-section, where the ratio of jet cross-sectional area to the area of ventilated space equals 0.24, the jet... 

When confined in a completely enclosed space—a room, or a tank—hydrogen can be detonated, i.e., exploded over a wide range of concentrations, ranging from 18 to 59 percent (by volume) in air. Methane explodes only in concentrations ranging from 6.3 to 14 percent, and gasoline and jet fuel detonate in a range from 1.1 to 3.3 percent. 

In the absence of confinement, ambient air entrainment effects may cause unpredictable effects for hot air impingement the heat transfer performance may worsen by 20%-50% depending upon the flow rate, difference between the jet and the ambient temperature, and nozzle-surface spacing. 

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