Document VJkyZVgXgEykqvNeQdpKEZNxq

710 CHAPTER 31 1956 Guide1 V. jy. St. N. .From Data of: o Alberteon (iewo) o Forihmonn (Germany) * Ruden (Germany) > Becher (Denmark) -- fe)'- *? ">($) > . % A* *, O 0.2 0.4 0.6 0.8 r 1.0 1.2 1.4 1.6 r0.9 Fig. 4. Cross-Sectional Velocity Profiles for Straightflow Turbulent Jets ro. 6 = the radial distance in the same cross-sectional plane from the axis to the point where the velocity is half the centerline velocity: (V = 0.5 F*). Fx = the centerline velocity in the same cross-sectional plane, feet per minute. V = the actual velocity at the point being considered, feet per minute.. ... Experiments show that the conical angle for 0.5 V% and r06 is approxi-' mately one-half of the total angle of divergence of a jet. The velocity pro file curve for one-half of a straight-flow turbulent jet (the other half beinga symmetrical duplicate) is shown in Fig. 4. For multiple-opening outlets, such as grilles, or perforated panels, the velocity profiles are similar, but the angles of divergence are smaller. Radial Jets In the radial jet (diagram B in Fig. 1) the cross-sectional area at any dis tance from the outlet varies as the square of this distance, the same as for an axial jet. Experiments have shown that the centerline velocity gradients and the cross-sectional velocity profiles are similar to those of Zone 3 of axial jets and that the angles of divergence are about the same. In using Fig. 3, X/H should be used as abscissa instead of X/y/~A. Jets from ceiling plaques (diagram C in Fig. 1) have the same form as one-half of a free radial jet. The jet is wider and longer than a free jet, with the maximum velocity close to the wall. This is demonstrated in Fig.;5 which also indicates that under the conditions shown the width of the slot Nozzle 5y* Nozzle Shoded Areas Represent Measured Velocity Profiles Air Distribution 711 Fig. 6. Shape of Air-Stream Envelopes as Slot Area is Increased between ceiling and plaque has' little effect on the jet pattern or velocities at some distance from the plaque.2 Discharge from a Long Slot When a long slot receives its air supply from one end only, the important design factor is the ratio of the area of the slot to the area of the supply duct, and both the air stream profiles and the duct pressure requirements are de termined by this ratio.6 Fig. 6 shows the changing profile as the slot area is increased for a rounded entrance slot (Ca = 0,93) with constant duct cross section. The air discharge from a slot in a tapered duct will be uniform (Fig. 7.) for a relationship between discharge angle and slot-duct dimensions7 where AgCd- cot = Ad- 0 = discharge angle, degrees. A. = slot area, square: feet. Ad = duct cross-sectional area at upstream end, square feet. Cd = coefficient of discharge. (6) Perforated Panels When air is discharged from perforated panels of relatively large sizes, the constant velocity core formed by the coalescence of the individual jets extends a considerable distance from the panel-face.-In this! Zone 1 region the proportionality constants jK: and K' do not apply. Therefore, the pro portionality constants given in Table 1 should be used only when the ratio (Distance from panel/a/Panel area) is larger than 5. When the ratio is less than 5, the equation - . Vx = V01.2\/Ca X Ri. should be used for estimating centerline velocities.8 (7) Fig. 5. Air Jets from a 14-in. Ceiling Plaque for Two Slot Widths with Same Rate of Flow Fig. 7. Uniform Air Flow from a Slot Supplied by a Tapered Duct