Document BydpK15oOm0Z6QbXY46By1o8m

676 CHAPTER 31 1954 Guide w Qa "V s. V 1. x. From Dcto of: e Albertson (lowo) a Forthmonn (Germany) * Ruden (Germany) Becher (Denmork) ---------(ifc)*- 33 l0(v-) X X V Vj bt-J A A > 0 2 0 4 0 6 0 8 1 0 1 2 1 4 1 6 1 e 2. Fig. 4. Cross-Sectional Velocity Profiles fob Straightflow Turbulent Jets ';-!,'; ' .i To.i = 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 V,): -40- V = the centerline velocity in the same cross-sectional plane, feet per minute.yw V = the actual velocity at the point being considered, feet per minute. ,-p; J- Experiments show that the conical angle for 0-5 Vx and r0.6 is approxfifSj mately one-half of the total angle of divergence of a jet. The velocity pro^l file curve for one-half of a straight-flow turbulent jet (the other half being a.i| symmetrical duplicate) is shown in Fig. 4. For multiple-opening outlets', such as grilles, or perforated panels, the velocity profiles are similar, buvgj the angles of divergence are smaller. "" .iO;-- Radial Jets In the radial jet (diagram B in Fig. 1) the cross-sectional area at any dis-'-y' 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 ofx;- axial .jets and,that the angles of divergence are about the same. In usingiR Fig. 3, X/H should be used as abscissa instead of X/y/A-' Jf c Jets from ceiling plaques (diagram C in Fig. 1) have the same form 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.^p-*1' which also indicates that under the conditions shown the width of the slot `J Nozzle 14* ploque H 2" 262 cfm --i-- -4v/ 5-` Nozzle IgWA*. AVAVAW Shoded Areos Represent Measured velocity Profiles H!!!t -istv- 14* Ploque h 4' 6` IISO fpm 18" 540 fpm 36" 300 fpm 48" 225 fpm Fig. 5. Air Jets from a 14-in. Ceiling Plaque for Two Slot Widths with Same Rate of Flow Air Distribution 677 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 deT termined by this ratio.6 Fig.^6 shows the changing.profile as the. slot area, is increased for a rounded entrance slot {C& = 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 AsCd cot 0 - ~Ad e = 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 K and K' do not apply. Therefore, the pro portionality constants given in Table 1 should be used only when the ratio (Distance from panel/VPanel area) is larger than 5. When the ratio is less than 5, the equation Vx = Vorl^VCd X Bf. should be used for estimating centerline velocities.8 (7) FlG' 7` Unifoem Air F"W from a Slot Supplied by a Tapered Duct