Document x1q8kv0B37LJ9n2kLk1Oj0mV1

672 CHAPTER 31 1954 Guide V0 -- nominal velocity of discharge based on the core area, feet per. minute. Cd = coefficient of discharge (usually between 0.65 and 0.90). , Rs& sa ratio of free area to gross (core) area. X = distance from face of outlet, feet: K and Kf -- proportionality constants, with X' = 1.13 K Z)0 = effective or equivalent diameter of stream at discharge from open-end duct or at a contracted section, feet. Ao = Ac X Cd X Ru = effective area of stream at discharge from an open- end duct or at a contracted section, square feet. A0 = measured gross (core) area of outlet, square feet. Q = discharge from outlet, cubic feet per minute. Equation 1 is nondimensional and requires'only that consistent units be used, as in the above nomenclature. Values of K and K' are listed in Table !.' 4 Table 1. Recommended Valdes of the Centebline Velocity Constant K oh K' (See Equationl) Ttpe of Outlet K\ Vo - . 600 to 1000 , Vo = 2000 to 10,000 K' mio iooo Vo = 2000 to 10,000 Free Openings Round or Square Rectangular, large aspect ratio (<40) Annular slots' axial or radial* Grilles and Grids ' Free area 40% or more Perforated Panels Free area 3 to 5% Free area 10 to 20% 5.0 4.3 4.1 2.7 3.5. 6.2 5.3 _ 5.0 3.3 4.3 . 5.7 4.9 3.9 4.7 3.0 4.0 7.0 6.0 4.8 5.7 3.7 4.9 ; For radial slota use X/H instead of H is the height or width of the slot. ' Note: K and K* are indexes of loss in axial kinetic energy. Interpolate as required. Departures from maxi* mum value indicate losses in first and second zones when compared with the jet from a rounded-entrancei circular nozzle. Low velocity test results, in the range Vx < 150 fpm, indicate that the normal values of K and K` should be reduced about 20 percent for Vx = 50 fpm, as used in later Equation 4b for throw. Fig. 2 gives the effective diameterDo in inches for single openings and includes the coefficient of dis charge.5 Similar values for grilles are available in the literature or can be experimentally determined. Values of Cd and Ru are required for deter mining Vo, Do and A0 for orifice-type and multiple-opening outlets, and should, therefore, be included in catalog data of these outlets. In the case of multiple-opening outlets and annular-ring outlets (see diagram A of Fig, 1), the streams coalesce into a solid jet before actual jet expansion takes place. This coalescence affects the experimentally de termined proportionality constants K or K' and accounts for some of the divergence in reported values for similar outlets. Centerline Velocities in Zones 1 and 2 Experimental evidence indicates that in Zone 2 yFx_ . /fCHo Vo ~ x (3) Air Distribution where 673 Ho ~ width of jet at outlet or at vena contracta. Approximately the same values of K' apply as for Zone 3 expansion from axial outlets. In Zone 1, the ratio Vx/Vo is constant and equal to the ratio of the cen- SLOT WIDTH OR ORIFICE OtAMETER-INCHES I0-2 Efpective Diame?p-nZ ii=chT r-- ; ter velocity of the jet at start of expansion to the average velocity, ranging from approximately 1.0 for rounded-entrance nozzles to about 1.2 for straight pipe discharge, but with much higher values for diverging-dissharge outlets. determining Centerline Velocities To permit correlation of data from all four zones, centerline velocity rahos are plotted against distance from outlet in Fig. 3 in accordance with