Document RK9JGBdG1ON9V7GOjEedp3gX

706 CHAPTER 31 1956 Guide Vc ==' nominal velocity of discharge based on the core sirea, feet per minute. Ca = coefficient of discharge (usually between 0.65and 0.90). . Ri,--; ratio of free area to gross (core) area. X = distance from face of outlet, feet. ... K and K' - proportionality constants, with K' = 1.13 K Di -- effective or equivalent diameter of stream at discharge from open-end duct or at a contracted section, feet. A = A, X Cd X Ri = effective area of stream at discharge from an openend duct or at a contracted section, square feet. Ac = 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 L2.4 Table i. Recommended Values of.the Centerline Velocity Constant K ob K` (See Equation 1) ' Type of Outlet K v9 = 500 to 1000 Ko = 2000 to 10,000 K Fo = 500 to 1000 F = 2000 to 10,000 Free Openings Round or Square 5.0 6.2 5.7 7.0 Rectangular, large as- 4.3 5.3 4.9 6.0 pect ratio (<40) Annular slots axial or _ _ 3.9 4.8 radial* Grilles and Grids . Free area 40% or more 4.1 5.0 4.7 5.7 Perforated Panels Free area 3 to 5% 2.7 3.3 3.0 3.7 Free area 10 to 20% 3.5 4.3 4.0 4.9 For radial slots use X/H instead of X/(A)1^*. If is the height or width of the slot. Note: K and K` are indexes of loss in axial kinetic energy. Interpolate aa required. Departures from maxi mum value indicate losses in first and second tones when compared with the jet from a rounded-entrance, circular nozzle. Low velocity test results, in the range V* < 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 diameter D,, in inches for single openings and includes the coefficient of dis charge.6 Similar values for grilles are available in the literature or can be experimentally determined. Values of Cd and Rt* are required for deter mining Vo, Da 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. I), the streams coalesce into a solid jet before actual jet expansion takes place. This coalescence affects the experimentally de termined proportionality constants K or K1 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 v, _ mu V, y X (3) Air Distribution 707 where Ho = width of jet at outlet or at vena contracta. Approximately the same values of A' apply as for Zone 3 expansion from axial outlets. In Zone 1, the ratio V*/Vo is constant and equal to the ratio of the ceri- Eig. 2. Effective Diametebs fob Round and Rectangulab Openings (Plenum Appboach) ter velocity of the jet at start of expansion to the average velocity, ranging rom approximately 1.0 for rounded-entrance nozzles to about 1.2 for straight pipe discharge, but with much higher values for diverging-dis- harge outlets. B6 Determining Centerline Velocities Permit correlation of data from all four zones, centerline velocity raos are plotted against distance from outlet in Fig. 3 in accordance with