Document Z4eQaz5MOE2a297LvxZ4mpEgY

790 CHAPTER 31 1957 Guide Table 2. Pressure Losses due to Elbows (Additional Equivalent Losses in Excess of Friction to Intersection of Center Lines) TYPE ILLUSTRATION N-OEC. 90-ocG. ROUND SECTION . 90-0EC. RECTANCULAR SECTION 40-DEC. SOUARE SECTION WITH SPUTTER VANES MITER WITH TURNING VANES Sid > FORMED CONDITIONS PRESSURE LOSS C* 1 L/o 1 L/w RECTANGULAR OR ROUND; WITH OR WITH OUT VANES MITER R/OsO.S 0.75 1.0 1.5 2.0 90 T`"E i VALUE FOR SIMILAR 90-1 EG. EL6Q W 1.50* 0,40 ' 0.45 0.55 0.24 0.14 65* 25 17 12 10 H/w R/w MITER 0.5 0.25 0.75 1.0 .1.5 MtTER O.S 0.5 0.75 1.0 1.5 MITER 0.5 1.0 0.75 1.0 .1.5 MITER 0.5 4.0 0.T5 1.0 1.5 *** ** S/n MITER 0 5 0.5 0.4 0.7 0.6 1.0 1.0 1.5 MITER O.S 0.5 0.5 0.2 0.4 0.75 0.4 0.7 1.0 0.7 1.0 1.5 IS 1.6 1-25* 1.25 0.60 0.57 0.19 1.47 1.10 0.50 0.28 0.15 1.50 1.00 0.41 0.22 0.09 1.56 0. 96 0.57 0.19 0.07 0.70* 0.15 0.12 0.45 0.12 0.10 0.15 25* 25 12 7 4 49 40 16 9 4 75 50 21 11 45 110 65 45 17 6 26'. 19 12 7.2 22' 16 PLATE VMCS 0.55* FORMED VANES 0.10* MITER TEE WITH VINES RADIUS TEE CONSIDER EQUAL TO A SIMILAR ELBOW. BASE LOSS ON ENTERING VELOCITY. * Values based on / values of approximately 0.02. b Values calculated from L/D and LfW values of Reference 6 for/ = 0.02. Note: Superscript numbers refer to references at end of chapter. DYNAMIC LOSSES Wherever eddying flow, is present, brought about by sudden changes in the direction or magnitude of the velocity of the air flowing, a greater loss in pressure takes place than would occur in a steady flow through a similar length of straight duct having a uniform cross section. The amount o' this loss, in excess of straight duct friction, is termed dynaritic loss. Al" though dynamic losses may be assumed to be caused by changes in area actually occupied by the air flow, for convenience they are divided into two general classes: (1) those caused by changes in direction of the duct and (*/ those caused by changes in cross-sectional area of the duct. Air Duct Design 791 Table 3. Pressure Losses due to Area Changes TYPE (-LUSTRA CONDI LOSS TION TIONS COEFFtCCNT TYPE ILLUSTRA CONDI LOSS TION TIONS COEFFICIENT ABRUPT EXPANSION d-- oN oA oV Od Oo oK Oo Oo 1 A|/A* e pO PQ OO O O k O |(i OA OO O; B C, c2 01 ABRUPT At 16 CONTRACTION 5 SQUARE 2.25 EDGE 00 0 45 0 e 006 001 CRADUAL CONTRACTION A, c* **/A| c* 0.0 02 04 06 08 0.5412 032 0.25 0 16 0.06 e 50* 45*. 60* 0.02 0.04 0 07 GRADUAL EXPANSION s' 7* 10* 20* 50* 40* 0.7 0 22 026 0.4 5 0.59 075 . ABRUPT EXIT *> !A Xop 1 00 (A,'09)1 SQUARE EDGE ORIFICE EXIT At -Ol -- Bar ACROSS OUCT PIPE ACROSS OUCT -? STREAM LINED STRUT ACROSS DUCT it i A./A, QO as 0.4 06 08 10 e/P0 10 025 0.50 E/0 0.10 0.25 0.50 E/0 0.10 0.25 0 50 C. 2S0,Z 244 2 26 96 1 54 1.00 c 0.7 4 4.0 C 0.20 0-55 2.0 C 0 07 0.25 0.90 equal AREA TRANSFOR QI^do }5m* MATION C 0.5* FLANCEO ENTRANCE c 0 3412 DUCT ENTRANCE ____L c 0 65 FORMED ENTRANCE A C 0 05 A./A* SQUARE EDGE ilr^ ORIFICE ENTRANCE- 00 02 04 0.6 O8 1.0 A., A SQUARE EDGE ORIFICE IN DUCT A| -- A* m* - A. --ox. 0.0 0.2 0.4 0.6 0.6 l.O c. 2S012 1.90 1.59 0.96 0.61 0 54 C. 2.5012 1.66 1 21 0.64 020 0.0 in 1: Subscript on C indicates cross section at which velocity is calculated. (See, lor example. Eauation iu iq text.) Note 2: Superscript cumbers refer to references at end of chapter. Dynamic losses vary substantially as the square of the mean velocity of the air, and are therefore conveniently expressed as a fraction of the velocity head: *-c(i5>)' where m = dynamic pressure loss, inches of water. V ~ mean velocity of air flow, feet per minute. ^ -- an experimentally determined constant (dynamic loss coefficient). Where different areas are involved, subscripts are used to denote the area which the coefficient applies, as Ci for inlet area, Ct for outlet area, and t-o lor orifice area. The dynamic loss coefficient C is dimensionless and represents the numer of velocity heads lost at the conduit transition or bend. Values of the ynamic loss coefficient for elbows and other duct elements have been de tuned experimentally and are given in Tables 2 and 3. It should be