5-40 Industrial Ventilation

he= 0.93 vPd PLAIN DUCT END

~Ectl~ /~ he= 1.78 VPOrifice SHARP-EDGED

ORIFICE

TAPERED HOODS Flanged or un flanged; round, square ar

rectangular. e is the major angle on rectangular hoods.

he= 0.49 VPd FLANGED DUCT END

he = 0.4 VPd (tapered take-off) he = 0.65 VPd (no taper)

STANDARD GRINDER HOOD

ENTRY LOSS (h d) e ROUND RECTANGULAR

15 0.15 VP 0.25 VP 30 0.08VP 0.16 VP 45 0.06 VP 0.15 VP 60 0.08VP 0.17 VP 90 0.15 VP 0.25 VP

120 0.26 VP 0.35 VP 150 0.40VP 0.48 VP 180 0.50VP 0.50 VP

f-

~ ~>'2D ~ --~

he= 0.04 VPd BELLMOUTH ENTRY

he = 1.5 VP d TRAP OR SETTLING CHAMBER

1.1 0 '---~--.----'--~--r-'----r---'---'

1.00 f---l---+--+--+-l--f---l---+---j 0.90 I--+---!--+--t---t--'f--+-+---l

C5 0.80 !---l---+--+--+-l--f---l---+---j 0.70 - Rectangular & Square -t----t---j

~ Transition to Round 17 () 0.60

~ 0.50 H--l----1--+--+__+-I--/f+v-~-----1 ~ 0.40 1-++----1--+--+__+-I-i/~/__+____1 n::: , ........ V 0.30 '\ V< tZ' 0.20 1---:--t.;.I'-----:----1I-__ -+../-:7"l-t--"'-"II.i'--'-I-C-o+n i-ca--11

0.10 1--+.-:-+.. .-1-.. -+--+-f--+----1--1 (Ref. 5-14) O. 00 '----'----'---L--'_"----'-~~~

Face area (A ) at I east 2 times the duct area. r

VP = Duct VF = VPd Note: 180' values represent round ducts bu:ted into back of booth or hood without a rectangular to round transition. o 20 40 60 80100120140160180

COMPOUND HOODS A compound hood, such as the slot/plenum shown to the right, would have 2 losses, one through the slot and the other through the transition into the duct.

The slot entry loss coefficient, Fs ' would have a value typically in the range of 1.00 to 1.78 (see Chapters 3 and 10). The duct entry loss coefficient is given by the obove data for tapered hoods.

AMERICAN CONFERENCE OF GOVERNMENTAL

INDUSTRIAL HYG IENISTS DATE

e, INCLUDED ANGLE IN DEGREES

MISCELLANEOUS V/\LUES

HOOD ENTRY LOSS COEFFI CI EN T Fd Abrasive blast chamber Abrasive blast elevator Abrasive separator Elevators (enclosures) Flanged pipe plus close elbow Plain pipe plus close elbow

HOOD ENTRY LOSS COEEFICIENTS

1.0 2.3 2.3 0.69 0.8 1.60

1-95 IFIGURE 5-13

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