Document Xzp7BvOwDvYRm0kZgb0dgmL6x

EXHAUST SYSTEMS, GENERAL ix COMFORT VENTILATION K, 0 99VP PLAIN DUCT END (t* on h#- O 9VP FLANGED DUCT END C, 0 6t h * I 76 VP ORIFICE SHARP-EDGED -ORIFIGE e, o go TAPERED HOODS niitn m nnutn imt loom n ttcruauu i iim huo uni 01 nctuCBiu moot h,t 0 SOVf DIRECT BRANCH BOOTH C, >0 G> * 15* 50* 1)5* 60* 60* 1*0* ISO* IMtt toil___ 1 ROWS___ tmntHlM 0 19 VP 0 25 v 0 06 VP 0 06 VP 0 06 VP 0 19 VP 0 M VP 0 90 VP 0 16 VP 0 16 VP 0 IT VP 0 26 VP 0 39 VP 0 ue VP ENTRY RPWP 0 99 0 BS 0 07 0 SI 0 63 0 69 0 64 COtFFICIKT meiniciHFi- 0 60 0 9 0 93 0 92 0 69 0 66 0 62 G y-B 0/t 3Z3--- S,i 0 oevp TO 0 IOTP ENTRANCE STANDARD GRINDER HOOD e,' an h.n5P TRAP OR SETTLING CHAMBER C| *0 OStVfra) s,. i ovp DOUBLE (inner conK) HOOD c# o to iippfM) Fig. 28-6. Entry lost factor (F) and entry coefficient (C.) for hoods of various design Entry loss (h.) in inches water gauge equals entry Iosb factor times the velocity pressure in the duct (h.) = (F) (VP) Air volume (Q) in cfm equals 4,005 times the cross section at the throat in square feet times the coefficient of entry times the square root of the static pressure at throat in inches water gauge Q = 4005A. SP With tapered hoods (upper right illustration), F varies with the motor angle 9, is lowest at about 40 deg. teased, the flow of convection currents should be toward the hood. If heavy parti cles are thrown off, as in rough grinding, their trajectory should be toward die hood intake But a caution should be noted the air-borne dust which is of health signifi cance is made up of particles that are ex tremely small, 0 1 to perhaps 5 microns in diameter (A micron is 1/25,000 in.) It has been shown by Hatch" and others that such particles, even if impelled at extreme ly high initial velocities, travel a very short distance in air-a matter of a few inches at the most Unlike chips or large particles, they can not be thrown into a hood any considerable distance away. The hood acts by confining a mass air movement into it which carries the dust along - For even distribution of the air flow through a large hood, flow may be con- T. F. Hatch. "Dust Control, Present and Future Design Considerations" Me chanical Engineering, 57'154,1935 28-10