CC PHNG PHP O LU LNG Trong cuc sng hng ngy cng nh trong cng nghip, o lu lng l mt trong nhng php o c s dng rng ri nht. Chng ta c kh nhiu nguyn l o lu lng v hu ht cc nguyn l o iu cho kt qu kh chnh xc. Sau y l mt s phng php o c bn v kh ph bin: - o lu lu lng theo nguyn l chnh p, - o lu lng theo nguyn l turbine, - o lu lng theo nguyn l t tnh, - o lu lng theo nguyn l Vortex, - o lu lu lng theo nguyn l chim ch, - o nguyn theo nguyn l gia nhit, - o theo nguyn l Coriolis. Trong by nguyn l o trn th nm nguyn l o u tin thuc nhm o lu lng th tch (Volumetric Flow-rate) v hai nguyn l o cui cng thuc nhm o lu lng khi lng (Mass Flow-rate). 1. o lu lng theo nguyn l chnh p Differential Pressure. y l nguyn l o c s dng rng ri nht trong cc ngnh cng nghip qu trnh (process industry). Nguyn l o ny da trn m t ton hc l: Lu lng th tch t l vi cn bt hai ca chnh p: Q = K.P. Theo , ngi ta s s dng cc thit b to chnh p bng cch thay i tit din ngang ca ng (theo hng nh li) nh: Tm Orifice, ng Venturi hoc Flow nozzle, trong tm Orifice thng c s dng nht v tnh c ng, d lp t, d bo tr... Khi tit din ngang ca ng thay i th s to nn chnh p P ca dng lu cht i trong ng. c th tnh ton ra lu lng ca lu cht t chnh p P ngi ta s dng mt transmitter chnh p. Transmitter ny c 2 u vo p sut tng ng vi p sut cao nht ti im khi tit din ngang ca ng cha thay i v p sut thp nht ti im dng chy c tit din ngang nh nht. o c lu lng chnh xc nht th vic lp t im ly p sut cn tun th cc yu cu k thut lin quan n hng dng chy, ng knh ng, v tr v khong cch gia hai im o p sut Vn dng chy tn ti c 2 pha (lng v kh) s nh hng n kt qu o. loi b iu ny ngi ta s dng tm Orifice c c l. Theo , nu lu cht l cht kh th tm Orifice s c c l pha y dng chy ( lng c th i qua) v nu lu cht l cht lng th tm Orifice c c l pha trn dng chy. 2. o lu lng theo nguyn l Vortex. Nguyn l o ny cng c s dng i vi lu cht l lng, hi hoc kh. Nguyn l o ny c m t nh sau: Ngi ta s dng mt thit b dng hnh cn (Bluff Body of

Vortex Shedder) t vung gc v chn gia dng chy. Khi lu cht gp thit b ny n s hnh thnh cc im xoy Vortex pha h ngun, lu lng cng ln th cc im xoy ny cng nhiu. xc nh lu lng ngi ta s t cm bin o dao ng do cc Vortex ny gy nn. Nguyn l o Vortex b nh hng bi s rung ng ca ng ng, s si bt ca lu cht. Tuy nhin, trong thc t thit b o theo nguyn l ny cho kt qu kh chnh xc (sai s