根據有害(hai)氣(qi)體密度(du)與空氣(qi)密度(du)大小的不同(tong),通(tong)(tong)風(feng)(feng)柜(ju)的形式(shi)有很多,不同(tong)的地方應用不同(tong)形式(shi)的通(tong)(tong)風(feng)(feng)柜(ju)。通(tong)(tong)風(feng)(feng)柜(ju)主要(yao)形式(shi)包含:上(shang)部排(pai)風(feng)(feng)的通(tong)(tong)風(feng)(feng)柜(ju),下部排(pai)風(feng)(feng)的通(tong)(tong)風(feng)(feng)柜(ju),上(shang)下聯合排(pai)風(feng)(feng)的通(tong)(tong)風(feng)(feng)柜(ju)。同(tong)時,還有節能型的供氣(qi)式(shi)通(tong)(tong)風(feng)(feng)柜(ju)。
通(tong)(tong)風(feng)(feng)(feng)柜的(de)罩面風(feng)(feng)(feng)速是(shi)(shi)(shi)衡量排風(feng)(feng)(feng)柜性能(neng)的(de)主要技術(shu)指(zhi)標,它(ta)是(shi)(shi)(shi)指(zhi)排風(feng)(feng)(feng)柜開口拉門處的(de)平均入口風(feng)(feng)(feng)速,通(tong)(tong)風(feng)(feng)(feng)柜罩面風(feng)(feng)(feng)速的(de)選(xuan)定準則是(shi)(shi)(shi):既要使有害氣體(ti)不能(neng)從(cong)柜內(nei)逸(yi)出,同時也(ye)要避免在通(tong)(tong)風(feng)(feng)(feng)柜內(nei)產生紊流。
過高(gao)的(de)(de)罩(zhao)面風(feng)速可(ke)導(dao)至(zhi)排風(feng)柜(ju)內工(gong)作(zuo)臺上方空間內氣流(liu)紊亂,污染(ran)物(wu)可(ke)能在(zai)柜(ju)內某個角落積聚,還有可(ke)能吹熄火焰(yan),破(po)壞正在(zai)進行(xing)的(de)(de)試驗,過低的(de)(de)罩(zhao)面風(feng)速勢必造成污染(ran)物(wu)的(de)(de)逃逸(yi),危害試驗人(ren)員的(de)(de)安全。
對于(yu)有(you)(you)毒(du)或(huo)有(you)(you)危險(xian)的有(you)(you)害物,其通風(feng)(feng)柜(ju)操作口罩面風(feng)(feng)速一般取0.4~0.5m/s。通風(feng)(feng)柜(ju)的排風(feng)(feng)量根據公式(1)計(ji)算[1]:
對于一般試驗室(shi)通風柜(ju)(ju),當考慮房(fang)間內的干擾(rao)氣流和通風柜(ju)(ju)操(cao)作(zuo)口上吸(xi)速度的不均勻性(xing),開(kai)(kai)啟面積應取操(cao)作(zuo)口量大的開(kai)(kai)啟面積。