根據(ju)有害氣體密度(du)與空氣密度(du)大小的(de)(de)不同,通(tong)(tong)(tong)風(feng)(feng)柜(ju)(ju)的(de)(de)形(xing)(xing)式(shi)有很多,不同的(de)(de)地方(fang)應用不同形(xing)(xing)式(shi)的(de)(de)通(tong)(tong)(tong)風(feng)(feng)柜(ju)(ju)。通(tong)(tong)(tong)風(feng)(feng)柜(ju)(ju)主要形(xing)(xing)式(shi)包含(han):上(shang)部排(pai)(pai)風(feng)(feng)的(de)(de)通(tong)(tong)(tong)風(feng)(feng)柜(ju)(ju),下部排(pai)(pai)風(feng)(feng)的(de)(de)通(tong)(tong)(tong)風(feng)(feng)柜(ju)(ju),上(shang)下聯合排(pai)(pai)風(feng)(feng)的(de)(de)通(tong)(tong)(tong)風(feng)(feng)柜(ju)(ju)。同時,還(huan)有節能型的(de)(de)供氣式(shi)通(tong)(tong)(tong)風(feng)(feng)柜(ju)(ju)。
通(tong)(tong)風(feng)(feng)(feng)柜(ju)的(de)罩面風(feng)(feng)(feng)速(su)(su)是衡量排(pai)風(feng)(feng)(feng)柜(ju)性(xing)能(neng)的(de)主要技術指標,它是指排(pai)風(feng)(feng)(feng)柜(ju)開口拉(la)門處的(de)平均入口風(feng)(feng)(feng)速(su)(su),通(tong)(tong)風(feng)(feng)(feng)柜(ju)罩面風(feng)(feng)(feng)速(su)(su)的(de)選定(ding)準則是:既(ji)要使有害氣體不(bu)能(neng)從(cong)柜(ju)內逸出,同(tong)時也要避免在通(tong)(tong)風(feng)(feng)(feng)柜(ju)內產生紊流。
過(guo)高的(de)罩面風(feng)速(su)(su)可導至(zhi)排風(feng)柜內(nei)(nei)工作(zuo)臺(tai)上(shang)方空間(jian)內(nei)(nei)氣流紊亂(luan),污(wu)(wu)染物可能在柜內(nei)(nei)某個角(jiao)落積聚(ju),還有可能吹熄火焰,破壞正在進行的(de)試驗,過(guo)低的(de)罩面風(feng)速(su)(su)勢必(bi)造成污(wu)(wu)染物的(de)逃(tao)逸,危害試驗人員的(de)安全。
對于有(you)毒或有(you)危險的有(you)害物,其通風(feng)柜操作(zuo)口罩面風(feng)速一般(ban)取0.4~0.5m/s。通風(feng)柜的排風(feng)量根據(ju)公式(1)計算[1]:
對于一般試驗室通風柜(ju),當考慮房間內的干(gan)擾氣流和通風柜(ju)操(cao)作口(kou)上吸速度的不均勻性,開(kai)(kai)啟(qi)面(mian)積應取操(cao)作口(kou)量大的開(kai)(kai)啟(qi)面(mian)積。