1、局部排氣導管設計,基本假設,非壓縮性流，流體密度不變，質量守恆風量（流量）守恆導管無洩漏,造成靜壓變化的因素,管壁摩擦（同時造成全壓損失）紊流（同時造成全壓損失）流速改變（不造成全壓損失）,管壁摩擦,DPS= F PV 導管風速動壓：增加若無其他損失：靜壓下降：且下降量 = 動壓增加量全壓不變考慮摩擦與紊流損失全壓下降靜壓下降，且下降量 動壓增加量,Ps = 0Pv = 0Pt = 0,若無摩擦與紊流損失Pv = 25 mmH2OPs = -25 mmH2OPt = 0考慮摩擦與紊流損失Pv = 25 mmH2OPs = -40 mmH2OPt = -15 mmH2O,v = 20 m/s,P
2、v,Ps,Pt,描述氣罩壓力損失的方法,壓損因數（Entry Loss Factor，Fh）進口係數（Coefficient of Entry，Ce）,氣罩壓損係數,氣罩後方 Pt = -Fh Pv or DPt = Fh PvPs = Pt Pv = -Fh Pv Pv = -(Fh + 1) Pv or DPs = (1 + Fh )Pv1 ：加速因數,Ps = 0Pv = 0Pt = 0,若無摩擦與紊流損失Pv = 25 mmH2OPs = -25 mmH2OPt = 0考慮摩擦與紊流損失Pv = 25 mmH2OPs = -40 mmH2OPt = -15 mmH2O,v = 20 m
3、/s,Pv,Ps,Pt,Fh = -Pt/Pv = 15/25 = 0.6or = -Ps/Pv 1 = 40/25 1 = 0.6,氣罩進口係數,Ce = 氣罩風量/無壓損之流量 = Q/Qmax,Ps = 0Pv = 0Pt = 0,若無摩擦與紊流損失Pv = 25 mmH2OPs = -25 mmH2OPt = 0考慮摩擦與紊流損失Pv = 25 mmH2OPs = -40 mmH2OPt = -15 mmH2O,v = 20 m/s,Pv,Ps,Pt,氣罩前後壓力變化,Pt = Fh Pv,Pv,Ps = (1+Fh) Pv,Fh,Ce,如何決定壓損係數,自行測試（壓力計，建議採用）廠
4、商提供資訊經驗公式或圖表（最後手段）,動壓,壓力損失,DPt = FPv,v = Q/A,DPt = KQ2,Pv = rv2/2,局部排氣導管設計基本要求,每一氣罩風量須高於需求值每一導管風速須高於搬運風速其他考慮因素：導管內物質濃度風速上限：靜電、管壁摩耗、物料損失出口排放風速排氣機進出口管徑,如何決定氣罩風量,法令要求：控制風速與抑制濃度要求作業人員個人採樣煙霧測試或追蹤氣體方法：測試（建議採用）圖表或經驗公式,log(個人採樣濃度),log(氣罩風量),log(容許濃度),log(氣罩設計風量),如何決定搬運風速,搬運風速愈大,污染物愈濕黏,導管設計主要目的,決定各導管管徑決定排氣機性
5、能要求,例題,具單一氣罩之局部排氣裝置氣罩風量：8.5 m3/min氣罩壓損係數：Fh = 0.85氣罩至排氣機導管：管壁摩擦因數：f = 0.024長度：11.6 m搬運風速：23 m/s 以上含有一肘管（Fe = 0.22）排氣機至出口導管長度：2.4 m直徑：10 cm,11.6 m,2.4 m,空氣密度 r = 1.2 kg/m3氣罩風量需求：Q = 8.5 m3/min氣罩壓損係數：Fh = 0.85肘管壓損係數：Fe = 0.22排氣機前導管最低搬運風速：vmin = 23 m/s排氣機後導管管徑：10 cm導管摩擦損失因數 f = 0.024,Pt0 = Pv0 = Ps0 =
6、0,Ps4 = 0,計算方向,計算方向,1,2,3,0,4,0-1,Q = (8.5 m3/min)(1 min/60 s) = 0.1417 m3/s導管截面積最大為：Amax = Q/vmin = (0.1417 m3/s)/(23 m/s) = 0.006159 m2若導管截面積大於此值，導管內風速會小於規定的 23 m/s導管最大管徑 dmax = (4Amax/p)1/2 = (4)(0.006159 m2)/p1/2 = 0.08856 mAmax = pdmax2/4,0-1（續）,若導管管徑只能使用 2、3、4、cm：取管徑 d1 = 8 cm = 0.08 m若以四捨五入取
7、d1 = 9 cm dmax，會使導管內風速小於規定的 23 m/s若導管管徑可以訂做（自由選取），則令 d1 = dmax = 0.08856 m若管徑 d1 已事先給定，則無需上述步驟,0-1（續）,以管徑 d1 = 0.08 m 繼續以下計算：導管截面積：A1 = pd12/4 = p (0.08 m)2/4 = 0.005027 m2v1 = Q/A1 = (0.1417 m3/s)/(0.005027 m2) = 28.18 m/s vmin = 23 m/sPv1 = rv12/2 = (1.2 kg m/s)(28.18 m/s)2/2 = 476.6 Pa在 20C 時，若要求
8、單位為 mmAq，則可使用 Pv1 = (28.18/4.04)2 = 48.7 mmAq,0-1（續）,氣罩壓損：DPth = Fh Pv1 = (0.85)(476.6 Pa) = 405.1 Pa氣罩後方（點 1）：Pt1 = 0 DPth = -405.1 PaPs1 = Pt1 Pv1 = -405.1 Pa 476.6 Pa = -881.7 Pa或 Ps1 = -(1 + Fh) Pv1 = (1 + 0.85)(476.6 Pa) = -881.7 Pa,氣罩後方導管動壓,acceleration factor,1-2,導管壓損：f(L12/d1)Pv1 = (0.024)(1
9、1.6 m)/(0.08 m)(476.6 Pa) = 1659 Pa肘管壓損：FePv1 = (0.22)(476.6 Pa) = 104.9 Pa1-2 的總壓損 DPt1-2 = 1659 Pa + 104.9 Pa = 1763 Pa通式：DPt1-2 = (fL12/d1 + SF)Pv1 =(0.024)(11.6)/(0.08) + 0.22(476.6 Pa) = 1763 Pa = DPs1-2,導管上配件壓損係數總和,導管摩擦壓損係數,A1 = A2，v1 = v2 ，Pv1 = Pv2，DPt 1-2 = DPs1-2,1-2（續）,排氣機入口（點 2）：Pv2 = Pv
10、1 = 476.6 PaPt2 = Pt1 DPt1-2 = -401.5 Pa 1763 Pa = -2168 PaPs2 = Pt2 Pv2 = -2168 Pa 476.6 Pa = -2645 Pa或 Ps2 = Ps1 DPs1-2 = -881.7 Pa 1763 Pa = -2645 Pa,4-3,排氣機後方導管：由出口往前算排氣機後方導管管徑已給定：d3 = d4 = 10 cm = 0.1 mA3 = A4 = pd42/4 = pd32/4 = p (0.1 m)2/4 = 0.007854 m2v3 = v4 = Q/A3 = Q/A4 = (0.1417 m3/s)/(
11、0.007854 m2) = 18.04 m/sPv3 = Pv4 = rv32/2 = rv42/2 = (1.2 kg/m3)(18.04 m/s)2/2 = 195.2 Pa,4-3（續）,出口（點 4）Ps4 = 0（大氣）Pt4 = Ps4 + Pv4 = 0 + 195.2 Pa = 195.2 Pa導管 3-4 壓損： DPt3-4 = fL34/d3 Pv3 = (0.024)(2.4 m)/(0.1 m)(195.2 Pa) = 112.4 Pa = DPs3-4,A3 = A4，v3 = v4 ，Pv3 = Pv4，DPt 3-4 = DPs3-4,4-3（續）,排氣機出口
12、（點 3）Pt3 = Pt4 + DPt3-4 = 195.2 Pa + 112.4 Pa = 307.7 PaPs3 = Pt3 Pv3 = 307.3 Pa 195.2 Pa = 112.4 Pa其實就是 DPs3-4 ，因為 Ps3 = Ps4 + DPs3-4 = 0 + DPs3-4,Ps,Pt,Pv,FTP,FSP,FTP 與 FSP,排氣機全壓（FTP） = 排氣機出口全壓 排氣機入口全壓 = Pt3 Pt2 = 307.7 Pa (-2168 Pa) = 2476 Pa用來計算耗電量排氣機靜壓（FSP）： = FTP 排氣機出口動壓（Pt3 Pt2 Pv3）= 排氣機出口靜壓 排氣機入口全壓（Ps3 Pt2）= 112.4 Pa (-2168 Pa) = 2281 Pa排氣機標準規格（可以提高多少壓力）,FTP,排氣機耗電量,總效率,P = (0.1417 m3/s)(2476 Pa)/0.4 = 877 W = 0.877 kW每運轉一小時耗電 0.877 度,h,系統需求曲線,設計點：FSP = 2281 Pa 8.5 m3/min,FSP Q2,排氣機風量,
