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局部排氣導管設計

局部排氣導管設計. 單一氣罩範例. 例題. 具單一氣罩之局部排氣裝置 氣罩風量： 8.5 m 3 /min 氣罩壓損係數： F h = 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（ F e = 0.22 ） 排氣機至出口導管 長度： 2.4 m 直徑： 20 cm. 0. P t 0 = P v 0 = P s 0 = 0. P s 4 = 0. 2. 3. 4. 1. 2.4 m. 11.6 m. 計算方向. 計算方向.

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局部排氣導管設計

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  1. 局部排氣導管設計 單一氣罩範例

  2. 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：20 cm

  3. 0 Pt0 = Pv0 = Ps0 = 0 Ps4 = 0 2 3 4 1 2.4 m 11.6 m 計算方向 計算方向 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

  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 • 若導管截面積小於此值，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)/p]1/2 = 0.08856 m • Amax = pdmax2/4

  5. 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

  6. 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 m2 • v1 = Q/A1 = (0.1417 m3/s)/(0.005027 m2) = 28.18 m/s > vmin = 23 m/s • Pv1 = rv12/2 = (1.2 kg m/s)(28.18 m/s)2/2 = 476.6 Pa • 在 20°C 時，若要求單位為 mmAq，則可使用Pv1 = (28.18/4.04)2 = 48.7 mmAq

  7. 0-1（續） 氣罩後方導管動壓 • 氣罩壓損：DPth = FhPv1 = (0.85)(476.6 Pa) = 405.1 Pa • 氣罩後方（點 1）： • Pt1 = 0 – DPth = -405.1 Pa • Ps1 = 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 acceleration factor

  8. 1-2 • 導管壓損：f(L12/d1)Pv1 = (0.024)(11.6 m)/(0.08 m)(476.6 Pa) = 1659 Pa • 肘管壓損：FePv1 = (0.22)(476.6 Pa) = 104.9 Pa • 1-2 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

  9. 1-2（續） • 排氣機入口（點 2）： • Pv2 = Pv1 = 476.6 Pa • Pt2 = Pt1 – DPt1-2 = -405.1 Pa – 1763 Pa = -2168 Pa • Ps2 = Pt2 – Pv2 = -2168 Pa – 476.6 Pa = -2645 Pa • 或Ps2 = Ps1 – DPs1-2 = -881.7 Pa – 1763 Pa = -2645 Pa • 一氣喝成求Pt2的方法： • Pt2 = -(Fh + fL12/d1 + SF)Pv1 =-[0.85 + (0.024)(11.6)/(0.08) + 0.22](476.6 Pa) = -2645 Pa = DPs1-2

  10. 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 m • A3 = A4 = pd42/4 = pd32/4 = p (0.1 m)2/4 = 0.007854 m2 • v3 = v4 = Q/A3 = Q/A4 = (0.1417 m3/s)/(0.007854 m2) = 18.04 m/s • Pv3 = Pv4 = rv32/2 = rv42/2 = (1.2 kg/m3)(18.04 m/s)2/2 = 195.2 Pa

  11. 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/d3Pv3 = (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

  12. 4-3（續） • 排氣機出口（點 3） • Pt3 = Pt4 + DPt3-4 = 195.2 Pa + 112.4 Pa = 307.7 Pa • Ps3 = 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

  13. Pv Pt FTP Ps FSP

  14. 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

  15. 排氣機耗電量 總效率 h 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

  16. 系統需求曲線 FSP ≈Q2 設計點： FSP = 2281 Pa @8.5 m3/min 排氣機風量

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