抽水機(jī) (Pump)

1、2021/7/51抽水機(jī) (Pump)Aquacultural EngineeringW 10 -112021/7/52What are pumps 泵是能夠?qū)⒛芰考舆M(jìn)流體的機(jī)器。 水及其他流體順應(yīng)能量梯度(energy gradient)移動(dòng)，朝向總能量(total energy)降低的方向移動(dòng)。 最普遍的需求是抵抗重力梯度將流體由低地移動(dòng)到高地。 泵有時(shí)候也用於增加流體系統(tǒng)中之壓力，因而使流體可以做功(do work)承受負(fù)載(load)。 2021/7/53Purposes of this chapter 根據(jù)操作原理特性及在不同流體系統(tǒng)之根據(jù)操作原理特性及在不同流體系統(tǒng)之應(yīng)用探討各種型

2、式之泵應(yīng)用探討各種型式之泵 討論抽水機(jī)選擇方法及驅(qū)動(dòng)系統(tǒng)之選擇討論抽水機(jī)選擇方法及驅(qū)動(dòng)系統(tǒng)之選擇 正確選擇抽水機(jī)對(duì)水產(chǎn)養(yǎng)殖業(yè)非常重要正確選擇抽水機(jī)對(duì)水產(chǎn)養(yǎng)殖業(yè)非常重要因抽水費(fèi)用為主要之費(fèi)用因抽水費(fèi)用為主要之費(fèi)用2021/7/54DEFINITIONS 自由水面自由水面(Free water surface) 開放至大氣或水面只承受大氣壓力之水面開放至大氣或水面只承受大氣壓力之水面淨(jìng)正吸水頭淨(jìng)正吸水頭): Net positive suction head (NPSH) 抽水機(jī)進(jìn)水口超出流體蒸氣壓力之絕對(duì)總水抽水機(jī)進(jìn)水口超出流體蒸氣壓力之絕對(duì)總水頭頭2021/7/55a positive NPS

3、H. hv = 液體蒸氣壓 (Pa) hf = 流體流經(jīng)進(jìn)水口管件產(chǎn)生之摩擦及黏滯力損失 (Pa) hh = 抽水機(jī)進(jìn)水口壓力損失 (Pa) NPSH = hb hv - hf + hh (11.1) hb = 大氣壓力 (Pa)2021/7/56 NPSH = hb hv hf hh (11.2) 進(jìn)水口在自由水面以上 2021/7/57進(jìn)水口與受壓力水槽連接 NPSH = hb hv hf hh + P1 (11.3) 2021/7/58壓力水頭壓力水頭(Pressure head) = 抽水機(jī)必須做工抵抗之總水頭或總壓力= h + P2 + V22/2g + hf NPSH (11.4)

4、h = 抽水機(jī)中心線以上至流體系統(tǒng)最高點(diǎn)之垂直距離g = 重力加速度 P2 = 流體系統(tǒng)最高點(diǎn)之靜水 V22/2g = 抽水機(jī)出水口速度水頭或動(dòng)力水頭 hf = 流體系統(tǒng)中摩擦水頭損失 NPSH = 淨(jìng)正吸水頭 (若大於大氣壓力則為負(fù)值, 低於大氣壓力則為正值)2021/7/59 The total pressure head(h; 總壓力水頭) 抽水機(jī)必須克服之總水頭 Brake power (BP):(制動(dòng)馬力) 驅(qū)動(dòng)器輸出之能量 = 抽水機(jī)需求之輸入能量 Pump output power (POP):(泵輸出馬力) 抽水機(jī)實(shí)際加於流體之能量 POP = CQh (11.5) 單位重 1

5、 g/ml 之淡水其 POP (watts) = 9800Q (m3/sec) h(m) 2021/7/510 Efficiency of a pump (e)e = output/input = POP/BP (11.7) 2021/7/511PUMP CLASSIFICATION 2021/7/512CENTRIFUGAL PUMPS 離心式抽水機(jī)之基本元件離心式抽水機(jī)之基本元件 動(dòng)力元件驅(qū)動(dòng)抽水機(jī)軸心(shaft), 使驅(qū)動(dòng)輪 (impeller)轉(zhuǎn)動(dòng) 驅(qū)動(dòng)輪上面葉片(vanes)導(dǎo)引水流方面及將能量加入水中 驅(qū)動(dòng)輪轉(zhuǎn)動(dòng)使其上所有粒子向外加速, 產(chǎn)生離心力 抽水機(jī)空間及進(jìn)水口充滿水時(shí),

6、驅(qū)動(dòng)輪上水向外移動(dòng)使驅(qū)動(dòng)輪中心壓力下降, 使其他水由進(jìn)水口吸入2021/7/5132021/7/514 驅(qū)動(dòng)輪轉(zhuǎn)動(dòng)使輪上邊緣水分子有較高的流速 這些水分子離開驅(qū)動(dòng)輪時(shí), 速度快速降低, 其所含動(dòng)能水頭轉(zhuǎn)變?yōu)殪o水壓力水頭( static pressure head) 因此離心式抽水機(jī)中水分子由進(jìn)水口網(wǎng)出水口流動(dòng)時(shí)壓力將增加 出水口壓力為進(jìn)水口壓力及抽水機(jī)特性之函數(shù)2021/7/515抽水機(jī)設(shè)有軸封盒(stuffing box) 內(nèi)填有軸封材料, 使轉(zhuǎn)動(dòng)軸能密封, 避免由轉(zhuǎn)動(dòng)軸漏水 2021/7/516Pump bearing: (軸承軸承) 抽水機(jī)有潤滑的軸承, 潤滑劑採用石化產(chǎn)品或水 水產(chǎn)養(yǎng)殖

7、用抽水機(jī)以水潤滑較適當(dāng) 2021/7/517Volute (渦形) Centrifugal Pumps 2021/7/518Diffuser (擴(kuò)散器) Centrifugal Pumps 2021/7/519Open impellers 2021/7/520Semienclosed impellers 2021/7/521Enclosed impellers 2021/7/522Performance Characteristics 抽水機(jī)之操作特性包含一些數(shù)據(jù)抽水機(jī)之操作特性包含一些數(shù)據(jù), 通常以通常以圖形表示圖形表示: 顯示抽水機(jī)水頭顯示抽水機(jī)水頭(head), 效率效率(efficie

8、ncy), 出水量出水量(discharge)及需求能及需求能量量(power requirements)等主要參數(shù)間之等主要參數(shù)間之關(guān)係關(guān)係2021/7/5232021/7/5242021/7/5252021/7/526Deep Well Turbine (深井渦輪式抽水機(jī)) multistage centrifugal pumps, either volute or diffuser type 2021/7/527ROTARY PUMPS Rotary pumps consist of a casing and rotating member(s) that force the fluid

9、 from the low to high pressure side. 2021/7/528Propeller (螺槳螺槳) Pumps Propeller pumps are best used for conditions of low head and high discharge 2021/7/5292021/7/530 Single-stage propeller pumps are limited to heads of 7 to 8 m, whereas multistage pumps are built for heads up to about 40 m. Pump di

10、scharges are available up to several thousand cubic meters per minute. Propeller pump speed is limited by cavitation at the propeller tips. Since the tip velocity increases with diameter, the larger the propeller diameter, the slower it must turn. Large pumps commonly operate in the 100 to 300 rpm r

11、ange, too slow for direct coupling to an electric motor. 2021/7/531Flexible Tube Pumps 2021/7/532 Low volume pumps. Generally used as metering pumps for metering corrosive liquids Provide adjustable and accurate flow rates and are particularly applicable for corrosive liquids. Pressure capabilities

12、of flexible tube pumps are relatively low, the maximum pressure depending on flexible tube strength. 2021/7/533RECIPROCATING PUMPS Piston (活塞) Pumps - theoretical suction lift of 10.3 m and a practical limit of 7 or 8 m 2021/7/534 Diaphragm (隔膜) Pumps 高壓、高揚(yáng)程、低流量抽水機(jī) 定量抽水機(jī)2021/7/535 Airlift Pumps (氣提泵

13、) hmm = hs1 2021/7/536若連續(xù)地注入足夠之空氣，則hm hs h1 ，氣提泵可連續(xù)運(yùn)轉(zhuǎn)。 使hmm恰好等於hs1之氣流，為維持氣提泵運(yùn)轉(zhuǎn)之最小氣流量。 設(shè)泵恰好可運(yùn)轉(zhuǎn)時(shí)之h1 = ho，則管子浸於水中之高度hs及氣體體積分量Qa之關(guān)係 (by Andeen, 1974) 為 ho = Qa/(1 - Qahs) 2021/7/537最小氣流量 (by Todoroki et al., 1973): 管徑 25 - 100 mm、管長 4 - 42 m及浸水比例0.4 - 0.8Qam = 0.35 (1 Ms) A(gd)1/2/(1.2 Ms 0.2) Qam = 啟動(dòng)泵

14、之最小氣流量，cm3/sMs = hs/hmA = 氣提管斷面積，cm2g = 重力加速度，cm/s2d = 氣提管管徑，cm 2021/7/538氣泡與液體之相對(duì)速度差 (slip) 與氣泡尺寸成比例，氣泡越小slip越小，能量損失越小，氣提泵效率越高。 靜止流體中氣泡之上升速度為slip之近似值 氣提泵中，氣泡之理想直徑為越小越好，但管柱中氣泡流僅於氣體體積10%以下時(shí)才能產(chǎn)生，氣液比更高時(shí)，氣泡將結(jié)合成大氣泡。注氣流量維持10%，則氣提泵之水頭提升為0.1 hs。 2021/7/5392021/7/540氣泡之產(chǎn)生：by orificeRb = (St)(Ro)/g(e - g)1/3

15、Rb = bubble radius (cm)St = surface tension (g-cm/s2)Ro = orifice diameter (cm)g = acceleration of gravity (cm/s2)e = density of liquid (g/cm3) g = density of gas (g/cm3) 2021/7/541氣提泵之效率經(jīng)驗(yàn)公式：提升1 liter 水所需之空氣體積 (m3) Q = 0.8 h1/C log (hs + 10.36)/10.36 2021/7/5422021/7/543Fitting a pump to the system 為一特定用途，選用正確水泵，需先瞭解：各種型式泵之特性、系統(tǒng)總水頭與出水量需求及待泵送流體之性質(zhì)。另外需知泵之吸水高度及井之液降特性。首先考慮泵水成本降低，應(yīng)使泵操作於最佳效率，並參考設(shè)備成本、操作成本及維修成本，綜合決定選用之泵。 泵之NPSH不可超過限度，否則產(chǎn)生穴蝕 (cavitation)，將增加維護(hù)費(fèi)及降低效率。泵所需總水頭 = 靜壓水頭 + 流體摩擦損失 + 流速水頭 2021/7/544井洩降 洩降影響泵之選擇：泵於形成之洩降錐條件下，仍有足夠之出水量，不可超過最大出水量；相鄰之井，洩降錐相互影響。 2021/