【正文】 run in this condition for a prolonged period． (7)It is much smaller than other pumps of equal capacity． It can， therefore， be made into a sealed unit with the driving motor and immersed in the suction tank． (8)Liquids containing high proportions of suspended solids are readily handled． The main disadvantages are： (1)The single—stage pump will not develop a high pressure． Multistage pumps will develop greater heads bat they are very much more expensive and cannot readily be made in corrosion—resistant material because of their greater plexity． It is generally better to use very high speeds in order to reduce the number of stages required． (2)It operates at a high efficiency over only a limited range of conditions。 7． 全開吸入管路閥門。三個半容量泵可以比一個大的泵便宜，加上備用。 2）降低流體的溫度 ?注射少量液體冷卻器往往是不切實際的。通料 口可以在寒冷的天氣凍結(jié) 。 (5) 解決方案和補(bǔ)救辦法：對于汽化 （蝕） 問題 1. 防止 汽化問題，必須增加吸頭，降低流體的溫度，或減少 NPSH（汽蝕余 量） 必需的。曾經(jīng)有 泡沫破滅 的壓力大于 1 GPA（ 145x106 磅）的報道。由于葉輪旋轉(zhuǎn)作用，氣泡達(dá)到非常高的速度，并最終達(dá)到葉輪內(nèi)的高壓地區(qū)，在那里他們開始崩潰。 （ 4）汽蝕的機(jī)理：氣蝕現(xiàn)象是一個循序漸進(jìn)的過程，如圖所示（下） 步驟之一，流動液體內(nèi)氣泡的形成。因此，重要的是理解現(xiàn)象，充分預(yù)測和減少汽蝕產(chǎn)生的危 害 ，也給診斷汽蝕問題找到切實可行的解決方案 1）汽蝕增強(qiáng)化學(xué)腐蝕 泵在汽蝕條件下 變得更容易受到腐蝕和化 學(xué)攻擊。 總能頭： 定義為總靜壓和總動壓的總和。在能源方面，靜態(tài)壓力是流體的勢能。 的液體汽化 而引起的 泡沫的形成。 （ 5）不能 有效處理粘性液體。因此，它可以利用電動機(jī)做成密封裝置沉浸在吸收罐中。 于是有： τ=Qρ（ u2r2cosθ2 – u1r1cosθ1） 離心泵的優(yōu)缺點 5 主要優(yōu)點有： （ 1）制造簡單，可用多種材料加工。在圖 c 中， 4 c. vu是液體相對于葉片的速度， tu 是葉片上某點的切向速度；將這兩個速度合成即可得到液體的速度 2u 。 流體通常在軸向上通過葉片的上升進(jìn)入泵殼。泵的整個外殼可用像聚丙烯這樣的塑料來建造，或者用腐蝕襯里加工。如 果 截止 閥泄露了，泵可以通過閥的入口，從外面的水源比如說蓄水池來取水灌注。 離心泵被認(rèn)為是旋轉(zhuǎn)泵，它有一個旋轉(zhuǎn)地葉輪，葉輪上 有 葉片，葉 片 是侵入液體中的 。在遠(yuǎn)古的中東，因為對農(nóng)場進(jìn)行灌溉的需求，所以有一種強(qiáng)大的動力去推進(jìn)水泵的進(jìn)程。 關(guān)鍵詞：離心泵 介紹 工作原理 汽蝕 汽蝕原理 預(yù)防措施 泵的 提出， 最先是用于 轉(zhuǎn)移或壓縮液體和氣體的設(shè)備。 從而 幫助我們 加深對離心泵的理解。螺旋泵經(jīng)常用在污水處理廠中，因為它 們可以運輸大量的水，而不會因為碎片而堵塞。這個泵有超過灌溉一百萬英畝的土地能力。也可以通過在吸入線上放另一個截止閥來實現(xiàn)，截止閥在泵停止工作時是液體保留在泵內(nèi)。它能輸送性能非常廣泛的液體和固體含量高的懸浮液，像泥 泥漿，可以用多種抗腐蝕材料建造 。由此可以看出，在很大程度上，葉片末端的角度決定了泵的工作特性 。液體的運動方向相對于泵殼 —— 和固定葉片所需的角度一樣 —— 是兩個速度的合 成方向。 如果流體在與切向方向成 θ 角上以速度 u 流動，則這部分質(zhì)量流體的角動量為 =dM(urcosθ ) 流體通過泵所產(chǎn)生的扭轉(zhuǎn)力等于角動量對時間的改變量 dτ=dM t?? (u r cosθ)=2πr bρdr t?? ( u r cosθ) 液體的體積流速為： Q=2π r b t?? Dr=Qρd(u r cosθ) 因此，液體在泵中受到總的扭轉(zhuǎn)力由 dτ 在小標(biāo) 1和 2之間積分而得，下標(biāo) 1引用的是泵入口處的條件，小標(biāo) 2是出口時的條件。 （ 7）與其它泵相比，體積較小。 （ 4）在輸送和吸收管道中，如果沒有止回閥，液體就會在泵停止瞬間倒流到吸入槽內(nèi)。 一般來說，液體內(nèi) 氣泡 的形成 有 兩種類型：蒸汽氣泡或氣 態(tài)空 泡。例如，當(dāng)提到 管 道，靜壓是內(nèi)管和外管的壓力之間的差異，而不用管 任何管道內(nèi)的氣流。的速度減慢的過程中 存在的壓力。 （ 3）汽蝕的危害 ：汽蝕可以摧毀泵和閥門，可立即引起泵的效率損失，并且設(shè)備會不斷增加的效率損失，加速對泵 部件的 侵蝕。鑄鐵和青銅泵在工作 20 年或以上的時間，是沒有任何問題的，即使這些泵遇到一些腐蝕。形成的 液體氣泡從葉輪眼沿葉 片后緣尖流向葉輪出口。微噴后泡沫破裂產(chǎn)生的 力量， 使氣泡爆破。了解它的機(jī)Phenomenon of Cavitation 8 制和概念，可以幫助確定氣泡的類型和他們的形成和崩潰的原因。 ，不妨礙。 11. 增加 泵的轉(zhuǎn)速。 ?使用幾個較小的泵。 6． 增加的壓力。 10 CENTRIFUGAL PUMPS IN THE CHEMICAL INDUSTRY Abstract : A centrifugal pump converts the input power to kiic energy in the liquid by accelerating the liquid by a revolving device an impeller. The most mon type is the volute pump. Fluid enters the pump through the eye of the impeller which rotates at high speed. The fluid is accelerated radially outward from the pump chasing. A vacuum is created at the impellers eye that continuously draws more fluid into the pump . This article stresses on a series of centrifugal pumps， From a brief introduction to the principles. Keywords : centrifugal pump ,Introduction ,Working principle , Cavitation ， Mechanism of Cavitation ， Solution and Remedies 1. Introduction Pump ,device used to raise ,transfer ,or press liquids and gases .Four general classes of pumps for liquids are described below .In all of them ,steps are taken to prevent cavitation (the formation of a vacuum) ,which would reduce the flow and damage the structure of the pump .Pumps used for gases and vapors are usually known as pressors .The study of fluids in motion is called fluid dynamics. Water pump ,device for moving water from one location to another ,using tubes or other machinery .Water pumps operate under pressures ranging from a fraction of a pound to more than 10,000 pounds per square inch .Everyday examples of water pumps range from small electric pumps that circulate and aerate water in aquariums and fountains to sump pumps that remove water from beneath the foundations of homes . One type of modern pumps used to move water is the centrifugal pump .Early version of the centrifugal pump ,the screw pump ,consists of a corkscrewshaped mechanism in a pipe that ,when rotated ,pulls water upward .Screw pumps are often used in wastewater treatment plants because they can move large amounts of water without being clogged with debris .In the ancient Middle East the need for irrigation of farmland was a strong inducement to develop a water pump .Early pumps in this region were simple devices for lifting buckets of water from a source to a container or a trench .Greek mathematician and inventor Archimedes is thought to have devised the first screw pump in the third century BC .Later Greek inventor Ctesibius develop the first lift pump .During the late 17th and early 18th Centuries AD ,British engineer Thomas Savery ,French physicist Denis Papin ,And British blacksmith and inventor Thomas Newen contributed to the development of a water pump that used steam to power the pump’ piston .The steampowered water pump’s first wide use was in pumping water out of mines .Modernday examples of centrifugal pumps are those used at the Grand Coulee Dam 11 on the Columbia River .This pump system has the potential to irrigate over one million acres of land . Also known as rotary pumps ,centrifugal pumps have a rotating impeller ,also known as a blade ,that is immersed in the liquid .Liquid enters the pump near the axis of the impeller ,and the rotating impeller sweeps the liquid out toward the ends of the impeller blades at high pressure .The impeller also gives the liquid