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渣漿泵的汽蝕現(xiàn)象怎么發(fā)生的與防止
什么是汽蝕現(xiàn)象呢?可以從日常生活來談起:如果在一個大氣壓力作用下，將水加熱到100°C就會有大量氣泡從水中析出——水沸騰了。但是在高山上，由于空氣稀薄而氣壓低，水不到100C就會冒出大量氣泡。如果水面壓力降低到0. 024atm以下時，水在20C的常溫下也會冒出大量的氣泡，水沸騰。所以水的汽化不但與溫度有關(guān)，而且還與壓力有關(guān)。在一一定溫度下，液體開始汽化的臨界壓力叫做汽化壓力(或稱飽和蒸汽壓力)，用p，表示。水在各種溫度下的汽化壓力P，見表1-1和表1-2，其他液體在各種溫度下的汽化壓力p,如圖3- 1所示。
從離心泵的工作原理中知道，泵能將低處的液體吸上來是由于葉輪轉(zhuǎn)動產(chǎn)生離心力，使泵的進口處壓力降低產(chǎn)生真空，也就是低于大氣壓力，而吸水池的液面上有一個大氣壓力，在其作用下把液體壓上來了。如果泵的安裝離吸入液面越高，則泵的進口的壓力要求更低，真空度更大，才能把液體吸上來。當(dāng)泵進口處的壓力低至該溫度下該液體的汽化壓
力時，雖然在常溫下，該液休也會汽化而產(chǎn)生大量氣泡，這些氣泡隨液體一起流入葉輪流道中。由于泵通過旋轉(zhuǎn)的葉輪對液體作功，使液體能量逐漸增加，液體的壓力又逐漸升高，液體中的氣泡受壓破裂，重新凝結(jié)成液體而消失。這時，氣泡四周的液體質(zhì)點以很高的速度運動補充，質(zhì)點互相撞擊，在瞬間產(chǎn)生很高的壓力(即水錘現(xiàn)象)，產(chǎn)生很強的水擊波就像無數(shù)個小彈頭連續(xù)打擊葉片表面，久而久之，金屬表面逐漸因疲勞破壞，在葉片上產(chǎn)生蜂窩狀的小塊剝落，通常稱為剝蝕。在所產(chǎn)生的氣泡中，還有一些活潑氣體( 如氧等)，借助氣泡凝結(jié)時所放出的熱量對金屬起化學(xué)腐蝕、電化腐蝕與機械剝蝕的共同作用，加快了對金屬的損壞速度，這種現(xiàn)象就叫做汽蝕現(xiàn)象。
泵開始發(fā)生汽蝕時，氣泡較少，區(qū)域也較小，對泵的正常工作沒有明顯影響，但當(dāng)發(fā)展到一定程度時，就會影響到泵的性能(流量、揚程、功率、效率)明顯下降(泵的汽蝕試驗就是利用這一現(xiàn)象進行判斷)， 并發(fā)生振動、噪聲。當(dāng)汽蝕進一步發(fā)展，氣泡大量產(chǎn)生就會造成性能曲線急劇下降(圖3-2)，液體產(chǎn)生斷流而泵無法工作。所以泵的汽蝕問題必須應(yīng)予重視與防止。
渣漿泵廠家
How to prevent cavitation of slurry pump
What is cavitation? We can start from our daily life: if water is heated to 100 ° C under the action of an atmospheric pressure, a large number of bubbles will come out of the water - the water will boil. But in the high mountains, because the air is thin and the air pressure is low, a lot of bubbles will appear when the water is less than 100C. If the water pressure drops below 0.024atm, a large number of bubbles will appear and the water will boil at 20c. So the vaporization of water is not only related to temperature, but also to pressure. At a certain temperature, the critical pressure at which the liquid begins to vaporize is called the vaporization pressure (or saturated steam pressure), which is expressed as P. See Table 1-1 and table 1-2 for the vaporization pressure P of water at various temperatures, and Figure 3-1 for the vaporization pressure P of other liquids at various temperatures.
From the working principle of centrifugal pump, it is known that the pump can suck up the liquid at the low position because the centrifugal force is generated by the rotation of the impeller, which reduces the pressure at the pump inlet and generates a vacuum, that is, the pressure is lower than the atmospheric pressure, and there is an atmospheric pressure on the liquid surface of the water suction tank, under the action of which the liquid body is pressed up. If the installation of the pump is higher than the suction liquid level, the pressure requirement of the pump inlet is lower and the vacuum degree is greater, then the liquid can be sucked up. When the pressure at the pump inlet is low to the vaporization pressure of the liquid at this temperature
In case of force, although at normal temperature, the liquid will also vaporize and generate a large number of bubbles, which will flow into the impeller passage together with the liquid. Because the pump works on the liquid through the rotating impeller, the liquid energy increases gradually, the pressure of the liquid increases gradually, and the bubbles in the liquid break under pressure and condense into liquid again and disappear. At this time, the liquid particles around the bubble move at a very high speed to supplement each other, and the particles collide with each other, generating a very high pressure (i.e. water hammer phenomenon) in an instant, and generating a strong water shock wave is like countless small warheads hitting the surface of the blade continuously. Over time, the metal surface gradually suffers from fatigue damage, resulting in honeycomb like small pieces of peeling off on the blade, which is usually called denudation. In the generated bubbles, there are also some active gases (such as oxygen, etc.), with the help of the heat released when the bubbles condense, they play a joint role of chemical corrosion, electrochemical corrosion and mechanical erosion on the metal, accelerating the speed of metal damage, which is called cavitation phenomenon.
When cavitation occurs at the beginning of the pump, there are fewer bubbles and smaller areas, which has no obvious impact on the normal operation of the pump. However, when it develops to a certain extent, it will affect the performance of the pump (flow, head, power, efficiency) significantly reduced (the cavitation test of the pump is to use this phenomenon for judgment), and vibration and noise will occur. When cavitation develops further, a large number of bubbles will cause a sharp decline in performance curve (Fig. 3-2), resulting in fluid cut-off and the pump can not work. Therefore, the cavitation problem of pump must be paid attention to and prevented.
Slurry pump
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