【正文】 is often practical. ? Insulate the piping from the sun39。F) is kept in a closed container and the system pressure is reduced to its vapor pressure (about psia), the water quickly changes to a vapor. Also, if the operating pressure is to remain constant at about psia and the temperature is allowed to rise above 77 176。 1）Cavitation Enhanced Chemical Erosion Pumps operating under cavitation conditions bee more vulnerable to corrosion and chemical attack. Metals monly develop an oxide layer or passivated layer which protects the metal from further corrosion. Cavitation can remove this oxide or passive layer on a continuous basis and expose unprotected metal to further oxidation. The two processes (cavitation amp。 Vapour pressure. Static pressure ：The static pressure in a fluid stream is the normal force per unit area on a solid boundary moving with the fluid. It describes the difference between the pressure inside and outside a system, disregarding any motion in the system. For instance, when referring to an air duct, static pressure is the difference between the pressure inside the duct and outside the duct, disregarding any airflow inside the duct. In energy terms, the static pressure is a measure of the potential energy of the fluid. Dynamic pressure：A moving fluid stream exerts a pressure higher than the static pressure due to the kinetic energy (189。 Velocity head, Static pressure head, Total pressure, Dynamic pressure, Static pressure, this applies especially to turbine pumps． (3)It is not usually selfpriming. (4)If a nonreturn valve is not incorporated in the delivery or suction line, the liquid will run back into the suction tank as soon as the pump stops． (5)Very viscous liquids cannot he handled efficiently． 3. Cavitation in centrifugal pump （1）The term ‘cavitation’ es from the Latin word cavus, which means a hollow space or a cavity. Webster’s Dictionary defines the word ‘cavitation’ as the rapid formation and collapse of cavities in a flowing liquid in regions of very low pressure. In any discussion on centrifugal pumps various terms like vapor pockets, gas pockets, holes, bubbles, etc. are used in place of the term cavities. These are one and the same thing and need not be confused. The term bubble shall be used hereafter in the discussion. In the context of centrifugal pumps, the term cavitation implies a dynamic process of formation of bubbles inside the liquid, their growth and subsequent collapse as the liquid flows through the pump. Generally, the bubbles that form inside the liquid are of two types: Vapor bubbles or Gas bubbles. bubbles are formed due to the vaporisation of a process liquid that is being pumped. The cavitation condition induced by formation and collapse of vapor bubbles is monly referred to as Vaporous Cavitation. bubbles are formed due to the presence of dissolved gases in the liquid that is being pumped (generally air but may be any gas in the system). The cavitation condition induced by the formation and collapse of gas bubbles is monly referred to as Gaseous Cavitation. （2）Important Definitions: To enable a clear understanding of mechanism of cavitation, definitions of following important terms are explored. 本科畢業(yè)設(shè)計（論文）外文翻譯譯文文獻(xiàn)名稱（外文）CENTRIFUGAL PUMPS IN THE CHEMICAL INDUSTRYAbstract : A centrifugal pump converts the input power to kinetic 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，F(xiàn)rom a brief introduction to the principles.Keywords : centrifugal pump ,Introduction ,Working principle , Cavitation ， Mechanism of Cavitation ，Solution and Remedies1. 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 developme