化工专业英语课件四

1、Specialized English for chemistry,化工专业英语,Unit OperationMass Transfer and Its Application,A group of operations for separating the components of mixtures are based on the tranfer of material from one homogenous phase to another. homogenous adj. 同性质的，同类的; Unlike purely mechanical separations,these met

2、hods utilize differences in vapor pressure,solubility,or diffusivity,not density or particle size. mechanical .adj. 机械的，机械学的;呆板的;体力的;手工操作的 utilize .vt. 利用，使用 solubility .n. 溶解度;可解决性;溶度 diffusivity .n. 扩散能力，扩散率;扩散性 density .n. 密度;稠密，浓厚;物浓度，比重;愚钝,The driving force for mass tranfer is a concentration d

3、ifference or a difference in activity,much as a temperature difference or a temperature gradient provides the driving force for heat tranfer. gradient .n. 物梯度，陡度;（温度、气压等）变化率，梯度变化曲线;（道路. adj. 倾斜的;动步行的，能步行的,These methods,covered by the term mass-tranfer operations,include such techniques as distillati

4、on,gas absorption,dehumidification,liquid extraction,leaching,crystallization,membrane separation,and a number of others. dehumidification .n. 除去湿气;除湿 crystallization .n. 结晶化,The function of distillation is to separate,by vaporization,a liquid mixture of miscible and volatile substances into individ

5、ual components or,in some cases,into groups of components. vaporization .n. 蒸发;汽化 miscible .adj. 易混合的 volatile adj. 易变的，不稳定的;（液体或油）易挥发的;爆炸性的;快活的，轻快的,The separation of a mixture of alcohol and water into its components;that of liquid air into nitrogen,oxygen and argon;and that of crude petroleum into

6、 gasoline,kerosene,fuel oil and lubricating stock are examples of distillation. alcohol .n. 乙醇，酒精;含酒精的饮料 argon n. 氩 petroleum .n. 石油 kerosene n.煤油，火油;灯油;洋油 lubricating vt.加油润滑;使润滑 vi.润滑,In practice, distillation may be carried out by either of two principal methods. The first method is based on the

7、return to the still in contract with the vapors. The second method is based on the return of part of the condensate to the still under such conditions that this returning liquid is brought into intimate contract with the vapors on their way to the condenser. condensate n.冷凝物 intimate adj.亲密的，亲近的;私人的

8、，个人的;内部的;直接的,Either of these methods may be conducted as a continuous or as a batch process. In chemical engineering,differential distillation,steam distillation,single-stage partial vaporization without reflux(flash distillation) and continuous distillation with reflux(rectification) are often used

9、. reflux n.逆流，退潮,In gas absorption a solute gas is absorbed from an inert gas into a liquid in which the solute is more or less soluble. solute n.溶解物，溶质 The washing of ammonia from a mixture of ammonia and air by means of liquid water is a typical example. ammonia 氨;氨水;氨气,The solute is subsequently

10、recovered from the liquid by distillation,and the absorbing liquid can be either discarded or reused. subsequently adv.其后，随后，接着 When a solute is transferred from the solvent liquid to the gas phase,the operation is known as desorption or stripping.,In dehumidification,a pure liquid is partially remo

11、ved from an inert or carrier gas by condensation. dehumidification Usually,the carrier gas is virtually insoluble in the liquid. virtually adv.实际上，实质上，事实上，几乎;无形中;无形 insoluble adj.不能解决的，不溶的,Removal of water vapor from air by condensation on a cold surface and the condensation of an organic vapor such

12、 as carbon tetrachloride out of a stream of nitrogen are examples of dehumidification. carbon tetrachloride 四氯化碳 dehumidification,In humidification operations the direction of transfer is from the liquid to the gas phase. In the drying of solids,a liquid,usually water,is separated by the use of hot,

13、dry gas(usually air) and so is coupled with the humidificationof the gas phase.,In membrane separation,including gas separations,reverse osmosis,and ultrafiltration,one component of a liquid or gaseous mixture passes through a selective membrane more readily than the other components. membrane rever

14、se osmosis 逆渗透;反渗;反渗透;反渗析 ultrafiltration n.超滤（作用）;超过滤,The fundamental driving force is the difference in thermodynamic activity,but in many cases the driving force can be expressed as a difference in concentration or partial pressure. partial pressure 局部压力;气体分压;分压力;部分压力 In adsorption a solute is re

15、moved from either a liquid or a gas through contact with a solid adsorbent,the surface of which has a special affinity for the solute. affinity n.密切关系，姻亲关系;（男女之间的）吸引力，吸引人的异性;类同;类,In general,drying a solid means the removal of a relatively small amount of a water or other liquid from the solid materi

16、al,to reduce the content of residual liquid to an acceptable low value. residual liquid Drying is usually the final step in a series of operations,and the product from a dryer is often ready for final packaging.,Water or other liquids may be removed from solids mechanically by presses or centrifuges

17、 or thermally by vaporization. mechanically adv.机械方面地;机械地;物理上地;呆板地 centrifuges n.离心机( centrifuge的名词复数 ) It is generally cheaper to remove water mechanically than thermally,and thus it is advisable to reduce the moisture content as much as practicable before feeding the material to a heated dryer.,Th

18、e moisture content of a dried substance varies from product to a product. Drying is a relative term and means merely that there is reduction in moisture content from an initial value to some acceptable final value. relative adj.相关的;相对的;相互有关的;比较而言的 n.亲属，亲戚;相关物;亲缘植物（或动物）;语法学关系词,In liquid extraction,so

19、metimes called solvent extraction,a mixture of two components is treated by a solvent that preferentially dissolves one or more of the components in the mixture. solvent extraction 溶剂提取 preferentially 优先地 The mixture so treated is called the raffinate,and the solvent-rich phase is called the extract. raffinate n.（石油）残油液，剩余液;萃余液;残液,The component tranferred from raffinate to extract is the solute,and the component left behind in the raffinate is the diluent. diluent adj.冲淡的，稀释的 n.稀释液，稀释药 The solvent in the extract leaving the extractor is usu