第九章-动力循环.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Chapter 9 Vapor Power Cycle,蒸汽动力循环,9.1 Basic Power Cycle using Water Vapor-Rankine Cycle,(基本蒸汽动力循环-朗肯循环),9.2 The Diesel Cycle(狄塞尔循环),9.3 燃气轮机装置循环,水蒸气：,火力发电、核电,低沸点工质：,氨、氟里昂,太阳能、余热、地热发电,动力循环：,以获得功为目的,朗肯循环的提出与卡诺循环,s,T,6,4,2,1,10,9,8,7,5,3,卡诺,最大；,等温吸热,41,难实现,11,点,x,太小,不利于汽机强度；,12-9,两相区难压缩；,w,net,卡诺,小,由于温差小，所以效率不会很高，且乏汽干度过小，,卡诺,朗肯,；,went,卡诺,w,net,朗肯,11,12,在温限,1234,对比5678,对比9-10-11-12,四个主要装置：,锅炉,汽轮机,凝汽器,给水泵,10-1,Basic Power Cycle using Water Vapor-Rankine Cycle,基本蒸汽动力循环-朗肯循环,1.水蒸气动力循环系统,锅,炉,汽轮机,发电机,给水泵,凝汽器,锅,炉,汽轮机,发电机,给水泵,凝汽器,朗肯循环,1,2,3,4,简化（理想化）：,1,2,汽轮机,s,膨胀,2,3,凝汽器,p,放热,3,4,给水泵,s,压缩,4,1,锅炉,p,吸热,RANKINE CYCLE,4,3,2,1,T,s,h,s,1,3,2,4,(2)朗肯循环T-s和h-s,图,1,2,汽轮机,s,膨胀,2,3,凝汽器,p,放热,3,4,给水泵,s,压缩,4,1,锅炉,p,吸热,h,s,1,3,2,4,2.朗肯循环功和热的,计算,汽轮机作功：,凝汽器中的定压放热量：,水泵绝热压缩耗功：,锅炉中的定压吸热量：,h,s,1,3,2,4,朗肯循环热效率的,计算,一般很小，占,0.8,1%,，忽略泵功,朗肯循环,与卡诺循环比较,s,T,6,4,2,1,10,9,8,7,5,3,卡诺,最大,；,等温吸热,41,难实现,11,点,x,太小,不利于汽机强度；,12-9,两相区难压缩；,w,net,卡诺,小,由于温差小，所以效率不会很高，且乏汽干度过小，,卡诺,朗肯,；,went,卡诺,缺点,T,s,6,5,4,3,1,b,2.蒸汽再热循环 (reheat cycle),When steam leaves the turbine,it is typically wet.,The presense of water causes erosion of the turbine blades.,To prevent this,steam is extracted from high pressure turbine(state 2),and then it is reheated in the boiler(state 2)and sent back to the low pressure turbine.,T,s,6,5,4,3,1,b,蒸汽再热循环的,热效率,再热循环本身,不一定,提高循环热效率,与再热压力有关,x,2,降低,给提高初压创造了条件，选取再热压力合适，一般采用,一次再热可使热效率提高,2,3.5,。,蒸汽再热循环的实践,再热压力,p,b,=,p,a,0.2,0.3,p,1,p,1,13.5MPa,，一次,再热,超临界机组，,t,1,600,，,p,1,25MPa,，,二次,再热,T,s,6,5,4,3,1,b,蒸汽再热循环的,定量计算,吸热量：,放热量,：,净功（忽略泵功）：,热效率：,10-3,热电联产(供)循环,用发电厂作了功的蒸汽的余热来满足热用户的需要，这种作法称为,热电联(产)供,。,背压式机组,(,背压0.1MPa,),热用户为什么要用换热器而不直接用热力循环的水？,Cogeneration,背压式,缺点,：,热电互相影响,供热参数单一,抽汽调节式热电联产(供)循环,抽汽式热电联供循环,可以自动调节热、电供应比例，以满足不同用户的需要。,热电联产(供)循环的经济性评价,只采用热效率 显然不够全面,能量利用系数,，但未考虑热和电的品位不同,Ex,经济学评价,热电联产、集中供热是发展方向，经济环保,Utilization factor,熟悉,朗肯循环,图示,与,计算,朗肯循环,与,卡诺循环,蒸汽参数,对朗肯循环热效率的影响,4.,再热,、,回热原理及计算,小 结,Summary,1.The Otto Cycle(奥托循环）,(1)Actual cycle(实际循环),The Otto cycle is an idealization of a set of processes used by spark ignition,internal combustion engines,(2-stroke or 4-stroke cycles).,10-4 Internal combustion engines,(内燃机),0 1:吸入空气;,1 2:压缩过程;,2 3:喷油燃烧过程;,3 4:喷油燃烧过程;,4 5:膨胀过程;,5 1:排气过程;,1 0:排出剩余的废气,Otto循环,a)ingest a mixture of fuel and air,b)compress it,c)cause it to react,thus effectively adding heat through converting chemical energy into thermal energy,d)expand the combustion products,and then,e)eject the combustion products and replace them with a new charge of fuel and air.,(2)Otto循环的简化,_,We model all of these happenings by a thermodynamic cycle consisting of a set of processes all acting on,a fixed mass of air,contained in a piston-cylinder arrangement.The exhaust and intake processes are replaced by constant-volume cooling.）,1,2:压缩过程;,2 3:喷油燃烧过程;,4 5:膨胀过程;,5 1,:排气过程;,1-2 Compress mixture quasi-statically and adiabatically,2-3 Ignite and burn mixture at constant volume(heat is added),3(4)-5 Expand mixture quasi-statically and adiabatically,5-1 Cool mixture at constant volume,Representation of the thermodynamic cycle.,(3)Thermal Efficiency of Otto Cycle,(奥托循环的热效率),提高循环的压缩比,提高循环的最高温度,2.The Diesel Cycle,(狄塞尔循环),The diesel internal combustion engine differs from the gasoline powered,Otto cycle,by using a higher compression of the fuel to ignite the fuel rather than using a spark plug(compression ignition rather than spark ignition),Thermal Efficiency of Disel Cycle,狄塞尔循环的热效率：,提高循环的压缩比,降低循环的预胀比,提高循环的最高温度,3.The Dual Cycle,(混合加热循环,),其中,1-2是定熵压缩过程,2-3是可逆定容加热过程,3-4是可逆定压加热过程,4-5是定熵膨胀过程,5-1是可逆定容放热过程.,几个定义：压缩比:,定容升压比:,定压预胀比:,:,混合加热循环的热效率:,提高热效率方法：,提高循环的压缩比降低循环的预胀比,提高循环的最高温度,由上面的三个定义,得:,讨论:随 ,的升高而升高;,随 的升高而降低.,(1)具有相同的压缩比,从T-S图可知:由于三个循环的放热量相同,故热效率的高低次序为:,4.活塞式内燃机三种理想循环的比较,(2)具有不同的最高压力和最高温度,从图可以看出，三循环的放热量相同，吸热量有：,所以,热效率的高低为:,考虑到实际的情况,三循环的热效率高低为:,1.燃气轮机装置,燃气轮机的构成:压气机,燃烧室,燃气轮机,简单的装置如图示:,10-5 燃气轮机装置循环,燃气轮机循环,功率的分析压气机耗功:燃气轮机做功:净功:,吸热量:,放热量:,热效率:,式中 ,称为增压比.,对于给定的气体,k一定时,热效率随增压比的升高而升高;,当增压比等于1 时,热效率为零.,提高循环的增压比,可提高循环的热效率.,讨论:,实际的燃气轮机循环存在不可逆因素,以压气机的绝热效率来修正.,