《泵与压缩机》练习题答案

1、泵与压缩机练习题第一章1-1解:32210854.71.044-=D As m A Q /203.110854.73600343=-, m g d L h 266.08.92203.11.01802.0222=h g g p H g p g +=222211 Pah g Hg g p p 5552522112105485.0104645.010013.1266.08.92203.14.48.9100010013.12=-= +-= +-= 521104645.0=-=p p p 真 mmHg p H 5.34828.133104645.028.1335=真真O mmH O mH p H 225

2、25597597.59800105485.09800=1-2解: gg p z H g g p z 2222222111+=+ gp g p z z H 1212-+-= Pa p 613168.9136003.010013.151=-= Pa p 24840014710010013.152=+=m H 95.258.9750613162484005.0=-+=1-5解:1当泵流量h m Q T /2.73=时s m nD u /8206022=s m B D Q c T r /555.036009.0007.0182.02.72222=s m ctg ctg c u

3、 c A r u /856.1230555.082.1302222=-=-=m c u g H r T 13.18856.1282.138.91122= 2当泵流量h m Q T /8.283=时s m B D Q c T r /221.236009.0007.0182.08.282222='s m ctg ctg c u c A r u /975.93022.282.1302222=-=-=' m c u g H r T067.14975.982.138.91122=' 3画出两种流量时叶轮出口的速度三角形(略随流量T Q 的增大,r c 2增加,u c 2减小,T

4、H 下降。1-6解:s m nD u /406.3360290022.06022=s m B D Q c T r /617.301.022.0025.0222=s m c w A r /655.922sin 617.3sin 0222=s m ctg ctg c u c A r u /454.2422617.3406.3302222=-=-=0222413.8454.24617.3=arctg c c arctgu r m c u g H r T 357.83454.24406.338.91122=1-7解:s m nD u /295.2460145032.06022=938.029sin 3

5、2.0005.061sin 102222=-=-=A D zs m nD u /3.12601450162.06011=809.018sin 162.0005.061sin 101111=-=-=A D z s m tg tg u c A r /997.3183.120111=s m c B D Q r T /054.0997.3809.0033.0162.031111= s m B D Q c T r /031.3938.0019.032.0054.02222=mctg R z ctg c u u g H A A r T 332.3229sin 30145016.06938.029031.3

6、295.24295.248.91sin 1002222222= -=-=s m Q Q T v /0513.0054.095.03= m H H T h 1.29332.329.0=kW gQHN e 629.1410001.290513.08.910001000=kW N N e84.1782.0629.14=1-13解:1根据等比定律: '='n n Q Q 2'='n n H H 3 '='n n N N将转速min /2900r 泵的性能参数换算为转速min /2320r 时性能参数,如下表所示: 2根据相似抛物线得2222203125.

7、04050Q Q Q Q H H =''= 求相似抛物线与转速为min /2900r 时的流量扬程曲线的交点,交点处的流量为h m /3.443,m 33.61点为相似工况点。20406080100120140050100150200HQmin /26183.44402900r Q Q n n = '='1-15解:1求泵在min /2900r 时的比转速min /32.584280360064290065.365.34343r i H Q n n s = = =泵为低比转速泵2求泵在min /1450r 时的比转速h m n n Q Q /3229001450

8、643='='m n n H H 702900145028022= '='min /32.58470360032145065.365.34343r i H Q n n s = =''='1-18解: 1绘出泵在min /2950r 时的Q H -和Q -曲线和比转速 H (m Q (L/s (%Q (L/smin /58.65748.1860051.0295065.365.34343r i H Q n n s = = =2绘出转速变化到min /1450r n ='时泵的效率下降%5=的工作范围 工作流量范围1.923.04L/s

9、 (%Q (L/s3求泵流量4.5L/s 、扬程180m 对应的泵转速根据相似抛物线22222889.85.4180Q Q Q Q H H =''=, 求相似抛物线与转速为min /2950r 时泵的流量扬程曲线的交点。交点处的流量s L /688.4,扬程m 454.195。12345678050100150200250H (m Q (L/smin /7.2831688.45.42950r Q Q n n = '=' 4求切割叶轮的直径通过切割叶轮外径,实现泵流量4.5L/s 、扬程180m 对应的泵叶轮外径。96.0688.45.422='='

10、;Q Q D D 04.096.01222=-='-D D D mm Q Q D D D D Q Q 5.17278.172688.45.41802222='=''=' 最高效率点处的流量为887.4,扬程。1-21.解:1判断在条件1下泵是否发生汽蚀选择液面的Z 坐标为零,建立液面到泵入口的伯努里方程:S A S S S AA h gV g p Z g V g p -+=+2222 S A Av A S S v S h gV g p p Z g V g p p ha -+-+-=+-=2222根据已知条件:0=A V ,0=-gp p vA ,2=-S

11、 A h ,81-=g S H Z 。故有效汽蚀余量a h 为: m h H ha S A g 6281=-=-=-,m h ha 4.4=>此时,故泵不发生汽蚀。2计算泵开始发生汽蚀时的液面高度当h h a <时,泵发生汽蚀。因此h h Z ha S A S <-=-m h h Z S A S 4.624.4-=-=->-m H g 4.61->时泵开始发生汽蚀。3当安装高度m H g 0.41-=,计算泵不发生汽蚀的最大工作流量根据流量为min /5.03m Q =时的r h 和f h ,计算0k 和1k ,即85.0222121=Q h k Q k h f

12、f 165.0422020=Q h k Q k h r r 当h h a 时,泵不发生汽蚀。因此h h H ha S A g =-=-1h h H S A g =-1min /387.01684.044.04.0301120211m k k H Q Q k Q k H g g =+-=+-=+=-4当转速由min /1450r 提高到min /2900r ,判断泵是否发生汽蚀 根据比例定律,得min /0.1145029005.03m n n QQ ='=' m Q k h f 0.80.10.8221= 0.160.116220=Q k h r 0881=-=-=-S A g

13、 h H har a h h <,泵发生了汽蚀。1-24.解:s m D QV /415.115.04025.0422=m g V D L h SA 99.08.92415.115.015037.06222= += +=- 建立液面到泵入口的伯努里方程:S A S S S AA h g V g p Z g p Z -+=+22S A S A S S A h gV Z Z g p p -+-=-22 S A S g S h gV H H -+=221r S A K S A A h h g pZ g p Z +=+- S A g KA r h H gp p h -=1 又因v K p p =

14、时,S S p p '=,对应的真空度为最大真空度max S H ,对应的安装高度为最大安装高度max 1g H 。因此S A S g S S A S g S h gV H H h g V H H -'+'+='+'+=22212max 1maxS A g v A S A g v A r h H gp p h h H g p p h -=-=1max 1 h gV g p p H h g V g p p H S v A S r S v A S -'+-=-'+-=2222maxK H H S S -=max由于泵的许用真空度是用清水在标准

15、条件下给出的,所以用清水计算许用汽蚀余量水h ,即:m H g V g p p h S S v a 568.55.48.92415.18.910002337100000222=-+-=- '+-=水水水根据题意,水与油的汽蚀余量基本相等,故h h =水。m h g V g p p H S v A S 974.6568.58.92415.18.975029425.95124222=-+-=-'+-=m h gV H H S A S S g 88.599.08.92415.1974.62221=+-= '+'-=-1-28.解:作单泵的H-Q 曲线。根据两泵并联时扬程不变,流量为相同扬程下各泵对应流量之和,作两泵并联时的H-Q 曲线。回归H-Q 曲线,得:单泵的H-Q 曲线:20.05815Q -1.10924Q +56.31092H = 两泵并联时的H-Q 曲线: