发布时间 : 星期日 文章流体力学课后作业更新完毕开始阅读b2441c99a216147916112800
很小，没有延伸到层流底层，可认为管道是光滑管。问管道是光滑管的可容许的最大粗糙度大约为多少？
6.11 As shown in Fig.6-32, neglect minor loss, to ensure fluid flowrate in the siphon is qv＝10-3m3/s, determine: (1) when H=2m, l=44m, ?＝l.0?10-4m2 /s, ?=900kg/m3, what is d for ensuring laminar flow? (2) if the limitation vacuum on section A with a distance l/2 to the pipe inlet is pv=52 920Pa, what is the maximum allowed height Zmax of the siphon above the surface of upper oil storage pool?
如图6-32所示，不计局部损失，要保证虹吸管中液体的流量为qv＝10-3m3/s，试确定：(1) 当H=2m，l=44m，?＝l.0?10-4m2 /s，?=900kg/m3时，为保证层流，d应为多少？(2)若在距管进口l/2处的A断面上的极限真空为pv=52 920Pa，虹吸管在上面贮油池油面以上的最大允许高度
Zmax为多少？ Fig. 6-32 Problem 6.11
((1) 0.055m (2) 4.97m)
6.12 Water flows in a smooth plastic pipe of 200mm diameter at a flow rate of 0.1m3/s. Determine the friction factor ? for this flow.
水以0.1m3/s的流量在直径为200mm的塑料管中流动，试确定流动的沿程损失系数?。
6.13 Water flows from a tank along a vertical pipe of l＝2m and diameter d＝4m into atmosphere, as shown in Fig. 6-?. Neglect minor loss, friction loss factor is ?=0.04, find: (1) the relationship between the pressure at pipe’s initial section area A and the water level h in the tank, and the magnitude of h when the absolute pressure at A equals atmospheric pressure; (2) the relationship of the flowrate qv and the pipe length l, and the relationship that water level h satisfies when it does not change with l.
水从水箱沿着高l＝2m，直径d＝4m的竖直管道流入大气，如图所示。不计局部损失，并且沿程损失系数
?=0.04，试求：(1)管道起始断面A的压强与箱内水位h之间的关系式，并求当h为多少时，A处的绝对压强等 Fig.6-33 Problem 6.13 于大气压强；(2)流量qv与管长l的关系，并求出在水位 h满足什么关系时，将不随l而变化？
((1) pA?pa??g(?h?d)/(??d/l) h=1m (2) qv?h?d?4d22gd(h?l)
d??l? )
6.14 Air flows through the fine mesh gauze shown in Fig. 6-34 with an average velocity of 1.5m/s in the pipe. Determine the loss coefficient for the gauze.
空气在管道中以1.5m/s的平均流速通过如图6-34所示的细纱布。试确定纱布的损失系数。(56.7)
Fig.6-34 Problem 6.14
6.15 As shown in Fig.6-35, the heating furnace consumes heavy oil at a rate of qm=300kg/h, density and kinetic viscosity of oil are ?=880kg/m3 and ?＝25?10-6m2/s respectively, the pressurized oil tank is h＝8m above the sprayer’s axis, oil transporting pipe’s diameter is d＝25mm and length is l=30m. Find the gauge
pressure of heavy oil in front of the oil sprayer.
如图6-35所示，加热炉消耗qm=300kg/h的重油，重油的密度?=880kg/m3，运动粘度?＝25?10-6m2/s，压力油箱位于喷油器轴线以上h＝8m处，而输油管的直径d＝25mm，长l=30m。求
在喷油器前重油的表压强。( 62504Pa) Fig.6-35 Problem 6.15
6.16 Determine the pressure drop per 300m length of new 0.2m diameter horizontal cast iron water pipe when the average velocity is 1.7m/s.
确定直径为0.2m、长300m、平均流速为1.7m/s的水平放置铸铁水管上的压降。
6.17 As shown in Fig. 6-36, the lubricant consumption of the engine is qv＝0.4cm3/s, the lubricant is supplied to the lubricant housings via an oil pipe from the pressurized tank, the pipe’s diameter is d＝6mm and length is l＝5m. The density of the lubricant is ?=820kg/m3，and kinetic viscosity is ?＝15?10-6m2 /s. If the terminal pressure of the lubricant pipe equals atmospheric pressure, find the elevation h needed by the pressurized lubricant tank.
如图6-36所示，发动机润滑油的用量qv＝0.4cm3/s，
油从压力箱经一输油管供给到润滑部位，输油管的直径d＝6mm，长度l＝5m。油的密度产?=820kg/m3，运动粘度?＝15?10-6m2 /s，如果输油管道终端的压强等于大气 Fig.6-36 Problem 6.17
压强，求压力油箱所需要的位置高度h。(0.095m)
6.18 An above ground reservior of diameter 9 m and depth 1.5m is to be filled from a garden hose(smooth interior) of length 30m and diameter 0.2m. If the pressure at the faucet to which the hose is attached remains at 38kPa, how long will it take to fill the pool? Water exits the hose as a free jet 1.8m above the faucet.
一直径为9m、水深为1.5m高于地面的水池由一根长30m、直径0.2m的橡胶软管（内部光滑）灌水。如果连接软管的龙头压强保持为38kPa，求灌满游泳池所需的时间为多少？水在高于龙头1.8m处射流流出。(32小时)
6.19 As shown in Fig. 6-37, oil pump transports oil from an open oil pool to the oil tank of gauge pressure p＝0.98 ?105Pa. it is known that oil pump’s flowrate qv＝3.14L/s, and the overall efficiency of the oil pump ?=0.8, oil density ?=800kg/m3，kinetic viscosity ?＝1.25cm2/s, oil pipe’s diameter d＝2cm, length l=2m, total minor loss coefficient ??=2, altitude difference of oil surface h＝3m. Find the power P of the oil pump.
如图6-37所示，油泵从开口油池中将油送到表压强p＝0.98 ?105Pa的油箱中。已知油泵流量qv＝3.14L/s，油泵总效率?=0.8，油的密度?=800kg/m3，运动粘度?＝
1.25cm2/s，油管直径d＝2cm，长度l=2m，总局部损失系数为??=2，油面高度差h＝3m。试求油泵的功率P。 Fig.6-37 Problem 6.19
(418.9W)
6.20 Water is to flow at a rate of 1.0m3/s through a rough concrete pipe(?=3mm) that connects two ponds. Determine the pipe diameter if the elevation difference between the two ponds is 10m and the pipe length is 1000m. Neglect minor losses.
如果两水水以1.0m3/s的流量流过一连接两水池的粗糙混凝土管(?=3mm)。
池水位差为10m、管长为1000m，确定管径。忽略局部损失。(0.748m)
6.21 Without the pump shown in Fig. 6- 38, it is determined that the flow rate is to small. Determine the power added to the fluid if the pump causes the flowrate to be doubled. Assume the friction factor remains at 0.02 in either case. 如图6-38所示，如果不加水泵，发现
流量太小。要使流量翻倍，试确定水泵施加在流体上的功率为多少。设在两种情况 Fig.6-38 Problem 6.21 下沿程损失系数均为0.02。(3.7kW)
6.22 Water drains from a pressurized tank through a pipe system as shown in Fig. 6-39. The head of the turbine is equal to 116m. If the entrance effects are negligible, determine the flowrate.
水从如图6-39的压力水箱经管道系统流出。涡轮的水头为116m。如果忽略入口处的损失，试确定流量为多少。 (qv=3.71?10-2m3/s)
Fig.6-39 Problem 6.22
6.23 As shown in Fig. 6-40, centrifugal pump transports condensed water with a flowrate of 20m3/h to a boiler, the diameter of pump’s sucking pipe is d＝90cm, total length is l=8m, there is an eblow of bending diameter R＝45mm and an inflow sluice valve of minor loss coefficient ?＝5, friction loss factor is ?＝0.02, according to specification, the inlet pressure of the pump should be 0.4?105Pa, find the maximum installation height of the pump above water surface.
离心泵把凝结水以20m3/h的流量输送到锅炉中，如图6－40所示，水泵吸入管直径d＝90cm，总长度l=8m，具有一个弯曲半径R＝45mm的弯头和一进水栅阀，进水栅阀的局部损失系数?＝5，沿程损失系数?＝0.02，按规定，水泵的进口压强应为0.4?105Pa，
试求水泵在水面以上的最大安装高度h。(h=5.88m) Fig.6-40 Problem 6.23
6.24 The three tanks shown in Fig. 6-41 are connected by pipes with friction factors of 0.03 for each pipe. Determine the water velocity in each pipe. Neglect minor loss.
如图6-41所示，三个水箱由沿程损失系数为0.03的管道连接。确定各管中的流速。忽略局部损失。
(v1=1.03m/s v2=0.835m/s)
Fig.6-41
Problem 6.24
6.25 Water pump pumps water into two tanks, as shown in Fig.6-42, elevations of the water pool and water tank are H1=2m and H2＝4m respectively, inner diameter of the pipe is d1＝d2=20cm, pipe lengths are l1＝40m, l2=45m, friction factors are ?1=?2=0.02, pump’s head of delivery is Hp=20m, and neglect minor loss. Find: (1) pump’s discharge; (2) when the overall efficiency of the pump is ?=70%, how much is the power which is transmitted to the pump by the motor driving the pump?
如图6－42所示，泵将水池中的水打入两水箱，水池与水箱水面的高度各为H1=2m，H2＝4m，圆管内径d1＝d2=20cm，管长l1＝40m，l2=45m，沿程
损失系数?1=?2=0.02，泵的扬程Hp=20m，不计局部损失。试求 (1) 泵的排水量；
(2) 当泵的总效率?=70%时，带动泵的电动机输给泵的功率应为多少？ Fig.6-42 Problem 6.25
((1) 0.57m3/s (2) 159.6kW)