流体力学课后作业(7)

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)

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