题目内容
(16分)四川省“十二五”水利发展规划指出,若按现有供水能力测算,我省供水缺口极大,蓄引提水是目前解决供水问题的重要手段之一。某地要把河水抽高20m,进入蓄水池,用一台电动机通过传动效率为80%的皮带,带动效率为60%的离心水泵工作。工作电压为380V,此时输入电动机的电功率为19kW,电动机的内阻为0.4
。已知水的密度为
,重力加速度取10
2。求
(1)电动机内阻消耗的热功率;
(2)将蓄水池蓄入864
的水需要的时间(不计进、出水口的水流速度)。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134454623333.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134454654720.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134454748445.png)
(1)电动机内阻消耗的热功率;
(2)将蓄水池蓄入864
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134454794398.png)
(1)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134454950554.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134454888698.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134454950554.png)
(1) 设电动机的电功率为P,则![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134455028454.png)
设电动机内阻r上消耗的热功率为Pr,则有![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134455075524.png)
代入数据解得:![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134454888698.png)
(2)设蓄水总质量为M,所用抽水时间为t。已知抽水高度为h,容积为V,水的密度为ρ则M=Ρv
设质量为M的河水增加的重力势能为△Ep,则△Ep=Mgh
设电动机的输出功率为P0,则![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134455216511.png)
根据能量守恒定律有:![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241344552781012.png)
代入数据可得![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134454950554.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134455028454.png)
设电动机内阻r上消耗的热功率为Pr,则有
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134455075524.png)
代入数据解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134454888698.png)
(2)设蓄水总质量为M,所用抽水时间为t。已知抽水高度为h,容积为V,水的密度为ρ则M=Ρv
设质量为M的河水增加的重力势能为△Ep,则△Ep=Mgh
设电动机的输出功率为P0,则
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134455216511.png)
根据能量守恒定律有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241344552781012.png)
代入数据可得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134454950554.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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