文档介绍：第十一节管路计算与流量测量
管路计算
管路计算使用的基本关系式
•物料衡算方程,即连续性方程式: ub1 A1 = ub2 A2
•机械能衡算方程,即柏努利方程式:
u 2 p u 2 p
gz + b1 + 1 + W&e = gz + b2 + 2 + å h
1 2 ρ 2 2 ρ f ,1­2
•流动阻力损失计算式:
L u 2 64
æ ö b λ= (层流)
ç λ+ å ζ j ÷ Re
è d ø 2
å h =
f L + å L u 2 æ e ö
λ e b λ= f ç Re, ÷ (湍流)
d 2 è d ø
Department of Chemical and
Xiamen University Biochemical Engineering
一. 简单管路计算
简单管路——全部流体从入口到出口只在一根管道中连续流动。
等径管路:最简单的一种管路,流动的总阻力可直
接应用下式计算。
分类æ L ö u 2 2
b L + å Le ub
å h f = ç λ+ åζ j ÷ 或åh = λ
è d ø 2 f d 2
串联管路:由不同管径的管道组成的管路。
V , d
s,1 1 Vs,2 , d2
Vs,3 , d3
Department of Chemical and
Xiamen University Biochemical Engineering
1
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n 在稳态流动下,串联管路的特点是:
① Vs,1=Vs,2=Vs,3=Vs (对不可压缩流体)
即 ub1 A1 = ub2 A2 = ub3 A3 = ×××
②
å h f = å h f ,1 + å h f ,2 + å h f ,3 + ××× = å å h f ,i
i =1
Department of Chemical and
Xiamen University Biochemical Engineering
(一)简单管路计算的分类 1 1‘
h
1. 已知:L、d、V、e,求h
2 2‘
解法:
4V du ρ e / d
V、d ® u = ® Re = b ¾¾® λ
b πd 2 µ
p ­ p u2 ­u2 L+SL u2
1 2 + g(z ­ z )+ b1 b2 = λ e b
ρ 1 2 2 d 2
L + SL u 2
® h = z ­ z = λ e b
1 2 d 2g
Department of Chemical and
Xiamen University Biochemical Engineering
2
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2. 已知:h、L、d、e,求ub或V (属操作型计算的题目)
解法:须用试差法
——先假设一个λ,利用柏努利方程式求出ub,再
du ρ
算出 Re = b ,查出λ,看查出的λ值
µ