ASPEN学习笔记 12 ：流体输送单元泵

The Net Positive Suction Head (NPSH) available for a pump is defined as:

$NPSHA = P{in} - P_{vapor} + H_v + H_s$

Where:

$NPSH_A$	=	Net Positive Suction Head Available 可获得的净正吸入压头
$P_{in}$	=	Inlet pressure 入口压力
$P_{vapor}$	=	Vapor pressure of the liquid at inlet conditions 入口条件下的液体蒸汽压
$H_v$	=	Velocity head = u2/2g where u is the velocity and g is the gravitation constant 动压头
$H_s$	=	Hydraulic static head corrected to the pump centerline 精确到泵的轴心线的水力学静压头

$NPSH_a$ 要比要求的 $NPSH_r$ 要大，否则可能发生汽蚀。

$NPSHr = [\frac{NQ^{0.5}}{N{ss}}]^{\frac{4}{3}}$

其中

$NPSH_r$	=	Net Positive Suction Head Required 要求的净正吸入压头
N	=	Pump shaft speed (rpm) 泵的轴速度
Q	=	Volumetric flow rate at the suction conditions 吸入条件下体积流率
$N_{ss}$	=	Suction specific speed 吸入比速

The units for Q and NPSHR are:

US: 英制	Q in gal/min and NPSHR in feet 英尺
Metric: 公制	Q in cum/hr and NPSHR in meters 米

上面提到了吸入比速，首先定义比速

$N_s = \frac{NQ^{0.5}}{Head^{0.75}}$

Head	=	Head developed across the pump 泵提升的压头
Ns	=	Specific speed 比速
N	=	Pump shaft speed (rpm) 泵轴转速
Q	=	Volumetric flow rate at the suction conditions 吸入条件下的体积流率

The units for Qand Head are:

US:	Head in feet, Q in gal/min 压头单位英尺和流率单位加仑每分钟
Metric:	Head in meters, Q in m3/hr 压头单位米，流率单位立方米每小时

The choice between US and Metric speed units is made on the Setup | Calculation Options sheet.

英制和公制可以在Setup – 计算选项中选择

知道了比速的定义后，再来定义吸入比速，其实就是将泵的NPSHr代替Head，

$N_s = \frac{NQ^{0.5}}{{NPSH_r}^{0.75}}$

吸入比速是泵的性能的一个判据该性能是有关气蚀方面的对于通常的泵设计

US 单位制时
ss N 值在 6000 到 12000 范围内变化典型值是 8500

$Head_c = \frac{Head * g}{u^2}$

Headc = 压头系数
Head= 通过泵所提升的压头
g= 重力加速度
u =叶轮末端速度

流通系数是排放喉管速度与叶轮末端速度之比，

$Flow_c = \frac{Q}{A_1u}$

$A_1 = \frac{\pi {d_1}^2}{4}$

Flowc = 流通系数
Q = 体积流率
$A_1$ = 喉管横截面积
$d_1$ = 喉管直径
u =叶轮末端速度

而由于

$N_s = 5500\frac{d_1}{Diam}$

$N_s$ 为最佳效率点的比速

Diam 为叶轮直径，在 Setup calculation 选项上也可以定义比速

$FHP = w g dH = \frac{wg *dP}{\rho g}$

其中

dH	=	head generated = $\frac{dP}{\rho g}$ 增加的压头
w	=	mass flow rate 质量流率
g	=	gravitational acceleration 重力常数
dP	=	the pressure difference across the pump 经过泵产生的压差
ρ	=	fluid mass density 流体密度