Pump

Figure 103: Pump Characteristic

A pump is characterized by a total head increase versus total flow curve (Figure 103). The total head $h$ is defined by:

$$h=z+\frac{p}{\rho g},$$ (36)

where $z$ is the vertical elevation, $p$ is the pressure, $\rho$ is the liquid density and $g$ is the value of the earth acceleration. The total flow $Q$ satisfies:

$$Q = \dot{m}/\rho,$$ (37)

where $\dot{m}$ is the mass flow. The pump characteristic can be defined underneath a *FLUID SECTION,TYPE=LIQUID PUMP by discrete data points on the curve. The data points should be given in increasing total flow order and the corresponding total head values must be decreasing. No more than 10 pairs are allowed. In between the data points CalculiX performs an interpolation (solid line in Figure 103). For flow values outside the defined range an extrapolation is performed, the form of which depends on the precise location of the flow (dashed lines in Figure 103). For positive flow values inferior to the lowest flow data point, the total head corresponding to this lowest flow data point is taken (horizontal dashed line). For negative flow values the total head sharply increases ( $\alpha=0.0001$) to simulate the zero-flow conditions of the pump in that region. For flow values exceeding the largest flow data point the total head decreases sharply with the same tangent $\alpha$.

The gravity acceleration must be specified by a gravity type *DLOAD card defined for the elements at stake. The material characteristic $\rho$ can be defined by a *DENSITY card.

Example files: centheat1.