.TRANSFORM.Fluid.Machines.BaseClasses.PartialPump

Information

This is the base model for pumps.

The model describes a centrifugal pump, or a group of nParallel identical pumps. The pump model is based on the theory of kinematic similarity: the pump characteristics are given for nominal operating conditions (rotational speed and fluid density), and then adapted to actual operating condition, according to the similarity equations.

Pump characteristics

The nominal hydraulic characteristic (head vs. volume flow rate) is given by the the replaceable function flowCharacteristic.

The pump energy balance can be specified in two alternative ways:

• use_powerCharacteristic = false (default option): the replaceable function efficiencyCharacteristic (efficiency vs. volume flow rate in nominal conditions) is used to determine the efficiency, and then the power consumption. The default is a constant efficiency of 0.8.
• use_powerCharacteristic = true: the replaceable function powerCharacteristic (power consumption vs. volume flow rate in nominal conditions) is used to determine the power consumption, and then the efficiency. Use powerCharacteristic to specify a non-zero power consumption for zero flow rate.

Several functions are provided in the package PumpCharacteristics to specify the characteristics as a function of some operating points at nominal conditions.

Depending on the value of the checkValve parameter, the model either supports reverse flow conditions, or includes a built-in check valve to avoid flow reversal.

It is possible to take into account the mass and energy storage of the fluid inside the pump by specifying its volume V, and by selecting appropriate dynamic mass and energy balance assumptions (see below); this is recommended to avoid singularities in the computation of the outlet enthalpy in case of zero flow rate. If zero flow rate conditions are always avoided, this dynamic effect can be neglected by leaving the default value V = 0, thus avoiding fast state variables in the model.

Dynamics options

Steady-state mass and energy balances are assumed per default, neglecting the holdup of fluid in the pump; this configuration works well if the flow rate is always positive. Dynamic mass and energy balance can be used by setting the corresponding dynamic parameters. This is recommended to avoid singularities at zero or reversing mass flow rate. If the initial conditions imply non-zero mass flow rate, it is possible to use the SteadyStateInitial condition, otherwise it is recommended to use FixedInitial in order to avoid undetermined initial conditions.

Heat transfer

The Boolean parameter use_HeatTransfer can be set to true if heat exchanged with the environment should be taken into account or to model a housing. This might be desirable if a pump with realistic powerCharacteristic for zero flow operates while a valve prevents fluid flow.

Diagnostics of Cavitation

The replaceable Monitoring submodel can be configured to PumpMonitoringNPSH, in order to compute the Net Positive Suction Head available and check for cavitation, provided a two-phase medium model is used (see Advanced tab).

Contents

Name	Description
FlowChar	Head vs. Volumetric flow rate
PowerChar	Power consumption vs. Volumetric flow rate
EfficiencyChar	Efficiency vs. Volumetric flow rate

Revisions

• 8 Jan 2013 by Rüdiger Franke:
  moved NPSH diagnostics from PartialPump to replaceable sub-model PumpMonitoring.PumpMonitoringNPSH (see ticket #646)
• Dec 2008 by Rüdiger Franke:
  
  • Replaced simplified mass and energy balances with rigorous formulation (base class PartialLumpedVolume)
  • Introduced optional HeatTransfer model defining Qb_flow
  • Enabled events when the checkValve is operating to support the opening of a discrete valve before port_a
• 31 Oct 2005 by Francesco Casella:
  Model added to the Fluid library