Read and understand Section 4.6 in the TRACE User's Guide,
and Section 5.1 (p. 264) of the Theory Manual (Both available on the
We are going to move from approximations to the flow
equations, to approximations used to model physical components
and physical processes. Today I'm
going to introduce the
numerical implementation of pump momentum source terms, and the concept
curves used as the basis of the physical model. This prepares you for
creating pump models with
TRACE, TRAC, RELAP, RETRAN, and CATHARE.
This pump model, based on homologous curves, is fairly
standard within TRACE and the RELAP, TRAC, and RETRAN code families. It
originated in the RELAP4 code series, which partially explains why
liquid and vapor velocities
are set equal at the pump momentum source junction. CATHARE permits
this form and
includes a mechanistic model, requiring detailed information about the
internal pump geometry.
- The pump junction momentum equation is modified to include Head
as a momentum source term. The wall friction and irrecoverable losses
are included in the Head Curves, so a
specific wall friction term or loss coefficient is not present. Only a
single mean momentum equation is
used, since the velocities are assumed to be equal within the pump.
- There are two general pump types
- Centrifugal: High volume variable flow, relatively low pressure
change. Can be
run in series to handle relatively high pressure changes
- Fixed Displacement, generally lower volumetric flows, high
delta p, little flow to
delta p dependence
- Units for Head, and nondimensional forms
- In normal hydraulics, head is defined as an equivalent height
of water. Here
Head is the induced pressure increase divided by the density. The
discrepancy probably lies in the Engineering System's use of pounds
mass and pounds force and the tendency to cheerfully cancel one with
other when operating with units.
- Gives units of meters squared divided by seconds squared.
- Nondimensional Head is true Head divided by the rated head for
- Nondimensional pump speed is the angular pump speed divided by
speed at rated flow.
- Nondimensional volumetric flow is the true volumetric flow
divided by rated volumetric flow
For a quick summary of the pump model take a look at this
- Review pump input specifications next time you look at SNAP.
Created and Maintained by John Mahaffy : email@example.com