Modeling Pumps

Assignment :

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 ANGEL site.)

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 of homologous 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 Curve information 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 the 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 the pump.
• Nondimensional pump speed is the angular pump speed divided by the angular speed at rated flow.
• Nondimensional volumetric flow is the true volumetric flow divided by rated volumetric flow
  

• Review pump input specifications next time you look at SNAP.
  

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