5.4. Liquid Temperature Calculations

In Section 5.2, we described how the liquid pressures and liquid mass flow rates are calculated during a time step, ignoring liquid temperature changes and gas mass flow rate changes during the same time step. In this section, we shall describe how liquid temperatures are calculated during a time step while still ignoring gas mass flow rate changes during the time step.

PRIMAR-4 contains liquid temperature calculations for a number of types of components. These include pipes, IHXs, steam generators, bypass channels, a general one-node perfect mixing model for compressible volumes, and a thermal stratification model for the outlet plenum. For the IHX two models are available: a detailed model of both the tube and the shell sides, and a simple table look-up model for the primary side only. Similarly there are two steam generator models available: a detailed model for both the sodium and the water sides, and a simple table look-up model for the sodium side only. Currently, valves, check valves, and pump impellers are treated as pipes when liquid temperatures are calculated.

For temperature calculations, the elements in a liquid segment are combined into temperature groups. Each temperature group contains one or more consecutive elements. All of the elements in a temperature group are treated with the same type of liquid temperature calculation, such as Pipe Temperatures, IHX Temperatures, and Bypass Channels. The number of nodes in a temperature group is defined by the input parameter NTNODE, and these are distributed over the elements in that group starting with element IFSTEL and ending with element ILSTEL.

The Lagrangian calculations used for pipe temperatures are more efficient and accurate if a number of connected pipe elements are strung together into a single temperature group, rather than calculating temperatures for each pipe element separately.

When the detailed IHX model is used, a temperature group is defined only for the primary side; the secondary side inherits the same temperature group. Both the tube-side element and the shell-side element are in the same temperature group, since temperatures on both sides are computed at the same time.

For table lookup and air-dump heat exchanger elements, the temperature group must contain exactly two nodes to represent the inlet and outlet conditions of the element.

• 5.4.1. Pipe Temperatures
  • 5.4.1.1. Eulerian Calculations
  • 5.4.1.2. Annular Element Temperatures
  • 5.4.1.3. Direct Element Heating
• 5.4.2. Heat Exchangers: Detailed Options
  • 5.4.2.1. Introduction
  • 5.4.2.2. Basic Equations
  • 5.4.2.3. Finite Difference Equations
  • 5.4.2.4. Solution
  • 5.4.2.5. Steady-State Temperatures
  • 5.4.2.6. PHX: Boundary Conditions and Coolant Options
  • 5.4.2.7. HX Input Description
• 5.4.3. Bypass Channels
  • 5.4.3.1. Introduction
  • 5.4.3.2. Basic Equations
  • 5.4.3.3. Finite Difference Equations and Solution
  • 5.4.3.4. Steady-State Bypass Channels
• 5.4.4. Compressible Volumes
  • 5.4.4.1. Thick-Walled Compressible Volumes
  • 5.4.4.2. CV Input Description
• 5.4.5. Table Look-Up for Steam Generators or Intermediate Heat Exchangers
  • 5.4.5.1. Table HX Input Description
• 5.4.6. Component-to-Component Heat Transfer
  • 5.4.6.1. Element to CV
  • 5.4.6.2. CV to CV
  • 5.4.6.3. Element to Element
• 5.4.7. RVACS/RACS Models
  • 5.4.7.1. Simple RVACS Model
  • 5.4.7.2. Detailed Air Side Model
  • 5.4.7.3. Coupled RVACS Model
  • 5.4.7.4. RVACS Input Description
• 5.4.8. Stratified Volume Model