.. _LiquidTemperatures:

.. _section-5.4:

Liquid Temperature Calculations
-------------------------------

In :numref:`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 :ref:`Pipe Temperatures<Pipe Temperatures>`, :ref:`IHX Temperatures<IHX Temperatures>`, and :ref:`Bypass Channels<Bypass Channels>`.
The number of nodes in a temperature group is defined by the input
parameter :sasinp:`NTNODE`, and these are distributed over the
elements in that group starting with element :sasinp:`IFSTEL` and ending
with element :sasinp:`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 :ref:`table lookup <TableLookupHX>` and :ref:`air-dump heat exchanger <section-5.6>` elements, the temperature group must contain exactly
two nodes to represent the inlet and outlet conditions of the element.

.. toctree::
	:maxdepth: 2

	temp-pipe
	temp-ihx
	temp-bypass
	temp-cv
	temp-table-hx
	temp-cp-cp
	temp-rvacs
	temp-strat