Step 5: Secondary Side

Complete input file for this step: 05_secondary_side.i

Figure 1: Model diagram

In this step, we will add the secondary side of the heat exchanger and set up the inlet mass flow rate boundary condition as a function of time.

Heat Exchanger

We will define the following heat exchanger parameters:

# heat exchanger parameters
hx_dia_inner = ${units 12. cm -> m}
hx_wall_thickness = ${units 5. mm -> m}
hx_dia_outer = ${units 50. cm -> m}
hx_radius_wall = ${fparse hx_dia_inner / 2. + hx_wall_thickness}
hx_length = 1       # m
hx_n_elems = 10

m_dot_sec_in = 1    # kg/s

We also define second fluid that we will be using on the secondary side:

[FluidProperties]
  [water]
    type = StiffenedGasFluidProperties
    gamma = 2.35
    cv = 1816.0
    q = -1.167e6
    p_inf = 1.0e9
    q_prime = 0
  []
[]

Components

To define the heat exchanger block, we will use the syntax for grouping components together.

The general syntax is:

[group]
  [component1]
  []
  [component2]
  []
[]

Then, individual components can be referred to as group/component1 and group/component2.

commentnote

Note: It is possible to define parameters within the group. Good candidates would be hx_length and hx_n_elems.

We will take advantage of this feature and set our heat exchanger as follows:

[Components]
  [hx]
    [pri]
      type = FlowChannel1Phase
      position = '1 0 1.75'
      orientation = '0 0 -1'
      length = ${hx_length}
      n_elems = ${hx_n_elems}
      roughness = 1e-5
      A = '${fparse pi * hx_dia_inner * hx_dia_inner / 4.}'
      D_h = ${hx_dia_inner}
    []

    [ht_pri]
      type = HeatTransferFromHeatStructure1Phase
      hs = hx/wall
      hs_side = inner
      flow_channel = hx/pri
      P_hf = '${fparse pi * hx_dia_inner}'
    []

    [wall]
      type = HeatStructureCylindrical
      position = '1 0 1.75'
      orientation = '0 0 -1'
      length = ${hx_length}
      n_elems = ${hx_n_elems}
      widths = '${hx_wall_thickness}'
      n_part_elems = '3'
      solid_properties = 'steel'
      solid_properties_T_ref = '300'
      names = '0'
      inner_radius = '${fparse hx_dia_inner / 2.}'
    []

    [ht_sec]
      type = HeatTransferFromHeatStructure1Phase
      hs = hx/wall
      hs_side = outer
      flow_channel = hx/sec
      P_hf = '${fparse 2 * pi * hx_radius_wall}'
    []

    [sec]
      type = FlowChannel1Phase
      position = '${fparse 1 + hx_wall_thickness} 0 0.25'
      orientation = '0 0 1'
      length = ${hx_length}
      n_elems = ${hx_n_elems}
      A = '${fparse pi * (hx_dia_outer * hx_dia_outer / 4. - hx_radius_wall * hx_radius_wall)}'
      D_h = '${fparse hx_dia_outer - (2 * hx_radius_wall)}'
      fp = water
      initial_T = 300
    []
  []
[]

Then, we connect the inlet boundary condition to the secondary side flow channel:

[Components]
  [inlet_sec]
    type = InletMassFlowRateTemperature1Phase
    input = 'hx/sec:in'
    m_dot = 0
    T = 300
  []
[]

And then, the outlet boundary condition for the same channel:

[Components]
  [outlet_sec]
    type = Outlet1Phase
    input = 'hx/sec:out'
    p = 1e5
  []
[]

This is the same as what we did in step 1 of this tutorial.

Inlet Mass Flow Rate

To set up the inlet boundary condition as a function of time, we first need to define a time-dependent function in the top-level [Functions] block:

[Functions]
  [m_dot_sec_fn]
    type = PiecewiseLinear
    xy_data = '
      0    0
      10 ${m_dot_sec_in}'
  []
[]

In the ControlLogic block, we bring the function value in using the GetFunctionValueControl block:

[ControlLogic]
  [m_dot_sec_inlet_ctrl]
    type = GetFunctionValueControl
    function = m_dot_sec_fn
  []
[]

And then we feed this value back into the system:

[ControlLogic]
  [set_m_dot_sec_ctrl]
    type = SetComponentRealValueControl
    component = inlet_sec
    parameter = m_dot
    value = m_dot_sec_inlet_ctrl:value
  []
[]

Alternative Solution

An alternative solution to this is to use a convenience block called TimeFunctionComponentControl which combines these two ControlLogic blocks into one. It takes three parameters component, parameter, and function.

The equivalent syntax would look like this:

[set_m_dot_sec_ctrl]
  type = TimeFunctionComponentControl
  component = inlet_sec
  parameter = m_dot
  function = m_dot_sec_fn
[]
commentnote

Note: This should be your preferred setup when you want to use time-dependent component parameters.

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