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PartialNTU Time Constant #207

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PartialNTU Time Constant #207

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7565771
Added Documentation for heat exchanger time constant
RaphaelGebhart Aug 14, 2024
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RaphaelGebhart Aug 14, 2024
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RaphaelGebhart Aug 14, 2024
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RaphaelGebhart Aug 14, 2024
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7 changes: 7 additions & 0 deletions ThermofluidStream/HeatExchangers/CounterFlowNTU.mo
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Expand Up @@ -123,5 +123,12 @@ equation
<p>The equations are derived from the generic effectiveness-NTU relations which can be found in the &quot;VDI W&auml;rmeatlas&quot; and noumerous standard literature.</p>
<p>For stream dominated applications the following assumptions are made for mass flow regularization close to zero:</p>
<p>- if the mass flow on both sides of the heat exchanger is zero, no heat is transferred</p>
<p>
The heat exchanger time constant <code>TC</code> is necessary to ensure robust simulation. It can approximate the transient behavior using a first order ODE.
The time constant is related to the ratio of thermal inertia (wall + fluid) <code>dU/dT</code> to enthalpy flow rate 'inertia' <code>dH_flow/dT</code>:
</p>
<p>
<code>TC ~ (m_Wall*c_Wall + m_Fluid*c_Fluid)/(m_flow*c_Fluid)</code>.
</p>
</html>"));
end CounterFlowNTU;
7 changes: 7 additions & 0 deletions ThermofluidStream/HeatExchangers/CrossFlowNTU.mo
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Expand Up @@ -173,5 +173,12 @@ equation
<p>The equations are derived from the generic effectiveness-NTU relations which can be found in the &quot;VDI W&auml;rmeatlas&quot; and noumerous standard literature.</p>
<p>For stream dominated applications the following assumptions are made for mass flow regularization close to zero:</p>
<p>- if the mass flow on both sides of the heat exchanger is zero, no heat is transferred</p>
<p>
The heat exchanger time constant <code>TC</code> is necessary to ensure robust simulation. It can approximate the transient behavior using a first order ODE.
The time constant is related to the ratio of thermal inertia (wall + fluid) <code>dU/dT</code> to enthalpy flow rate 'inertia' <code>dH_flow/dT</code>:
</p>
<p>
<code>TC ~ (m_Wall*c_Wall + m_Fluid*c_Fluid)/(m_flow*c_Fluid)</code>.
</p>
</html>"));
end CrossFlowNTU;
9 changes: 8 additions & 1 deletion ThermofluidStream/HeatExchangers/Internal/PartialNTU.mo
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Expand Up @@ -14,7 +14,7 @@ partial model PartialNTU "Partial heat exchanger model using the epsilon-NTU met
annotation (Dialog(tab="Advanced"));
parameter Modelica.Units.SI.MassFlowRate m_flow_reg=dropOfCommons.m_flow_reg "Nominal mass flow rate for regularization"
annotation (Dialog(tab="Advanced", group="Regularization parameters"));
parameter Modelica.Units.SI.Time TC=0.01 "Time constant for specific enthalpy difference dh"
parameter Modelica.Units.SI.Time TC=0.01 "Heat exchanger time constant"
annotation (Dialog(tab="Advanced"));

// ------ Parameter Display Configuration ------------------------
Expand Down Expand Up @@ -231,5 +231,12 @@ flow regularization close to zero:
is transferred
</li>
</ul>
<p>
The heat exchanger time constant <code>TC</code> is necessary to ensure robust simulation. It can approximate the transient behavior using a first order ODE.
The time constant is related to the ratio of thermal inertia (wall + fluid) <code>dU/dT</code> to enthalpy flow rate 'inertia' <code>dH_flow/dT</code>:
</p>
<p>
<code>TC ~ (m_Wall*c_Wall + m_Fluid*c_Fluid)/(m_flow*c_Fluid)</code>.
</p>
</html>"));
end PartialNTU;
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