diff --git a/ThermofluidStream/HeatExchangers/CounterFlowNTU.mo b/ThermofluidStream/HeatExchangers/CounterFlowNTU.mo
index 8384f2db..85b79994 100644
--- a/ThermofluidStream/HeatExchangers/CounterFlowNTU.mo
+++ b/ThermofluidStream/HeatExchangers/CounterFlowNTU.mo
@@ -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;
diff --git a/ThermofluidStream/HeatExchangers/CrossFlowNTU.mo b/ThermofluidStream/HeatExchangers/CrossFlowNTU.mo
index 4bf8cc68..ce5ea536 100644
--- a/ThermofluidStream/HeatExchangers/CrossFlowNTU.mo
+++ b/ThermofluidStream/HeatExchangers/CrossFlowNTU.mo
@@ -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;
diff --git a/ThermofluidStream/HeatExchangers/Internal/PartialNTU.mo b/ThermofluidStream/HeatExchangers/Internal/PartialNTU.mo
index 3fe56017..d38771bd 100644
--- a/ThermofluidStream/HeatExchangers/Internal/PartialNTU.mo
+++ b/ThermofluidStream/HeatExchangers/Internal/PartialNTU.mo
@@ -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  ------------------------
@@ -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;