Fix: correct temperature initialisation in lumped and x_full thermal … (#5248)

* Fix: correct temperature initialisation in lumped and x_full thermal models

* docs(changelog): add entry for lumped thermal model domain and T_init fix

* Remove domain from T_vol_av since it's a scalar (review fix)

Author: swastim01

CHANGELOG.md

@@ -51,6 +51,7 @@
 
 ## Bug fixes
 
+- Fixed domain handling and temperature initialization in the lumped thermal model to ensure consistent behavior with spatial `T_init`. ([#5248](https://github.com/pybamm-team/PyBaMM/pull/5248))
 - Fixed non-deterministic plotting CI issues ([#5150](https://github.com/pybamm-team/PyBaMM/pull/5150))
 - Fix non-deterministic ShapeError in 3D FEM gradient method ([#5143](https://github.com/pybamm-team/PyBaMM/pull/5143))
 - Fixes negative electrode boundary values for half-cell voltage contributions. ([#5139](https://github.com/pybamm-team/PyBaMM/pull/5139))

src/pybamm/models/submodels/thermal/lumped.py

@@ -89,7 +89,8 @@ def set_rhs(self, variables):
 
     def set_initial_conditions(self, variables):
         T_vol_av = variables["Volume-averaged cell temperature [K]"]
-        self.initial_conditions = {T_vol_av: self.param.T_init}
+        T_init_av = pybamm.x_average(self.param.T_init)
+        self.initial_conditions = {T_vol_av: T_init_av}
 
     def calculate_Q_cr_W(self, current, contact_resistance):
         Q_cr_W = current**2 * contact_resistance

src/pybamm/models/submodels/thermal/pouch_cell/x_full.py

@@ -179,4 +179,8 @@ def set_initial_conditions(self, variables):
         T_cn = variables["Negative current collector temperature [K]"]
         T_cp = variables["Positive current collector temperature [K]"]
         T_init = self.param.T_init
-        self.initial_conditions = {T_cn: T_init, T: T_init, T_cp: T_init}
+        self.initial_conditions = {
+            T_cn: pybamm.boundary_value(T_init, "left"),
+            T: T_init,
+            T_cp: pybamm.boundary_value(T_init, "right"),
+        }