pybamm-team#1788 try to fix diff of U

pybamm/models/submodels/thermal/base_thermal.py

@@ -164,8 +164,9 @@ def _get_standard_coupled_variables(self, variables):
             D_p = variables["Positive particle effective diffusivity [m2.s-1]"]
             Ueq_n = variables["Negative electrode open-circuit potential [V]"]
             Ueq_p = variables["Positive electrode open-circuit potential [V]"]
-            dUeq_n = Ueq_n.diff(c_n)
-            dUeq_p = Ueq_p.diff(c_p)
+            # Drop the blow-up term as it has spatial operators and diff doesn't work
+            dUeq_n = Ueq_n.children[0].diff(c_n)
+            dUeq_p = Ueq_p.children[0].diff(c_p)
             integrand_r_n = D_n * dc_n_dr**2 * dUeq_n
             integrand_r_p = D_p * dc_p_dr**2 * dUeq_p
             integration_variable_r_n = [pybamm.SpatialVariable("r", integrand_r_n)]

pybamm/parameters/lithium_ion_parameters.py

@@ -578,12 +578,14 @@ def U(self, sto, T, lithiation=None):
         u_ref = pybamm.FunctionParameter(
             f"{self.phase_prefactor}{Domain} electrode {lithiation}OCP [V]", inputs
         )
+
+        dudt_func = self.dUdT(sto)
+        u_ref = u_ref + (T - self.main_param.T_ref) * dudt_func
+
         # add a term to ensure that the OCP goes to infinity at 0 and -infinity at 1
         # this will not affect the OCP for most values of sto
-        # see #1435
-        u_ref = u_ref + 1e-6 * (1 / sto + 1 / (sto - 1))
-        dudt_func = self.dUdT(sto)
-        out = u_ref + (T - self.main_param.T_ref) * dudt_func
+        # see #1435       
+        out = u_ref + 1e-6 * (1 / sto + 1 / (sto - 1))
 
         if self.domain == "negative":
             out.print_name = r"U_\mathrm{n}(c^\mathrm{surf}_\mathrm{s,n}, T)"