ValueError: all the input arrays must have same number of dimensions, but the array at index 0 has 1 dimension(s) and the array at index 1 has 2 dimension(s)
Solving sequentially is fine:
eq_sca.solve(dt=1)
eq_vec.solve(dt=1)
For stability reasons, it may be necessary to use a sequential approach, anyway (e.g. SIMPLE), but FiPy shouldn't prevent trying to solve coupled.
As illustrated
If we attempt to represent
$$ \begin{aligned} \frac{\partial C}{\partial t} &= \nabla\cdot(DC \nabla C) + \nabla\cdot(C \vec{v}) \ \frac{\partial \vec{v}}{\partial t} &= \nabla\cdot(D\vec{v} \nabla \vec{v}) \end{aligned} $$
as
FiPy raises
Solving sequentially is fine:
For stability reasons, it may be necessary to use a sequential approach, anyway (e.g. SIMPLE), but FiPy shouldn't prevent trying to solve coupled.