  When a Coulombic fluid is confined between two parallel charged plates, an
exact relation links the difference of ionic densities at contact with the
plates, to the surface charges of these boundaries. It no longer applies when
the boundaries are curved, and we work out how it generalizes when the fluid is
confined between two concentric spheres (or cylinders), in two and in three
space dimensions. The analysis is thus performed within the cell model picture.
The generalized contact relation opens the possibility to derive new exact
expressions, of particular interest in the regime of strong coulombic
couplings. Some emphasis is put on cylindrical geometry, for which we discuss
in depth the phenomenon of counter-ion evaporation/condensation, and obtain
novel results. Good agreement is found with Monte Carlo simulation data.
