  Internal phoretic flows due to the interactions of solid boundaries with
local chemical gradients may be created using chemical patterning.
Alternatively, we demonstrate here that internal flows might also be induced by
geometric asymmetries of chemically-homogeneous surfaces. We characterise the
circulatory flow created in a cavity enclosed between two eccentric cylindrical
walls of uniform chemical activity. Local gradients of the diffusing solute
induce a slip flow along the surface of the cylinders, leading to a circulatory
bulk flow pattern which can be solved analytically in the diffusive limit. The
flow strength can be controlled by adjusting the relative positions of the
cylinders and an optimal configuration is identified. These results provide a
model system for tunable phoretic pumps.
