“…These techniques are based on the so‐called shape derivative, which measures the sensitivity of a shape due to infinitesimal deformations, and the topological derivative, which measures the sensitivity of a geometry with respect to the insertion of an infinitesimally small hole, see, e.g., [14, 61] for shape calculus and [45] for topological sensitivity analysis. In recent years these techniques have been applied to many industrial problems, e.g., the shape design of polymer spin packs [27, 37–39], electric motors [20, 21], acoustic horns [5, 57], automobiles [18, 46, 48], aircrafts [41, 55, 56] or pipe systems [25, 28, 58]. To the best of our knowledge, the optimization of a microchannel cooling system by means of shape calculus has only been investigated in our earlier work [6], where we rigorously analyzed the theoretical aspects of this problem.…”