Cylinders with an elliptical, oblong, lenticular, sinus or diamond transveral shape are very interesting geometries for the design of compact heat exchangers. This work investigates the role of the porosity and of the apex angle of diamond-shaped cylinders networks on the pressure losses, at moderate Reynolds numbers, inside micro heat regenerators. The design of the geometry under test has been chosen so that the cross section of the flow remains almost constant along the path of the flow between cylinders. Experiments have been performed at 1 ? Re ? 30 and a porosity range 0.40 ? ? ? 0.90 for an apex angle of ? " 33?. Numerical simulations have been conducted using the same Reynolds and porosity ranges but varying the apex angle 33? ? ? ? 90?. Experimental measurements and dimensional analysis have shown that the friction factor can be affected by the porosity. 2D numerical simulations confirmed that the friction factor increases with the porosity but also with the apex angle. An analysis at the scale of a channel flanked by adjacent cylinders has provided a original correlation able to describe easily the evolution of the Poiseuille number and the collective effects on the drag coefficient as a function of ? and ?. Such a diamond-shaped design is found to induce much lower Poiseuille numbers than those expected from conventional stacked spheres, woven wires and circular cylinders arrays. The findings of this study can help for better understanding the optimization of low pressure drop regenerators and how to reduce associated hydraulic power.

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