ARTICLE INFO ABSTRACT Keywords:Micro-heat sink Tip clearance Pressure dropThis article presents an experimental study on the optimisation of micro-heat sink configurations when both thermal effects and pressure drop are accounted fon The interest of the latter is that the practical engineering viability of some of these systems also depends on the required pumping power. The working ñuid was water and, according to typical power dissipation and system size requirements, the considered ñuid regime was either laminar or transitional, and not fully developed from the hydrodynamics point of view. Five configurations were considered: a reference geometry (selected for comparison purposes) made up of square section micro-channels, and four alternative configurations that involved the presence of a variable tip clearance in the design. The performance of the different configurations was compared with regard to both cooling efficiency and pressure drop. Finally, we also provide some practical guidelines for the engineering design of these types of systems.

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A closed-form analytical solution for the Stokes flow generated by a corotating two-roll mill is used to generate two-dimensional elongational flows with well-defined amounts of vorticity. These flow devices can generate conditions found between simple shear and purely elongational flows, and are among the few systems that can take into account the presence of nearby boundaries. In the laboratory, these devices have been used for studies of the microstructural dynamics of complex fluids such as polymeric solutions, colloids, bubbles and drops, etc., and allow pointwise optical studies of the flow parameters. Hence, a comparison is presented of available experimental and numerical results for the stagnation point versus the analytical solution presented here. Based upon this solution, a new design for the two-roll mill is presented for the purpose of minimizing the disadvantages of current mills.