The characterization of novel obstacle-type μDiffusers for oscillatory μPump applications in μFluidic cooling systems

peer-reviewedPhotonic Integrated Circuits (PICs) are essential components of optical telecommunication networks. The embedded laser-bar arrays generate high heat fluxes (≈103 W/cm2) — representing some of the highest found in contemporary engineering applications. In order to cool these devices within their temperature tolerance of ±0.1K, a combination of micro-thermoelectrics (μthermoelectrics) and chip-embedded μfluidics has been proposed. To successfully implement a μfluidic cooling system, a μpump is required which can achieve high flow rates (≈10 — 30 ml/min) and differential pressures (≈7 — 35 kPa). State-of-the-art μpumps fulfil these requirements with difficulty, although oscillatory μpumps show promise. An essential component of oscillatory valveless μpumps responsible for their performance are the μdiffusers. By introducing novel obstacle-type μdiffusers, the achievable flow rates and differential pressures of an oscillatory μpump could be improved to successfully implement a μfluidic cooling system into next generation PICs, which will enable significantly denser laser-bar arrays and, consequently, higher data throughput. This thesis presents three novel obstacle-type planar μdiffusers — vaned, V-shaped, and X-shaped. Each element is designed to improve the rectification capability compared to a state-of-the-art μdiffuser/nozzle element by introducing additional channels and protrusions inside the μdiffuser chamber. The objective of this thesis is to determine the rectification capability of the novel obstacle-type μdiffusers, and to understand their underlying flow behaviour. To this end, three experiments were performed to measure their performance in an oscillatory μpump, to determine their rectification capability via pressure drop measurements, and to record their velocity fields via Particle-Image Velocimetry (PIV). The performance measurements were conducted using 3D printed μpumps with operating frequencies between 10 — 175 Hz. For the rectification capability measurements, two different diffusing passage angles were investigated (5° and 10°) for a Re range of 10 — 500. The velocity fields were visualised using PIV for the best performing diffusing passage angle of each novel μdiffuser elements for three different Re numbers (Re = 100, 260, and 460). It was found that all novel obstacle type μdiffusers showed higher rectification capabilities (≈39 — 77%) than the state-of-the-art μdiffuser/nozzle element. For the investigated Re = 10 —500, the best performing novel μdiffuser elements were identified concerning differential pressure and net flow rate. For practical μpump applications, the best performing novel μdiffuser can be chosen from the findings presented in this work, which will give improved performance compared to μpumps with state-of-the-art μdiffuser/nozzle elements. The measured rectification capabilities of the novel μdiffusers were confirmed by performance measurements of the 3D printed μpump. The obtained velocity fields were used to identify flow separation regions and are essential for further improvement of the presented novel obstacle-type μdiffusers