The characterization of a low-profile channel-confined jet for targeted hot-spot cooling in microfluidic applications

Photonics Integrated Circuits (PICs) are the backbone of the optical-fiber networks that enable high-speed communication on a global scale. Contemporary devices contain laser-bars (∼μm length-scale) which must be controlled within ±0.1 K, and are capable of generating heat fluxes ∼1 kW/m2. This represents one of the highest heat fluxes found in nature or engineering applications, and the thermal challenge places a limitation on the density of laser-bar arrays on an individual chip. Chip-integrated μfluidic cooling has been proposed for the thermal management of next-generation PICs to create more energy efficient devices, capable of greater data throughput. Jet impingements are of interest as the primary heat exchangers in this system due to the large heat transfer rates that can be achieved. The objective of this work is to generate a novel, low profile jet impingement within an individual channel suitable for targeting hot-spots in a densely packed circuit, at the low Reynolds numbers prevalent in micro-fluidic applications (Re < 500). To this end, two experiments were performed to non-invasively observe the velocity field and local heat transfer in a square miniature channel containing a curved orifice-plate to manipulate the fluid flow. A range of Reynolds numbers (channel Re = 100 − 200) and obstruction opening area ratios (β = 0.2 − 0.5) were investigated through Particle-Image Velocimetry and infrared thermography of a Joule-heated foil. The velocimetry data showed that the curved orifice-plate geometry successfully generated an inclined jet within the channel, and maximum improvements in the area-averaged heat transfer coefficient of 495% (relative to a channel containing no obstruction) were measured. The heat transfer data showed Nu ∼ Re0.59scaling, similar to that of a micro-fluidic array of normally impinging jets, and this physical relationship is beneficial in the design and modeling of μfluidic cooling systems. The findings illustrate the impact of a channel confined jet on spatial heat transport, and demonstrate the potential for controlled heat transfer enhancement using unconventional obstructions within laminar channel flows.