The thermal and hydrodynamic behaviour of submerged and confined, normally-impinging, laminar slot jets

Optical networks are a critical element of contemporary communications infrastructure, due to their efficacy in transmitting high-speed data over large distances. Photonic integrated circuits (PICs) offer compelling advantages in terms of performance and miniaturization, but increasing the power density of these components, coupled with shrinking packaging footprint, presents a significant thermal management challenge. This has driven the need for the integration of liquid-based micro fluidic cooling artefacts into next generation PIC packages. Liquid microjets are emerging as a candidate primary or secondary heat exchanger for such packages, however, the thermal-hydraulic behaviour of confined, low Reynolds number liquid slot jets is not comprehensively understood. The objective of this thesis is to characterise the inf uence of slot jet geometry modi cations as a technique for the passive control and enhancement of single-phase convective heat transfer. The slot jets investigated featured five different nozzle aspect ratios (L/W), and five different passive outlet structures in the form of tabs and chevrons. The investigation was carried out for slot jets in the laminar ow regime, over a Reynolds number range of 100 ≤ ReDh ≤ 500 { and with a xed con nement height to hydraulic diameter ratio (H=Dh) of 1. Particle - Image Velocimetry (PIV) and an iso ux foil technique were utilised to identify the uidic mechanisms associated with each geometry and to understand their corresponding in uence on the spatial temperature distributions along the heated surface. The hydrodynamic penalty of any enhancements in heat transfer achieved were then determined through the measurement of the pressure drop across each nozzle geometry. It was found that increasing the jet nozzle aspect ratio from 1 to 8 resulted in enhancements in area-averaged Nusselt number (NuAvg) of up to 68%, and a corre- sponding decrease in head loss coe cient (K) of 12%. Within the stagnation zone, correlations extrapolated from the experimental results showed that the stagnation point Nusselt number (Nu0) had a very weak dependency on the jet nozzle aspect ratio, but scaled with Re0:55 Dh . This Reynolds number scaling was indicative of the potential core of the jet striking the impingement surface. O -center peaks observed in the velocity ow elds of the impinging jets were postulated to be as a result of the stagnation zone uid dynamics and local ow entrainment. When compared to the baseline case, all outlet tab geometries resulted in increased local and area-averaged heat transfer and, for the same pumping power, enhancements in NuAvg of up to 29% were achieved through the application of the major triangle outlet tab geometry. It was also determined that the geometry and location of the outlet tabs were found to in uence the local heat transfer coe cients within both the stagnation and wall jet zones. It was concluded that the passive control and enhancement of an integrated microjet cooling solution could be achieved through geometry modification { without compromising the stringent design constraints of an integrated microf uidic package, such as confinement height, flow rate, and the required pumping power.