Passive Control and Enhancement of Low Reynolds Number Slot Jets Through the Use of Tabs and Chevrons

Abstract

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 the increase in power density of these components, coupled with shrinking packaging restrictions, presents a significant thermal management challenge. This has driven the need for the integration of liquid-based microfluidic cooling artefacts into next generation PIC packages. Liquid micro-jets are emerging as candidate primary or secondary heat exchangers for such packages, however the thermal behavior of confined, low Reynolds number liquid slot jets is not comprehensively understood. This investigation utilized a hot foil technique to experimentally determine the influence of implementing jet outlet modifications — in the form of tabs and chevrons — as techniques for passive control and enhancement of single-phase convective heat transfer. The investigation was carried out for slot jets in the laminar flow regime, with a Reynolds number range, based on the conventional slot jet hydraulic diameter, of 100 to 500. The investigation was carried out with a slot jet aspect ratio of 4, and a fixed confinement height to hydraulic diameter ratio (H/Dh) of 1. It was found that all outlet modifications increased local and area-averaged Nusselt number compared to a conventional slot jet. Modifications to the major axis (or long edge) of the slot jet were most effective, achieving increases in area-averaged Nusselt number of up to 61%. It was also determined that the location and magnitude of Nusselt number peaks within the slot jet stagnation region, could be passively controlled and enhanced through the application of outlet tabs at varying locations, allowing for more flexible targeted hotspot cooling. Therefore, it was concluded that enhancements in an integrated microjet cooling artefact can be achieved through passive geometry devices, without compromising the stringent packaging restrictions of such systems, such as confinement height and nozzle geometry.