Thermo-Hydrodynamics of Single-Phase and Two-Phase Flow Boiling in a Novel Design Recharging Microchannel Heat Sink

Abstract

As the world is shifting towards a digital era with advances in technology, demand for high-performance electronic devices is ever increasing. Every electronic device consists of many integrated circuits, which are the soul of such devices. According to Moore’s law, every two years, the number of transistors doubles in an integrated circuit. This indicates that the performance of electronic devices is directly proportional to the number of transistors. Though these electronic devices' performance increases, the size, and weight of these devices are decreasing due to the compact packaging of miniaturized transistors. Due to the presence of many transistors in integrated circuits, more heat is generated in these high-performance electronic devices. Thus, requiring removal of high heat flux generated in these devices continuously for maintaining the temperature below a certain threshold temperature called safe operating temperature. Non-compliance with this will lead to higher component failure and a reduced average life of these electronic devices. Due to its compact size, lightweight, and higher surface area to volume ratio, the microchannel heat sink (MCHS) is one of the most promising cooling techniques for thermal management of high-performance electronic devices. Though traditional straight MCHSs extract heat at a better rate from high-performance electronic devices, they are not fully suitable for ever-increasing high heat flux cooling applications. Therefore, several researchers developed various heat transfer enhancement techniques (i.e., passive techniques) to augment the heat transfer performance of MCHSs using the concept of breaking and redeveloping thermal and hydrodynamic boundary layers by incorporating flow obstructions like ribs, cavities, obstacles, dimples, and protrusions, etc. Still, new techniques/methods can be proposed and explored that can provide higher thermal performance without using ribs and cavities. In this background, this thesis proposed a novel approach/method, “recharging microchannel” for heat transfer enhancement in microchannel heat sinks. The proposed design divides a simple/straight microchannel into multiple divisions by placing transverse walls at equal intervals, and each division will have an individual inlet and outlet through the top cover-plate. In this design, coolant at inlet temperature enters multiple times through the total length of a conventional microchannel or the substrate; thus, making the system equivalent to multiple smaller length microchannels placed end to end and fresh fluid (at ambient temperature) supplied to every channel simultaneously. Due to independent inlet and outlet, both thermal and hydrodynamic boundary layers develop in each smaller channel. The flow remains mostly developing in nature across the substrate length, thus carrying more heat out of the system and maintaining almost uniform temperature distribution on the substrate bottom surface. The main objective of this work is to investigate or explore the overall performance of the proposed design recharging microchannel (RMC) compared to simple/straight microchannel (SMC) by considering both single-phase and two-phase (i.e., flow boiling) approach. The results of this study are covered in the following chapters:
Chapter 2 compares the thermo-hydrodynamic performance of recharging microchannel and simple microchannel to investigate the advantages of the proposed microchannel over referenced microchannel. The effects of geometrical and thermo-physical parameters on the thermo-hydrodynamic performance of recharging microchannel are also discussed in this chapter by considering a wide range of geometrical and thermo-physical parameters. Additionally, the effect of axial wall conduction is also investigated in both recharging and simple microchannels.
Chapter 3 discusses and compares entropy generation in recharging microchannel and simple microchannel. This chapter also discusses the effects of geometrical and thermophysical parameters on entropy generation in recharging microchannel.
Chapter 4 highlights the effects of working fluid on thermo-hydrodynamic performance and entropy generation in recharging microchannel by considering water-based graphenesilver (Gr-Ag) hybrid nanofluid as the working fluid.
Chapter 5 investigates the thermo-hydrodynamic performance of two-phase flow boiling in a recharging microchannel and compares it with a simple microchannel.
Chapter 6 concentrated on the effect of inlet/outlet manifold configurations on thermohydrodynamic performance of recharging microchannel heat sink by considering different types of inlet/outlet manifold designs. The author believes that the proposed design recharging microchannel can be beneficial for high heat flux removal applications as it shows better thermo-hydrodynamic performance and reduced entropy generation compared to simple/straight microchannel.