Heat and Fluid Flow In an Integrated Rectangular Microchannel: A Combined Numerical-Experimental Study

Abstract

This thesis work presents numerical and experimental investigations on flow maldistribution based conjugate axial conduction problems in parallel type channels for high density electronic cooling applications. Majorly, three issues relating to the practicality of the integrated parallel channel heat sinks are explored in the thesis: (a) The effect of integrated heat spreaders in mitigating the flow induced high temperature zones using parallel type heat sink, (b) The study of axial conduction and entrance effects of heterogeneous integrated heat sink and (c) the use of inertial channels to reduce flow maldistribution induced axial conduction in parallel flow type configuration heat sink. In the first part, heat transfer investigations are performed to reduce hotspots with heat spreader integrated microchannel using nanofluid. The results of Nusselt number are compared with the benchmark literatures. Numerical simulations on microchannel heat sink are performed to understand the temperature distribution in the spreader and an elaborate discussion is provided for the deviations observed between numerical and experimental data. Critical effects like response time and bulk diffusion are discussed by varying hotspot, aspect ratio and processor cores. Reduction in flow induced hotspot has been observed by providing graphene oxide nanofluid with very low volume fraction. In the second part, both the numerical and experimental analyses are performed to investigate axial conduction in heterogeneous integrated microchannel using TiO2 nanofluid. The inlet flow rate, volume fraction and power rating are varied to check the effects of axial conduction on heterogeneously integrated substrates. The thermo physical properties of the TiO2 nanofluid are measured and characterized. Significant effect of axial conduction is seen for nanofluid at higher concentration at reduced flow rates. On the other hand, it has been observed that the effect of conjugate heat transfer decreases at higher flow rates. The last part of the work presents the investigation on the special type of inertial channels to reduce the maldistribution induced axial conduction. The study is carried out on ribbed channels with three different geometrical configurations i.e. normal, inclined and lifted channels. The average temperature of the sink reduces for ribbed channels than normal straight channels. The effect of axial conduction is observed less for ribbed inclined channel due to the obstruction in flow, flow separation and increased fluid momentum in extreme channels.