The advancement of high performance thermal systems has stimulated interest in methods to improve heat transfer rates. Considerable efforts have been made to increase heat transfer rates by implementing passive convective heat transfer enhancement methods that require no direct consumption of external power. This is mainly achieved by modifying heat transfer surfaces which either play a role in disrupting the flow field without increasing the surface area (effect of surface roughness) or by increasing the surface area and in some cases even both. This thesis provides an insight into the microscale convective heat transfer enhancement using surface modification technique. Carbon nanostructures, such as carbon nanofibers (CNFs) and carbon nanotubes (CNTs), are used for surface modification. The scope of the study covers: (a) a systematic synthesis and characterization of the carbon nanostructured layer on heat transfer surfaces and (b) the heat transfer performance test of the synthesized material. Emphasis was given to the synthesis of several types of carbon nanostructured surfaces which composed of either CNFs or CNTs. The key parameters playing a role in the process of heat transport from the CNFs/CNTs such as fiber diameter, porosity, permeability, layer thickness, area coverage, surface roughness, surface area, crystallinity of the layer deposited were investigated. Tuning these parameters aided in understanding the direct and indirect influence on heat transfer behavior. The structural influences of the modified surfaces on the convective heat transport are investigated using three different fluid flow configurations. These are: (a) cross flow to a cylindrical micro-wire, (b) impinging flow and (c) microchannel. During the course of the study, the global heat transfer performances of the nanostructured materials are compared to the smooth heat transfer surface. Significant heat transfer enhancement is obtained for the entire heat transfer configuration. The obtained heat transfer performance is discussed based on both morphological and topological characteristics of the samples.
|Award date||9 Sep 2015|
|Place of Publication||Enschede|
|Publication status||Published - 9 Sep 2015|