Other Applications - Hierarchical Nanostructures for Energy Devices - page 280

d n 3 r 4 n g | 8

Figure 12.7 Growth manipulation of the ZnO/CuO heterohierarchical nanostruc-
tures using different concentrations of Zn(NO 3 ) 2 salt for 10 h. (a) 0.01 M
(sample a), (b) 0.025 M (sample b), (c) 0.05 M (sample c), (d) 0.1 M
(sample d). The inset in panel d is a side cross-sectional view of an
individual ZnO/CuO nanotree.
Reproduced with permission from ref. 75. Copyright 2013, American
Chemical Society.

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more heat dissipation, such as in CPU cores, pool boiling heat transfer was
suggested. It uses the phase change of liquid coolant, where latent heat
transfer should be considered, leading to a huge amount of heat dissipated
in a specific area compared to other cooling methods without a significant
temperature change. Therefore, no significant thermal stress is induced in
the devices, increasing device reliability and lifetime. The boiling incipient
temperature, heat transfer coecient (HTC), and critical heat flux (CHF) are
important parameters to be considered in pool boiling heat transfer and it
was reported that CHF increased with an increase in surface roughness.
However, it has been noted that nucleation does not merely correlate to the
geometric roughness but also to aging, surface chemistry, surface-liquid
combination and wettability, producing limited heat transfer enhancement.
In order to increase CHF and HTC, microstructures, such as drilled holes, 97
pin-fin arrays, 98,99 micro-dimples, 100 re-entrant cavities, 101 porous surface
structures, 102 finned tubes 102,103 etc were suggested and were found to pro-
duce high nucleate boiling heat transfer. However, an optimum design of