Fast mass transport-assisted convective heat transfer through a multi-walled carbon nanotube array.

Abstract

The recently reported fast mass transport through nanochannels provides a unique opportunity to explore nanoscale energy transport. Here we experimentally investigated the convective heat transport of air through vertically aligned multi-walled carbon nanotubes (VAMWNTs). The flow through the unit cell, defined as an interstitial space among four adjacent nanotubes (hydraulic diameter = 84.9 nm), was in the transition (0.62 ≤ Knudsen number ≤ 0.78) and creeping flow (3.83 × 10-5 ≤ Reynolds number (Re) ≤ 1.55 × 10-4) regime. The constant heat flux (0.102 or 0.286 W m-2) was supplied by a single-mode microwave (2.45 GHz) instantly heating the VAMWNTs. The volume flow rate was two orders of magnitude greater than the Hagen-Poiseuille theory value. The experimentally determined convective heat transfer coefficient (h, 3.70 × 10-4-4.01 × 10-3 W m-2 K-1) and Nusselt number (Nu, 1.17 × 10-9-1.26 × 10-8) were small partly due to the small Re. A further increase in Re (2.12 × 10-3) with the support of a polytetrafluoroethylene mesh significantly increased h (5.48 × 10-2 W m-2 K-1) and Nu (2.37 × 10-7). A large number of nanochannels in a given cross-section of heat sinks may enhance the heat dissipation significantly.