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