Thermal resistance analysis of micro heat pipes incorporated with carbon nanotubes nanocapillaries

Abstract

The remarkable performance improvement and thermal optimization of micro heat pipes (MHPs) incorporated with carbon nanotubes (CNTs) of different density are analysed using a thermal resistance model. The ultrafast water transport characteristic of CNT-nanocapillaries induces large-surface-area water film where the evaporation, condensation, and condensate circulation processes, which govern the MHP's overall performance, are simultaneously enhanced. By employing a thermal resistance model, the pertinent parameters inside an MHP, which are not measurable due to the miniature size of the microchannels, are estimated. By benchmarking with the uncoated MHP, the condenser and evaporator heat transfer coefficients of the optimal 5 mg/CNTs MHPs are enhanced remarkably by the up to 249% and 264%, respectively. Furthermore, the circulation rate attains a maximum increase of 212%. Consequently, an enhancement up to 250% in the overall performance of MHP gauged by the effective thermal conductivity and a significant temperature drop of 20.8 °C on the heat source as compared to the uncoated MHP case are achieved. By minimizing the total thermal resistance of MHP, the optimized length ratio of the evaporator and condenser, which is useful in the optimal design of the MHP, can be obtained. The thermal resistance model serves as a useful analytical tool to provide insightful thermal analysis and optimized design of an MHP.