Enhancement of boiling heat transfer with nano-patterned substrates

• Main Author: Subramaniam, Suresh.
• Other Authors: Leong Kai Choong
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/53295
• Institution: Nanyang Technological University

Heat transfer is a crucial process which is applied in various thermal load designs. Many applications within the electrical and energy fields incorporate this process through the use of pool boiling due to its unique combination of fluid circulation and high heat flux capability. But the limiting factor would be the critical heat flux (CHF) which restricts the overall cooling capacity. Hence, to overcome this issue, past researchers had adopted techniques such as the introduction of porous surfaces as effective media with the sole purpose of enhancing the heat transfer performance in the nucleate boiling regime. Not to be outdone, there has been a new discovery which consists of applying nanotechnology as a coating on the surface of the specific material for a better enhancement of heat transfer. One such nanotechnology would be the use of carbon nanotubes (CNTs). Currently, only few researchers such as Ujereh et al. [1-2] and Ahn [3] had opted to use this technology thus making it new within the industry. Realising its potential and wanting to prove its credibility, the author decided to apply this carbon nanotube technology within his experiment. His experimental work consists of introducing CNT-arrays on the silicon surface (model as a chip) to check for the possibility of delaying the critical heat flux as well as enhancing the boiling heat transfer. The CNT-arrays were grown in campus through the use of chemical vapour deposition (CVD). The end product was vertically grown multi-wall CNT-arrays (MWCNT) with different heights. They were then tested on 10mm by 10mm silicon substrates in the working fluid, FC-72 and subjected to specific heat fluxes (power) while being conducted simultaneously within a thermosyphon. Pool boiling curves for the bare and CNT-coated silicon surfaces were obtained. The end results revealed that there were significant boiling enhancements. It was observed that the reduction of wall superheat temperature for the CNT-coated surfaces were from 13.4% to 40%. There was also enhancement of the heat transfer coefficients from 7.7% to 54% with increasing CNT heights (coating thickness).