Boiling is a common mechanism for liquid-vapor phase transition and is widely exploited in power generation, refrigeration and many other systems. The efficacy of boiling heat transfer is characterized by two parameters: (a) heat transfer coefficient (HTC) or the thermal conductance; (b) the critical heat flux (CHF). Increasing the CHF and the HTC has significant impacts on system-level energy efficiency, safety and cost. As the surface modification at nano-scale has proven to be an effective approach to improve pool boiling heat transfer, the enhancement due to combination of nanomaterials with micro-scale structures on boiling heat transfer is an area of current interest. In this study, metallic- and semiconductor- material based nanowire structures were fabricated and studied for boiling enhancement. A new technique is developed to directly grow Cu nanowire (CuNW) on Si substrate with electro-chemical deposition, and to produce height-controlled hydrophilic nanowired surfaces. Using a two-step electroless etching process, silicon nanowire (SiNW) have been selectively fabricated on top, bottom, and sidewall surfaces of silicon microchannels. An array of the SiNW coated microchannels functioned as a heat sink and was investigated for its pool boiling performance with water. This microchannel heat sink yielded superior boiling performance compared to a sample substrate with only microchannels and a plain substrate with nanowires. The enhancement was associated with the area covered by SiNWs. The sidewalls with SiNWs greatly affected bubble dynamics, resulting in a significant performance enhancement. The maximum heat flux of the microchannel with SiNW on all surfaces was improved by 150% over the microchannel-only heat sink and by more than 400% over a plain silicon substrate. These results provide a viable solution to meet the demands for dissipating a high heat transfer rate in a compact space, with additional insight gained into the boiling mechanism for the microchannel heat sinks with nanostructures.
Library of Congress Subject Headings
Nanowires--Testing; Heat--Transmission; Heat exchangers--Fluid dynamics
Microsystems Engineering (Ph.D.)
Department, Program, or Center
Microsystems Engineering (KGCOE)
Yao, Zhonghua, "Development of nanowire structures on 2d and 3d substrates for pool boiling heat transfer enhancement" (2013). Thesis. Rochester Institute of Technology. Accessed from
RIT – Main Campus