Abstract

This study experimentally investigates the impact of the subcooling magnitude, the carbon-infiltrated carbon nanotube (CICNT) diameter, the time duration of condensation, and amount of non-condensable gases on the nature of dropwise condensation and condensate removal, and heat flux and heat transfer coefficient measurements. Experiments were conducted in a vacuum chamber on a vertically oriented test CICNT surface. The CICNT diameter was varied between 15-120 nm and the subcooling ranged from 0.5-9 °C. Each test ran for a duration of at least one hour and video was recorded at 20-minute intervals. Three modes of condensation were observed: drop jumping, drop wetting of the CICNTs, and surface flooding (film formation). The results reveal that drops retain their mobility at CICNT diameters smaller than ~60 nm and at subcooling temperatures less than ~7 °C. Here drops are mobile and self-remove from the surface by the mechanism of jumping. The results also show that as the CICNT diameter is increased to ~65 nm, the drops lose mobility and become pinned to the surface and the nature of the condensation was observed to transition from droplet jumping to surface flooding. This same transition was observed at subcooling magnitudes greater than 6-8 °C, regardless of the CICNT diameter size. The amount of time the condensate interacts with the surface also affects the drop mobility. After an hour exposure time, the transition from drop jumping to drop wetting occurs at smaller CICNT diameters and lower surface subcooling. The mode of condensation is not noticeably affected when non-condensable gases (NCGs) are introduced to the test chamber, but a larger subcooling is required to induce condensation. Temperature measurements obtained using several thermocouples positioned throughout the experimental setup allowed for heat flux and heat transfer coefficient magnitudes to be obtained. The results show heat transfer coefficient measurements between 2-8 kW/m2K. These results are not significantly impacted by CICNT diameter or time duration of condensation. The introduction of NCGs reduces the heat transfer coefficient by 1-2 kW/m2K. Experimental drop distributions will also be presented showing how drop densities are affected by the experimental parameters. CICNT diameter and surface subcooling can increase the density of smaller drops (10 range) and decrease the density of larger drops (100µ range). The distributions are not affected by condensation duration and the introduction of NCGs results in smaller distributions.

Degree

College and Department

Ira A. Fulton College of Engineering; Mechanical Engineering

Rights

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