Rapid transient cooling utilizing flash boiling and desorption on graphitic foams
Transient thermal systems present significant challenges. Neglecting the time constants of the system, such as the thermal mass, is common to reach solutions that are both practical and simple; however, such transient effects must be accounted for when engineering the thermal performance on the same timescale. Rapidly actuated and dynamically controlled systems may experience severe inefficiencies or even catastrophic failure during the transient regime if designed solely for steady-state performance. This dissertation focuses on transient thermal phenomena, in particular, for the cooling of high-heat-flux devices. The duration of the transient regime is established as well as metrics describing the expected thermal performance. These considerations allow the thermal engineer to determine if and how to enact transient design. Despite the challenges, dynamically actuated thermal systems provide opportunities for enhanced performance. Cooling performance can be improved during transient events by utilizing thermal energy storage and augmenting the cooling mechanisms. Desorption cooling and flash boiling from graphitic foams are evaluated to determine their aptitude for dynamic thermal applications. The efficacy of desorption cooling for high-heat-flux loads is limited primarily by the surface area available. Sufficient surface-area enhancement to commercial graphitic foams was not obtained, but may be possible. Flash boiling is augmented to resemble conventional cooling systems and appears appropriate for stabilizing the temperature of dynamically actuated devices operating at a power density of 10-100W/cm2 for 1-10 s.
Fisher, Purdue University.
Aerospace engineering|Mechanical engineering|Materials science
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