Identifier

etd-07012014-114811

Degree

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Document Type

Dissertation

Abstract

Nucleate boiling is an attractive method for achieving high heat flux at low superheat temperatures. It is frequently used for industrial applications such as heat exchangers and is being considered to cool advanced central processing units (CPU) which produce heat fluxes on the order of 1 MW/m2 and are becoming increasingly less efficient to cool via forced conduction of air. The issue with implementing nucleate boiling as a cooling mechanism lies in the difficulty of quantifying the numerous and complex mechanisms which control the process. A comprehensive nucleate boiling model has yet to be formulated and will be required in order to safely and reliably cool high performance electronics. Spatially periodic systems with localized asymmetric surface structures (ratchets) can induce directed transport of matter (liquid/particles) in the absence of net force. It was hypothesized that ratchets may enhance pool boiling heat transfer by aiding in the removal of vapor which forms on the heated surface. Therefore, preliminary experiments on pool boiling using asymmetric micro ratchets with de-ionized (DI) water and various concentrations of alumina particles and DI water as the working fluids were investigated. Results indicated that ratchets indeed improve heat transfer performance. However, few conclusions could be drawn regarding the underlying physics. A more advanced boiling system was designed in order to more accurately measure heat transfer, test multiple working fluids, and perform condensing experiments. Various micro ratchet geometries were tested to study the effects of ratchet parameters on pool boiling performance using FC-72 as the working fluid. The samples underwent surface characterization to determine roughness and wettability which are important parameters influencing pool boiling heat transfer. Results indicate that, as in the previous study, micro ratchets significantly improve heat transfer. Various parameters were studied in order to better understand the influence of surface geometry on heat transfer. The results were found to be under-predicted by various models found in the literature.

Date

2014

Document Availability at the Time of Submission

Secure the entire work for patent and/or proprietary purposes for a period of one year. Student has submitted appropriate documentation which states: During this period the copyright owner also agrees not to exercise her/his ownership rights, including public use in works, without prior authorization from LSU. At the end of the one year period, either we or LSU may request an automatic extension for one additional year. At the end of the one year secure period (or its extension, if such is requested), the work will be released for access worldwide.

Committee Chair

Park, Sunggook

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