A novel heat transfer enhancement technology is proposed for gas convection electronic cooling applications. Use of heat sinks with surface arrays of microscale flexible pin fins, oscillating at their fundamental frequency in response to unsteady flow, is expected to significantly increase heat dissipation rates. The small size of the proposed flexible pin fins will result in slip flow occurring on the fin surface. Non-continuum effects of slip flow and temperature jump at the surface, coupled with fluid structure interaction (FSI), produces a unique and challenging computational problem that has not been investigated before. An existing methodology that combines a computational fluid dynamics algorithm (ICE) with the material point method (MPM) for solids modeling will be modified to account for the momentum and energy exchange between a rarified gas and a deformable surface. The resulting FSI algorithm will be validated using four representative cases of slip flow for which analytical and/or numerical data are available. The proposed work will naturally lead to other slip flow FSI studies, such as associated with atomic force microscope probes, microscale diaphragm pumps and valves, and micro air vehicle wings and control flaps. Following the implementation and validation of slip flow and temperature jump conditions into the MPM-ICE methodology, a systematic study will be conducted to gain physical understanding into the FSI behavior and heat transfer enhancement of microscale flexible pin fins, individually, in pairs, and in arrays. Single microscale flexible pin fin studies will a) confirm the existence of unsteady flow at Reynolds numbers Re > 47 in the continuum regime and b) produce data for the flow and heat transfer characteristics in the slip flow regime as functions of Re, Knudsen number Kn, fin aspect ratio, and material properties. The thermal fluid interaction of two microscale flexible pin fins, aligned with the principal flow direction, will be examined to determine optimal spacing. An array of microscale flexible pin fins will be studied to ascertain optimal configurations for maximum overall heat transfer rates, taking into account the previously mentioned parameters.
Intellectual Merit: Computational modeling of fluid structure interaction in the slip flow regime has not been reported in the literature. Thus, the proposed project is expected to be transformative, resulting in an enabling technology for the design and analysis of a number of novel micro- and nano-fluidic systems, including the proposed microscale flexible pin fin concept for enhancement of air-side heat transfer. Data from continuum flow rigid pin fins and microscale flexible pin fin studies will increase the understanding of mechanisms related to drag and heat transfer enhancement in this complex FSI system. In addition, for the first time, data will also be produced for a system with FSI in the slip flow regime with concurrent momentum and thermal transport.
Broader Impacts: The algorithm will enable modeling of systems in which fluid structure interaction takes place in the slip flow regime. Many other microscale systems, such as particulate flows, two-phase flows, and microactuators could be modeled with the modified MPM-ICE methodology. The optimized design of microscale flexible pin fin arrays could be extensively applied to a wide variety of electronic packages to enhance heat dissipation in applications limited to air cooling. Local impact will occur through the introduction of project results into two existing undergraduate/graduate course within the College of Engineering. Project results will be conveyed to the scientific community through refereed archival journal publications and by presentations at multidisciplinary meetings, providing opportunities for cross-fertilization of ideas. Graduate students involved in the project will be actively recruited from underrepresented groups in engineering. Research outcomes will be converted into engaging video presentations for outreach and recruitment activities. Underrepresented groups in engineering will be the focus of outreach, utilizing existing College of Engineering activities. Examples of these programs include Utah's Engineers: A Statewide Initiative for Growth, an NSF-funded initiative to increase engineering graduation rates, and Hi-GEAR Girls Summer Camp which is a residence summer program for high school females.
