Suppressing flow boiling instabilities using surface structures
Abstract
(Approved for Public Release)The increasing power densities in gallium nitride and gallium oxide power electronics, RF devices and lasers are demanding aggressive thermal management solutions to dissipate high heat fluxes with stable performance. Two-phase flow boiling in micro and mini channels has been proposed as an attractive approach to address this problem due to the high latent heat ofvaporization and compact form factor. However, a critical issue associated with flow boiling is dynamic flow instability which results in sustained oscillations in flow rate, pressure drop and temperature. Extensive theoretical and experimental research has shownthat flow instability results from the interaction and feedback between internal characteristics (pressure drop vs flow rate insidethe two-phase channel) and external (flow loop) characteristics. Different instability modes include Ledinegg instability, pressure-drop oscillations and density-wave oscillations, which correspond to different external characteristics. Recently, micro/nanoscale surface structures have been integrated into flow boiling microchannels. Enhancements in the heat transfer coefficient as well as CHF have been reported. Although the preliminary results are promising, most studies have not investigated these surface-structure coated channels in different flow loops. How surface structure will affect each mode of flow instability has not been studied. The goals of this proposal are to understand the influence of surface structures on different modes of flow boiling instabilities (Ledinegg, density-wave and pressure-drop oscillations), and to enhance heat transfer performance of dielectric fluid microchannel flow boiling using a combination of surface structures and flow loop control. The study will bridge local mechanisms that occur on surface structures within channels to system-level instabilities that result from the interactions and feedbacks between individual channel and flow-loop components. The main tasks of this proposals are:Task 1: We will characterize the internal characteristics (pressure drop vs flow rate) curves for channels with surface structures in various flow loop configurations leading to Ledinegg, density-wave and pressure-drop instabilities, respectively. The internal characteristics of structured surface channels will be compared to smooth surface channels, and flow instabilities for these surface structure and loop combinations will be analyzed. Task 2: We will investigate the role of surface structures on heat transfer characteristics within the channels under different flow instability modes. Using a high-speed infrared camera, we will map the local wall temperature distribution and transient response on the surface structures and correlate them with inlet mass flux oscillations.Task 3: Based on the hydrodynamic and thermal measurements in Tasks 1 and 2, we will extend classical models on flow boiling instabilities to include the effect of surface structures, and generate a regime mapto identify the optimal working conditions with the most heat transfer enhancement and suppressed instability.Task 4: Develop active flow control to enhance dielectric-fluid flow boiling in microchannels with surface structuresThis study will generate a more comprehensive understanding of the role of surface structures in different flow boiling systems, which will guide the development of advanced two-phase thermal management systems highly relevant to DoD applications.As an educational institution, UCSB performs fundamental and unclassified research. Any data or information developed or provided by UCSB, including but not limited to publications and reports, shall be unclassified fundamental research exempt from dissemination controls or review requirements.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Dec 15, 2023
- Source ID
- N000142412086
Entities
People
- Yangying Zhu
Organizations
- Office of Naval Research
- United States Navy
- University of California, Santa Barbara