Understanding the role of surface structures on flow boiling instability
Abstract
Approved for Public Release)The increasing power densities in gallium nitride and gallium oxide power electronics, RF devices and la,sers are demanding aggressive thermal management solutions to dissipate high heat fluxes with stable performance. Two-phase flow boi,ling in micro and mini channels has been proposed as an attractive approach to address this problem due to the high latent heat of v,aporization and compact form factor. However, a critical issue associated with flow boiling is dynamic flow instability which result,s in sustained oscillations in flow rate, pressure drop and temperature. Extensive theoretical and experimental research has shown t,hat flow instability results from the interaction and feedback between internal characteristics (pressure drop vs flow rate inside t,he two-phase channel) and external (flow loop) characteristics. Different instability modes include Ledinegg instability, pressure-d,rop oscillations and density-wave oscillations, which correspond to different external characteristics. Recently, micro/nanoscale su,rface structures have been integrated into flow boiling micro channels. Enhancements in the heat transfer coefficient (HTC) as well, as critical heat flux (CHF) have been reported. Although the preliminary results are promising, most studies have not investigated, these surface-structure coated channels in different flow loops, and how surface structures affect each mode of flow instability ha,s not been studied. The goal of this proposal is to understand the influence of surface structures on different modes of flow boili,ng instabilities (Ledinegg, density-wave and pressure-drop oscillations). The study will bridge local mechanisms that occur on surfa,ce structures within channels to system-level instabilities that result from the interactions and feedbacks between individual chann,el and flow-loop components. The main tasks of this proposals are:Task 1: We will characterize the internal characteristics (pressur,edrop vs flow rate) curves for channels with surface structures in various flow loop configurations leading to Ledinegg, density-wav,e and pressure-drop instabilities, respectively. The internal characteristics of structured surface channels will be compared to smo,oth surface channels, and flow instabilities for these surface structure and loop combinations will be analyzed. Task 2: We will inv,estigate 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 struct,ures and correlate them with inlet mass flux oscillations.Task 3: Based on the hydrodynamic and thermal measurements in Tasks 1 and2,, we will extend classical models on flow boiling instabilities to include the effect of surface structures, and generate a regime m,ap to identify the optimal working conditions with the most heat transfer enhancement and suppressed instability.This study will gen,erate a more comprehensive understanding of the role of surface structures in different flow boiling systems, which will guide the d,evelopment 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
- Jul 08, 2022
- Source ID
- N000142212427
Entities
People
- Yangying Zhu
Organizations
- Office of Naval Research
- United States Navy
- University of California, Santa Barbara