Advanced Measurements of Enhanced Flow Boiling Heat Transfer at the Micro Scale
Abstract
Flow boiling in micro scale pin fin heat sinks is a promising heat transfer method for high power electronics. However, fundamental knowledge pertinent to the heat transfer processes dominating in these systems is severely lacking primarily because of inadequate experimental capabilities. Advanced high frequency experimental methods that allow overcoming this shortcoming were recently developed by our group through an ONR Thermal Management Program grant to study flow boiling in a plain microchannel. This study seeks to leverage these experimental techniques and extend knowledge about enhanced flow boiling heat transfer processes downstream a micro scale pin fin with/without a steady jet. As was shown in two of our recent papers, local high-speed temperature measurements synchronized with high–speed flow visualization and a numerical model will enable to resolve transient heat transfer coefficient at O(1kHz). This in turn will provide measurements at the micro scale corresponding to the stages comprising the ebullition cycle of a single bubble, sliding bubbles, and other slower processes like evaporation of thin liquid films, and transient heating during bubble incubation period. The proposed experimental study extends and integrates two of our current research efforts. One titled “Bubble agitation in subcooled flow boiling — size scale effect,” which is currently supported by the ONR Thermal Management Program (Effort 1), and another (Effort 2) titled “Heat transfer enhancement in microchannels using flow control,” which is currently supported through a one year grant, $100K from the Israeli Ministry of Defense (IMOD). In Effort 1, we developed high-frequency surface temperature measurement techniques synchronized with high speed visualizations to study nucleate and convective boiling heat transfer processes in a plain microchannel. These new capabilities will be leveraged in the proposed study to gain insight pertinent to Effort 2, which currently only aims to elucidate time and space average heat transfer coefficients, but not local, transient surface temperature measurements and high-speed visualization. Without these local, transient measurements, fundamental heat transfer processes cannot be quantified and validated. The proposed study will overcome these issues by integrating the newly developed experimental techniques from Effort 1. The transient heat transfer coefficient at various stages of the bubble ebullition will be obtained and used to construct the processes determining the averaged heat transfer coefficient based on its transient components. Beside the heat transfer coefficient, bubble size and frequency as a function of pin fin size and shape, mass flux, mass quality, and heat flux will be obtained. These variables will then be evaluated and used to reconstruct the average heat transfer coefficient and divulge the processes controlling it. Higher mass qualities for which convective boiling dominates will also be studied, and the role of thin liquid film rupture will be quantified and carefully evaluated.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2016
- Source ID
- N000141512071
Entities
People
- Yoav Peles
Organizations
- Office of Naval Research
- United States Navy
- University of Central Florida