Session: 12-06-01: Boiling Heat Transfer and Flow Instabilities

Paper Number: 165620

Experimental Study of Ultra-Thin Fin and Cavity Arrays in Flow Boiling for Heat Transfer Enhancement 

Flow boiling continues to be an ever-growing topic in the heat transfer field, showing significance in applications for high-power electronics systems like servers to nuclear power plants. Understanding and comparing the best ways to improve the single and multiphase flow for an increased heat transfer rate is crucial to this. The effectiveness can be tested by keeping the temperature of the incoming fluid low and by altering the surface geometry the fluid passes. This study investigates methods of enhancing heat transfer by using interchangeable plate specimens with different protuberances. The different protuberances include a variety of micro-fin and cavity arrays with various patterns. These include a straight fin array, a diamond fin array, a segmented fin array, a staggered array, and a straight-aligned cavity array. The straight-aligned cavity array also included an internal cavity within the cavities that were initially drilled. A baseline specimen with no protuberances or cavities was used for comparison. These specimens were secured to the bottom of a mini-channel cover that allowed the fluid to pass through thermocouples measuring the inlet and outlet temperatures. The mini-channel was then secured to a heated surface that was kept at constant power for each test run. A thermocouple was placed between the heated surface and the bottom of the specimen. Each specimen had a variety of tests done with different constant flow rates and constant powers. The flow rate ranged from 0.1, 0.2, and 0.3 L/min. The heating power that were tested include 217.6 W, 340.2 W, and 500 W. Tests were run until steady-state conditions were reached or it became clear that steady-state conditions were not reasonably achievable. After some time in steady-state conditions, the power was turned off, but the temperatures were still recorded for 10 minutes afterward to collect data on how the specimens cooled. The convective heat transfer coefficient was experimentally calculated and the surface temperatures over time were compared for each specimen. The setup of the tests includes two cycles. The main cycle had deionized water flowing from the water reservoir, into the pump. The pump pushed the water through the mini-channel. Then, the fluid flows through a Coriolis flow meter that keeps track of the flow rate. After flowing through the flow meter, the deionized water flows into a heat exchanger that connects to another cycle before flowing back into the water reservoir. The other cycle has a water cooler that ensures that the temperature is kept at a constant temperature. A few temperatures are tested, including 4 ^oC, 10 ^oC, and 15 ^oC. The ultra-thin fin arrays have a high surface area compared to the other specimens. This allows for heat transfer to be more efficient in single-phase and multi-phase flow. The cavity array specimens have shown increased effectiveness during flow boiling. This is due to the cavities having distinct bubble nucleation qualities during the different stages of the boiling process. Additionally, the heat transfer through the solid copper specimen is inversely proportional to the thickness. Preliminary results have demonstrated the effectiveness of the diamond fins. The cavity specimens have also proved to be more effective than the baseline specimens. While both specimens undergo flow boiling, the straight-aligned cavities specimen showed to be very similar in effectiveness to the straight-aligned fins specimen.

Presenting Author: Alexander Nees Florida Polytechnic University

Presenting Author Biography: Alexander Nees is a researcher and Master's student in the Mechanical Engineering Department at Florida Polytechnic University. His research interests are centered on heat transfer, with a specific focus on the phase change phenomena, ever since he began working on heat transfer-related research in 2022. He is a co-author of "Study of Phase Change Materials for Heat Dissipation of Systems With Transient Heat Generation" and the lead author of "Effects of Flow Boiling on Mini Channels With Ultra-Thin Fins and Cavity Arrays." Both these have been presented at the ASME International Mechanical Engineering Congress & Exposition (IMECE).

Authors:

Alexander Nees Florida Polytechnic University
Gerardo Carbajal Florida Polytechnic University
Edwar Romero-Ramirez Florida Polytechnic University
Younggil Park Florida Polytechnic University