Session: 11-01: Micro/Miniature Two-Phase Devices/ Systems

Paper Number: 131567

131567 - Flash Boiling in Microchannels for High Heat Flux Devices 

Abstract: 

High-heat-flux cooling technologies enable electronic hardware to operate at its maximum performance. One such example is a wafer-scale system that requires thermal management technology to handle more than 0.5 W/mm² and kilowatts of total heat load, depending on the wafer size. Flash boiling is considered here as a promising and dynamic two-phase thermal management technology in which liquid-vapor phase change is induced by controlled pressure changes. When a suitable liquid coolant at atmospheric pressure enters an environment of low pressure, its saturation temperature can drop below the ambient temperature, thus facilitating both homogeneous and heterogeneous boiling, resulting in rapid heat extraction due to the latent heat capacity of the operating liquid. In the reported work, a closed loop system is developed with the components including evaporator, accumulator, vacuum pump, condenser, and reservoir. Methanol is chosen as the working fluid owing to its relatively high latent heat capacity and low boiling temperature. Furthermore, a pulsed supply of methanol is introduced to disrupt stable vapor film formation at high-heat-flux conditions that occur in continuous flow boiling experiments. The pulsing of the flow is achieved with the controlled operation of a solenoid valve in concert with a peristaltic pump. Two different cold plates – a serpentine loop cold plate and a microchannel cold plate with channel size of 160 μm are considered for the evaporator component. Both evaporators have an active base area of 625 mm². The effect of flow rate and pulse time are elucidated for various heat fluxes. The peristatic pump controls the average flow rate, and a ceramic heater with resistance heating elements is employed. Temperature and pressure data are acquired with the aid of LabVIEW software. The results indicate that at steady-periodic conditions, the temperature oscillations in the evaporator base range from ±1°C to ±3.5°C for a wall heat flux range of 0.2 W/mm² to 1 W/mm² . The oscillations are more pronounced for higher pulse times at a given heat flux and average flow rate. Moreover, the oscillations are higher at higher heat flux and lower flow rates.  From the experiments conducted, a lowest thermal resistance of 0.115 K/W is observed. Further, flash-flow boiling characteristic curves (i.e., wall superheat against applied heat flux) are reported for both evaporator designs and under varying flow rate and pulse times. The flash boiling phenomena in microchannels is characterized by performing experiments such as variable heat fluxes, variable flow rates and variable pulse cycle time. Future research will focus on the near-critical heat flux condition regime and strategies to avoid dry-out conditions enabled by pulsed operation.

Presenting Author: Rishi Pugazhendhi UCLA

Presenting Author Biography: Rishi Pugazhendhi joined NTRG in Fall 2022 as a MS student in Mechanical Engineering, with a focus on Heat and Mass Transfer. He received his B.E. degree in Mechanical Engineering from Anna University, Chennai in 2021. Prior to his graduate study, he worked as Thermal and Energy Specialist in the R&D department of Nestlives Private Limited, Chennai. He is passionate about developing innovative and sustainable solutions for thermal management challenges in various domains, such as electronics, HVAC and aerospace. His Thesis Project focuses on elevating Technology Readiness Level (TRL) of Two-Phase Pulsed Flash Cooling Technology for High Heat Flux Cooling Applications. He conceptualized and improved flash cooling technology in terms of design, prototype development and evinced technology’s ability to effectively cool a heat flux up to 100 W/cm2. With persistent learning, collaboration, meticulous conceptualization and analysis, he has proposed numerous innovative solutions for complex challenges resulting in 21 influential scientific research and review studies in the field of energy and thermal domain, gaining over 1150+ citations. Further, he serves as a recognized reviewer for Elsevier journals including Applied Energy and International Journal of Heat and Mass Transfer. His Core competencies include single and two-phase cooling, Design of Experiments (DOE), thermal modelling and simulation, thermal validation, data analytics and HVAC systems.

Authors:

Naarendharan Meenakshi Sundaram UCLA
Rishi Pugazhendhi UCLA
Timothy S. Fisher UCLA
Subramanian S. Iyer UCLA