Research Summary
Phase transition processes such as boiling, evaporation, condensation, and icing are ubiquitous natural phenomena and are essential to various industrial processes including thermal power plants, micro-reactors and microfluidics, fuel cells, and thermal management of high power electronics. Phase-change heat transfer such as boiling and evaporation has been widely exploited in various water-energy industries owing to its efficient heat transfer mode. My research interests are experimental and theoretical understanding of boiling heat transfer in microscale domains and thin film evaporation on wicking microstructures. The understanding of phase-change heat transfer mechanisms could provide fundamentally new solutions in thermal management and energy conversion.
Since 2013, I have been working in micro/nanoscale two-phase transport to understand complex two-phase phenomenon. I have undertaken and completed many significant research projects in boiling heat transfer. During my PhD study, I have demonstrated two innovative methodologies, named "two-phase oscillation" and "two-phase separation", in effectively manipulating or even controlling the naturally stochastic two-phase flow patterns in microchannels. First time, my research both experimentally and theoretically demonstrated that the chaotic liquid-vapor interface in the conventional two-phase regimes can be completely and favorably rectified into a single highly desirable two-phase flow regime with a sustainable and stable liquid boundary layer structure on both DI water and even highly wetting HFE-7100 in microchannels. The reconstruction of two-phase flow pattern as well as the boundary layer structure is observed in a large range of working conditions. My series breakthrough work in microchannels opens a door to two-phase transport research as well as leads to successfully solve long-existing issues facing unstable two-phase flows and to address the dilemma in enhancing transport performance in microchannels without compromise, which makes direct cooling feasible in high power microchips.
More recently, I have started to worked on the thermal management of electric vehicle motor and its power electronics using embedded two-phase cooling techniques, which would outperform the state-of-the-art EV motor cooling appraoch of the low efficient water-jacket cooling. The other research topics I have worked on include engergy storage and acoustic microfluidics to study fluids spraying using pyramidal micro-nozzle array and manipulation of cells/bio-particles.
My major academic achievements can be reflected by his publication record. I have published papers in prestigious journals such as Advanced Materials, Applied Physics Letters, International Journal of Heat and Mass Transfer, Journal of Applied Thermal Engineering and Journal of MEMS. You may find that they are related to areas including Thermal Management of High-power Electronics and Electric Vehicle Motor, Microfluidics, Energy Storage, 3D Materials, and Numerical Simulation.
Phase transition processes such as boiling, evaporation, condensation, and icing are ubiquitous natural phenomena and are essential to various industrial processes including thermal power plants, micro-reactors and microfluidics, fuel cells, and thermal management of high power electronics. Phase-change heat transfer such as boiling and evaporation has been widely exploited in various water-energy industries owing to its efficient heat transfer mode. My research interests are experimental and theoretical understanding of boiling heat transfer in microscale domains and thin film evaporation on wicking microstructures. The understanding of phase-change heat transfer mechanisms could provide fundamentally new solutions in thermal management and energy conversion.
Since 2013, I have been working in micro/nanoscale two-phase transport to understand complex two-phase phenomenon. I have undertaken and completed many significant research projects in boiling heat transfer. During my PhD study, I have demonstrated two innovative methodologies, named "two-phase oscillation" and "two-phase separation", in effectively manipulating or even controlling the naturally stochastic two-phase flow patterns in microchannels. First time, my research both experimentally and theoretically demonstrated that the chaotic liquid-vapor interface in the conventional two-phase regimes can be completely and favorably rectified into a single highly desirable two-phase flow regime with a sustainable and stable liquid boundary layer structure on both DI water and even highly wetting HFE-7100 in microchannels. The reconstruction of two-phase flow pattern as well as the boundary layer structure is observed in a large range of working conditions. My series breakthrough work in microchannels opens a door to two-phase transport research as well as leads to successfully solve long-existing issues facing unstable two-phase flows and to address the dilemma in enhancing transport performance in microchannels without compromise, which makes direct cooling feasible in high power microchips.
More recently, I have started to worked on the thermal management of electric vehicle motor and its power electronics using embedded two-phase cooling techniques, which would outperform the state-of-the-art EV motor cooling appraoch of the low efficient water-jacket cooling. The other research topics I have worked on include engergy storage and acoustic microfluidics to study fluids spraying using pyramidal micro-nozzle array and manipulation of cells/bio-particles.
My major academic achievements can be reflected by his publication record. I have published papers in prestigious journals such as Advanced Materials, Applied Physics Letters, International Journal of Heat and Mass Transfer, Journal of Applied Thermal Engineering and Journal of MEMS. You may find that they are related to areas including Thermal Management of High-power Electronics and Electric Vehicle Motor, Microfluidics, Energy Storage, 3D Materials, and Numerical Simulation.
Research interests
1. Thermal management of microelectronics under extreme working conditions, such as ultra-high heat flux and thermal shock;
2. Thermal management of EV motor and power electronics of drive;
3. Silicon micro-heat pipe integrated with novel wicking microstructures;
4. Microfluidics, for example, micro-pump, fluids/biocells/bioparticles separation and mixer;
5. Energy storage using phase change materials.
1. Thermal management of microelectronics under extreme working conditions, such as ultra-high heat flux and thermal shock;
2. Thermal management of EV motor and power electronics of drive;
3. Silicon micro-heat pipe integrated with novel wicking microstructures;
4. Microfluidics, for example, micro-pump, fluids/biocells/bioparticles separation and mixer;
5. Energy storage using phase change materials.
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On-going Project at Georgia Tech:
ARAP-E: High power density compact drive integrated motor for electric transportation, May/2019-May/2022
State-of-the-art high torque density motor systems for transportation applications require a separate motor, drive, and externally attached heat rejection units, which results in both a large size and a heavy weight of the overall system. This is a barrier to their use in large power and torque density future transportation applications, such as electrified trucks, buses, and aircraft. Advanced cooling approaches are proposed into the motor and drive electronics. Ambient heat rejection is integrated into a single unit to dramatically reduce system size and weight. Our innovations will reduce greenhouse gas emissions due to more electrification, and improve the energy efficiency of transportation systems utilizing electric motors
Project at Washington University in St. Louis
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Acoustic Microfluidics
Fluids spraying and cells/bio-particles manipulation using accoustics, including fluids spraying using pyramidal micro-nozzle array and manipulation of cells/bio-particles. Related paper: M. M. Binkley, M. Cui, W. Li, S. Tan, M. Y. Berezin, and J. M. Meacham, Design, modeling, and experimental validation of an acoustofluidic platform for nanoscale molecular synthesis and detection, Physics of Fluids 31, 082007 (2019) |
Completed Projects during my PhD study at USC:
As the project leader, I have been responsible for three projects listed below:
- ONR: Bubble/vapor slug dynamics in a confined domain
- NSF: Nanotips induced boundary layers to enhance flow boiling in microchannels
- ONR: Mechanisms of enhanced flow boiling with high frequency self-modulated microbubble-switched oscillations
Testing platform for flow boiling in silicon microchannels. All my PhD studies were carried out on this testbed.
Bubble/Vapor Slug Dynamics in a Confined Domain
In this project, a single bubble grow-collapse process in a single channel was investigated. Bubble dynamics is the key to understand fundamentals of boiling heat transfer. This process associates with bubble nucleation from heated surface, bubble growth rate, departure diameter and frequency, and condensation of bubble in subcooled liquid. Therefore, bubble dynamics is governed by two important phenomena: (1) evaporation during bubble nucleation and growth phase, and (2) bubble condensation in subcooled liquid. Bubble or vapor slug dynamics in a confined domain is significantly different from that in an ordinary domain due to the restriction by the channel wall.
Once the HTC models on bubble/vapor slug surfaces and criteria of collapse-coalesces of bubbles/vapor slugs are established and experimentally validated, it becomes feasible to model continuous flow pattern/regime transition with a high accuracy as well as to model associated two-phase transport performances.
In this project, a single bubble grow-collapse process in a single channel was investigated. Bubble dynamics is the key to understand fundamentals of boiling heat transfer. This process associates with bubble nucleation from heated surface, bubble growth rate, departure diameter and frequency, and condensation of bubble in subcooled liquid. Therefore, bubble dynamics is governed by two important phenomena: (1) evaporation during bubble nucleation and growth phase, and (2) bubble condensation in subcooled liquid. Bubble or vapor slug dynamics in a confined domain is significantly different from that in an ordinary domain due to the restriction by the channel wall.
Once the HTC models on bubble/vapor slug surfaces and criteria of collapse-coalesces of bubbles/vapor slugs are established and experimentally validated, it becomes feasible to model continuous flow pattern/regime transition with a high accuracy as well as to model associated two-phase transport performances.
Enhance flow boiling by rectifying chaotic two-phase flow regimes into a single annular flow regime in microchannels
Over the past decades, despite significant progresses, conflicting performance trade-offs inevitably exist, primarily due to the highly stochastic and transitional nature of two-phase flow and boundary layer structures inherent in the conventional channels. Herein we show that, both experimentally and theoretically, by designing novel fence-like microscale structures on the sidewalls of microchannels, the chaotic liquid-vapor interface in the conventional two-phase flow can be rectified to a highly stable and desirable boundary layer structure (as illustrated), leading to both high HTC and high CHF simultaneously without sacrificing the Δp in a wide range of working conditions. This exceptional work was selected in review in Nature and Nature Materials. Finally, this study was published in Advanced Materials in 2019. This breakthrough work in microchannels would extend and promote two-phase transport research. The long-existing issues facing unstable two-phase flows could be successfully solved. With the concept of two-phase separation, high performances of thermal management in high power microchips cooling are feasible.
Related Paper:
1. Li, W., Wang, Z., Yang, F., Alam, T., Jiang, M., Qu, X., Kong, F., Khan, A. S., Liu, M., Alwazzan, M., Tong, Y., and Li, C., Supercapillary Architecture-Activated Two-Phase Boundary Layer Structures for Highly Stable and Efficient Flow Boiling Heat Transfer, Advanced Materials, p. 1905117 (2020/01). (Frontispiece)
2. Li, W., Wang, Z., Yang, F., Alam, T., and Li, C., Microstructure-Activated Two-Phase Boundary Layers to Enhance Flow Boiling in Microchannels, International Journal of Heat and Mass Transfer, under review
Over the past decades, despite significant progresses, conflicting performance trade-offs inevitably exist, primarily due to the highly stochastic and transitional nature of two-phase flow and boundary layer structures inherent in the conventional channels. Herein we show that, both experimentally and theoretically, by designing novel fence-like microscale structures on the sidewalls of microchannels, the chaotic liquid-vapor interface in the conventional two-phase flow can be rectified to a highly stable and desirable boundary layer structure (as illustrated), leading to both high HTC and high CHF simultaneously without sacrificing the Δp in a wide range of working conditions. This exceptional work was selected in review in Nature and Nature Materials. Finally, this study was published in Advanced Materials in 2019. This breakthrough work in microchannels would extend and promote two-phase transport research. The long-existing issues facing unstable two-phase flows could be successfully solved. With the concept of two-phase separation, high performances of thermal management in high power microchips cooling are feasible.
Related Paper:
1. Li, W., Wang, Z., Yang, F., Alam, T., Jiang, M., Qu, X., Kong, F., Khan, A. S., Liu, M., Alwazzan, M., Tong, Y., and Li, C., Supercapillary Architecture-Activated Two-Phase Boundary Layer Structures for Highly Stable and Efficient Flow Boiling Heat Transfer, Advanced Materials, p. 1905117 (2020/01). (Frontispiece)
2. Li, W., Wang, Z., Yang, F., Alam, T., and Li, C., Microstructure-Activated Two-Phase Boundary Layers to Enhance Flow Boiling in Microchannels, International Journal of Heat and Mass Transfer, under review
Two-phase oscillations in microchannels:
Challenge: Confined bubble blocks two-phase flow in main channel, resulting in decrease of performance and high pressure drop.
Solution: Crack the bubble confined in mainchannel using the Jetting flows generated by auxiliary channels/nozzle.
The concept and structure of the microchannel with integrated multiple microscale nozzles and reentry cavities is illustrated above. (a) Improved global liquid supply to main channels through auxiliary channels via nozzles, the bubbles nucleate from nozzles and cavities, and local liquid spreading by microscale reentry cavity-induced capillary flows. The effectiveness of high frequency two-phase oscillations in enhancing flow boiling by passively collapsing vapor slugs was demonstrated tin microchannels with the following achievements:
•CHF exceeding 1 kW/cm2,
•~ 2x HTC enhancement, and
•> 75 % reduction in pressure drop compared to plain-wall microchannels
Related Paper:
1. W. Li, F. Yang, T. Alam, J. Khan and C. Li, Experimental and theoretical studies of critical heat flux of flow boiling in microchannels with microbubble-excited high-frequency two-phase oscillations, International Journal of Heat and Mass Transfer, 88 (2015) 368-378.
2. W. Li, X. Qu, T. Alam, F. Yang, W. Chang, J. Khan and C. Li, Enhanced Flow Boiling in Microchannels through Integrating Multiple Micro-nozzles and Reentry Microcavities, Applied Physics Letters, 110 (1), p. 014104, 2017.
3. W. Li, T. Alam, F. Yang, X. Qu, B. Peng, C. Li, Enhanced Flow Boiling in Microchannels using Auxiliary Channels and Multiple Micronozzles Part Ⅱ : Enhancement of CHF and Reduction of Pressure drop, International Journal of Heat and Mass Transfer, 2017 (115), 264-272.
4. W. Li, F. Yang, T. Alam, X. Qu, B. Peng, J. Khan, C. Li, Enhanced Flow Boiling in Microchannels using Auxiliary Channels and Multiple Micronozzles Part Ⅰ : Characterizations of flow boiling heat transfer, International Journal of Heat and Mass Transfer, 2018 (116), 208-217.
5. W. Li, J. Ma, T. Alam, F. Yang, J. Khan and C. Li, Flow Boiling of HFE-7100 in Silicon Microchannels Integrated with Multiple Micro-nozzles and Reentry Micro-cavities, International Journal of Heat and Mass Transfer, 123 (2018) 354-366.
Challenge: Confined bubble blocks two-phase flow in main channel, resulting in decrease of performance and high pressure drop.
Solution: Crack the bubble confined in mainchannel using the Jetting flows generated by auxiliary channels/nozzle.
The concept and structure of the microchannel with integrated multiple microscale nozzles and reentry cavities is illustrated above. (a) Improved global liquid supply to main channels through auxiliary channels via nozzles, the bubbles nucleate from nozzles and cavities, and local liquid spreading by microscale reentry cavity-induced capillary flows. The effectiveness of high frequency two-phase oscillations in enhancing flow boiling by passively collapsing vapor slugs was demonstrated tin microchannels with the following achievements:
•CHF exceeding 1 kW/cm2,
•~ 2x HTC enhancement, and
•> 75 % reduction in pressure drop compared to plain-wall microchannels
Related Paper:
1. W. Li, F. Yang, T. Alam, J. Khan and C. Li, Experimental and theoretical studies of critical heat flux of flow boiling in microchannels with microbubble-excited high-frequency two-phase oscillations, International Journal of Heat and Mass Transfer, 88 (2015) 368-378.
2. W. Li, X. Qu, T. Alam, F. Yang, W. Chang, J. Khan and C. Li, Enhanced Flow Boiling in Microchannels through Integrating Multiple Micro-nozzles and Reentry Microcavities, Applied Physics Letters, 110 (1), p. 014104, 2017.
3. W. Li, T. Alam, F. Yang, X. Qu, B. Peng, C. Li, Enhanced Flow Boiling in Microchannels using Auxiliary Channels and Multiple Micronozzles Part Ⅱ : Enhancement of CHF and Reduction of Pressure drop, International Journal of Heat and Mass Transfer, 2017 (115), 264-272.
4. W. Li, F. Yang, T. Alam, X. Qu, B. Peng, J. Khan, C. Li, Enhanced Flow Boiling in Microchannels using Auxiliary Channels and Multiple Micronozzles Part Ⅰ : Characterizations of flow boiling heat transfer, International Journal of Heat and Mass Transfer, 2018 (116), 208-217.
5. W. Li, J. Ma, T. Alam, F. Yang, J. Khan and C. Li, Flow Boiling of HFE-7100 in Silicon Microchannels Integrated with Multiple Micro-nozzles and Reentry Micro-cavities, International Journal of Heat and Mass Transfer, 123 (2018) 354-366.
Scalable nanowires for enhanced microfluidic cooling
SiNW enables gravity-insensitive bubble departure mechanism (enhances bubble nucleation site density and departure frequency; reduces bubble departure diameter). Regulate the transitional flow boiling regimes (slug/churn/ wavy) to a single annular flow. Enhanced heat transfer performances can be achieved with extended critical heat flux limit, reduced flow boiling instabilities and pressure drop and excellent orientation independency. SiNW can reduce intermittent flow regimes (slug/ churn), improve rewetting, maintain thin film and thus, helps to improve system performances.
Related Paper:
1. F. Yang, W. Li, X. Dai and C. Li, Flow Boiling Heat Transfer of HFE-7000 in Nanowire-coated Microchannels, Applied Thermal Engineering, 2016 (93), 260-268
2. T. Alam, W. Li, F.H. Yang, W. Chang, J. Li, Z. Wang, J. Khan and Chen Li, Force Analysis and Bubble Dynamics during Flow Boiling in Silicon Nanowire Microchannels, Int. J. of Heat and Mass Transfer, 2016 (101), 915-926.
3. T. Alam, W. Li, W. Chang, F. Yang, J. Khan, C. Li, A comparative study of flow boiling HFE-7100 in silicon nanowire and plainwall microchannels, International Journal of Heat and Mass Transfer, 124 (2018) 829-840.
SiNW enables gravity-insensitive bubble departure mechanism (enhances bubble nucleation site density and departure frequency; reduces bubble departure diameter). Regulate the transitional flow boiling regimes (slug/churn/ wavy) to a single annular flow. Enhanced heat transfer performances can be achieved with extended critical heat flux limit, reduced flow boiling instabilities and pressure drop and excellent orientation independency. SiNW can reduce intermittent flow regimes (slug/ churn), improve rewetting, maintain thin film and thus, helps to improve system performances.
Related Paper:
1. F. Yang, W. Li, X. Dai and C. Li, Flow Boiling Heat Transfer of HFE-7000 in Nanowire-coated Microchannels, Applied Thermal Engineering, 2016 (93), 260-268
2. T. Alam, W. Li, F.H. Yang, W. Chang, J. Li, Z. Wang, J. Khan and Chen Li, Force Analysis and Bubble Dynamics during Flow Boiling in Silicon Nanowire Microchannels, Int. J. of Heat and Mass Transfer, 2016 (101), 915-926.
3. T. Alam, W. Li, W. Chang, F. Yang, J. Khan, C. Li, A comparative study of flow boiling HFE-7100 in silicon nanowire and plainwall microchannels, International Journal of Heat and Mass Transfer, 124 (2018) 829-840.
