Current Research
High Efficiency Compact Air-Cooled Heat Exchangers
The effect of dimples on fins, fin thickness, and fin height on air side heat transfer enhancement and pumping power penalty has been evaluated for elliptical tube cross-flow heat exchangers. Dimpled fins results are compared to plain fins of two different heights and thicknesses. Wavy fins are also investigated and results are compared with plain fins. Applications are easily scaled and include cooling for large power plants. Funded by ARPA-E.
Optimization of Pulsating Heat Pipes
The physics behind the seemingly random motion of liquid plugs and vapor slugs are analyzed to model dynamic behavior and failure modes in variable gravity operation. The effect of thin film hydrodynamics and phase change on overall heat spreader thermal conductivity is explored through numerical simulation and prototype experimentation. Funded by NASA JPL.
Micro-Structured Surfaces for Boiling Heat Transfer Enhancement
Investigation of the critical heat flux on heater surfaces, the size of a single bubble departure diameter, both confined and unconfined, and the effects of wettability and surface modification such as microstructures. Experimental confined heater simulation of microgravity boiling effects.
Variable Heater Size Effect on Critical Heat Flux
Investigation of separate and interacting effects of surface size (larger than the diameter of a vapor column), boundary wall spacing, wettability, and micro/nanostructures on the critical heat flux (CHF) on horizontal surfaces.
Additional studies are being performed on the physical mechanism of CHF enhancement by observing the distribution and departure mode of bubbles in both far and near field of micro/nanostructured surfaces.
Dynamic Flash Evaporation and Vapor Separation System
A dynamic desalination approach is being studied that combines evaporation and separation of phases in one step. Solar energy can be used to heat brackish or sea water before it is flashed and is injected into swirl flow phase separator.
Mechanically Pumped Phase Change Fluid Loop
Analysis and modelling of hybrid two-phase evaporator for high performance cooling for thermal control of deep space missions. Funded by NASA JPL.
Numerical Simulation of Bubble Dynamics
Physics-based simulation of vapor bubble nucleation, merger, and departure is being performed in two dimensions. For a single cavity site confined within a given heater area, the changes in vapor removal patterns and wall heat flux are studied as the wall superheat is parametrically increased for varying waiting times. The work will be extended to include multiple cavity sites (in 3D) and to include the effect of transient conduction in the solid rather than assuming constant wall superheat. This would enable us to obtain a more realistic prediction of the bubble ebullition cycles and explain the thermal interaction between neighboring nucleation sites on a heater surface.
Bubble Dynamics under flash evaporation
Flash evaporation phenomena occur when a liquid is subjected to a sudden drop in pressure resulting in rapid vaporization. Understanding of this phenomena is essential as it is applied in various industrial processes such as desalination, waste heat recovery, cooling of electronic components etc. Experiments are being performed to understand the bubble dynamics during flash on a static pool to develop further insights.
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