Nanoporous Membrane Evaporative Cooling Without Flow Instability
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Solution Overview
Problem
Current thermal management technologies face limitations in dissipating high heat fluxes due to flow instabilities and increased pumping power requirements, particularly in microchannel systems, where capillary pressure is coupled with liquid transport, restricting maximum heat flux and increasing thermal resistance.
Innovation Solution
A heat transfer system utilizing a nanoporous membrane with parallel ridges to create vertical liquid manifolds, where a dielectric fluid is pumped across the edges and drawn through the membrane via capillarity, decoupling capillary pressure from fluidic delivery, and allowing high capillary pressures to drive liquid to the heated surface, thereby enhancing heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If flow boiling in microchannels is used to increase heat transfer coefficients, then heat transfer performance is improved, but flow instabilities occur
Solution Approach 1:
The patent extracts the capillary pressure generation function from the liquid transport path by using a separate nanoporous membrane structure. The membrane generates capillary pressure to drive liquid flow without being part of the main liquid transport channel, thereby eliminating flow instabilities while maintaining high heat transfer coefficients.
Solution Approach 2:
The nanoporous membrane acts as an intermediary between the liquid reservoir and the heated surface. It mediates the liquid transport by providing capillary pressure-driven flow, decoupling the pressure generation from the flow path and ensuring stable operation without flow instabilities.
2Power
If wick height is increased to achieve higher heat fluxes, then liquid transport capacity is improved, but thermal resistance increases
Solution Approach 1:
The patent transitions from vertical liquid transport through a tall wick to a planar nanoporous membrane structure. By changing the dimensionality of the liquid transport path from vertical (through-height) to lateral (across-membrane), the thermal resistance is dramatically reduced while maintaining sufficient capillary pressure for high heat flux operation.
Solution Approach 2:
The patent uses a thin nanoporous membrane instead of a thick wick structure. The membrane thickness is optimized to be minimal (on the order of micrometers), providing both sufficient capillary pressure generation and minimal thermal resistance, unlike traditional thick wicks that require heights >100 μm.
3Power
If active pumping is used to drive liquid to the membrane, then liquid delivery is improved, but power consumption increases
Solution Approach 1:
The nanoporous membrane is designed to generate sufficient capillary pressure autonomously to drive liquid from the reservoir to the heated surface. This self-service mechanism eliminates the need for active pumping, reducing power consumption while maintaining adequate liquid delivery rates for high heat flux operation.
Solution Approach 2:
The patent optimizes the pore size and porosity parameters of the nanoporous membrane to achieve the desired balance between capillary pressure generation and liquid flow rate. By carefully selecting these parameters, the membrane can drive liquid flow at rates sufficient for high heat flux without requiring external pumping power.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves high heat transfer coefficients and reduced thermal resistance, enabling the dissipation of greater than 1 kW/cm² on a 1 cm² area with a 200×200 μm² hotspot, while maintaining low pumping power and avoiding flow instabilities, with a combined heat transfer coefficient of 0.18 kW/cm²K, an order of magnitude higher than state-of-the-art two-phase cooling solutions.
Implementation Method 1
The fluid is drawn through the liquid manifolds via capillarity provided by the nanoporous membrane
Implementation Method 2
The fluid evaporates to dissipate heat flux through the substrate
Implementation Method 3
evaporates to dissipate heat flux
Data Source
AI summary
Evaporative heat transfer system. The system includes a substrate and a plurality of substantially parallel, spaced-apart ridges extending from the substrate forming vertical liquid manifolds therebetween. A nanoporous membrane is supported on the ridges and a pump delivers a dielectric fluid across the ridges. The fluid is drawn through the liquid manifolds via capillarity provided by the nanoporous membrane and evaporates to dissipate heat flux through the substrate. A preferred dielectric fluid is pentane. It is preferred that membrane porosity vary across the membrane to tailor thermal resistances to limit temperature rises.