3D microstructures for rapid absorption/desorption in mechanically constrained liquid absorbents
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Solution Overview
Problem
Absorption and desorption processes in absorption refrigeration systems, particularly with lithium bromide (LiBr) solutions, face limitations due to diffusion constraints, leading to low absorption and desorption rates, which are further hindered by the need for significant surface superheat and high pressure drops in thin solution channels.
Innovation Solution
The implementation of 3D-structured surfaces with staggered herringbone ridges on the heat-exchanging surface of microchannels promotes vortices, enhancing mixing and reducing diffusion limitations, thereby improving absorption and desorption rates while minimizing pressure drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the solution channel thickness is reduced to enhance absorption rate, then the absorption rate increases, but the pressure drop increases significantly
Solution Approach 1:
The patent introduces 3D-structured surfaces with staggered herringbone ridges that create secondary flow patterns and vortices within the thin solution channel. This transforms the flow from simple laminar flow to a more complex three-dimensional flow structure, enhancing mixing and mass transfer without requiring increased channel thickness, thereby maintaining low pressure drop while improving absorption rate
Solution Approach 2:
The patent utilizes hydraulic principles by creating controlled turbulence and vortex flows within the thin solution channel through the 3D-structured surfaces. The staggered herringbone ridges generate secondary flows that enhance convective mass transfer, allowing the system to achieve high absorption rates in thin channels without the prohibitive pressure drops associated with conventional thin-film designs
2Stress or pressure
If the solution channel thickness is increased to reduce pressure drop, then the pressure drop decreases, but the absorption rate reduces due to reduced mass transfer efficiency
Solution Approach 1:
The 3D-structured surfaces introduce complex three-dimensional flow patterns including vortices and secondary flows within the solution channel. This dimensional complexity enhances the convective mass transfer coefficient, allowing thicker channels to achieve absorption rates comparable to or exceeding those of thin channels, while the increased thickness provides lower pressure drop
Solution Approach 2:
The staggered herringbone ridges create dynamic flow structures that adapt to the solution flow conditions. The vortices and mixing zones generated by the 3D structures enhance mass transfer dynamically throughout the channel, ensuring high absorption rates are maintained even at increased channel thicknesses where pressure drop would otherwise be reduced
3Productivity
If conventional mixing methods are used to enhance absorption rate, then the absorption rate increases, but the device complexity increases
Solution Approach 1:
The 3D-structured surfaces with staggered herringbone ridges enable the solution flow to self-mix through the generation of vortices and secondary flows. The geometry itself performs the mixing function without requiring external mixing devices, mechanical agitators, or complex control systems, thereby achieving enhanced absorption rates while maintaining simple device architecture
Solution Approach 2:
The patent replaces mechanical mixing systems with a passive geometric structure that generates flow-induced mixing. The staggered herringbone ridges create hydrodynamic vortices that accomplish the mixing function through fluid mechanics alone, eliminating the need for mechanical mixers, pumps, or actuators, thus reducing device complexity while enhancing absorption
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 significantly increases absorption and desorption rates, reduces the required surface superheat temperature, and lowers the heating medium temperature, making the process more efficient and scalable for applications like solar-thermal collectors and photovoltaics.
Implementation Method 1
The implementation of 3D-structured surfaces with staggered herringbone ridges on the heat-exchanging surface of microchannels promotes vortices, enhancing mixing
Implementation Method 2
promotes vortices, enhancing mixing and reducing diffusion limitations
Implementation Method 3
Absorption of species into a liquid is widely used in many technologies... Absorption is limited by the rate of absorbate diffusion into the absorbent
Implementation Method 4
In cases involving an absorbate with a high heat of phase change, such as water vapor absorption into a lithium bromide (LiBr) solution in an absorption heat pump or a dehumidifier, the absorption rate is also limited by thermal diffusion
Implementation Method 5
When the heat released at the vapor-liquid interface due to phase change is not removed, there is an increase in temperature and equilibrium water vapor pressure at the interface
Implementation Method 6
Thin solution high velocity flow reduces the heat diffusion path to the cooling surface beneath the solution film
Implementation Method 7
a high solution flow velocity diminishes the thickness of any concentration boundary layer
Implementation Method 8
Chaotic Mixer for Microchannels Science 2002, 295, 647-51 where chaotic advection is generated within the flow through stretching and folding the laminar streamlines
Data Source
AI summary
An absorber or desorber contains one or more micro-channels that have a 3-D structured heat-exchanging surface and a membrane on the microchannel situated distal to the 3-D structured heat-exchanging surface, where the membrane is permeable to a solvent of a solution employed in the absorber or desorber. The 3-D structured surface promotes mixing of hot and cold solution between the 3-D structured heat-exchanging surface and a vapor-exchanging surface proximal to the membrane. The mixing reduces the differences in concentration and temperature of the bulk solution and the solution at the vapor-exchanging surface to enhance the efficiency and rate of absorption or desorption of the solvent.