Enhanced Pool Boiling System and Method
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Solution Overview
Problem
Current technologies for pool boiling heat transfer around tubes are limited, particularly for low-pressure refrigerants, as they fail to effectively enhance heat flux and delay the onset of critical heat flux, which is crucial for efficient energy conversion and equipment protection.
Innovation Solution
A boiling heat exchange system utilizing a thermally conductive open-cell porous material, such as metal foam, is applied to the outer surface of evaporator tubes, providing a larger surface area and increased nucleation sites to enhance heat transfer and delay critical heat flux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional smooth tube surfaces are used for pool boiling heat transfer, then the device complexity is low, but the heat transfer coefficient is insufficient and critical heat flux occurs early
Solution Approach 1:
The patent applies porous materials (metal foams, ceramic foams, or sintered metals) as coatings or inserts on the evaporator tube surfaces. These porous structures provide numerous nucleation sites for bubble formation, significantly enhancing the heat transfer coefficient and delaying critical heat flux occurrence compared to conventional smooth tubes, while maintaining reasonable structural complexity.
Solution Approach 2:
The patent employs composite structures combining different materials with complementary properties, such as metal foam coatings on copper tubes or ceramic foam inserts in stainless steel evaporators. This composite approach optimizes both heat transfer performance and structural integrity, resolving the contradiction between enhanced heat transfer and device complexity.
2Power
If porous structures are added to enhance boiling heat transfer, then heat transfer coefficient improves, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent segments the porous structure integration into separate, manufacturable components: pre-formed metal foam coatings, insertable ceramic foam elements, or modular porous inserts. This segmentation allows each component to be manufactured independently using optimized processes, then assembled into the final evaporator assembly, reducing overall manufacturing difficulty while maintaining heat transfer enhancement.
Solution Approach 2:
The patent uses intermediary bonding layers or mounting structures to facilitate the integration of porous materials with base tubes. These intermediaries simplify the manufacturing process by providing standardized interfaces and attachment methods, reducing the complexity of directly integrating porous structures with evaporator tubes.
3Power
If thicker porous foam layers are used to increase surface area, then heat transfer enhancement increases, but the pressure drop across the structure increases
Solution Approach 1:
The patent applies local quality by varying the porous structure characteristics along the evaporator tube length or around the tube circumference. Regions with higher heat flux demands receive thicker or higher porosity foam layers, while regions with lower demands have thinner layers, optimizing heat transfer enhancement while minimizing overall pressure drop across the system.
Solution Approach 2:
The patent implements partial action by applying porous foam coatings or inserts only to specific sections of the evaporator tubes where heat transfer enhancement is most needed, rather than covering the entire surface. This selective application provides sufficient heat transfer enhancement while reducing the total pressure drop penalty associated with thicker porous layers.
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
The system achieves significant enhancements in heat transfer coefficients, with the metal foam tubes showing 100-212% improvement over bare tubes, delaying critical heat flux and maintaining high heat transfer capacity at higher heat fluxes, thus improving energy conversion efficiency and protecting equipment.
Implementation Method 1
heat from the source fluid will pass through the wall and the thermally conductive open-cell porous material to cause the heat exchange liquid within the open-cells to boil
Implementation Method 2
cause the heat exchange liquid within the open-cells to boil to a heat exchange vapor
Implementation Method 3
heat exchange liquid will enter the pores and open-cells of the open-cell porous material... cause the heat exchange liquid within the open-cells to boil to a heat exchange vapor
Implementation Method 4
heat exchange liquid will enter the pores and open-cells of the open-cell porous material... heat exchange vapor will move through the open cells of the thermally conductive porous material and will be replaced in the open-cells by more heat exchange liquid
Data Source
AI summary
A boiling heat exchange system includes a heat exchanger including a chamber configured to hold a heat exchange fluid including a heat exchange vapor and a pool of heat exchange liquid and an evaporator tube having an outer surface and a thermally conductive open-cell porous material disposed on the outer surface and comprising a plurality of pores. The evaporator tube can be immersed in the heat exchange liquid held in the chamber and the heat exchange liquid will enter the pores. The open-cells of the open-cell porous material will heat the heat exchange liquid to cause the heat exchange liquid to boil to a heat exchange vapor and exchange heat with a source fluid flowing through the evaporator tube or with a component in thermal contact with the evaporator. A method of performing heat exchange is also disclosed.