Diffusion-Bonded Heat Pipe Wick for Capillary Flow Balance
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Solution Overview
Problem
Existing heat pipe wick formation technologies face challenges in achieving high power density operation, efficient condensate flow, and maintaining capillary continuity, particularly in high-temperature alkali metal heat pipes.
Innovation Solution
A method for forming a heat pipe wick involves wrapping multiple layers of fine mesh screen around a mandrel, inserting the assembly into a dissolvable sheath or non-dissolvable tube, and applying pressure to form a diffusion bond at high temperature, followed by etching to remove the mandrel and sheath, resulting in a porous tube wick.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a homogeneous wick with uniform pore structure is used, then capillary pressure rise is generated, but resistance to condensate flow is high limiting axial heat transfer rate
Solution Approach 1:
The wick is segmented into multiple functional zones: a homogeneous wick section for capillary pressure generation, and a compound wick section with low-resistance flow paths for rapid condensate return. This segmentation allows each zone to optimize its specific function without compromising the other.
Solution Approach 2:
Different regions of the wick are given different pore structures and material properties. The homogeneous region has fine uniform pores for capillary action, while the compound region has larger pores and open channels for low-resistance flow, matching local functional requirements.
2Productivity
If the wick cross-sectional area is increased to reduce flow resistance, then condensate flow improves, but area available for vapor and unconstrained liquid flow decreases
Solution Approach 1:
The wick cross-section is segmented into flow channels and solid matrix regions. The flow channels occupy minimal space but provide low-resistance paths, while the remaining cross-sectional area is maintained for vapor flow and liquid reservoir functions.
Solution Approach 2:
The compound wick uses porous materials with optimized pore size distributions that provide high permeability for condensate flow while maintaining sufficient solid structure for capillary pressure generation and vapor flow pathways.
3Stress or pressure
If fine pores are used to maximize capillary pressure rise, then capillary continuity is improved, but manufacturing complexity increases
Solution Approach 1:
Commercially available porous materials with controlled pore sizes and distributions are used to achieve the required capillary pressure characteristics without complex manufacturing processes. The materials are selected to provide both fine pores for capillary action and larger pores for low-resistance flow.
Solution Approach 2:
The compound wick combines different porous materials or porous and non-porous elements in a composite structure that achieves both capillary pressure generation and low-resistance flow paths through material selection rather than complex fabrication.
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 method enables the creation of high-performance heat pipe wicks with optimized pore structure and minimal cross-sectional area, enhancing heat transfer efficiency and ensuring long-term corrosion-free operation.
Implementation Method 1
diffusion bonding the assembly at a temperature sufficiently high achieving self-diffusion of the plurality of layers of the fine mesh screen, used to form the wick, to themselves
Implementation Method 2
These menisci collectively produce a capillary pressure rise that is a driving potential enabling heat pipe operation
Implementation Method 3
In the heated zone of a heat pipe, evaporation of the liquid produces vapor
Data Source
AI summary
A method for forming an annular heat pipe wick in a controlled atmosphere includes wrapping a plurality of layers of a fine mesh screen around a mandrel to form a wick. The method also includes inserting the mandrel and the wick into a sheath, and compressing the wick between the sheath and the mandrel to form an assembly. The compressing of the wick comprises applying pressure to an exterior of the mandrel and the sheath. The method further includes diffusion bonding the assembly at a temperature sufficiently high achieving self-diffusion of the plurality of layers of the fine mesh screen used to form the wick to themselves. The method also includes cooling the diffusion bonded assembly to room temperature, and etching the mandrel and sheath from the diffusion bonded assembly, leaving the wick as a porous tube.