Brazed Heat Pipe Sealing for Freeze Thaw Reliability
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Solution Overview
Problem
Conventional copper/water heat pipes fail in low-temperature environments due to imperfections at the seams and internal surfaces, which cause water to accumulate and freeze, leading to damage and failure during freeze/thaw cycles.
Innovation Solution
The use of brazing instead of welding to seal the seams, combined with surface polishing and the application of end caps and graded wick structures, helps to eliminate imperfections and prevent water accumulation, allowing heat pipes to function effectively in low-temperature environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If welding is used to seal heat pipe seams, then manufacturing cost and ease of application are improved, but water accumulates in seam imperfections and freezes during low-temperature cycles causing heat pipe failure
Solution Approach 1:
The patent changes the sealing method from welding to brazing, which fundamentally alters the manufacturing process parameters. Brazing creates a more reliable seal that prevents water accumulation in imperfections, thereby extending heat pipe lifespan in freeze/thaw environments while maintaining ease of manufacture
Solution Approach 2:
The patent acknowledges that welded heat pipes have limited lifespan in low-temperature environments and must be repeatedly replaced. By transitioning to brazed heat pipes, the service life is extended from hundreds to thousands of cycles, reducing replacement frequency despite similar manufacturing complexity
2Power
If water is used as working fluid in copper heat pipes, then heat transfer efficiency is improved, but water freezes in imperfections during low-temperature cycles causing cracks and deterioration
Solution Approach 1:
The patent extracts and removes the harmful factor (water accumulation in imperfections) by implementing multiple protective measures: smoothing internal surfaces to eliminate imperfections, applying brazing material to seal potential defect areas, and adding end caps to prevent water ingress. This allows water to remain as the working fluid while eliminating the freezing damage mechanism
Solution Approach 2:
The patent applies preliminary protective actions during manufacturing: internal surfaces are smoothed to eliminate imperfections before water can accumulate, brazing material is applied to seal potential defect areas, and end caps are installed to prevent water ingress. These preventive measures are implemented before the heat pipe enters service, preventing freezing damage before it can occur
3Productivity
If heat pipe internal surfaces have imperfections from manufacturing, then production ease is improved, but water accumulates in these imperfections and freezes causing heat pipe failure
Solution Approach 1:
The patent implements preliminary smoothing of internal surfaces during the manufacturing process, eliminating imperfections before water accumulation can occur. This preliminary action prevents the root cause of freezing damage while maintaining production efficiency by integrating smoothing into the manufacturing workflow
Solution Approach 2:
The patent introduces brazing material as an intermediary substance that seals imperfections in the heat pipe seams and internal surfaces. This intermediary layer prevents water from contacting and accumulating in manufacturing defects, thereby preventing freezing damage while allowing standard manufacturing processes to continue
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
Brazed heat pipes with polished surfaces and end caps can withstand thousands of freeze/thaw cycles without failure, maintaining their operational integrity by preventing water from accumulating and freezing within imperfections.
Implementation Method 1
a vacuum defined in the internal chamber
Implementation Method 2
The phase changes of the working fluid are used to dissipate heat from the heat source
Implementation Method 3
The heat received from the heat source is absorbed by and vaporizes the working fluid (i.e., changes the phase of the working fluid), thereby transporting the heat away from the heat source
Implementation Method 4
The heated vapor then flows to the cooler condenser region of the heat pipe, where the vaporized working fluid condenses and changes phase back to its liquid state. Condensation of the vaporized working fluid dissipates the absorbed heat
Implementation Method 5
Many heat pipes are hollow, and may include a wick structure disposed along an internal wall of the heat pipe to generate a capillary action to facilitate return of working fluid from the condenser region to the evaporator region
Data Source
AI summary
A heat transfer device includes a hollow metal body. The hollow body defines a wall having a thickness, an internal chamber defined at least in part by the wall, a vacuum defined in the internal chamber, a seam defined between two different portions of the wall and extending through the thickness of the wall, a brazing material applied to the seam to hermetically seal the internal chamber and maintain the vacuum in the internal chamber, an evaporation region in which heat is received in the hollow metal body, and a condenser region from which heat is discharged from the hollow metal body. The heat transfer device further includes a charge of ice within the internal chamber, the charge of ice sufficiently large to define, when in a thawed state, a working fluid drawing heat from the evaporator region and discharging heat from the condenser region in a working cycle of the heat transfer device.