Loop Heat Pipe Evaporator Radial Thermal Spreader
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Solution Overview
Problem
Conventional loop heat pipes face limitations in heat flux due to non-uniform heat distribution and concentration at the interface between the wick and evaporator casing, leading to unstable operation and dry-out, with a maximum heat flux limit of approximately 25 W/cm2.
Innovation Solution
An annular heat pipe is integrated as a thermal spreader on the outer surface of the evaporator casing, distributing heat from limited input areas to the entire surface of the loop heat pipe evaporator, increasing the heat transfer area and reducing thermal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If heat is input through a limited area at the evaporator, then heat input efficiency is improved, but heat flux concentration causes dry-out and unstable operation
Solution Approach 1:
The patent introduces a second heat pipe layer arranged in the radial direction, perpendicular to the first heat pipe layer. This dimensional transformation allows heat to be distributed not only in the axial direction but also in the radial direction, effectively spreading heat over a larger surface area and reducing heat flux concentration at the heat input location.
Solution Approach 2:
The second heat pipe layer acts as an intermediary thermal distribution system between the heat input source and the evaporator wick. It receives heat from the first heat pipe layer and redistributes it uniformly across the evaporator surface, preventing direct heat flux concentration at the wick interface.
2Ease of operation
If vapor grooves are located between the wick and evaporator casing, then vapor flow path is provided, but heat transfer area is reduced and heat flux is concentrated
Solution Approach 1:
By adding the second heat pipe layer in the radial direction, the patent creates additional heat transfer pathways that bypass the limitation imposed by vapor grooves in the axial direction. Heat can now transfer through multiple dimensional paths, effectively compensating for the area reduction caused by vapor grooves.
Solution Approach 2:
The heat transfer function is segmented into two independent layers: the first heat pipe layer handles axial heat distribution, while the second heat pipe layer handles radial heat distribution. This segmentation allows each layer to optimize its specific function without interfering with the other, maintaining adequate heat transfer area despite the presence of vapor grooves.
3Device complexity
If conventional loop heat pipe wick structure is used, then simple construction is achieved, but heat flux limit is approximately 25 W/cm2
Solution Approach 1:
The second heat pipe layer serves as an intermediary thermal management system that decouples the heat input interface from the evaporator wick interface. This allows the wick structure to remain simple while the overall system heat flux capability is enhanced through the additional thermal distribution layer.
Solution Approach 2:
The dual-layer heat pipe structure adds a radial dimension to heat distribution, enabling the system to handle higher heat flux inputs without increasing the complexity of the wick structure itself. The heat is spread out before reaching the wick, allowing the simple wick design to operate within its capabilities.
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 solution allows for a higher heat flux capability, effectively spreading heat across the entire evaporator surface, thereby increasing the tolerated heat input without issues of dry-out or instability, with heat flux limits extended to 75-500 W/cm2.
Implementation Method 1
The present invention adds an annular heat pipe as a thermal spreader in good thermal contact with the outer surface of the evaporator casing
Implementation Method 2
Conduction requires heat to move from the location of heat input through the evaporator casing directly to the liquid-saturated wick
Implementation Method 3
the heat pipe wick on the inside of the heat pipe outer wall at the heat input area produces vapor
Implementation Method 4
vapor that travels throughout the entire heat pipe and condenses in near uniform fashion on the entire inside surface of the heat pipe
Implementation Method 5
convection of the vapor in the vapor grooves that are along the casing inner surfaces and/or the wick outer surfaces
Data Source
AI summary
An evaporator for a loop heat pipe with high input heat transfer. The heat transfer is attained by constructing a heat pipe on the loop heat pipe evaporator heat input surface. The heat pipe then distributes the heat from limited input areas over the entire surface of the loop heat pipe evaporator, and that entire evaporator surface functions as the loop heat pipe heat input area as opposed to limited smaller areas into which the heat usually enters.