Multi-Layer Wick Structure for Loop Heat Pipe Evaporator
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Solution Overview
Problem
Existing loop heat pipes face challenges in maintaining high evaporation performance of the working fluid in the evaporator, leading to heat leaks and decreased cooling efficiency due to the trade-off between heat transfer rate and discharge resistance.
Innovation Solution
The evaporator is designed with a wick structure comprising three layers: a high thermal conductivity first layer, an elastic intermediate layer with lower thermal conductivity, and a liquid transport layer with a lower void ratio, which prevents heat leaks and enhances discharge efficiency by controlling heat transfer and fluid flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the wick is formed with metal high in heat transfer rate, then the evaporation performance of the working fluid is improved, but heat leak occurs to the liquid phase working fluid in the reservoir
Solution Approach 1:
The wick is constructed with multiple layers having different thermal conductivities in different regions. The first layer (near evaporator) has high thermal conductivity for efficient heat transfer, while the second layer (near reservoir) has low thermal conductivity to prevent heat leak to the liquid reservoir, thus resolving the contradiction between evaporation performance and heat leak prevention
Solution Approach 2:
The wick uses composite material structure with at least two different materials having different thermal conductivities. This composite construction allows the wick to simultaneously achieve high heat transfer rate for evaporation while blocking heat leak to the liquid phase working fluid in the reservoir
2Object-generated harmful factors
If the thickness of the wick is increased to suppress heat transfer toward the reservoir, then heat leak is reduced, but the discharge resistance of the vapor phase working fluid becomes high
Solution Approach 1:
The wick thickness and thermal conductivity are optimized locally: the first layer near the evaporator has smaller thickness and high thermal conductivity to facilitate vapor discharge with low resistance, while the second layer near the reservoir has larger thickness and low thermal conductivity to block heat leak, thus resolving the contradiction between heat leak reduction and pressure loss
Solution Approach 2:
The wick is segmented into multiple functional layers with different properties. The first layer is optimized for vapor discharge (thin, high thermal conductivity), while the second layer is optimized for heat blocking (thick, low thermal conductivity), allowing each segment to address a specific aspect of the contradiction
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 configuration effectively prevents heat leaks, reduces pressure loss, and enhances the cooling efficiency of the cooling target by promoting efficient phase change and heat transfer.
Implementation Method 1
The working fluid in the liquid phase soaks into the wick from a liquid reservoir in the housing due to a capillary action
Implementation Method 2
The evaporator receives heat from a heat generator to evaporate the working fluid in the liquid phase to change the phase of the working fluid to the vapor phase
Implementation Method 3
evaporate the working fluid in the liquid phase with a heat transferred from a cooling target
Implementation Method 4
The condenser condenses the working fluid in the vapor phase due to heat radiation to perform a phase change from the working fluid in the vapor phase to the working fluid in the liquid phase
Implementation Method 5
The condenser condenses the working fluid in the vapor phase due to heat radiation
Implementation Method 6
the first layer has a plurality of first apertures disposed along the plurality of flow channels, and has higher thermal conductivity than both thermal conductivity of the second layer and thermal conductivity of the third layer
Data Source
AI summary
A cooling device includes an evaporator, a condenser, a vapor pipe, and a liquid pipe. The evaporator includes a housing having a reservoir, a wick disposed in the housing and retaining the working fluid in the liquid phase, and a groove member having a plurality of flow channels through which the working fluid in the vapor phase flows. The wick has first, second and third layers. The first layer has a plurality of first apertures, and is higher in thermal conductivity than both the second and third layers. The third layer transports the working fluid in the liquid phase in the reservoir to the second layer. The second layer has a plurality of second apertures corresponding to the first apertures, the second apertures having aperture area larger than corresponding one of the first apertures. The second layer transports the working fluid in the liquid phase to the first layer.