Passive Heat Switch Using Liquid Metal Slug and Bimetallic Actuator
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Solution Overview
Problem
Existing passive heat switches are bulky, heavy, and require complex support structures due to the need for metallic structure movement, limiting their scalability and integration in various thermal management applications, especially in extreme temperature environments like spacecraft.
Innovation Solution
A passive heat switch device featuring a closed channel with a bimetallic strip actuator and a liquid slug that moves between insulating and thermally conductive regions based on temperature changes, inducing a Laplace pressure gradient for reversible switching between conductive and isolative states without moving heat sinks or sources, thus simplifying the structural integrity and reducing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metallic structure movement is used to close the switch, then the switching function is achieved, but the device becomes bulky and heavy with complex support structures
Solution Approach 1:
The invention extracts and eliminates the complex metallic support structures from the switch assembly. Instead of using traditional metallic structures that require bulky support systems, the patent employs a liquid metal slug contained within a flexible channel that can move freely to establish thermal contact, thereby achieving the switching function without the need for complex support structures.
Solution Approach 2:
The invention uses a liquid metal slug as the switching element, leveraging fluid dynamics principles. The liquid metal is contained within a flexible channel and moves in response to thermal expansion of the actuator material, using hydraulic-like pressure transmission to achieve switching without mechanical linkages or complex support structures.
2Reliability
If metallic structure movement is used to close the switch, then the switching function is achieved, but the device mass increases significantly
Solution Approach 1:
The invention removes the heavy metallic moving structures from the switch assembly and replaces them with a lightweight flexible channel containing a small volume of liquid metal. This extraction of metallic components dramatically reduces the mass of the moving parts while maintaining the switching function through the movement of the liquid metal slug.
Solution Approach 2:
The invention changes the physical state and material parameters of the switching element from solid metallic structures to liquid metal within a flexible channel. This parameter change allows the switching element to be much lighter in mass while still achieving the required thermal switching function through phase change and thermal expansion actuation.
3Reliability
If liquid metal is used as switching element, then thermal contact resistance is reduced, but the device requires a closed channel structure
Solution Approach 1:
The invention uses a flexible channel structure to contain the liquid metal slug. This flexible channel allows the liquid metal to move freely and conform to the thermal contact surfaces, ensuring good thermal contact without requiring complex rigid channel structures. The flexibility of the channel simplifies the overall structure while maintaining effective thermal coupling.
4Device complexity
If passive thermal actuator is used, then active actuation components are eliminated, but the switching ratio must be optimized through material selection
Solution Approach 1:
The invention achieves the required switching ratio by carefully selecting materials with appropriate thermal expansion coefficients for the passive actuator and by controlling the volume and properties of the liquid metal slug. The passive actuator material is chosen to expand sufficiently at the target temperature to move the liquid metal slug from the thermal contact position to the isolated position, thereby achieving high switching ratio without active actuation components.
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 solution achieves a high switching ratio with reduced thermal contact resistance and complexity, enabling efficient thermal management in diverse applications by adapting to rough surfaces and arbitrary shapes, and integrating well with flexible thermal systems.
Implementation Method 1
inducing a Laplace pressure gradient for reversible switching between conductive and isolative states
Implementation Method 2
The passive thermal actuator is configured to deform when an actuator temperature of at least a portion of the passive thermal actuator falls within a switching temperature range
Implementation Method 3
The movement of the liquid slug ranges between the insulating region and the thermally conductive region of the closed channel over the switching temperature range
Data Source
AI summary
A passive heat switch device is disclosed that includes a casing defining a closed channel, as well as a passive thermal actuator and liquid slug positioned inside the closed channel. The closed channel includes a heat conducting region made of a heat conducting material and an insulating region made of an insulating material. The passive thermal actuator is thermally coupled to the heat conducting material of the heat conducting region and extends into the insulating region of the closed channel. The passive thermal actuator deforms when an actuator temperature falls within a switching temperature range. The liquid slug is positioned within the closed channel and contacts at least a portion of the passive thermal actuator and the closed channel and is configured to move along the closed channel between the insulating region and the thermally conductive region in response to deformation of the passive thermal actuator.