SMA Torque Tube Heat Transfer Structure for Faster Cooling
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Solution Overview
Problem
Shape memory alloy actuators face challenges in cooling rates due to physical deformation and low thermal conductivity, making it difficult to effectively implement cooling fins, which limits their overall cycle time and efficiency.
Innovation Solution
A shape memory alloy actuator with a heat transfer structure that extends between the ends of a torque tube, exerting a retention force to maintain contact and enhance heat transfer, even during deformation, and a method of manufacturing involving a dimension-modifying force to secure the heat transfer structure in place.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If cooling fins are attached to the shape memory alloy element to increase heat transfer surface area, then cooling rate is improved, but the physical deformation of the element during phase transition makes it difficult to reliably attach the cooling fins
Solution Approach 1:
The cooling fin structure is designed to be flexible rather than rigid, allowing it to dynamically adapt to the dimensional changes of the shape memory alloy element during phase transition. The flexible fin maintains thermal contact throughout the deformation cycle, ensuring reliable heat transfer without requiring rigid attachment that would fail during deformation.
Solution Approach 2:
The cooling fin is implemented as a flexible structure that can conform to the changing geometry of the shape memory alloy element. This flexible design allows the fin to maintain intimate thermal contact during martensite-austenite transitions, solving the attachment reliability problem while preserving enhanced heat transfer surface area.
2Ease of operation
If the shape memory alloy element undergoes significant physical deformation during phase transition, then actuation function is achieved, but it becomes difficult or impossible to operatively attach cooling fins to the element
Solution Approach 1:
The cooling fin structure is designed to be flexible rather than rigid, allowing it to dynamically adapt to the dimensional changes of the shape memory alloy element during phase transition. The flexible fin maintains thermal contact throughout the deformation cycle, ensuring reliable heat transfer without requiring rigid attachment that would fail during deformation.
3Reliability
If the shape memory alloy has low thermal conductivity, then material properties are maintained for shape memory effect, but cooling fins defined by the element itself are not effective at improving convective cooling
Solution Approach 1:
A separate heat transfer structure with higher thermal conductivity is introduced as an intermediary between the shape memory alloy element and the cooling fluid. This intermediate structure conducts heat more effectively from the low-conductivity alloy surface to the cooling fin, amplifying the convective cooling effect without requiring changes to the intrinsic properties of the shape memory alloy.
Solution Approach 2:
The system effectively creates a composite heat transfer path combining the shape memory alloy element with a high thermal conductivity heat transfer structure. This composite approach leverages the shape memory properties of the alloy while utilizing the superior thermal conduction of the attached structure to overcome the alloy's inherent low thermal conductivity limitation.
4Temperature
If convective cooling is used with a heat transfer fluid stream, then cooling function is achieved, but the cooling process takes significantly longer than heating and becomes rate-limiting to the overall cycle time
Solution Approach 1:
The cooling fin structure is designed to be flexible rather than rigid, allowing it to dynamically adapt to the dimensional changes of the shape memory alloy element during phase transition. The flexible fin maintains thermal contact throughout the deformation cycle, ensuring reliable heat transfer without requiring rigid attachment that would fail during deformation.
Solution Approach 2:
The patent extends the heat transfer structure in the radial dimension, projecting cooling fins outward from the shape memory alloy element. This dimensional extension dramatically increases the surface area available for convective heat transfer with the cooling fluid, enabling faster heat removal and reducing the rate-limiting cooling time in the overall actuation cycle.
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 significantly improves heat transfer rates, allowing for faster transitions between martensite and austenite states, thereby enhancing the actuator's cycle time and efficiency.
Implementation Method 1
The heat transfer structure is in mechanical and thermal contact with the elongate surface of the SMA torque tube... significantly improves heat transfer rates... allowing for faster transitions between martensite and austenite states
Implementation Method 2
the shape memory alloy element may transition from a martensite state to an austenite state upon being heated and also may transition from the austenite state to the martensite state upon being cooled
Implementation Method 3
Heating of the shape memory alloy element historically has been accomplished utilizing a heating assembly, such as a resistive heating element and/or an inductive heating element
Implementation Method 4
Heating of the shape memory alloy element historically has been accomplished utilizing a heating assembly, such as a resistive heating element and/or an inductive heating element
Data Source
Figure 1~3
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Figure 8~9
AI summary
Shape memory alloy actuators with heat transfer structures, actuated assemblies including the shape memory alloy actuators, and methods of manufacturing the same are disclosed herein. The shape memory alloy actuators include a shape memory alloy torque tube and a heat transfer structure. The actuated assemblies include a base structure, an attached component, and a shape memory alloy actuator that operatively attaches the attached component to the base structure. The methods include providing a shape memory alloy torque tube, providing a heat transfer structure, applying a dimension-modifying force to the heat transfer structure, combining the heat transfer structure with the shape memory alloy torque tube, and releasing the dimension-modifying force.