Analysis of oscillating flow cooled SMA actuator

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Title: Analysis of oscillating flow cooled SMA actuator
Author: Pachalla Seshadri, Rajagopal
Abstract: Shape Memory Alloys (SMA ) are a group of metallic alloys that have the ability to return to some previously defined shape or size when subjected to an appropriate thermal cycling procedure . In recent years there has been a lot of research on the development of small , light and , yet , powerful actuators for use in areas like robotics , prosthetics , biomimetics , shape control and grippers . Many of the miniaturized conventional actuators do not have sufficient power output to be useful and SMAs can be used advantageously here . The widespread use of SMAs in actuators is limited by their low bandwidth . Use of SMAs in two -way actuators requires that they undergo thermal cycling (heating and cooling ) . While SMAs can be heated quickly by resistive heating , conventional convection cooling mechanisms are much slower as the exothermic austenitic to martensitic phase transformation is accompanied by the release of significant amount of latent heat . While a number of cooling mechanisms have been studied in SMA actuator literature , most of the cooling mechanisms involve unidirectional forced convection . This may not be the most effective method . Oscillating flow in a channel can sometimes enhance heat transfer over a unidirectional flow . One possible explanation for this heat transfer enhancement is that the oscillatory flow creates a very thin Stokes viscous boundary -layer and hence a large time -dependent transverse temperature gradient at the heated wall . Therefore heat transfer takes place at a large temperature difference , thereby enhancing the heat transfer . In this work , the heat transfer from an SMA actuator under an oscillating channel is investigated and is compared to steady , unidirectional flow heat transfer . Oscillating flow is simulated using a finite volume based method . The resulting velocity field is made use of in solving the heat transfer problem using a finite difference scheme . A parametric study is undertaken to identify the optimal flow conditions required to produce the maximum output for a given geometry of the SMA actuator . The latent heat of transformation of the SMA is accounted for by means of a temperature dependent specific heat .
URI: http : / /hdl .handle .net /1969 .1 /2669
Date: 2005-11-01


Analysis of oscillating flow cooled SMA actuator. Available electronically from http : / /hdl .handle .net /1969 .1 /2669 .

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