On the role of thermoelectric heat transfer in the design of SMA actuators: theoretical modeling and experiment

Abstract

A combined theoretical/experimental study of the heat transfer in thermoelectric Shape Memory Alloy (SMA) actuators is undertaken in this paper. A one-dimensional model of a thermoelectric unit cell with a SMA junction is developed rst and the transient temperatures in the SMA are evaluated for dierent applied electric current densities. As a rst step towards the design of an actuator, a thermoelectric module is assembled in the laboratory for cooling/heating the SMA. Transient temperature proles are recorded for the monotonic heating and cooling runs for two dierent materials copper and SMA (with or without the phase transformation). These recorded proles are then compared with the predictions from the model; the agreement is reasonable, particularly during the cooling process. Temperature proles are also recorded for cyclic cooling and heating of copper at a frequency of 0.5 Hz and a good comparison is obtained. Theoretical predictions for thermal cycling of SMA show that it is possible to achieve a frequency of 2 Hz on full phase transformation and 17 Hz on partial transformation of 25%.

Aerospace applications of shape memory alloys

“…by direct Joule heating via the application of electricity), the speed of energy removal is limited by the mechanisms of heat conduction and convection. Several methods have been employed in the hopes of expediting heat transfer, including forced convection via flowing cooled water [67] and forced conduction through the use of thermoelectric cooling modules [68]. A second challenge is the low actuation efficiency.…”

Adaptive Control of Robotic arm with Hysteretic Joint

“…The latent heat is modelled as a variation of specific heat of the SMA with respect to temperature. During phase transformation in SMA the heating and cooling are slowed due to the latent heat of transformation [18,1]. The empirical model of the relationship between specific heat and temperature has been discussed in [18,1] .…”

“…In our current model a constant value for ∆H = 0.06183 J mm −3 was used based on [1] where further details of the constant can be obtained.…”

Thermomechanical behaviour of thermoelectric SMA actuators

“…In order to increase the rates of cooling in high frequency applications different methodologies have been proposed and compared with more traditional techniques such as free and forced convection [1]. Some such methodologies require dealing with multilayered structures which complicates the analysis and modelling of material dynamics [8].…”

“…The foundations for modelling thermoelectric devices have been laid by the group of researchers led by Ioffe [5] and since then various models of thermoelectricity have been extensively developed in the context of specific (both steady-state and transient) applications by many researchers (see, for example, [4,12,1,6] and references therein). In the context of sandwich-type SMA actuators consisting of SMA and semiconductor layers, due to the Peltier effect, the "heat pumping" along a temperature gradient leads to the heat absorption at the high temperature junction and the heat dissipation at the cold junction.…”