Concept of mechanocaloric granular material made from shape memory alloy

Abstract

Shape memory alloys (SMAs) are promising mechanocaloric materials for the creation of innovative heating/cooling systems. The present paper proposes a simple concept of “porous” SMA material in the form of a two-dimensional (2D) “granular” system. The basic idea is to place SMA cylinders in parallel and in contact, thus creating a 2D granular material, with fluid circulation in the third dimension (i.e. in the longitudinal direction of the cylinders). The study is dedicated to the validation of the mechanocaloric character of such a material system subjected to confined compression. First, experiments were conducted using superelastic nickel-titanium rods of various diameters, enabling us to create different bidispersity levels for the granular medium. Infrared thermography was used to analyze the temperature changes within the cylinders. Second, air was used as the circulating fluid for the sake of concept validation. Comparison between different levels of bidispersity of the granular system showed that a nearly-monodisperse configuration could be advantageous to optimize the concept.