revisiting the solid-state fridge

Some research into a "thermally elastic" alloy for use in solid-state refrigeration system recently came to light.

The work at the University of Maryland was highlighted here by the University and then here by Popular Mechanics.  As in most areas of technology that rely on mechanical systems a solid-state entrant is of interest.

Between the two articles we are told; the material is a two-state Shape Memory Alloy (SMA), the application of stress makes it undergo a transformation, and it can be returned to its original state by absorbing heat.  It seems simple enough, a two-state alloy that is forced to a second state through the application of some form of stress and absorbs heat to return to the a first, or original state.

The above two articles seem to end here.  What else might behind this development?  Two things come to mind.

First, use in a refrigeration system would require any alloy be subject to a very large cycle count.  One can only imagine how often each “unit” of alloy would have to undergo an energy absorbing cycle to remove the requisite amount of heat.  To meet this requirement the transformation would need to be completely reversible with essentially no loss of energy in a cycle.  That brings us to this paper in Advanced Functional Materials.  The paper describes research in and a process for selecting such an alloy.  The authors focus in on a particular four component alloy composition with “unprecedented functional stability”.

Second, the use of a solid-state phase transformation does not right-away suggest a continuous process.  The ability to absorb heat requires the alloy be in the second state.  Any alloy that is in the first state must first be driven to the second state for it to absorb heat.  This consideration might be addressed with a combination of grain size and overall system structure, depending on the nature of the applied stress, creating an engineered structure suited to the application.

In terms of patentability one can envision novelty on several different levels from the basic alloy chemistry to a more macroscopic alloy structure to the overall system structure incorporating the alloy.  It will be interesting to see how this work develops and how the basic materials properties are engineered and scaled to a commercial system.