Another refrigeration alternative is thermoacoustic refrigeration
(TAR). TAR systems can be divided into two different
classes—heat engines and heat pumps. Heat engines take heat
energy from a hot reservoir, convert some of the heat energy into
acoustic energy and dump the unused heat to a cool reservoir.
Heat pumps use acoustic energy to pump heat from one heat
reservoir to another, resulting in a temperature gradient between
the two reservoirs (Zoontjens et al., 2005).