Device for improved heat transfer within a compression and/or expansion system

A method of optimizing heat transfer in a compression and expansion system comprising a pressure vessel having a variable volume working chamber therein and having a conduit through which at least one fluid can be introduced into and discharged from the working chamber, the pressure vessel having a heat transfer element disposed within the working chamber and comprising a layer and at least one of a fin and a spacing element, the method comprising:

• introducing a first quantity of fluid into the working chamber;
• compressing the first quantity of fluid;
• transferring heat energy from the compressed fluid to the layer and fin or spacing element of the heat transfer element;
• introducing a second quantity of fluid into the working chamber;
• expanding the second quantity of fluid;
• and
• transferring heat energy from the layer and the fin or spacing element of the heat transfer element to the expanded fluid.