Systems, methods and devices for optimizing heat transfer within a device or system used to compress and/or expand a gas, such as air, are described herein. For example, systems, methods and devices for optimizing the heat transfer within an air compression and expansion energy storage system are described herein. A compressor and/or expander device can include one or more of various embodiments of a heat transfer element that can be disposed within an interior of a cylinder or pressure vessel used in the compression and/or expansion of a gas, such as air. Such devices can include hydraulic and/or pneumatic actuators to move a fluid (e.g., liquid or gas) within the cylinder or pressure vessel. The heat transfer element can be used to remove heat energy generated during a compression and/or expansion process.