An Apparatus for Rotational Energy Storage with Variable Inertia

Energy storage is important for many applications. Form fossil fuel and hybrid automotives to off-peak electric power to rotary and pressing machinery and to spacecrafts. Generally, flywheels are used to minimize shaft angular speed fluctuation, equalize energydistribution and to store rotational energy. In many situations it is desirable to store energy at a constant angular velocity. Variable inertia flywheels are common in the field of electric power generation. This type of flywheels was used to vary inertia either byinterconnecting multiple flywheels having different inertia or using a fluid to alter the total mass of a flywheel. Such technologies were not useful enough to be widely implemented mainly because of plurality of moving part, liquid storage limitations and noticeableliquid drag force. This work proposes a pneumatic centrifugal variable inertia flywheel that can maintain a constant angular velocity across a range of energy storage. The pneumatic flywheel uses solid mass to compress air inside a heat insulated pneumatic aircylinder. A force balance is created due to the pressure gradient of the air stored inside the cylinder. Energy added to system is stored in two forms: increases the kinetic energy of the flywheel at a constant angular velocity and increasing the energy of the compressed airinside cylinders. Availability, noticeable compression capacity and desirable energy storage density are some of the reasons to utilize air in such a flywheel. A design example shows that this variable inertia flywheel maintains a constant angular velocity with up to an orderof magnitude lower mass than a conventional flywheel.

Keywords:

Angular speed conversion , Energy storage , Flywheel , Pneumatic systems , Variable inertia.