No abstract

Energy storage systems are being more important to compensate irregularities of renewable energy sources and yields more profitable to invest. Compressed air energy storage systems provide sufficient of system usability, and large scale plants are found around the world. The compression process is the most critical part of these systems and different designs must be developed to improve efficiency such as liquid piston. In this study, a liquid piston is analyzed with CFD tools to look into the effect of piston speed, compression ratio, and cylinder geometry on compression efficiency and required work. It is found that, increasing piston speeds do not affect the piston work but efficiency decreases. Piston work remains constant at higher than 0.05 m/s piston speeds but the efficiency decreases from 90.9 % to 74.6 %. Using variable piston speeds has not a significant improvement on the system performance. It is seen that, the effect of compression ratio is increasing with high piston speeds. The required power, when the compression ratio is 80, is 2.39 times greater than the power when the compression ratio is 5 at 0.01 m/s piston speed and 2.87 times greater at 0.15 m/s. Cylinder geometry is also very important because, efficiency, power and work alter by L/D, D, and cylinder volume, respectively.

No abstract

Using compressed air to store energy is one of the energy storage methods. In this study, a small scale compressed air energy storage (CAES) system is designed and modeled. The energy storage capacity of designed CAES system is about 2 kW. The system contains a hydraulic pump unit, expansion-compression liquid pistons, valves, a tank, and a control unit. The aim of the designed system is basically to store air under a defined pressure. The designed CAES system is modeled and simulated by MATLAB/Simulink program. Pressure changes in the tank and pistons are obtained. Besides, energy storage capacity of the system for different pressures is investigated in isothermal conditions.