Modeling and parametric optimization of a liquid piston compressor with inner cooling tubes

This work proposes a new configuration of liquid piston compressors and a methodology for their optimization, with special attention to heat removal from the compressing gas, in order to minimize the mechanical work required for the compression process. The adopted approach starts with the solution of the governing equations through a 0D model (lumped approach). A new correlation for the heat transfer coefficient is presented to calculate the sensible heat transfer from the compressing gas to the cooling liquid. The results of the 0D model are validated by comparison with experimental and numerical data from the literature and with performed CFD calculations. In the proposed geometric configuration, heat is removed from the compressing gas through a tubes bundle inserted in the compression chamber, the liquid cooling medium flowing inside the tubes. This geometric configuration was chosen because it is simple to design and common materials and manufacturing processes can be used for its manufacturing. In addition, no regeneration of the inserts is required from cycle to cycle, making that configuration ideal for cyclic operation. The parametric study performed focuses on the dependence of the overall efficiency on the number and diameter of the cooling tubes and the speed of the liquid piston. It is found that the overall efficiency is highest for a given number of tubes with at a specific diameter, and that the combination of a few cooling tubes with a larger diameter and a higher piston speed gives the best overall efficiency.