Heat Transfer in a Long, Thin Tube Section of an Air Compressor: An Empirical Correlation from CFD and a Thermodynamic Modeling

Heat transfer during compression of air in a long, thin tube is studied by CFD. The tube represents one of the many in a honeycomb geometry inserted in a liquid piston air compressor to minimize temperature rise. A dimensionless number for the heat flow rate that includes the changing heat transfer area between the tube wall and air during compression is used. From the CFD results, alinear relation between the inverse of this dimensionless heat flow rate and the Stanton number is found. Using thisrelation, the transient volume-averaged temperature, and heat flow rate from the air can be well predicted by thermodynamic modeling.With the heat transfer model, a non-linear ODE is solved numerically todetermine the average temperature and pressure. The application of this study can be found in liquid piston air compressors for compressed air energy storage systems.