Graphic Analytical Methods for Determining Moist Air Characteristics in Multistage Compressors

The purpose of the study is a comparative analysis of methods for graphic analytical determination of the characteristics of moist air in multistage compressors. Two methods are compared, which differ in the used I-d-diagrams: unified in terms of pressure and atmospheric. I-d-diagrams unified in terms of pressure differ from atmospheric ones by diagrams of saturated air relative humidity () only at various pressures. For multistage compressors, curves are plotted on unified I-d-diagrams at atmospheric pressure and compressed air pressure in intercoolers and receivers. It is assumed that the isobaric cooling of compressed air and condensation of its water vapor occurs in coolers and receivers at the final compression pressure in the previous compressor stages. The method, which uses I-d-diagrams unified by pressure, involves the diagram plotting of air compression and cooling on a grid of curves. An example of plotting such diagrams for a two-stage compressor with an intercooler and a receiver is given. A detailed description of the thermodynamic state of moist air in such a compressor is given. The nodal points of the processes in the compressor are plotted on a pressure-unified I-d-diagram according to the known values of moisture content and air temperature. The pressure and temperature at the end points of compression are calculated by the equations of the polytropic process at n = 1.26. The dew points in the cooler and receiver are graphically defined as the intersection of the curves for the final compression pressures with the corresponding straight lines for constant air moisture content in the compressor stages. The technique using atmospheric (barometric) I-d-diagrams is used in the absence of unified I-d-diagrams suitable for pressure. The essence of the developed technique is to determine the curves on the atmospheric I-d-diagrams, graphically coinciding with the curves A numerical example of the application of such a technique is given. The advantages and disadvantages of both methods are evaluated.