Methods for Constructing and Properties of Unified and Individual Pressure Diagrams “Enthalpy - Moisture Content” of Compressed Air

Abstract

In engineering practice, when determining the characteristics of atmospheric air, I-d Ramzin diagrams are widely used, developed for a certain average barometric pressure. Direct transfer (without recalculation) of characteristics from atmospheric I-d diagrams to compressed air leads to serious errors. For compressed air, only individual and unified pressure I-d diagrams are applicable. Research objectives: creation of working (up to the level of algorithms) methods for constructing such I-d diagrams and establishing the boundaries of their applicability to air in a different state and at a different pressure. To construct I-d diagrams of compressed air, the atmospheric I-d diagram field is used. Humid air is assumed to be an ideal gas, the enthalpy of which does not depend on pressure. Isotherms and isoenthalps are copied from atmospheric I-d diagrams with their scale preserved. Also, the graph of the partial pressure of water vapor is copied, but its scale changes in proportion to the ratio of compressed air pressure to the accepted barometric pressure. Section 1 gives an algorithm for constructing pressure-individual I-d diagrams with a grid of curves of constant relative humidity. A method is given for determining at a given point such an I-d diagram of relative air humidity for a different pressure. This technique makes it possible to depict compressed air relative humidity curves on an atmospheric I-d diagram. For practical problems with the condensation of compressed air water vapor, it is convenient to use I-d diagrams unified by pressure, which are distinguished by the presence of a grid of saturated air relative humidity curves for a number of pressure values. Section 2 provides an algorithm for constructing unified I-d diagrams and gives a method for determining the relative humidity of unsaturated air at pressure P at a given point of such a diagram. The paper gives examples of the application of this technique.