Document 3y2eoN684kpJodLr0axLq2nD

so CHAPTER 3 1948 Guide the processes occurring most frequently in air conditioning practice. Thus if moist air is flowing through a duct it carries across any section of ' the duct energy of amount mh Btu per minute and water of amount mW pounds per minute, if m denotes the weight of dry air crossing the section per minute. The foregoing considerations suggest the importance of having accurate knowledge regarding the enthalpy of the fluid in question and the desir ability of using enthalpy as one of the coordinates in graphical repre sentation. The use of enthalpy h and humidity ratio W as coordinates in the case of moist air is due to Mollier *. A convenient modification of the Mollier diagram introduced by Goff is obtained by taking humidity ratio W as ordinate and reduced enthalpy (h-lOQOW) as abscissa. A Mollier Diagram modified in this way is enclosed in the envelope attached to the inside back cover and an abridgement of the Diagram is shown in Fig. 1. The Mollier Diagram is a constant-pressure chart, the one provided - with this book being drawn for standard atmospheric, pressure from the data in Table 1. Along the axis of abscissae (W = 0, n = 0) are plotted values of the specific enthalpy of dry air ha at one-degree intervals of tem perature. Values of humidity ratio at saturation Ws plotted against values of reduced enthalpy at saturation (Aa-1000IFS) determine the satu ration curve ((i = 100 per cent). Lines of constant temperature connect points on the saturation curve with corresponding points on the dry-air axis and are inclined upward to the right. They are drawn straight in ac cordance with Equations 3 and 5 because the curvature contributed by the correction term 5a is inappreciable at all temperatures within the range of the chart. The portion of each isotherm lying between the dry-air axis and the saturation curve is divided into 10 equal parts by curves of constant per cent saturation. The per cent saturation of any point below the saturation curve is readily determined by linear interpolation along the isotherm through that point. Each isotherm breaks at the saturation curve to incline upward to the left into the. two-phase region above the saturation curve. The ordinate of a point in this region is the total weight of water in both the vapor phase (moist air) and the condensed phase (liquid or solid) per pound of dry air in both phases. Neglecting the very small amount of dissolved air in the condensed phase, it is the weight of water in both phases per pound of dry air in the vapor phase. The ordinate at the break in the isotherm through the point in question is the weight of water per pound of dry air in the vapor phase. Consequently, the difference between the two ordinates is the weight of condensed phase per pound of dry air in the vapor phase. It has been stated that the region above the saturation curve is the two-phase region. This is so except in the wedge with apex on the satu ration curve at 32 F where three distinct phases, namely, solid, liquid, and vapor coexist. In fact, this wedge separates the liquid-vapor region above the wedge from the solid-vapor region below it. A point inside the wedge divides the horizontal line extending through it from one boundary to the other into two segments which are in the same ratio as are the weights of solid and liquid. The temperature is 32 F throughout the wedge. The isotherms in the two-phase regions above the saturation curve have been extended downward to the right into the vapor-phase region Thermodynamics o.oeo Abridgement of M ollier Diagram for M oist A ir 51