Document Ex7MzBxQQX90V47J6gb7vRMML

22 CHAPTER 2 1950, Guide IDENTIFICATION OF PIPING SYSTEMS BY COLOR The color scheme for identification of piping systems-listed in the.foUowx mg table and shown in Fig. I, is reprinted from Part V, Fourth Edition, of the Engineering Standards of the Healing, Piping and Air Conditioning Contractors National Association.7 - All piping systems are classified according to the material carried in the pipes, and colors are assigned as follows : Class F--Fire-protection D--Dangerous materials S--Safe Materials . and, when required P--Protective materials V--Extra valuable materials Color - Red Yellow or Orange Green (or the achromatic colors, white, black, fgray or aluminum) Bright blue Deep purple ,, * Fran8chmo for Identifiution of Pipint Beating, Piping and Air Conditioning Contmeton ' National Auoeiatian, Part V. Fourth Edition, p. 17. Used by penmidon. 1 So* Sohoma for Idantifioation of Pipinc Byatama, A1S-1828, American Standard* Aiuxiation, CHAPTER 3 THERMODYNAMICS Thermodynamic Properties of Moist Air and of Water; Degree of Saturation; Goff Diagram for Moist Air; Derived Properties;.Typical Air Conditioning Processes, Heating, Cooling, Adiabatic Mixing; Wet-Bulb Temperatures Below 32 F; Dalton's Rule; Steady Flow Energy Equation, U. S. Standard Atmosphere THE working substance of the air conditioning engineer is called moist air. In order to be able to apply the laws of conservation of energy and rnmat to the analysis of typical air conditioning processes, it is neces sary to know the thermodynamic properties of moist air, particularly its enthalpy and volume. When the limitations imposed by the Second Law of Thermodynamics have to be considered, it is also necessary to know its entropy. For the purpose of analysis, moist air may be regarded as a mixture of only two constituents, namely, dry air and water vapor. It has long been customary to predict the thermodynamic properties of the mixture from a knowledge of those of dry air and water vapor separately by means of Dalton's Rule. According to this rule: each constituent of a gas mixture occupies the whole volume of the mixture just as if no other constituent were present; it therefore exerts a partial pressure equal to the pressure it would exert if alone in the whole volume at the temperature of the mixture; the observed pressure of the mixture is the sum of these so-called partial pres sures ; the enthalpy of the mixture is the sum of separate contributions from the individual constituents as determined by their partial pressures, their weights, and the temperature of the mixtime; and the entropy of the mixture is obtained in a similar manner. - Dalton's Rule has long been regarded erroneously as a fundamental law of nature. Actually it is not, and in many cases its predictions are quite unreliable. In the case of moist air at atmospheric pressure, it happens to give a close approximation to the truth; but as progress is made the need for greater accuracy than the rule can afford is felt even in this case. For tunately, most of the complications involved in following a correct pro cedure, based on the predictions of statistical mechanics, are met in pre paring suitable tables of thermodynamic properties; and, once these tables have been prepared, their use in the analysis of typical air conditioning processes is actually simplified by abandonment of the rule together with its fictitious concepts of partial pressure, relative humidity, etc. Thermodynamic Properties of Moist Air Table 1, Thermodynamic Properties of Moist Air (Standard Atmos pheric Pressure, 29.921 In. Hg), contains results of a cooperative investi gation between the American Society, of Heating and Ventilating 1 Engineers and the Towne Scientific School, University of Pennsylvania. These results are being studied by an International Joint Committee on Psychrometric Data as a possible starting point from which to reach agree ment on standard properties of moist air. . A detailed explanation of the data and methods used in constructing Table 1 is given in a paper1 presented before the A.S.H.V.E. '/