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Focus on the Enthalpy Deviation.  I am not clear how the two enthalpies were obtained.  Begin where it states "For example, ..."  The enthalpies are 45.0 and -0.52

Focus on the Enthalpy Deviation.  I am not clear how the two enthalpies were obtained.  Begin where it states "For example, ..."  The enthalpies are 45.0 and -0.52

Introduction to Chemical Engineering Thermodynamics
Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
Section: Chapter Questions
Problem 1.1P
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Focus on the Enthalpy Deviation.  I am not clear how the two enthalpies were obtained.  Begin where it states "For example, ..."  The enthalpies are 45.0 and -0.52

||! PD Elementary Principles of Chemica X PDF *Elementary Principles of Chemic X + ✪ File 61°F Sunny Draw E:/Elementary%20Principles%20of%20Chemical%20Processes,%204th%20Edition%20(%20PDFDrive%20).pdf T Read aloud Example 8.4-5 456 of 695 + Enthalpy deviation The remaining curves on the psychrometric chart are almost vertical and convex to the left, with labeled values (on Figure 8.4-1) of -0.05, -0.1, −0.2, and so on. (The units of these numbers are kJ/kg DA). These curves are used to determine the enthalpy of humid air that is not .saturated. The procedure is as follows: (a) locate the point on the chart corresponding to air at its specified condition; (b) interpolate to estimate the enthalpy deviation at this point; (c) follow the constant wet-bulb temperature line to the enthalpy scale above the saturation curve, read the value on that scale, and add the enthalpy deviation to it. For example, air at 35°C and 10% relative humidity has an enthalpy deviation of about -0.52 kJ/kg DA. The specific enthalpy of saturated air at the same wet-bulb temperature is 45.0 kJ/kg DA. (Verify both of these numbers.) The specific enthalpy of the humid air at the given condition is therefore (45.0-0.52) kJ/kg DA = 44.5 kJ/kg DA. The basis for the construction of the psychrometric chart is the Gibbs phase rule (Section 6.3a), which states that specifying a certain number of the intensive variables (tempera- ture, pressure, specific volume, specific enthalpy, component mass or mole fractions, etc.) of a system automatically fixes the value of the remaining intensive variables. Humid air contains one phase and two components, so that from Equation 6.2-1 the number of degrees of freedom is 11 F=2+2-1 =3 Specifying three intensive variables therefore fixes all other system properties. If the system pressure is fixed at 1 atm, then all other properties may be plotted on a two-dimensional plot, such as those shown in Figures 8.4-1 and 8.4 2. The Psychrometric Chart Use the psychrometric chart to estimate (1) the absolute humidity, wet-bulb temperature, humid volume, dew point and specifie enthalpy of humid af at 41°C and 10% relative humidity, and (A) the amount of water in 150 m³ of air at these conditions. 11 ¹ Since the components of dry air do not condense and are present in fixed proportion, dry air may be considered a single Q Search {" 33 ENG Sign in 00 : 8:58 AM 5/28/2023
Transcribed Image Text:||! PD Elementary Principles of Chemica X PDF *Elementary Principles of Chemic X + ✪ File 61°F Sunny Draw E:/Elementary%20Principles%20of%20Chemical%20Processes,%204th%20Edition%20(%20PDFDrive%20).pdf T Read aloud Example 8.4-5 456 of 695 + Enthalpy deviation The remaining curves on the psychrometric chart are almost vertical and convex to the left, with labeled values (on Figure 8.4-1) of -0.05, -0.1, −0.2, and so on. (The units of these numbers are kJ/kg DA). These curves are used to determine the enthalpy of humid air that is not .saturated. The procedure is as follows: (a) locate the point on the chart corresponding to air at its specified condition; (b) interpolate to estimate the enthalpy deviation at this point; (c) follow the constant wet-bulb temperature line to the enthalpy scale above the saturation curve, read the value on that scale, and add the enthalpy deviation to it. For example, air at 35°C and 10% relative humidity has an enthalpy deviation of about -0.52 kJ/kg DA. The specific enthalpy of saturated air at the same wet-bulb temperature is 45.0 kJ/kg DA. (Verify both of these numbers.) The specific enthalpy of the humid air at the given condition is therefore (45.0-0.52) kJ/kg DA = 44.5 kJ/kg DA. The basis for the construction of the psychrometric chart is the Gibbs phase rule (Section 6.3a), which states that specifying a certain number of the intensive variables (tempera- ture, pressure, specific volume, specific enthalpy, component mass or mole fractions, etc.) of a system automatically fixes the value of the remaining intensive variables. Humid air contains one phase and two components, so that from Equation 6.2-1 the number of degrees of freedom is 11 F=2+2-1 =3 Specifying three intensive variables therefore fixes all other system properties. If the system pressure is fixed at 1 atm, then all other properties may be plotted on a two-dimensional plot, such as those shown in Figures 8.4-1 and 8.4 2. The Psychrometric Chart Use the psychrometric chart to estimate (1) the absolute humidity, wet-bulb temperature, humid volume, dew point and specifie enthalpy of humid af at 41°C and 10% relative humidity, and (A) the amount of water in 150 m³ of air at these conditions. 11 ¹ Since the components of dry air do not condense and are present in fixed proportion, dry air may be considered a single Q Search {" 33 ENG Sign in 00 : 8:58 AM 5/28/2023
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