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Unformatted text preview: 1 PGE 312 Physical and Chemical Behavior of Fluids Home Work 2 Solution Problem 2-4 Given: Pure n-butane Temperature = 200 o F Solution: The pressure corresponding to the point when the first few drops of liquid n-butane are formed is the bubble point pressure of the component. The pressure at this point is equal to the vapor pressure of the substance. From the Fig. 2-7 the vapor pressure of n-butane at 200 o F is 200psia. The pressure corresponding to the point where the last few bubbles of n-butane gas remain is the dew point pressure of the component. For a pure substance, the dew point pressure is equal to the bubble point pressure. Therefore, the pressure at this state is also equal to 200psia. Problem 2-5 Using the Coxs Chart (Fig 2-7 McCain), at different temperatures, determine the corresponding vapor pressures up to the critical point, which is 90.1 F & 708.5 psi. From (80; 560) until (80; 800), the vapor-pressure line is crossed. Therefore, there is a sharp change in the density of the ethane, passing form the vapor phase to the liquid phase. From (80; 800) to 2 (100; 800), there is no abrupt phase change (Vapor pressure line is not crossed) but at the final condition, the system will be vapor or gas (Temperature is greater than the critical temperature). From (100,800) to (100,560), no abrupt change in the properties of ethane is noticed as the vapor pressure line is not crossed. The system will remain as gas, although the density decreases. From (100,560) to (80,560) the system remains as gas but the density increases. By using the Pressure-Volume diagram, it is easy to identify and visualize how pressure- temperature changes take place when conditions of the system change and how these conditions determine the existence of a particular phase. Thus, passing from a condition where only the vapor phase is present to one where both liquid and vapor coexist is readily described by this kind of plot. Problem 2-7 The average densities of the liquid and gas will plot as a straight line which passes through the critical point. This property is known as the Law of Rectilinear Diameters. Temperature Average Density -253 13.15 -235 12.76 -217 12.38 -199 11.98 -181 11.55 -163 11.15 5 10 15 20 25 30-300...
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This note was uploaded on 11/27/2011 for the course PGE 312 taught by Professor Peters during the Spring '08 term at University of Texas at Austin.
- Spring '08