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PGE_312_Fall08_Solution_HW2 - PGE 312 Physical and Chemical...

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1/8 PGE 312 – Physical and Chemical Behavior of Petroleum Fluids I Homework 2 Solution Key Problem. 2-4.: The pressure is 200 psi in both cases At (1), the system is at its dew point. At (2) the system is a t its bubble point. See P-V diagram. Therefore, the pressure in the vessel equal to the dew point pressure, the bubble point and the vapor pressure , all which are equal for a pure substance. From Fig. 2-7 (McCain), for n-butane, at T = 200 F, P = Pv = Pb = Pd = 200 psia. Problem 2-5 Using the Cox’s (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 (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 larger than the critical). From (100,800) to (100,560), again there is no an abrupt change in the properties of the ethane as the vapor pressure line is not crossed. The system will remain as gas. By using the Pressure-Volume diagram, it is easy to identify and visualize how pressure-temperature changes take place during a particular change of conditions of the system and how these conditions determine the existence of a particular phase. Thus, passing for 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.
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2/8 Vapor-Pressure Curve for Ethane 80, 800 100, 800 100, 560 80, 560 (Tc,Pc) 400 450 500 550 600 650 700 750 800 850 40 50 60 70 80 90 100 110 Temperature (F) P r e s s u r e ( p s i ) Problem 2-7 The density @ the critical point is 10.12 lb/cuft.
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PGE_312_Fall08_Solution_HW2 - PGE 312 Physical and Chemical...

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