Unformatted text preview: Due Friday September 2 Process Thermodynamics Homework #1 1. Sandler Problem 2.1 2. Liquid/vapor saturation pressure Psat is often represented as a function of temperature by an equation of the form: log 10 P sat ( torr) a b t ( C) c
o Here, parameters a, b, and c are substance‐specific constants. Suppose it is required to represent Psat by the equivalent equation: ln P sat (kPa) A B T (K ) C Show how the parameters in the two equations are related. 3. Liquids that boil at relatively low temperatures are often stored as liquids under their vapor pressures, which at ambient temperatures can be quite large. Thus, n‐butane stored as a liquid/vapor system is at a pressure of 2.581 bar for a temperature of 300 K. Large‐scale storage (>50 m3) of this kind is sometimes done in spherical tanks. Suggest two reasons why. 4. The variation of fluid pressure with height is described by the differential equation: dP g dz Here is specific density and g is the local acceleration of gravity. For an ideal gas, = MP/RT, where M is molar mass and R is the universal gas constant. Modeling the atmosphere as an isothermal column of ideal gas at 10 ºC, estimate the ambient pressure in Denver, where z = 1 mile relative to sea level. For air, M = 29 g mol‐1. 5. A group of engineers has landed on the moon, and they wish to determine the mass of some rocks. They have a spring scale calibrated to read pounds mass at a location where the acceleration of gravity is 32.186 ft s‐2. One of the moon rocks gives a reading of 18.76 on this scale. What is its mass? What is its weight on the moon? Take gmoon = 5.32 ft s‐2. 6. A gas is confined in a 1.25 ft diameter cylinder by a piston, on which rests a weight. The mass of the piston and weight together is 250 lbm. The local acceleration of gravity is 32.169 ft s‐2, and atmospheric pressure is 30.12 (in Hg). a. What is the force in lbf exerted on the gas by the atmosphere, the piston, and the weight, assuming no friction between the piston and cylinder? b. What is the pressure of the gas in psia? c. If the gas in the cylinder is heated, it expands, pushing the piston and weight upward. If the piston and weight are raised 1.7 ft, what is the work done by the gas in ft lbf? What is the change in potential energy of the piston and weight? 7. Verify that the SI unit of kinetic and potential energy is the joule. 8. The turbines in a hydroelectric plant are fed by water falling from a 50 m height. Assuming 91% efficiency for conversion of potential to electrical energy, and 8% loss of the resulting power in transmission, what is the mass flowrate of water required to power a 200‐watt light bulb? ...
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 Fall '11
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 8%, electrical energy, 29 g

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