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College of Engineering and Computer Science Mechanical Engineering Department Mechanical Engineering 370 Thermodynamics Spring 2003 Ticket: 57010 Instructor: Larry Caretto Solution to Quiz One – Properties of Pure Substances Instructions: Work all problems in the space provided. Remember that more credit is given for showing your basic approach to the problem and developing a method for obtaining the answer than is given for completing the final details of algebra or arithmetic. Where appropriate you should state all your assumptions and show all your reasoning in solving a problem. 1. A volume of 2 m3 contains neon at temperature of 200 K and a pressure of 2 MPa. Use the attached tables to find the mass of neon in the container. From the attached tables we can find the specific volume at the initial state, v(2 MPa, 200 K ) = 0.04264 m3/kg. With this specific volume and the container volume, V = 2 m 3, we can find the mass as follows. m V v 2 m3 m3 0.04164 kg = 48.03 kg 2. What would your answer to first question be if the neon behaved as an ideal gas with an engineering gas constant, R = 0.4119344 kJ/(kg∙K)? Applying the ideal gas law to the input data gives the following result for the mass. 1000 kJ PV MPa m 3 = 48.55 kg m 0.4119344 kJ RT ( 200 K ) kg K ( 2 MPa )( 2 m 3 ) 3. If the neon at the initial state in question 1 were cooled to a final temperature of 30 K holding the volume constant what would its pressure be? If the final state is in the mixed region compute the quality. The final state would have the same specific volume, 0.04146 m 3/kg, as the initial state and the given temperature of 30 K. At this temperature, the specific volume is between the saturated liquid and saturated vapor specific volumes, vf = 0.000869 m3/kg and vg = 0.05016 m3/kg, respectively. This means that the final state is in the mixed region so the pressure is the saturation pressure. We find this pressure from the saturation tables at a temperature of 30 K. P = 0.2238 MPa The quality is found as follows. x v vf vg v f Engineering Building Room 1333 E-mail: [email protected] 0.04164 m 3 0.05016 m 3 kg kg 0.00869 m 3 0.00869 m 3 Mail Code 8348 kg 0.7946 kg Phone: 818.677.6448 Fax: 818.677.7062