ME300 Spring 2011 - Special Problems SP18 A piston-cylinder arrangement, as shown below, contains methane. Weight is slowly added to the piston, so that the methane is compressed isothermally during the process. The initial molar specific volume is 1v=2.2522 m3/kmol and the temperature is T1=382 K. The gas is compressed isothermally to a final molar specific volume of 2v=0.1284 m3/kmol. Do not use the ideal gas equation. Use the van der Waal’s equation of state to analyze the process. (a) Find the initial and final pressures, p1and p2[bar]. (b) Find the entropy change 21ss[kJ/kmol K] for the process. Answers: (a) p2=232 bar, (b) -27.02 kJ/kmol K Hint:See Table A-24 for appropriate constants, and start part (b) with equation 11.48, page 590. SP19 An individual having a mass of 81.647 kg is ice skating on blades which have a total area in contact with the ice of 20.645 mm2. The temperature of the ice is -2 ºC. Will the ice melt under the blades? (Answers: T2= 270.3 K) Hints: 1) Look at figure 3.1b on page 83, and the solid liquid line.
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