Homework2 solution - Homework #2 solution ME040 1/ 3 18C...

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Unformatted text preview: Homework #2 solution ME040 1/ 3 18C Completely vaporizing 1 kg of saturated liquid at 1 atm pressure since the higher the pressure, the lower the hfg 2/ 3 39 A piston ­cylinder device that is filled with R ­134a is heated. The final volume is to be determined. Analysis This is a constant pressure process. The initial specific volume is The initial state is determined to be a mixture, and thus the pressure is the saturation pressure at the given temperature The final state is superheated vapor and the specific volume is The final volume is then P R ­134a  ­26.4°C 10 kg 1.595 m3 1 2 v 3/ 3 76 A balloon is filled with helium gas. The mole number and the mass of helium in the balloon are to be determined. Assumptions At specified conditions, helium behaves as an ideal gas. Properties The universal gas constant is Ru = 8.314 kPa.m3/kmol.K. The molar mass of helium is 4.0 kg/kmol (Table A ­1). Analysis The volume of the sphere is Assuming ideal gas behavior, the mole numbers of He is determined from He D = 9 m 27°C 200 kPa Then the mass of He can be determined from 4/ 3 87 The specific volume of steam is to be determined using the ideal gas relation, the compressibility chart, and the steam tables. The errors involved in the first two approaches are also to be determined. Properties The gas constant, the critical pressure, and the critical temperature of water are, from Table A ­1, R = 0.4615 kPa·m3/kg·K, Tcr = 647.1 K, Pcr = 22.06 MPa Analysis (a) From the ideal gas equation of state, (b) From the compressibility chart (Fig. A ­15), Thus, (c) From the superheated steam table (Table A ­6), H2O 15 MPa 350°C 5/ 3 89 The specific volume of R ­134a is to be determined using the ideal gas relation, the compressibility chart, and the R ­134a tables. The errors involved in the first two approaches are also to be determined. Properties The gas constant, the critical pressure, and the critical temperature of refrigerant ­134a are, from Table A ­1, R = 0.08149 kPa·m3/kg·K, Tcr = 374.2 K, Pcr = 4.059 MPa Analysis (a) From the ideal gas equation of state, (b) From the compressibility chart (Fig. A ­15), Thus, (c) From the superheated refrigerant table (Table A ­13), P = 0.9 MPa Ⱥ Ⱥ v = 0.027413 m3 /kg T = 70°C Ⱥ R ­134a 0.9 MPa 70°C € 6/ 3 106 Carbon dioxide is compressed in a piston ­cylinder device in a polytropic process. The final temperature is to be determined using the ideal gas and van der Waals equations. Properties The gas constant, molar mass, critical pressure, and critical temperature of carbon dioxide are (Table A ­1) R = 0.1889 kPa·m3/kg·K, M = 44.01 kg/kmol, Tcr = 304.2 K, Pcr = 7.39 MPa Analysis (a) The specific volume at the initial state is According to process specification, The final temperature is then CO2 1 MPa 200°C (b) The van der Waals constants for carbon dioxide are determined from Applying the van der Waals equation to the initial state, Solving this equation by trial ­error or by EES gives According to process specification, Applying the van der Waals equation to the final state, Solving for the final temperature gives ...
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This note was uploaded on 10/15/2010 for the course PHY 27 taught by Professor Drittle during the Spring '10 term at Université de Sherbrooke.

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