# Thermo-Ch3 - 3-1Chapter 3 PROPERTIES OF PURE SUBSTANCES...

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Unformatted text preview: 3-1Chapter 3 PROPERTIES OF PURE SUBSTANCES Pure Substances, Phase Change Processes, Property Diagrams 3-1CYes, since the chemical composition throughout the tank remain the same. 3-2CA liquid that is about to vaporize is saturated liquid; otherwise it is compressed liquid. Property Tables3-11CA perfectly fitting pot and its lid often stick after cooking as a result of the vacuum created inside as the temperature and thus the corresponding saturation pressure inside the pan drops. An easy way of removing the lid is to reheat the food. When the temperature rises to boiling level, the pressure rises to atmospheric value and thus the lid will come right off. 3-23-14CYes. Otherwise we can create energy by alternately vaporizing and condensing a substance. 3-15CNo. Because in the thermodynamic analysis we deal with the changes in properties; and the changes are independent of the selected reference state. 3-16CThe term hfgrepresents the amount of energy needed to vaporize a unit mass of saturated liquid at a specified temperature or pressure. It can be determined from hfg= hg- hf. 3-17CYes; the higher the temperature the lower the hfgvalue. 3-18CQuality is the fraction of vapor in a saturated liquid-vapor mixture. It has no meaning in the superheated vapor region. 3-33-23[Also solved by EES on enclosed CD]Complete the following table for H2 O: T, °C P, kPa v, m3 / kg Phase description 50 12.352 4.16 Saturated mixture 120.21 200 0.8858 Saturated vapor 250 400 0.5952 Superheated vapor 110 600 0.001051 Compressed liquid 3-43-25EComplete the following table for H2 O: T, °F P, psia u, Btu / lbm Phase description 300 67.03 782 Saturated mixture 267.22 40 236.02 Saturated liquid 500 120 1174.4 Superheated vapor 400 400 373.84 Compressed liquid 3-29Complete the following table for Refrigerant-134a: T, °C P, kPa u, kJ / kg Phase description 20 572.0795 Saturated mixture -12 185.3735.78Saturated liquid 86.24400 300 Superheated vapor 8 600 62.26Compressed liquid 3-30EComplete the following table for Refrigerant-134a: T, °F P, psia h, Btu / lbm xPhase description 65.8980 78 0.566Saturated mixture 15 29.75969.920.6 Saturated mixture 10 70 15.35- - - Compressed liquid 160180 129.46 - - - Superheated vapor 110 161.16117.231.0Saturated vapor 3-31A piston-cylinder device contains R-134a at a specified state. Heat is transferred to R-134a. The final pressure, the volume change of the cylinder, and the enthalpy change are to be determined. Analysis(a) The final pressure is equal to the initial pressure, which is determined from kPa90.4=+=+==2222atm12kg.m/s1000kN1/4m)(0.25)m/skg)(9.81(12kPa88/4ππDgmPPPp(b) The specific volume and enthalpy of R-134a at the initial state of 90.4 kPa and -10°C and at the final state of 90.4 kPa and 15°C are (from EES) 3-5v1= 0.2302 m3/kg h1= 247.76 kJ/kg QR-134a 0.85 kg -10°C v2= 0.2544 m3/kg h2= 268.16 kJ/kg The initial and the final volumes and the volume change are 3m0.0205=−=∆======1957.2162....
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Thermo-Ch3 - 3-1Chapter 3 PROPERTIES OF PURE SUBSTANCES...

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