Chapter(s) :
CB Ch 1 & 3
LT Ch 1 & 2

Due Date :
April 6, 2011
Total Problems / Points :
15 / 71


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Cengel & Boles: Ch 1: 7E(3pts), 11E(4pts), 37E(2pts), 41E(3pts), 78(6pts)

WB-1 Mass, Force and Gravitational Acceleration - 4 pts
Statement :

A closed system consists of 0.5 lbmole of liquid water and occupies a volume of 0.145 ft3. Determine the weight of the system, in lbf, and the average density, in lbm/ft3, at a location where the acceleration of gravity is g = 30.5 ft/s2.

  Hints :

gc is the key.

Ans.: W ~ 8.5 lbf

WB-2 Absolute and Gauge Pressures - 5 pts
Statement :

Tank A lies inside of Tank B, as shown in the figure, below. Pressure gauge A is located inside Tank B and reads 1.4 bar. Both tanks contain air. The manometer connected to Tank B contains mercury (ρ = 13.59 g/cm3). The manometer reading is h = 20 cm, atmospheric pressure is 101 kPa and g = 9.81 m/s2. Determine the absolute pressures inside Tank A and Tank B in kPa.

Problem diagram.

  Hints :

Careful application of the manometer equation and unit conversions should go a long way toward solving this problem correctly.

Ans.: PA ~ 270 kPa , PA ~ 130 kPa

Cengel & Boles: Ch 3: 26(4pts),
29E(4pts) -
The internal energy of subcooled liquid R-134a at 10oF and 100 psia is 15.169 Btu/lbm (using the same reference state as the thermodynamic table in your textbook),
Do not use T1 = -30oF. Use T1 = 30oF ! Ans: T2 ~ 76.7oF.
in part (d) sketch the process path on a PV Diagram that includes the two-phase envelope and relevant isobars,
83(6pts) -
Assume that the air in the tire behaves as an ideal gas, but then check the validity of this assumption. Determine the mass of air bled off and then determine the volume this mass of air would occupy at Patm and 25oC.

WB-3 An Application of Equations of State - 10 pts
Statement :

A 0.016773 m3 tank contains 1 kg of R-134a at 110°C. Determine the pressure of the refrigerant using:
a.) the ideal gas EOS
b.) the generalized compressibility chart
c.) the refrigerant tables
d.) van der Waals EOS
e.) Soave-Redlich-Kwong EOS

  Hints :

Properties of R-134a:
Tc = 374.25 K , Pc = 4.067 MPa , MW = 102.03 g/mole , ω = 0.332
This problem is very similar to an example problem that we discussed in class.

Ans.: Ans.: a.) P ≈ 1900 kPa , d.) P ≈ 1600 kPa , e.) P ≈ 1600 kPa

WB-4 Relative Humidity - 5 pts
  Problem Statement : On entering a dwelling maintained at 20°C from the outdoors where the temperature is 10°C, a person's eye-glasses are observed not to become fogged. A humidity gauge indicates the relative humidity in the dwelling is 55%. Can this reading be correct? Provide supporting calculations.
  Hints :

The key to this problem is to assume that the glasses are at 10°C when they come in from the outdoors.