TE 303 - HW #3, P5 - Clapeyron & Clausius-Clapeyron Equations - 16 pts

Estimate the latent heat of vaporization, in Btu/lbm, of ammonia at -10oF using:

a.) The Clapeyron equation
b.) The Clausius-Clapeyron equation
c.) The ammonia tables

In your analysis, be sure to include a comparison of these three methods and propose a reason for any significant differences. (4 pts)

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TE 303 - HW #3, P6 - Hypothetical Process Paths and the Latent Heat of Vaporization - 24 pts

Determine the change in enthalpy in Joules for 20.0 g of heptane (C7H16) as it changes from a saturated liquid at 300 K [State 1] to a temperature of 370 K and a pressure of 58.7 kPa [State 4]; you can follow the hypothetical process path in the diagram to the right. Do not use tables of thermodynamic properties, except to check your answers. (In other words, you will not get credit for the problem if you use the tables.)

First, draw the states on a P-V or T-V diagram (4 pts). Then, calculate the DH for each step in the path using what you know about the enthalpy for each step. You might want to use the Antoine Equation to estimate the heat of vaporization of heptane at 300 K. Use the average heat capacity of heptane gas over the temperature range of interest (is this assumption valid?).

Assume heptane gas is an ideal gas at the relevant temperatures and pressures.

For the analysis section, be sure to discuss how this result differs than what you would have done using just the thermodynamics data tables, as well as the validity of your assumptions (5 pts).

HINTS: The key to the first step in this HPP is the Clausius-Clapeyron Equation. Use the Antoine equation to help you estimate the latent heat of vaporization at T1. In the second step, interpolate on the Cp data from the NIST WebBook to determine Cp(T1) and Cp(T2). Then, use the average of these two Cp's to evaluate the change in enthalpy. All you need to do is think a little bit and you will see how to evaluate ΔU34.

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TE 303 - HW #2, P1 - Steam Table Fundamentals - 8 pts

Complete the following table for water. Be sure to cite which source of thermodynamic data tables that you used.

T(oC) P(kPa) H(kJ/kg) x(kg vap/kg) Phase Description

a.) P = 200 kPa and x = 0.7 kg vap/kg
b.) T = 140 degC and H = 1800 kJ/kg
c.) P = 950 kPa and x = 0 kg vap/kg
d.) T = 80 degC and P = 500 kPa
e.) P = 800 kPa and H = 3161.7 kJ/kg

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TE 303 - HW #2, P2 - R-134a Table Fundamentals - 8 pts

Complete the following table for R-134a. Be sure to cite which source of thermodynamic data tables that you used.

T(oF) P(psia) U(Btu/lbm) x(lbm vap/lbm) Phase Description

a.) P = 80 psia and U = 126 Btu/lbm
b.) T = 15 degF and x = 0.6 lbm vap/lbm
c.) T = 10 degF and P = 70 psia
d.) P = 180 psia and U = 226 Btu/lbm
e.) T = 110 degF and x = 1.0 lbm vap/lbm

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TE 303 - HW #2, P3 - R-134a Table Fundamentals - 9 pts

A 0.5 m3 vessel contains 10 kg of R-134a at -20oC. Determine…

a.) The pressure in kPa
b.) The total internal energy in kJ
c.) The volume occupied by the liquid phase in m3

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TE 303 - HW #2, P4 - Isochoric Heating of Water - 8 pts

Five kilograms of H2O are contained in a closed, rigid tank at an initial pressure of 20 bar and a quality of 50%. Heat transfer occurs until the tank contains only saturated vapor. Determine the volume of the tank, in m3, and the final pressure in bar.

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TE 303 - HW #2, P5 - Isobaric Expansion of Water - 12 pts

A piston-and-cylinder device initially contains 50 L of liquid water at 25oC and 300 kPa. Heat is added to the water at constant pressure until the entire liquid is vaporized.

a.) What is the mass of the water in the cylinder in kg ?
b.) What is the final temperature of the water in the cylinder in oC ?
c.) Determine the total enthalpy change of the water for this process, in kJ.
d.) Show the process on a completely labeled TV Diagram.

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TE 303 - HW #2, P6 - Inflating an Automobile Tire - 12 pts

The air in an automobile tire with a volume of 0.53 ft3 is at 90oF and 20 psig. Determine the mass of air that must be added to raise the pressure to the recommended value of 30 psig. Assume atmospheric pressure is 14.7 psia and both the temperature and the volume of the air in the tire remain constant as it is inflated. Assume that the air in the tire behaves as an ideal gas, but then check the validity of this assumption.

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TE 303 - HW #2, P7 - An Application of Equations of State - 25 pts

A 0.016773 m3 tank contains 1 kg of R-134a at 110oC. Determine the pressure of the refrigerant using:

a.) The Ideal Gas EOS
b.) The Compressibility Factor EOS
c.) The R-134a Tables
d.) The van der Waal EOS
e.) The Soave-Redlich-Kwong EOS

In your analysis, be sure to discuss a comparison of these equations of states (5 points).

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TE 303 - HW #2, P8 - Relative Humidity and Fogged Glasses - 8 pts

The Campus Police heard that you were a thermodynamics guru, so they have come to you to help figure out if a witness to a crime is credible. The eyewitness claims that upon entering her apartment complex, she saw the suspect leaving the downstairs apartment with some electronics equipment. Since the eyewitness must wear glasses and stated that she was wearing them at the time, the Campus Police want to know if her glasses would have fogged up when entering the building and thus obstructed her view. The temperature of the apartment complex was measured to be 20 °C, and the outdoor temperature to be 10oC. A humidity gauge indicated that the relative humidity in the apartment complex is 55%. Assuming that the eyewitness did not have anti-fog lenses, do you think that this eyewitness could have been obstructed by fogged lenses? Provide supporting calculations.

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TE 303 - Welcome to the LearnThermo Blog

For each homework problem that Dr. Pasquinelli assigns, I will post the problem statement on this blog. If you have any questions about the problem, click on the small red "comments" at the end of the problem statement. This will take you to a page where you can see all of the questions that you classmates asked, as well as my answers. If nothing you find on this page answers your question, then you can type in a new question for me. You should probably choose the "Name/URL" option for your identity. This will let you make up any name you like. This helps me state which question I am answering. But you don't need to use your real name. That way you and I can interact and no one will know who you are.

I will check this blog twice per day during the week, but you cannot rely on me on the weekend. I will probably only check the blog on Sunday night.

BUT I encourage you to answer each others questions ! You don't really, really (Shrek) understand something until you can explain it to someone else. So, try to help someone. It is anonymous. You might get a deeper understanding of the problem, and helping someone learn is a good thing to do.

I have blogged (with my students) many of the problems Dr. Pasquinelli will use in this course. You can search this blog to see the questions and answers that are already posted. I suggest you focus your search on March through June 2007.

You might also consider the supplemental example problems for Thermo-CD. These are posted on my LearnThermo webiste. Here is the link that goes directly to the additional example problems:
LearnThermo.com Examples

I look forward to working with you.

Adios,
Dr. B

TE 303 - HW #1, P1 - Mass, Force, Density and Acceleration - 10 pts

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.

TE 303 - HW #1, P2 - Mass, Weight and Acceleration - 6 pts

The weight of an object on an orbiting space station is measured to be 42 N based on an artificial acceleration of 6 m/s2. What is the weight o f the object, in N, on Earth, where g = 9.81 m/s2 ?

TE 303 - HW #1, P3 - NOx Emissions: UNITS - 6 pts

A typical car driven 12,000 miles/year emits to the atmosphere about 11 kg/year of NOx (nitrogen oxides), which causes smog in cities. Natural gas burned in a home furnace emits about 4.3 g of NOx per therm and electric power plants emit about 7.1 g NOx per kWh of electricity produced. Consider a household that has two cars and consumes 9,000 kWh of electricity and 1,200 therms of natural gas. Determine the amount of NOx emission to the atmosphere per year for which the household is responsible.

TE 303 - HW #1, P4 - Temperature Conversions: Celsius to Fahrenheit - 12 pts

Convert the following temperatures from oC to oF.
a.) 21 oC
b.) -17.78 oC
c.) -50 oC
d.) 300 oC
e.) 100 oC
f.) -273.15 oC

TE 303 - HW #1, P5 - Temperature Conversions: Fahrenheit to Celsius - 12 pts

Convert the following temperatures from oF to oC.

a.) 212 oF
b.) 68 oF
c.) 32 oF
d.) 0 oF
e.) -40 oF
f.) -459.67 oF

TE 303 - HW #1, P6 - Temperature Change - 6 pts

The temperature of a system rises by 72oC during a heating process. Express this temperature increase in Kelvins and degrees Rankine.

TE 303 - HW #1, P7 - Absolute and gauge Pressures - 15 pts

Tank A lies inside of Tank B, as shown in the figure. 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 (r = 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.

TE 303 - HW#1, P8 - Differential, Multi-Fluid Manometer - 18 pts

Fresh water and seawater flowing in parallel, horizontal pipelines are connected to each other by a double u-tube manometer, as shown in the figure. Determine the pressure difference between the two pipelines in kPa. Assume the density of seawater to be 1035 kg/m3. Can the air column be ignored in this analysis ?

Final Exam 2007

Please post any questions you have here. I will be responsive on Sunday, but not much on Saturday.

It has been a pleasure working with all of you. I hope you do well on the final. Remember you can use 3 8.5" x 11" cheat sheets (with writing on both sides) during the final.

We will take the class photo before the final on Monday morning. Sorry I forgot about it today. It is optional, you can choose not to be in the photo if you wish.

Best of luck in your career and in life.

Adios,
Dr. B