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Unformatted text preview: AERO 489502: Thermodynamics for Aerospace Engineers
1” Midterm examination
Feb. 22, 2006
Make sure that your copy of the exam has 5 numbered pages. While checking, please write
your name and UIN on the ﬁrst page, and your name at the bottom of each page in the exam.
Read the problems carefully before starting. Some problems are easier than others, and you
may want to approach these ﬁrst (or last). While solVing the problems, try to write as cleanly as possible. If you ﬁnd that you need more space for any problem, please write on the
reverse of the page. Note: Feel free to use any notes or books you may consider useful. You have 120 mins. Good luck! “An Aggie does not lie, cheat, or steal, or tolerate those who do.” Name & UID Problem 1 (30%): Using the tables of properties of superheated water vapor (pp. 764767 of the class text), calculate
k of water vapor at P = 3 bar and T = 500° C (k=c,,/c..) (Hint: use the original deﬁnition of 6,, and 0,). Next, calculate k for water vapor assuming it is an ideal gas (use Table A21; if you’re pressed for time, use Fig. 3.13). Compare the
two k’s, and comment briefly. ~ falméﬂz 2%/2 9.1.4..
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diaphragm into two compartments A and B. Both compartments contain water vapor (which CAN NOT be assumed to
be an ideal gas). Compartment A has a volume of l m3 and the initial conditions in it are PA=lO bar, TA=600°C.
Compartment B has a volume of 2 m3 and the initial conditions in it are PB=l bar, TB=200°C. Suddenly, the
diaphragm is ruptured and the tw0 quantities of vapor mix until a ﬁnal state is reached. What is the final pressure and temperature in the chamber? (Hint: if you need to interpolate between table values, assume that property
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DiMethylHydrazine (DMH for short, chemical formula C2H3N2). This is a rather dangerous rocket propellant ﬂuid
(not a solid). One day, a colleague brings a sealed container of DMH to your bench, stating that the container holds
1 kg of saturated DMH. You forget to ask if the DMH is saturated liquid or saturated vapor. You leave the container
on your bench, next to a lLiter bottle of your favorite soda (not too close, DMH is really dangerous) and start
thinking about the problem: What is the quality x of the DMH in the container? The National Institute of Health
(NIH) offers the following information on DMH (amongst numerous warnings): Critical temperature 523 K, critical pressure 5.42 MPa. Atomic Weights of C: l2, of H: l, and of N: l4 (all in kg/kmol). (Hint: drawing what you know on
a pv, or Tv diagram may help.) 5.3
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24 0C with a quality of 50%. Expansion occurs to a state Where the pressure is 1 bar. During the process the pressure
and specific volume are determined by pv : constant. For the refrigerant, determine the work and heat transfer per
unit mass, each in kJ/kg. Sketch the process in a p—v diagram, and consider the question: is the process isothermal? TM; 3:» a «Exijlﬂook Pmi’ﬁj’q’ asg‘xguzj 0x5 Lﬁwemvk‘Tl/u' W
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 Spring '08
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