ChEE 326
AssignmentTutorOnline
HW 3
DRAFT – May be updated 1-28-22
Individual HW
1) Hydrofluoroethers (HFEs) were developed originally as a replacement for harmful refrigerator fluids such as CFCs, HFCs, and PFCs. Answer following questions for HFE – 143 m.
- Calculate acentric factor for this substance. You may need to find peer reviewed publications. If you do find an acentric factor, still do the work of confirming it is correct, showing all work
- Estimate Z for this substance from figure 7.4 of textbook for T= 72 °C and P=14.25 atm.
- Estimate Z for this substance from the Felder and Rousseau charts for T= 72 °C and P=14.25 atm.
- Calculate Z for this substance using Peng-Robinson EOS for T= 72 °C and P=14.25 atm.
2) In pharmaceutical manufacturing, chemical reactions are carefully monitored and extremely sensitive. Due to this, equipment to be used must be sterilized to kill all microorganisms to avoid contamination. The most commonly used sterilization method for equipment is steam sterilization. This is typically done by introducing the equipment to be sterilized into an autoclave with rigid volume in which 121 °C steam is introduced for 12 minutes. Some autoclaves have ability to heat up to 140 °C which gives a much lower cleansing time necessary to complete steam sterilization (0.9 minutes). While the sterilization time is attractive for higher temperatures it is important to take into account the amount of energy necessary during start-up to bring the system up to a higher temperature.
- What is the excess enthalpy change required to bring the system from ambient conditions to 140 °C and 37.7 psig using the ideal gas equation of state?
- What is this enthalpy change using a real gas equation of state?
- Compare values and explain what it tells you about the system?
- Compare all your values to the steam table. What do you conclude?
Size of autoclave is 23 L, Pressure of typical sterilization conditions is found to be 15.4 psig, H2O volume is 450 mL.
Group HW
Blowers and an undergraduate student published a paper in 2010 and the reference is here:
Blowers, P., and Lownsbury, J. M.: Carbon Dioxide Emission Implications if Hydrofluorocarbons are Regulated: A Refrigeration Case Study, Environ. Sci. Technol., 44, 1526-1529, 10.1021/es9023354, 2010. The supplemental information available at the journal has details of their calculations.
a) In that work, they computed two different quantities. They did calculations across a valve, like what we did in class for enthalpy. They used this to find the fraction of the refrigerant that was a liquid after flashing a saturated liquid at a pressure of 14.25 atm through a valve. They assumed ideality. How much would their answer change if they used what you know how to do using departure functions and two different equations of state that you can use in departure functions? Your team will pick and choose which two you use.
b) In that work, they also did a computation by assuming the gas being compressed was ideal and then assumed an efficiency of the compressor and used that to back calculate what the temperature would be. You can see their abbreviated work in the papers supplementary section available from the publisher. Using two different equations of state, how different would their answer for the outlet temperature from the compressor have been if they had used departure functions instead of the assumptions they made using compressor efficiency?
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