01.5 Real Fluids and Tabulated Properties

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Double interpolation (uakron, 8min) is exactly what it sounds like: to find a steam property when neither the pressure nor temperature are among the tabulated values, you need to interpolate twice. We interpolate first on pressure, then on temperature. It is a bit tedious, but straightforward.

Comprehension Questions:
1. Describe how you would use double interpolation to obtain H if given T=275 C and P=0.45MPa.
2. Describe how you would use double interpolation to obtain H if given T=275 C and V=0.555m3/kg.

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When you use a spreadsheet like Steam.xlsx(uakron, 15min), interpolation can be greatly expedited. It is recommended that you enable the solver before applying Steam.xls.

Comprehension Questions:
1. Compute H if given T=275 C and P=0.45MPa.
2. Compute H if given T=275 C and V=0.555m3/kg.
3. Which would be more practical for solving a project, double interpolation or steam.xlsx?

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Steam quality given temperature and volume (LearnChemE.com, 9min) Steam quality is the fraction of H2O that exists as vapor. Its computation can be accomplished by knowing one of the saturation properties (T or P) and one of the tabulated properties (V,U,H,S). This kind of calculation is sometimes known as the "lever rule" or "inverse lever rule" because the given property acts like the fulcrum on a lever, specifying whether the liquid or vapor property receives the heavier weight. e.g. if the given property is closer to the saturated vapor value, then the vapor value receives a hevierer weight.


Comprehension Questions:
1. Compute the enthalpy (kJ/kg) at 100 C and a quality (q) of  33%.
2. Compute the entropy (kJ/kg-C) at 200 C and a quality of 90%.

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