The Cengel and Boles text uses R134a data where enthalpy and entropy of saturate

Question

The Cengel and Boles text uses R134a data where enthalpy and entropy of saturate liquid are set to zero at T = -40 degree C/-40 degree F. Borgnakke Sonntag text uses R134a tables where the IIR (International standard) is used. Here enthalpy h = 200 k/kg and entropy s = kJ/kg-K for a saturated liquid at 0 degree C. Both tables are at the end of this Hw handout. Compare the values of h_f and s_f at -40 degree C, -20 degree C, 0 degree C, +20 degree C, and +40 degree C. Provide your answers in a table form as shown below. Give the values from the two tables, the difference between them (table vs table at same Temp), and the difference between the entropy and enthalpy for the same temperature and the previous one. For example: Comment on the differences. And note that all thermodynamic data does not completely agree with each other. The link: http://webbook.nist.gov/chemistry/fluid/provides choices if you wish to peruse/pursue/use in the future.

Explanation / Answer

At the given Temperatures we have to find the data of saturated vappour enthalapies.

the quality can be found as x=(h-hf)/hfg

We use Table A-11E on page 976 to get the saturation data.At the given temperature the pressure is in the saturation pressure and we compute te enthalapy from the found quality..

where hf=enthalapy of saturated liquid

hfg=enthalapy change between saturated liquid and saturated vapour(hf-hg)

final enthalapy can be found by h=hf+x*hfg

if you get a quality(x) of 1 this means you have a saturated vapour

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