| 2C-1 : | Specific Volume of Saturated Mixtures | 4 pts |
|---|
| Calculate the specific volume for the following
situations: a.) Water at 300oC and 72% quality b.) R-134a at -50oC and 83% quality c.) Ammonia at 750 kPa and 48% quality |
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| Read : | This is an exercise designed to drive home the meaning and use of the new concept of the quality of a saturated mixture. It is crucial to remember that if a quality is given, then the system contains a saturated mixture and you probably need to look up properties of both the saturated liquid and the saturated vapor. | ||||||||||||
| Given: | a.) | Water | T | 300 | oC | x | 0.72 | kg vap/kg tot | |||||
| b.) | R134a | T | -50 | oC | x | 0.83 | kg vap/kg tot | ||||||
| c.) | Ammonia | P | 750 | kPa | x | 0.48 | kg vap/kg tot | ||||||
| Find: | V | ??? | m3/kg | for each of the three parts of this problem. | |||||||||
| Assumptions: | None. | ||||||||||||
| Equations / Data / Solve: | |||||||||||||
| Part a.) | Data from the Saturation Temperature Table of the Steam Tables at 300oC: | Vsat liq | 0.0014042 | m3/kg | |||||||||
| Vsat vap | 0.02166 | m3/kg | |||||||||||
| P* | 8587.9 | kPa | |||||||||||
| The key equation for this problem is the relationship between the properties of a saturated mixture and the properties of saturated liquid and vapor and the quality. | |||||||||||||
|
Eqn 1 | ||||||||||||
| Now, we can plug numbers into Eqn 1 to answer this part of the question. | V | 0.01599 | m3/kg | ||||||||||
| Notice that I kept 4 significan figures in this answer istead of the usual 2 or 3 because there are 4 significant digits in the sat'd liquid and sat'd vapor values. Perhaps I should have only retained 2 significant digits because there only appear to be 2 significant digits in the quality. I have assumed that there are more than 2, really 4 or more, digits in the quality. This may not be a good assumption. | |||||||||||||
| Part b.) | Data from the Saturation Temperature Table of the R-134a Tables at -50oC: | Vsat liq | 0.00069142 | m3/kg | |||||||||
| Vsat vap | 0.60620 | m3/kg | |||||||||||
| P* | 29.451 | kPa | |||||||||||
| Now, we can plug numbers into Eqn 1 to answer this part of the question. | V | 0.50326 | m3/kg | ||||||||||
| Significant figures are a bit tricky here. | |||||||||||||
| Part c.) | Data from the Saturation Pressure Table of the Ammonia Tables at 400 kPa: | Vsat liq | 0.0016228 | m3/kg | |||||||||
| Vsat vap | 0.16980 | m3/kg | |||||||||||
| Tsat | 15.88 | oC | |||||||||||
| Now, we can plug numbers into Eqn 1 to answer this part of the question. | V | 7.7095 | m3/kg | ||||||||||
| Significant figures are a bit tricky here as well. | |||||||||||||
| Verify: | No assumptions to verify. | ||||||||||||
| Answers : | a.) | V | 0.015988 | m3/kg | b.) | V | 0.50326 | m3/kg | |||||
| c.) | V | 7.7095 | m3/kg | ||||||||||
