Liquid HFC-134a at its boiling point at 12 bars pressure is throttled to 1 bar pressure. What is the final temperature? What fraction of liquid vaporizes?
The final temperature and the fraction of liquid that vaporizes.
Answer to Problem 29P
Explanation of Solution
Given:
Initial pressure, P =12 bars
Final pressure, P = 1 bar
Formula used:
Here, a is the fraction of the HFC-134a, which ends up as liquid.
Calculation:
Initial temperature and enthalpy of the HFC-134a at the pressure of 12.0 bar using table 4.3 is as follows:
The final temperature HFC-134a at the pressure of 12.0 bar is as follows:
Hence, the final temperature of the liquid HFC-134a is
At the boiling point, the enthalpy of the liquid phase of HFC-134a at the final pressure of 1.0bar is 16 kJ while thatof the gas phase would be 231 kJ.
The enthalpy is conserved to a throttling process. The initial enthalpy of the liquid HFC-134a116 kJlies between 16 kJ and 231 kJ.The final state of the HFC-134a is a combination of liquid and gas at the boiling point
Substitute
The initial and final enthalpies of HFC-134a are equal to each other.
Substitute
Solve the equation for a
Hence, the fraction of liquid vaporizes is as follows:
Therefore, thefraction of the liquid vaporizes is0.465.
Conclusion:
Thus, the liquid vaporization is
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