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Consider the following statements: When dry saturated steam is throttled from a higher pressure to a lower pressure, the (a) Pressure decreases and the volume increases. (b) Temperature decreases and the steam becomes super heated. (e) Temperature and the dryness fraction increase. (d) Entropy increases without any change in Enthalpy. Which of these statements are correct?

Consider the following statements: When dry saturated steam is throttled from a higher pressure to a lower pressure, the (a) Pressure decreases and the volume increases. (b) Temperature decreases and the steam becomes super heated. (e) Temperature and the dryness fraction increase. (d) Entropy increases without any change in Enthalpy. Which of these statements are correct? Correct Answer (a), (b) & (d)

Explanation:

  • When dry saturated steam is throttled from higher pressure to a lower pressure, the pressure decreases and the volume increases, Temperature decreases, the steam becomes superheated, and  Entropy increases without any change in Enthalpy.

  • The throttling process is the constant enthalpy process as well as an expansion process so the pressure of the steam decreases and volume increases.

  • Since the throttling process is irreversible (adiabatic but not isentropic) so the entropy generation takes place.

  • Thus the change in entropy will be positive and from the h-s curve, the state takes place in the rightward direction from one equilibrium state to the second equilibrium state which leads to a super-heated region.

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