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Process Calculations
Laws of Thermodynamics
GATE 2010
Medium

A saturated liquid at 1500kPa and 500K, with an enthalpy of 750kJ/kg, is throttled to a liquid-vapour mixture at 150kPa and 300K. At the exit conditions, the enthalpy of the saturated liquid is 500kJ/kg and the enthalpy of the saturated vapour is 2500kJ/kg. The percentage of the original liquid which vaporizes, is

  • A87.5%
  • B67%
  • 12.5%
  • D10%

Explanation

Throttling is isenthalpic: hin=hout=hf+x(hg−hf). 750=500+x(2500−500)=500+2000x ⟹ x=250/2000=0.125=12.5%.

Source: GATE CH 2010 (2010)

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