You complete a preliminary design of a Rankine heat engine. The calculated quality of the VLE mixture exiting the turbine is too low. Which of the following modifications to the Rankine heat engine will NOT lead to an increase in the quality of the stream leaving the turbine, assuming the total rate of shaft work in the turbine(s) is unchanged after the modification?
A. Adding (super)heat to the steam entering the turbine
B. Lowering the outlet pressure of the turbine, while maintaining the same inlet stream
C. Use two turbines with an inter-stage heater between them, instead of a single turbine
D. Increase the steam flowrate
E. None of these options
A. Incorrect. This is a classic method of increasing turbine outlet quality. See Figure 5-5.
B. Incorrect. Lower pressure favors vapor compared to liquid so this will increase the quality, provided the rate at which energy is removed in the form of work is unchanged.
C. Incorrect. This is another method of quality management discussed in Section 5.2.3
D. Incorrect. If the same amount of energy is removed from more steam, then the change in specific enthalpy will be smaller, which means the fraction of steam condensing is smaller.
E. Correct. All of these will increase the quality of the steam leaving the turbine.
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