Why Quality x >=1? (TFS)

In Some steam turbine problem, when using entropy calculate turbine outlet enthelpy.  The quality x>=1. Is this correct? I thought the quality must always be less 1. 

Quality is defined as mass of vapor divided by mass of liquid plus mass of vapor. It is only defined for liquid-vapor mixtures and cannot be greater than one. 

Can you post a screenshot of whatever you’re looking at?

A steam power plant operates at maximum pressure of 500 psia and a low pressure value of 14.7 psia. All of the steam is extracted from the turbine at 60 psia and is reheated back to maximum temperature. The maximum temperature is 1000 f. What is the work out put at the turbine.? Assume the turbine is 100% efficient. 

This is reheat rankine cycle. After reheat and enter turbine,the enthlopy is h=1530 btu/lbm, and s=1.98 btu/lb-r at 60 psia and 1000 F. The outlet of turbine is 14.7 psia. If s=1.98 to calculate quality x, it is more than 1. 

Since “s” is greater than “sg” you don’t calculate quality. What you do is use that value of “s” to interpolate within the superheated vapor table (at 14.7 psi) to find the exit enthalpy.

However, this all takes too long. This problem can be solved almost instantly with a Mollier diagram instead of tables and interpolation.

You are correct. I used Mollier diagram to find h exit. I wondering why this happened?

Nothing strange happened. If you wanted to use tables instead of the Mollier diagram you could have. The first step is recognizng that since s > sg then the exit is superheated vapor (therefore is outside the saturation dome) so it makes no sense to calculate quality. Therefore you don’t calculate quality. You stick with the superheated vapor table. Use the known exit entropy and pressure to find the exit enthalpy in the superheated vapor table.

Thanks