Steam turbine evaluation 1

[sqsqsq]

Hi everybody,
As it was mentioned in the texts, the power of steam turbine (non-condensing type)could be calculated through the thermodynamic laws (enthalapy balance). An important point is that the turbine steam outlet temperature should be measured. But I have read a short sentence that by usual equipment(thermowell and thermocouple), the measeured temperature has not enough accuracy. Does anybody have idea and explanation for the reasons? And what are the methods for accurate measuring the outlet steam temperature?
Thanks

 

[stgrme]

Calculation of steam turbine power requires the accurate measurements of inlet pressure and temperature (to establish the inlet state point), exhaust pressure and temperature (to establish the exhaust state point) and steam flow.

Accurate temperature measurements both at the inlet and at the exhaust require calibrated thermocouples. Typical thermocouples have an accuracy of 0.75% of range or 4 degrees Fahrenheit (2.2 degrees Celsius), whichever is greater. See ASME PTC 19.3 for guidance on temperature measurements.

If you want to calculate power, measuring steam flow accurately is much more difficult than measuring temperature. However, you can calculate the efficiency of the turbine easily, using the enthalpies of state points at the inlet and at the exhaust along with the isentropic enthalpy at the exhaust. If you want to evaluate steam turbine performance, efficiency may be sufficient.

Best of luck!

 

[rmw]

Can it be that you were reading about a turbine exhausting below saturation pressure? If that is what the reference is to, it is because you can't measure the moisture in the exhaust - or steam quality (directly) with just temperture measuring equipment.

rmw